Tratamiento de ortodoncia para el apiñamiento dental en niños
Resumen
Antecedentes
El apiñamiento dental se produce cuando no hay suficiente espacio en los maxilares para que puedan brotar los dientes. El apiñamiento puede afectar los dientes de leche (dentición temporal), los dientes adultos (dentición permanente) o ambos, y es un motivo habitual de derivación al ortodoncista. El apiñamiento dental puede afectar la autoestima y la calidad de vida del niño. La pérdida precoz de los dientes de leche como consecuencia de una caries o un traumatismo, puede provocar el apiñamiento de los dientes permanentes. El apiñamiento tiende a aumentar con la edad, especialmente en el maxilar inferior.
Objetivos
Evaluar los efectos de la intervención ortodóntica para prevenir o corregir el apiñamiento dental en los niños.
Probar la hipótesis nula de que no hay diferencias en los desenlaces entre las diferentes intervenciones ortodónticas para prevenir o corregir el apiñamiento dental en los niños.
Métodos de búsqueda
El documentalista del Grupo Cochrane de Salud oral (Cochrane Oral Health) realizó búsquedas en cuatro bases de datos bibliográficas hasta el 11 de enero de 2021 y utilizó métodos de búsqueda adicionales para identificar estudios publicados, no publicados y en curso.
Criterios de selección
Se incluyeron los ensayos controlados aleatorizados (ECA) que evaluaron cualquier intervención activa para prevenir o corregir el apiñamiento dental en niños y adolescentes, como los aparatos de ortodoncia o las extracciones, en comparación con ningún tratamiento o un tratamiento diferido, un tratamiento placebo u otra intervención activa. Los estudios debían incluir al menos un 80% de participantes de 16 años o menos.
Obtención y análisis de los datos
Dos autores de la revisión, de forma independiente y por duplicado, extrajeron la información relacionada con los métodos, los participantes, las intervenciones, los desenlaces, los efectos perjudiciales y los resultados. Los desacuerdos se resolvieron a través de un tercer autor de la revisión. Se utilizó la herramienta Cochrane de riesgo de sesgo para evaluar el riesgo de sesgo en los estudios. Se calcularon las diferencias de medias (DM) con intervalos de confianza (IC) del 95% para los datos continuos y odds ratio (OR) con IC del 95% para los datos dicotómicos. Se realizó un metanálisis cuando los estudios de comparaciones similares informaron medidas de desenlace comparables, y se utilizó el modelo de efectos aleatorios. Se utilizó la estadística I2 como medida de la heterogeneidad estadística.
Resultados principales
La búsqueda identificó 24 ECA que incluyeron 1512 participantes, de los cuales 1314 se incluyeron en los análisis. Se consideró que 23 estudios tenían alto riesgo de sesgo y uno riesgo incierto.
Los estudios investigaron 17 comparaciones. Veinte estudios evaluaron aparatos fijos y auxiliares (arco lingual inferior, escudo labial [lip bumper] inferior, brackets, arcos de alambre, retroligadura [lacebacks] distal en 8, arcos extraorales y faciales [headgear] y aparatos vibratorios adyuvantes); dos estudios evaluaron aparatos removibles y auxiliares (aparato de Schwarz, aparato de guía de la erupción dental); y dos estudios evaluaron extracciones dentales (caninos temporales inferiores o terceros molares).
La evidencia se debe interpretar con cautela, ya que su grado de certeza es muy bajo. La mayoría de las intervenciones se evaluaron en un único estudio.
Aparatos fijos y auxiliares
Un estudio determinó que el uso de un escudo labial podría reducir el apiñamiento en la dentición permanente temprana (DM ‐4,39 mm; IC del 95%: ‐5,07 a ‐3,71; 34 participantes). Un estudio evaluó el arco lingual inferior pero no midió la cantidad de apiñamiento.
Un estudio concluyó que los arcos de alambre coaxial de níquel‐titanio (NiTi) podrían provocar un mayor movimiento de los dientes en la arcada inferior que los arcos monofilares de NiTi (DM 6,77 mm; IC del 95%: 5,55 a 7,99; 24 participantes). Otro estudio, que comparó arcos de cobre NiTi versus arcos de NiTi, determinó que el NiTi fue más efectivo para reducir el apiñamiento (DM 0,49 mm; IC del 95%: 0,35 a 0,63; 66 participantes). Los estudios individuales no mostraron evidencia de que un tipo de arco fuera mejor que otro en el caso de Titinol versus Nitinol; níquel‐titanio versus acero inoxidable o acero inoxidable multitrenzado; ni acero inoxidable multitrenzado versus acero inoxidable.
Los estudios individuales tampoco encontraron evidencia de una diferencia en la cantidad de apiñamiento entre los brackets de autoligado y los convencionales, los brackets de autoligado activos y pasivos, la retroligadura distal en 8 agregada a los aparatos fijos versus los aparatos fijos solos, o el arco extraoral y facial de tracción cervical versus los procedimientos interceptivos menores.
El metanálisis de dos estudios no mostró evidencia de que el agregado de aparatos vibratorios a los aparatos fijos reduzca el apiñamiento a las ocho o diez semanas (DM 0,24 mm; IC del 95%: ‐0,81 a 1,30; 119 participantes).
Aparatos removibles y auxiliares
Un estudio determinó que el uso del aparato de Schwarz podría ser efectivo para tratar el apiñamiento dental en la arcada inferior (DM ‐2,14 mm; IC del 95%: ‐2,79 a ‐1,49; 28 participantes). Otro estudio determinó que un aparato de guía de la erupción dental podría reducir el número de niños con apiñamiento dental después de un año de tratamiento (OR 0,19; IC del 95%: 0,05 a 0,68; 46 participantes); sin embargo, esto se podría deber a un aumento de la proinclinación de los incisivos inferiores en el grupo tratado. No se evaluó si estas ganancias se mantuvieron a largo plazo.
Extracciones dentales
Un estudio determinó que la extracción de los caninos inferiores de los niños tuvo más efecto sobre el apiñamiento después de un año que ningún tratamiento (DM ‐4,76 mm; IC 95: ‐6,24 a ‐3,28; 83 participantes), pero esto se produjo junto con una reducción de la longitud del arco. Un estudio encontró que la extracción de las muelas del juicio no pareció reducir el apiñamiento, en comparación con conservarlas (DM ‐0,30 mm; IC del 95%: ‐1,30 a 0,70; 77 participantes).
Conclusiones de los autores
La mayoría de las intervenciones se evaluaron en estudios únicos y pequeños. Se encontró evidencia de certeza muy baja de que el escudo labial, utilizado en la dentición mixta, podría ser eficaz para prevenir el apiñamiento en la dentición permanente temprana, y el aparato de Schwarz podría reducir el apiñamiento en la arcada inferior. También se encontró evidencia de certeza muy baja de que el NiTi coaxial podría ser mejor para reducir el apiñamiento que el NiTi monofilar, y que el NiTi podría ser mejor que el NiTi de cobre. Como la evidencia actual es de certeza muy baja, los resultados de esta revisión podrían cambiar con futuros estudios de investigación.
PICO
Resumen en términos sencillos
¿Cuál es el mejor tratamiento para los niños con dientes apiñados?
¿Qué son los dientes apiñados?
Cuando los dientes erupcionan (salen a través de la encía hacia la boca), se pueden torcer, sobresalir, quedarse atrás o superponerse si no hay suficiente espacio en la boca. La pérdida temprana de los dientes de leche por caries o traumatismos puede provocar el apiñamiento de los dientes permanentes. Si los dientes apiñados afectan la autoestima del niño o le causan dolor, efectos perjudiciales o problemas de masticación, el niño puede ser remitido a un dentista especialista conocido como ortodoncista para corregirlos. La ortodoncia se ocupa del crecimiento de los maxilares y la cara, así como del desarrollo de los dientes y la mordida.
¿Qué es el tratamiento de ortodoncia?
Los dientes apiñados se pueden prevenir o corregir mediante el uso de brackets si el apiñamiento es leve (menos de 4 mm). También podría ser necesaria la eliminación de algunos dientes (extracción) si el apiñamiento es moderado (de 4 mm a 8 mm) o grave (más de 8 mm). Los aparatos fijos se utilizan en los dientes permanentes. Los aparatos removibles se pueden utilizar en los dientes de leche, en los permanentes o en ambos. Se pueden extraer dientes de leche o permanentes.
Aparatos de ortodoncia fijos
Los aparatos fijos adhieren piezas a cada diente mediante pegamento dental, con brackets que sostienen un alambre que ejerce una fuerza sobre los dientes, para moverlos y enderezarlos. El alambre se sujeta con bridas metálicas, pequeñas bandas de goma o un clip integrado en el bracket ("autoligado").
Un arco lingual inferior (ALI) o un escudo labial (EL) retienen los dientes posteriores inferiores (molares) mientras permiten que los dientes frontales inferiores se enderecen y se muevan hacia delante. Para eliminar la presión sobre los dientes, un alambre del ALI se sitúa en el lado interno de los dientes; un alambre del EL se sitúa en el lado externo. Los alambres de acero inoxidable de 0,9 mm se fijan a bandas metálicas alrededor de los dientes posteriores (molares) en ambos extremos, y el alambre del EL tiene un revestimiento de plástico en la parte delantera.
A veces se utilizan elementos adicionales con los aparatos fijos, como el arco extraoral y facial (correas sujetas a un marco fuera de la boca), las placas vibratorias o la retroligadura distal en 8 (alambres finos que mantienen los dientes unidos).
Aparatos de ortodoncia removibles
Los aparatos removibles suelen estar hechos de plástico duro que une las partes activas que mueven los dientes y los sujetadores que aseguran el aparato. Algunos aparatos removibles están hechos de plástico flexible moldeado.
El aparato de Schwarz tiene un tornillo que los padres giran una vez a la semana, para ensanchar el arco del maxilar inferior y hacer más espacio en el que puedan moverse los dientes permanentes.
El aparato de guía de la erupción dental guía los dientes permanentes hacia una mejor posición a medida que brotan. Se trata de un aparato de ortodoncia superior e inferior combinado que sujeta el maxilar inferior hacia delante y tiene ranuras de guía para alinear los dientes delanteros y mejorar la mordida de los dientes laterales.
Extracción
Los colmillos de leche (caninos) se extraen cuando los niños tienen una mezcla de dientes definitivos y de leche, para proporcionar espacio en el que puedan moverse otros dientes.
Las muelas del juicio (terceros molares) se pueden extraer en cualquier momento desde que se forman (al principio de la adolescencia) hasta la edad adulta, para evitar que ejerzan presión hacia delante sobre los demás dientes.
¿Qué se quería averiguar?
El objetivo fue evaluar la investigación científica sobre la efectividad de los tratamientos de ortodoncia (aparatos fijos, aparatos removibles, extracción de dientes) utilizados para prevenir o corregir el apiñamiento de los dientes en niños de 16 años o menos. Se buscaron estudios que compararan estos tratamientos con ningún tratamiento, el tratamiento diferido, placebo (tratamiento simulado) u otro tratamiento de ortodoncia.
¿Qué estudios se encontraron?
Se incluyeron 24 estudios que presentaron resultados de 1314 niños de siete a 16 años de edad en diferentes países. Veinte estudios probaron aparatos fijos, dos probaron aparatos removibles y dos probaron extracciones.
¿Cuáles fueron los principales resultados?
Aparatos de ortodoncia fijos y aspectos relacionados
Un escudo labial inferior podría evitar el apiñamiento cuando los dientes adultos comienzan a salir. Los alambres de níquel‐titanio podrían corregir el apiñamiento mejor que los alambres de cobre‐níquel‐titanio, y los arcos de níquel‐titanio trenzados (coaxiales) podrían ser mejores que los de un solo hilo. Sin embargo, no es posible tener confianza en estos resultados.
En las demás comparaciones evaluadas, no fue posible demostrar que un grupo lo hiciera mejor o peor que el otro para reducir el apiñamiento.
Aparatos de ortodoncia removibles y aspectos relacionados
El aparato de Schwarz podría reducir el apiñamiento en la arcada inferior, cuando se mide a los nueve meses. El uso de un aparato de guía de la erupción dental, durante un año, podría reducir la probabilidad de apiñamiento, pero podría haber otras explicaciones para esto. Una vez más, no es posible tener confianza en estos resultados.
Extracción
La extracción de las muelas del juicio (terceros molares) no parece afectar al apiñamiento más adelante, mientras que la extracción de los colmillos de leche (caninos) del maxilar inferior, podría reducir el apiñamiento a corto plazo, pero no es posible estar seguros de ello. Probablemente haya otras explicaciones para este hallazgo.
¿Cuáles son las limitaciones de la evidencia?
La evidencia no está clara. Consiste en pequeños estudios individuales que prueban diferentes tratamientos. Algunos de ellos tienen problemas con la forma en que se realizaron. No se puede tener confianza en las conclusiones y las investigaciones futuras podrían cambiarlas.
¿Cuál es el grado de actualización de esta evidencia?
La evidencia está actualizada hasta enero de 2021.
Authors' conclusions
Summary of findings
| Fixed appliances and auxiliaries versus other treatment or no treatment to prevent or correct dental crowding in children | ||||||
|---|---|---|---|---|---|---|
| Population: children or adolescents, or both (age ≤ 16 years) having treatment to prevent or correct dental crowding Settings: Australia, Brazil, Finland, India, Turkey, UK, USA Intervention: fixed appliances and auxiliaries (lip bumper, headgear, lower lingual arch, brackets, archwires, lacebacks, vibrational appliances) Comparison: control (brackets, archwires, fixed appliances only, minor interceptive procedures, no active treatment) | ||||||
| Outcomes | Illustrative comparative risks* (95% CI) | Relative effect
| Number of participants | Certainty of the evidence | Comments | |
| Assumed risk | Corresponding risk | |||||
| Control | Fixed appliances and auxiliaries | |||||
| Lower lip bumper ‐ lower lip bumper versus no active treatment (control) | ||||||
| Change in the amount of crowding at 6 months | Mean change −0.7 mm | Mean change −5.09 mm ± 0.97 mm |
| 34 (1) | ⊕⊝⊝⊝ Very lowa,b | There was less crowding in the lip bumper group (MD −4.39 mm, 95% CI −5.07 to −3.71). |
| Headgear ‐ cervical pull headgear versus minor interceptive procedures (control) | ||||||
| Amount of crowding at 2 years | Mean change 2.45 mm | Mean change 2.78 mm ± 1.91 mm |
| 64 (1) | ⊕⊝⊝⊝ Very lowa,b | There was no difference between groups in the amount of crowding at 2 years (MD 0.33 mm (95% CI −0.60 to 1.26). There was also no difference at 13 years follow‐up of the remaining 34 participants (MD 0.26, 95% CI −1.35 to 1.87). |
| Lower lingual arch ‐ lower lingual arch versus no active treatment (control) | ||||||
| Amount of crowding | Not measured | |||||
| Brackets ‐ self‐ligating brackets versus conventional brackets | ||||||
| Amount of crowding at 10 weeks | Mean amount of crowding 2.7 mm | Mean amount of crowding was 0.40 mm less (0.93 mm less to 0.13 mm more) |
| 60 (1) | ⊕⊝⊝⊝ Very lowa,b | There was no difference between groups in the amount of crowding. |
| Archwires ‐ coaxial nickel‐titanium archwire versus nickel‐titanium archwire | ||||||
| Amount of tooth movement at 12 weeks | Mean amount of tooth movement 3.1 mm | Mean amount of tooth movement was 6.77 mm more (5.55 mm to 7.99 mm more) |
| 24 (1) | ⊕⊝⊝⊝ Very lowa,b | There was more tooth movement with the coaxial nickel‐titanium archwire than the nickel‐titanium archwire. |
| Archwires ‐ copper nickel‐titanium archwire versus nickel‐titanium archwire | ||||||
| Amount of crowding at 12 weeks | Mean amount of crowding 6.33 mm | Mean amount of crowding was 0.49 mm more (0.35 mm to 0.63 mm more) |
| 66 (1) | ⊕⊝⊝⊝ Very lowa,b | There was less residual crowding with the nickel‐titanium archwire than the copper‐nickel titanium archwire. |
| Archwires ‐ Titanol versus Nitinol | ||||||
| Change in the amount of crowding up to 37 weeks | Mean change 1.42 mm ± 0.79 mm | Mean change 1.7 mm ± 1.15 mm |
| 40 (1) | ⊕⊝⊝⊝ Very lowa,b | There was no difference between groups in the change in the amount of crowding (MD −0.28 mm, 95% CI −0.89 to 0.33). |
| Archwires ‐ nickel‐titanium archwire versus multistranded stainless steel archwire | ||||||
| Change in the amount of crowding at 8 weeks | Mean change −29.2 mm | Mean change −27.6 mm ± 26.5 mm |
| 25 (1) | ⊕⊝⊝⊝ Very lowa,b | There was no difference between groups in the overall change in the amount of crowding (MD 1.60 mm, 95% CI −22.16 to 25.36). |
| Archwires ‐ nickel‐titanium archwire versus stainless steel archwire | ||||||
| Change in the amount of crowding at 8 weeks | Mean change −10.8 mm | Mean change −27.6 mm ± 26.5 mm |
| 24 (1) | ⊕⊝⊝⊝ Very lowa,b | There was no difference between groups in the overall change in the amount of crowding (MD 16.80 mm, 95% CI −42.79 to 9.19). |
| Archwires ‐ multistranded stainless steel archwire versus stainless steel archwire | ||||||
| Change in the amount of crowding at 8 weeks | Mean change −10.8 mm | Mean change −29.2 mm ± 33.4 mm |
| 23 (1) | ⊕⊝⊝⊝ Very lowa,b | There was no difference between groups in the overall change in the amount of crowding (MD −18.40 mm, 95% CI −47.12 to 10.32). |
| Lacebacks ‐ lacebacks and fixed appliances versus fixed appliances only (control) | ||||||
| Change in the amount of crowding at 6 months | Mean change −2.67 mm | Mean change −3.00 mm ± 8.94 mm |
| 62 (1) | ⊕⊝⊝⊝ Very lowa,b | There was no difference between groups in the change in the amount of crowding (MD −0.33 mm, 95% CI −5.90 to 5.24). |
| Vibrational appliances ‐ vibrational appliances with fixed appliances versus fixed appliances only (control) | ||||||
| Change in the amount of crowding at 10 to 30 weeks | Mean change −0.7 mm | Mean change ranged from 4.0 mm to 5.5 mm |
| 119 (2) | ⊕⊝⊝⊝ Very lowc,d | There was no difference between groups in the change in the amount of crowding (MD 0.24, 95% CI −0.81 to 1.30). |
| *The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; MD: mean difference; mm: millimetre | ||||||
| GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect. | ||||||
| aDowngraded one level as study at high risk of bias. | ||||||
| Removable appliances and auxiliaries to prevent or correct dental crowding in children | ||||||
| Population: children or adolescents (age ≤ 16 years) having treatment to prevent or correct dental crowding Setting: Japan, Norway Intervention: removable appliances, e.g. Schwarz appliance Comparison: fixed appliances only, no treatment | ||||||
| Outcomes | Illustrative comparative risks* (95% CI) | Relative effect | Number of participants | Certainty of the evidence | Comments | |
| Assumed risk | Corresponding risk | |||||
| Control | Experimental | |||||
| Schwarz appliance ‐ Schwarz appliance versus no active treatment (control) | ||||||
| Change in the amount of crowding at 9 months (after 6 months treatment) | Mean change −0.66 mm | Mean change −2.80 mm ± 1.14 mm |
| 28 (1) | ⊕⊝⊝⊝ Very lowa,b | Use of a Schwarz appliance reduced crowding (MD −2.14, 95% CI −2.79 to −1.49). |
| Eruption guidance appliance (EGA) ‐ EGA versus no active treatment (control) | ||||||
| Number of children with crowding after 1 year | 14 out of 22 children | 6 out of 24 children | OR 0.19 (95% CI 0.05 to 0.68) | 46 (1) | ⊕⊝⊝⊝ Very lowa,b | Use of an EGA reduced the number of children with dental crowding after a year. |
| *The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval;MD: mean difference; mm: millimetre; OR: odds ratio | ||||||
| GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect. | ||||||
| aDowngraded as study at high risk of bias. | ||||||
| Extractions to prevent or correct dental crowding in children | ||||||
| Population: children or adolescents (age ≤ 16 years) having treatment to prevent or correct dental crowding Settings: Italy, Germany, Wales, UK Intervention: extraction of wisdom teeth or deciduous canines Comparison: no active treatment | ||||||
| Outcomes | Illustrative comparative risks* (95% CI) | Relative effect | Number of participants | Quality of the evidence | Comments | |
| Assumed risk | Corresponding risk | |||||
| Control | Experimental | |||||
| Extraction of wisdom teeth ‐ extraction of wisdom teeth versus no active treatment (control) | ||||||
| Change in the amount of crowding at 5 years | Mean change 1.1 mm | Mean change 0.8 mm ± 1.23 mm |
| 77(1) | ⊕⊝⊝⊝ Very low | There was no difference between extracting wisdom teeth and not extracting them in terms of the mean change in the amount of crowding (MD −0.30 mm (95% CI −1.30 to 0.70). |
| Extraction of deciduous canines ‐ extraction of deciduous canines versus no active treatment (control) | ||||||
| Change in the amount of crowding at 1‐2 years | Mean change −1.27 mm | Mean change −6.03 mm ± 4.44 mm |
| 83(1) | ⊕⊝⊝⊝ Very low | There was a greater change in the amount of crowding when lower canines were extracted compared to when they were not (MD −4.76 mm (95% CI −6.24 to −3.28). |
| *The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; MD: mean difference; mm: millimetre | ||||||
| GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect. | ||||||
| aDowngraded one level as study at high both studies were at unclear risk of bias. | ||||||
Background
Description of the condition
Crowded teeth develop when there is not enough space in the jaws into which the teeth can erupt. This gives the child crooked or 'wonky' teeth that may be the focus of teasing at school (Shaw 1980; Shaw 1981), or later in life (Shaw 1985), and can result in low self‐esteem (Jung 2010). Crowded teeth is the problem seen most commonly by orthodontists. Prevalence of crowding varies, but it affects nearly half of 12‐year‐old children in the UK (Holmes 1992).
Crowding can affect baby teeth (deciduous dentition) or adult teeth (permanent dentition). Crowding tends to increase with age, especially in the lower jaw, so that only a third of adults have well‐aligned lower front teeth (incisors) (Proffit 1998). Crowding occurs when there is a difference between the size of the jaws and teeth, for example, the jaws are too small to hold the teeth. Crowding of the adult teeth can also occur when space is lost following the early loss of baby teeth, either as a result of tooth decay or trauma (Bhujel 2014; Bhujel 2016).
Description of the intervention
Orthodontics is the branch of dentistry concerned with the growth of the jaws and face, the development of the teeth and the way the teeth and jaws bite together. It also involves treatment of the teeth and jaws when they are irregular or bite in an abnormal way, or both. There are many reasons why the teeth may not bite together correctly. These include the position of the teeth, jaws, lips, tongue or cheeks, or may be due to a habit or the way people breathe. The need for treatment can be decided by looking at the effect of any particular tooth position on the life expectancy of the teeth, the function of the teeth or the effect that the appearance of the teeth has on how people feel about themselves (Shaw 1991).
There are many different orthodontic interventions that can be used to prevent or correct crowded teeth. The purpose of this review is to assess the current body of available evidence and determine which intervention or interventions are the most effective.
Several dental brace (orthodontic) treatments have been proposed to correct or prevent crowding. Some treatments use braces to expand the teeth or jaws. These treatments can be carried out early, before children are six years of age, when only baby teeth are present. Other treatments can be carried out when children have a mixture of baby and adult teeth (around 7 to 11 years of age). Treatments carried out at this stage use braces to maintain the space that arises when the baby back teeth (molars) are lost and replaced by smaller adult sized teeth (premolars).
Other treatments can be used later when all the adult teeth have come into the mouth (around 12 to 16 years of age), either using braces to expand the teeth or jaws, or removing teeth to create space so that the remaining teeth can be straightened using a brace. Braces can either be removed from the mouth or fixed to the teeth with special glue. Other types of brace are attached, via the teeth, to devices (headgear) that allow a force to be applied to the teeth and jaws from the back of the head.
Interventions to prevent or correct dental crowding in children can be divided into the following categories: fixed braces and auxiliaries, removable braces and auxiliaries, and extraction of teeth.
How the intervention might work
Fixed appliances and auxiliaries
Several interventions have been used to prevent or correct dental crowding in children using fixed appliances and auxiliaries.
The lip bumper and lingual arch maintain the space resulting from the total width of the adult eye teeth (canines) and side teeth (premolars) being less than the baby eye teeth (canine) and back teeth (molars) that they are replacing. The crowded teeth can then move into this extra (leeway) space, which allows the crowding to reduce.
Cervical pull headgear is attached to the back teeth (molars) and used to move them backwards to make more space nearer the front of the mouth into which crowded teeth can be aligned.
Different orthodontic bracket designs (self‐ligating versus conventional; active self‐ligating versus passive) claim to provide less resistance (friction) to tooth movement, allowing the teeth to move and align more quickly.
Different orthodontic archwires (copper nickel‐titanium versus nickel‐titanium; coaxial nickel‐titanium versus nickel‐titanium; nitinol versus titinol; nickel‐titanium versus multistranded stainless steel; nickel‐titanium versus stainless steel; multistranded stainless steel versus stainless steel) claim to move the teeth more gently or more consistently, or both, over a longer period of time, depending on the characteristics of the wires, allowing the teeth to move and align more efficiently.
The use of lacebacks, with fixed appliances, has also been claimed to help align the teeth more quickly and reduce the amount of crowding by influencing the position of the front teeth (incisors).
Vibrational appliances are used with fixed appliances. It is claimed that the vibrations increase the rate of tooth movement so the teeth straighten more quickly.
Removable appliances and auxiliaries
The Schwarz appliance is used to expand the lower teeth and provide extra space into which crowded teeth can be aligned.
The eruption guidance appliance again uses the difference between the size of the baby back (molar) teeth and adult side (premolar) teeth to provide extra space space into which the erupting adult teeth can be guided and to relieve any crowding.
Extractions
The lower deciduous eye teeth (canines) can be extracted to provide space into which the permanent front teeth (incisors) can spread and align.
Extraction of wisdom teeth (third molars) has been claimed to prevent the development of crowding of the front teeth (incisors) in later life.
Why it is important to do this review
As dental crowding has been found to affect oral health‐related quality of life (Jung 2015), and self‐esteem (Jung 2010) significantly, it is reasoned that treating crowding in children will improve psychological health, well‐being and body image in adulthood (Javidi 2017). Dentists, orthodontists, parents and children need guidance on whether and how best to intervene to prevent or correct crowded teeth.
Objectives
To assess the effects of orthodontic interventions for preventing or correcting crowded teeth in children.
To test the null hypothesis that there are no differences in outcomes between different orthodontic interventions for preventing or correcting crowded teeth in children.
Methods
Criteria for considering studies for this review
Types of studies
All randomised controlled clinical trials (RCTs) of orthodontic treatments to prevent or correct crowded teeth where one intervention was compared concurrently to a placebo, no intervention or another method to prevent or correct dental crowding.
Types of participants
Studies were eligible for inclusion in the review if they had recruited children (aged 16 years old or under) receiving orthodontic treatment to prevent or correct crowded teeth.
We excluded studies involving participants with a cleft lip or palate or other craniofacial syndromes. We excluded studies where less than 80% of participants were aged 16 years old or less.
Types of interventions
We assessed the following active interventions to prevent or correct dental crowding:
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fixed appliances and auxiliaries;
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removable appliances and auxiliaries;
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extractions.
We evaluated any intervention or combination of treatments, at any time during treatment.
Controls
Control conditions could be: no treatment, delayed treatment, placebo or another active intervention.
Types of outcome measures
We recorded clinically important outcomes at the most common endpoints that were reported for all ages. If harms were identified, we recorded them and reported them in descriptive terms.
Primary outcomes
Amount of crowding (measured in mm or by any index of malocclusion)
Secondary outcomes
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Size of the upper jaw (arch length)
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Size of the lower jaw (arch length)
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Upper incisors to maxilla
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Lower incisors to mandible
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Lower molars to mandible
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Time to alignment
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Time for ligation
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Self‐esteem
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Participant satisfaction
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Jaw joint problems
Other outcomes
Harms (recorded and reported in descriptive terms)
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Health of the gums
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Damage to the teeth (such as tooth decay)
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Pain (including the use of analgesia)
Search methods for identification of studies
Electronic searches
Cochrane Oral Health’s Information Specialist conducted systematic searches in the following databases for RCTs and controlled clinical trials. There were no language, publication year or publication status restrictions:
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Cochrane Oral Health’s Trials Register (searched 11 January 2021; Appendix 1);
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Cochrane Central Register of Controlled Trials (CENTRAL; 2020, Issue 12) in the Cochrane Library (searched 11 January 2021; Appendix 2);
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MEDLINE Ovid (1946 to 11 January 2021; Appendix 3);
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Embase Ovid (1980 to 11 January 2021; Appendix 4);
Subject strategies were modelled on the search strategy designed for MEDLINE Ovid. Where appropriate, they were combined with subject strategy adaptations of the highly sensitive search strategies designed by Cochrane for identifying RCTs and controlled clinical trials (as described in the Cochrane Handbook for Systematic Reviews of Interventions, Version 6.1, (Lefebvre 2020)).
Searching other resources
Ww searched the following trials registries for ongoing studies:
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US National Institutes of Health Ongoing Trials Register ClinicalTrials.gov (clinicaltrials.gov; searched 11 January 2021; Appendix 5);
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World Health Organization International Clinical Trials Registry Platform (apps.who.int/trialsearch; searched 11 January 2021; Appendix 6).
We handsearched the British (BJO), European (EJO), and American (AJO‐DO) journals of orthodontics and the Angle Orthodontist (AO), from 1994‐1998. However, these journals are now indexed on MEDLINE so we discontinued the handsearching from 1998 onwards. We searched the bibliographies of papers identified in this search for relevant studies.
We contacted the first‐named authors of all study reports in an attempt to identify unpublished studies and to obtain any further information about the studies.
We searched the reference lists of included studies and relevant systematic reviews, for further appropriate studies.
We did not perform a separate search for harms of interventions used; we considered adverse effects described in included studies only.
We checked that none of the included studies in this review were retracted due to error or fraud.
Data collection and analysis
Selection of studies
Two review authors (JH and DM or JH and FS or ST and DO), independently and in duplicate, assessed the titles and abstracts (when available) of all reports that were identified as potentially relevant by the search. The search was designed to be sensitive and include controlled clinical trials, these were filtered out early in the selection process if they were not randomised.
We obtained the full text of studies that were potentially relevant, studies that had insufficient information in the title and abstract to make a decision about inclusion, and studies where the review authors disagreed about eligibility. At least two review authors then assessed these full‐text papers, independently and in duplicate, to establish whether or not the studies met the inclusion criteria. The review authors were not blinded to study author(s), institution or site of publication. We resolved disagreements by discussion between JH and DM or JH and FS or ST and DO with JH. We kept a record of all decisions made about the potentially eligible studies.
Data extraction and management
At least two review authors independently extracted data including the year of publication, interventions assessed, outcomes, sample size and age of participants. The primary outcome was the amount of crowding and secondary outcomes were size of the upper and lower jaws (arch length); relationship of the upper front teeth (incisors) to the upper jaw (maxilla); relationship of the lower front teeth (incisors) and lower back teeth (molars) to the lower jaw (mandible); self‐esteem; participant satisfaction; jaw joint problems; time to alignment and time for ligation.
We recorded other outcomes, such as harms. For example, we recorded health of the gums or damage to the teeth (such as tooth decay) and pain, and reported the results in descriptive terms.
We extracted outcome data at all time points and reported the most common time points.
Assessment of risk of bias in included studies
At least two review authors assessed the risk of bias independently and in duplicate using the Cochrane risk of bias tool (RoB 1), as described in Chapter 8 of the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2017). We assessed the risk of bias in seven domains: random sequence generation; allocation concealment; blinding of participants and personnel, blinding of outcome assessment; incomplete outcome data; selective outcome reporting and 'other sources of bias'. For each domain, we assigned a judgement of high, low or unclear risk of bias according to the following criteria:
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low risk of bias if plausible bias unlikely to seriously alter the results;
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high risk of bias if plausible bias that seriously weakens confidence in the results;
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unclear risk of bias if plausible bias that raises some doubt about the results.
We assessed sequence generation, allocation concealment and selective outcome reporting for the study as a whole. We assessed blinding and incomplete outcome data on the level of the study and for each outcome as appropriate.
We considered the overall risk of bias in each study as 'low' if we assessed all seven domains as low risk; unclear if all domains were at low or unclear risk of bias; and high if we assessed at least one domain as being at high risk of bias.
Measures of treatment effect
For continuous outcomes (e.g. amount of crowding (mm) or arch length) measured using the same scale, we used the mean values and standard deviations (SDs) reported in the studies in order to express the estimate of effect as mean difference (MD) with 95% confidence interval (CI). Where available, we used the change in the outcome measured from baseline.
For dichotomous outcomes (e.g. harm: yes or no), we expressed the estimate of effect as a risk ratio (RR) with 95% CI.
Unit of analysis issues
The unit of analysis was the participant. For multi‐arm studies, we selected the most appropriate arms to compare, or combined arms, using methods described in where possible and appropriate.
Dealing with missing data
We attempted to contact the study author(s) in cases of missing data for all included studies, when feasible, in order to gather details of outcomes that were measured but not reported, or for clarification and details. We did not need to use the methods described in Chapter 5 of the Cochrane Handbook for Systematic Reviews of Interventions to estimate missing standard deviations due to unclear or unavailable data (Li 2021). We used the RevMan calculator to combine continuous outcomes of different arms in multi‐arm parallel trials comparing two or more active treatments against a control. We did not use any other statistical methods or perform any further imputation to account for missing data.
Assessment of heterogeneity
We assessed clinical heterogeneity by identifying the participants, interventions and outcomes and considering whether a meaningful summary would be produced by combining the results. We also assessed heterogeneity statistically using a Chi2 test, where a P value less than 0.1 indicates statistically significant heterogeneity. We quantified heterogeneity using the I2 statistic (Higgins 2003). A guide to interpretation of the I2 statistic given in Section 10.10.2 of the Cochrane Handbook for Systematic Reviews of Interventions is as follows (Deeks 2021):
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0% to 40% might not be important;
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30% to 60% may represent moderate heterogeneity;
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50% to 90% may represent substantial heterogeneity;
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75% to 100% represents considerable heterogeneity.
Assessment of reporting biases
We had planned to assess reporting bias via funnel plot asymmetry if more than 10 studies were to be included in a meta‐analysis, as described in section 10.10.4.1 of the Cochrane Handbook for Systematic Reviews of Interventions (Deeks 2021). Whilst we had a sufficient number of studies included in this review for the primary outcome, the results were diluted due to the multiple different interventions and comparisons undertaken; we were therefore unable to use funnel plots to assess publication bias.
Data synthesis
We only carried out meta‐analyses when there were studies of similar comparisons reporting the same outcomes. We combined mean differences (MDs) for continuous data, and RRs for dichotomous data. Our general approach was to use a random‐effects model. With this approach, the CIs for the average intervention effect were wider than those that would have been obtained using a fixed‐effect approach, leading to a more conservative interpretation. We presented the results of single studies where a comparison and outcome was measured in only one study.
Subgroup analysis and investigation of heterogeneity
Had sufficient relevant data been available, we would have carried out a subgroup analysis on the age (stage of dental development) at which treatment was undertaken.
Sensitivity analysis
We did not plan or carry out any sensitivity analyses.
Summary of findings and assessment of the certainty of the evidence
We created a summary of findings table for each type of intervention (fixed appliances and auxiliaries, removable appliances and auxiliaries, and extractions). We presented summary information for the amount of crowding as this was our primary and most clinically relevant outcome. Two review authors independently assessed the certainty of the evidence using GRADE criteria (GRADE 2004; Schünemann 2021).
Results
Description of studies
Results of the search
The electronic search identified 2225 references to studies after the removal of duplicates. We identified nine additional articles from additional sources. We screened all titles and abstracts, where available, and discarded 2123. For the remaining 111 articles, we obtained full‐text articles where possible, and excluded 62 records at this stage (see Excluded studies). Ten studies were systematic reviews whose reference lists we searched (Afzal 2020; Chen 2019; El‐Angbawi 2015; Ke 2019; Papageorgiou 2019; Song 2009; Vieira 2018; Wang 2018; Wazwaz 2021; Yu 2013). Of the remaining studies, we were able to include 32 records of 24 studies, five studies await classification and two studies are ongoing (see Studies awaiting classification and Ongoing studies). Figure 1 summarises our study selection process.
Study flow diagram
Included studies
We included 24 RCTs, involving a total of 1512 participants in this review of whom they included 1314 in analyses. All 24 studies provided data for the review. However, two of these studies only provided data for harms; we have reported these data descriptively. The studies investigated 17 different comparisons.
Characteristics of the study designs and settings
Design
All studies were of parallel design. Four studies had three arms (Gravina 2013; Ong 2011; Songra 2014; Woodhouse 2015). The remaining studies had two arms.
Setting
Five studies took place in the UK (Harradine 1998; Irvine 2004; O'Brien 1990; Songra 2014; Woodhouse 2015); four studies were conducted in Australia (Miles 2010; Miles 2012; Miles 2016; Ong 2011); three in Corfu, Greece (Pandis 2009; Pandis 2010a; Pandis 2011); three in Turkey (Aras 2018; Atik 2014; Aydin 2018); two in India (Sandhu 2013; Sebastian 2012), and one in each in Brazil (Gravina 2013); Finland (Finland 2004); Japan (Tai 2010); Norway (Myrlund 2015); and the USA (Davidovitch 1997). The setting for one study is unknown (Rebellato 1997). One study was multinational, being conducted in Wales, Italy and Germany (Kau 2004).
Centres
There were two studies with three centres (Kau 2004; Woodhouse 2015). Myrlund 2015 recruited across two centres, but all treatment was carried out in one centre. The other studies involved a single centre.
Funding
Seven studies reported their funding source: one received independent funding from government (Kau 2004), four from charity (Aydin 2018; Finland 2004; Miles 2016; Ong 2011), and two from orthodontic companies (Myrlund 2015; O'Brien 1990). The remaining studies did not report any funding source.
Conflict of interest
In five studies, the authors declared that they had no commercial or financial conflicts of interest (Aras 2018; Aydin 2018; Songra 2014; Tai 2010; Woodhouse 2015). However, one of these studies later acknowledged an engineering company for developing the software that the authors used to disprove their null hypothesis (Tai 2010). Another study declared that their appliances were supplied by the company that developed the appliance (Woodhouse 2015). Two other studies declared that commercial companies supplied them with materials or appliances (Myrlund 2015; O'Brien 1990). The remaining 15 studies did not report on any conflicts of interest.
Characteristics of the participants
We included 24 studies, which randomised a total of 1512 participants and analysed data from 1314 participants (see Characteristics of included studies). The mean age of participants within the studies ranged from 7.6 years to 15.3 years. Fifteen studies reported the number of male and female participants (Aras 2018; Atik 2014; Aydin 2018; Finland 2004; Gravina 2013; Harradine 1998; Irvine 2004; Myrlund 2015; Ong 2011; Pandis 2009; Pandis 2011; Sebastian 2012; Songra 2014; Tai 2010; Woodhouse 2015). The percentage of male participants ranged from 23.3% to 58.8% in these studies, other than in two that included female participants only (Atik 2014; Sebastian 2012).
Characteristics of the interventions and comparisons
We identified studies that compared interventions to prevent the perpetuation of crowding from the mixed dentition into the permanent dentition or to correct crowding in the permanent dentition. The interventions could be broadly divided into the following three categories: fixed appliances and auxiliaries; removable appliances and auxiliaries; and extractions.
Fixed appliances and auxiliaries
Twenty studies evaluated fixed appliances and auxiliaries. These interventions included: lip bumper (Davidovitch 1997), cervical pull headgear (Finland 2004), lingual arch (Rebellato 1997), brackets (Aras 2018; Atik 2014; Miles 2010; Pandis 2010a; Pandis 2011; Songra 2014), archwires (Aydin 2018; Gravina 2013; O'Brien 1990; Ong 2011; Pandis 2009; Sandhu 2013; Sebastian 2012), lacebacks (Irvine 2004), and adjunctive vibrational appliances (Miles 2012; Miles 2016; Woodhouse 2015).
Lower lip bumper
One study compared treatment with a lip bumper therapy to a control group, which did not receive any active treatment, to assess changes in the arch perimeter changes (Davidovitch 1997).
Cervical pull headgear
One study compared cervical pull headgear to a control group, which received interceptive procedures during the study duration to improve the alignment of the anterior teeth if deemed necessary (Finland 2004). The interceptive procedures consisted of extraction of the upper deciduous canines, extraction of the lower deciduous canines or interdental stripping. We identified three reports to this study that reported different outcomes at different time points.
Lower lingual arch
One study compared the passive lower lingual arch appliance against a control group that did not receive any active treatment during the study period. The aim was assess changes in arch length and lower incisor inclination arch length and incisor inclinational changes (Rebellato 1997).
Brackets
Six studies compared different types of orthodontic brackets.
Three studies compared a combination of conventional brackets with passive or active, or both, self‐ligating metal brackets (Atik 2014; Pandis 2011; Songra 2014). In Atik 2014, the conventional group underwent treatment with a quad‐helix before fixed appliance therapy.
One study compared ceramic self‐ligating brackets with conventional ceramic brackets (Miles 2010), one study compared active and passive self‐ligating brackets (Pandis 2010a), and one study compared metal self‐ligating brackets with conventional metal brackets (Aras 2018).
Archwires
Seven studies compared different archwire types against one another.
Two studies had three parallel arms. One compared two different nickel‐titanium archwire sequences (for which we combined the data) and a copper nickel‐titanium archwire sequence (Ong 2011), and one compared stainless steel, multistranded stainless steel and nickel‐titanium archwires (Gravina 2013).
The remaining five studies had two parallel arms. One study compared stabilised nickel‐titanium (Nitinol) against super–elastic nickel‐titanium (Titinol; O'Brien 1990); two compared nickel‐titanium against copper nickel titanium (Aydin 2018; Pandis 2009), one compared nickel‐titanium to multistranded stainless steel (Sandhu 2013), and one study compared coaxial nickel‐titanium against single stranded nickel‐titanium (Sebastian 2012).
Lacebacks
One study compared the use of lacebacks with fixed appliances to a control group where only fixed appliances were used (Irvine 2004).
Vibrational appliances
Three studies investigated the effects of vibrational appliances on crowding.
Two studies had two parallel arms: one study compared the vibrational appliance (Tooth Masseuse) and fixed appliances with fixed appliances alone (Miles 2012); the other compared a vibrational appliance (AcceleDent) and fixed appliances to fixed appliances alone (Miles 2016). The third study had three parallel arms consisting of participants who underwent mandibular first premolar extractions and received the vibrational appliance (AcceleDent) and fixed appliances versus fixed appliances only (Woodhouse 2015). There was an arm with a sham AcceleDent device and fixed appliances that we did not use in our review.
Removable appliances and auxiliaries
Two studies evaluated removable appliances and auxiliaries: the Schwarz appliance (Tai 2010), and the eruption guidance appliance (Myrlund 2015).
Schwarz appliance
One study compared the use of the Schwarz appliance to expand the upper and lower arches against a control group where the participants received no treatment (Tai 2010).
Eruption guidance appliance
One study compared the use of an eruption guidance appliance for both the upper and lower arches to a control group where the participants received no treatment (Myrlund 2015).
Extractions
Two studies looked at extracting teeth in order to prevent or correct dental crowding in children. The two extraction patterns were: extraction of lower deciduous canines (Kau 2004) and extraction of wisdom teeth (Harradine 1998).
Extraction of lower deciduous canines
One study compared the extraction of lower deciduous canines against a control group that received no treatment during the study period in order to treat dental crowding in the mixed dentition (Kau 2004).
Extraction of wisdom teeth
One study compared extraction of wisdom teeth to a control group that received no treatment during the study period to prevent dental crowding from developing in later life (Harradine 1998).
Characteristics of the outcomes
Primary outcome
The primary outcome was crowding, measured in millimetres or by any index of malocclusion.
Twelve of the studies used Little’s Irregularity Index to assess crowding in the mandible (Aras 2018; Aydin 2018; Finland 2004; Harradine 1998; Kau 2004; Miles 2012; Myrlund 2015; Ong 2011; Pandis 2009; Sebastian 2012; Songra 2014; Woodhouse 2015), one study used a 3D irregularity index (Gravina 2013), one study reported on mandibular crowding in the lower labial segment by comparing the amount of available space to the mesio‐distal widths of the teeth in the lower labial segment (Irvine 2004), and two studies were not clear as to what method they used to measure crowding (Davidovitch 1997; Tai 2010). Five studies reported on maxillary crowding (Harradine 1998; Miles 2010; Myrlund 2015; O'Brien 1990; Pandis 2010a). All of the studies that reported crowding used millimetres and recorded crowding in the anterior region of the maxilla or mandible.
Nineteen different time points were recorded across these studies, which ranged from pre‐treatment records to one study with a 13‐year follow‐up (Finland 2004). These time points varied greatly, with some readings in days, some in weeks or months and a few in years.
For most interventions, there was only one study available, but for the comparison of vibrational appliances against a control, we combined data from two studies by converting the time points into weeks (Miles 2012; Woodhouse 2015). This was considered to be the most clinically relevant time descriptor for the reduction of irregularity and also a reliable unit, as the days in a month can vary.
Secondary outcomes
Upon data extraction, we decided that certain outcomes were of interest and clinically relevant. The data for these were extracted as an amendment to the original protocol and include upper incisors to maxilla, lower incisors to mandible, arch length, time to alignment and ligation time (Harrison 2002). Abbreviations used in these studies are outlined in Table 1.
| 1. Relationship of the top front teeth (incisors) to the upper jaw (maxilla) | |
|---|---|
| U1‐CT (°) | Angle formed between the upper incisor axis and the CT horizontal plane |
| U1–Vp | Distance from the vertical plane to the upper incisor crown tip |
| U1–CT | Distance from the CT horizontal plane to the upper incisor crown tip |
| 2. Relationship of the top back teeth (molars) to the upper jaw (maxilla) | |
| U6–CT (°) | Angle formed between the upper first molar axis and the CT horizontal plane |
| U6d–Vp | Distance from the vertical plane to the upper first molar distal point |
| U6–CT | Distance from the CT horizontal plane to the upper first molar mesiobuccal crown tip |
A‐P: antero‐posterior; APog: A‐point to pogonion line; SN: sella‐nasion
Arch length
Seven studies reported this as the change in arch length but for differing comparisons, so it was not appropriate to combine the results (Davidovitch 1997; Finland 2004; Harradine 1998; Irvine 2004; Kau 2004; Rebellato 1997; Tai 2010). Changes occurring between the start and the end of the individual studies were measured.
Upper incisors to maxilla
Three studies reported on the position of the upper incisor position relative to the maxilla but for differing comparisons, so it was not appropriate to combine the results of these studies (Finland 2004; Myrlund 2015; Tai 2010). Two studies reported on the angle formed between the upper incisors and the line between sella and nasion (Myrlund 2015; Tai 2010). One study reported on the angle of the upper incisor to the maxillary plane (line between anterior and posterior nasal spines; Finland 2004).
Lower incisors to mandible
Six studies reported on the position of the lower incisor position relative to the mandible (Davidovitch 1997; Finland 2004; Kau 2004; Myrlund 2015; Rebellato 1997; Tai 2010), but each study investigated a different comparison and so it was not appropriate to combine the results.
Lower molars to mandible
Two studies reported on the relationship of the lower molars to the mandible and investigated two different comparisons: lip bumper (Davidovitch 1997), and lingual arch (Rebellato 1997), versus control. The studies measured the molar position in two different ways; molar inclinational change in degrees and molar anterior‐posterior movement change in millimetres. Rebellato 1997 measured angular change relative to the functional occlusal plane, which they described as a line drawn through maximum inter‐cuspation of the occlusion, whereas Davidovitch 1997 measured it relative to the mandibular plane, described as the line drawn between gnathion and pogonion.
Time to alignment
Eight studies reported on time to alignment of the teeth; two of which were for copper nickel‐titanium versus nickel‐titanium archwires ( Ong 2011; Pandis 2009), two were for self‐ligating brackets versus conventional brackets (Pandis 2011; Songra 2014), and two were for vibrational appliances compared to fixed appliances only (Miles 2016; Woodhouse 2015), so the results were combined. The other two studies compared different comparisons so it was not appropriate to combine the results (Pandis 2010a; Pandis 2011).
Ligation time
One study reported on the ligation time for the two different types of brackets investigated (Miles 2010).
Self‐esteem
No study reported on this outcome.
Patient satisfaction
No study reported on this outcome.
Jaw joint problems
No study reported on this outcome
Other outcomes
Harms
Six studies reported on the discomfort experienced for differing comparisons.
Two studies used a 7‐point Likert Scale (Miles 2010; Ong 2011), and four used a 100 millimetre visual analogue scale (VAS; Atik 2014; Miles 2012; Sandhu 2013; Woodhouse 2015).
One study reported on Plaque Index, Gingival Index and probing depths (Atik 2014).
One study reported on root resorption (Aras 2018).
Excluded studies
We excluded 61 studies from this review for the following reasons (see Characteristics of excluded studies).
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15 were not RCTs
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18 because participants were not primarily receiving treatment to prevent or correct dental crowding
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25 did not fulfil the eligibility criteria for age
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1 did not fulfil criteria for participant crowding
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2 had insufficient information to allow inclusion of data
Risk of bias in included studies
We assessed 23 studies as being at high risk of bias and one study as being at an unclear risk of bias. We determined all but one study as being at a high risk of bias due to the nature of the interventions, meaning that the participants and personnel could not be blinded. See Figure 2 and Figure 3 for a graphical representation of our assessments.
Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies
Risk of bias summary: review authors' judgements about each risk of bias item for each included study
Allocation
We assessed 13 studies as being at low risk of selection bias because they described an adequate method of random sequence generation and allocation concealment based on information published in the papers and further information received via correspondence with the study authors when required (Aydin 2018; Finland 2004; Kau 2004; Miles 2016; Myrlund 2015; Ong 2011; Pandis 2009; Pandis 2010a; Pandis 2011; Sandhu 2013; Sebastian 2012; Songra 2014; Woodhouse 2015). Despite being at a low risk of selection bias, the two groups described by Kau 2004 had differences in the amount of baseline crowding. The remaining 11 studies did not mention any method used to conceal the random sequence or allocation, and we assessed them as being at unclear risk of selection bias; Tai 2010 also described a longer pre‐treatment arch length in the Schwarz appliance group compared to the control.
Blinding
Performance bias
One study described adequate methods of blinding of participants and personnel and we therefore assessed it as being a low risk of bias for this domain (Pandis 2009). We assessed the other 23 studies as being at high risk of performance bias as it was either not possible to blind participants or clinicians, or both, or the study did not mention having done so.
Detection bias
We assessed 12 studies as low risk of detection bias as assessors were blinded (Harradine 1998; Kau 2004; Miles 2010; Miles 2016; Myrlund 2015; Ong 2011; Pandis 2011; Sandhu 2013; Sebastian 2012; Songra 2014; Tai 2010; Woodhouse 2015). We assessed 10 studies as unclear because information about the blinding of assessors was not reported (Atik 2014; Aydin 2018; Davidovitch 1997; Finland 2004; Gravina 2013; Irvine 2004; O'Brien 1990; Pandis 2009; Pandis 2010a; Rebellato 1997). We also deemed an additional study as being at unclear risk of detection bias (Miles 2012); although the assessors were blinded when measuring crowding and measuring the VAS scores, the participants had not been blinded to the intervention when they were measuring their own discomfort. We deemed Aras 2018 at a high risk of bias as the assessor could not be blinded.
Incomplete outcome data
We assessed 15 studies as being at low risk of attrition bias as dropout was less than 20 per cent (Atik 2014; Aydin 2018; Irvine 2004; Kau 2004; Miles 2012; Miles 2016; Myrlund 2015; O'Brien 1990; Pandis 2009; Pandis 2010a; Pandis 2011; Sandhu 2013; Sebastian 2012; Songra 2014; Woodhouse 2015).
We considered two studies to be at high risk due to high level of attrition across the studies (Finland 2004; Harradine 1998). However, these studies had long follow‐up periods.
The remaining seven studies did not report on dropouts and so we assessed them as being at unclear risk (Aras 2018; Davidovitch 1997; Gravina 2013; Miles 2010; Ong 2011; Rebellato 1997; Tai 2010).
Selective reporting
We assessed one study as being at unclear risk of selective reporting bias as it did not state any specific outcomes in the methods section, though it did report on appropriate outcomes in the results (Tai 2010). O'Brien 1990 was also unclear as they did not report final contact point displacement. The other studies were at low risk of bias.
Other potential sources of bias
We assessed three studies as having a high risk of other sources of bias (Aydin 2018; Irvine 2004; Woodhouse 2015). For Irvine 2004, it was unclear who or how many examiners took the measurements and they did not report intra/inter‐rater reliability. For Woodhouse 2015, in the follow‐up study looking at the secondary outcome of root resorption, the study was under‐powered (20% to 30%). For Aydin 2018, the participants were treated in a single centre by one clinician so the results may not be generalisable. In addition, their sample size calculation was based on one of the secondary outcomes rather than the primary outcome. It is worth noting that two studies (Atik 2014; Sebastian 2012), had gender bias in their sampling, having recruited only female participants; this, however, is a source of diversity or applicability rather than bias.
We considered 11 studies to have unclear risk of bias for this domain. One was because there was a clear difference in the baseline crowding between the two groups of participants (Kau 2004). Another study had clear differences for the same outcome, measured by two different methods, in the same study (Davidovitch 1997). Harradine 1998 had an unclear risk of bias due to the recall rate and O'Brien 1990 and Gravina 2013 did not report a sample size calculation. Two studies (Pandis 2010a; Pandis 2011), were conducted in a single‐centre, private practice with a per protocol analysis. In one study, participants in the control group received a variety of interceptive procedures, which were active treatments but not received by all participants in the group, as prescribed in the protocol, whilst comparing against the main intervention (Finland 2004). Another study removed the results for two participants in order to balance the two groups for numbers (Miles 2010). Rebellato 1997 had no sample size calculation, no mention of source of participants, proportion of male and female participants, or allocation concealment. Sebastian 2012 based their sample size just on the pilot study data.
We did not consider the remaining 10 studies to have any other potential sources of bias and we therefore assessed them as being at low risk of bias for this domain.
Effects of interventions
See: Summary of findings 1 Fixed appliances and auxiliaries to prevent or correct dental crowding in children; Summary of findings 2 Removable appliances and auxiliaries to prevent or correct dental crowding in children; Summary of findings 3 Extractions to prevent or correct dental crowding in children
See summary of findings Table 1 Fixed appliances and auxiliaries versus other treatment or no treatment to prevent or correct dental crowding in children; summary of findings Table 2 Removable appliances and auxiliaries to prevent or correct dental crowding in children; summary of findings Table 3 Extractions to prevent or correct dental crowding in children.
Fixed appliances and auxiliaries
Comparison 1: Lower lip bumper versus no active treatment (control)
We assessed Davidovitch 1997 as being at overall high risk of bias as it was not possible to blind personnel and participants.
Crowding
Davidovitch 1997 investigated change in mandibular incisor crowding, in millimetres, for a six‐month follow‐up period. They measured crowding at baseline and six months into treatment. In total, data from 34 participants were used for this outcome.
There was evidence of a greater reduction in lower incisor crowding of 4.39 mm in the lip bumper group, when compared to the control group, at six months (95% CI −5.07 to −3.71; P < 0.001; Analysis 1.1).
Arch length
Davidovitch 1997 investigated arch length change in the mandible, in millimetres, up to a six‐month follow‐up period. They measured crowding at baseline and six months into treatment. In total, data from 34 participants were used for this outcome.
There was evidence of a greater increase in arch length of 3.34 mm in the lip bumper group (95% CI 2.71 to 3.97, P < 0.001) when compared with the control group, at six months (Analysis 1.2).
Lower incisors to mandible
Davidovitch 1997 reported on the relationship on the lower incisors to the mandible, in degrees to the mandibular plane and in millimetres to A‐Pogonion, for up to a six‐month follow‐up period. In total, data from 34 participants were used for this outcome.
There was less labial movement of the lower incisors (0.49 mm) between baseline and six months, in the control group (95% CI 0.09 to 0.89; Analysis 1.3).
The lower incisors proclined 3.14 degrees more in the lip bumper group than the control (95% CI 1.73 to 4.55; Analysis 1.4).
Lower molars to mandible
Davidovitch 1997 reported on the lower molar to the mandibular plane, in degrees and in millimetres, for up to a six‐month follow‐up period. In total, data from 34 participants were used for this outcome.
The lower molar moved distally by 0.61 mm in the lip bumper group, compared to a 0.3 mm mesial movement in the control group. This difference of 0.91 mm (95% CI −1.58 to −0.24) favoured the lip bumper group (Analysis 1.5).
The lower molars tipped distally by 3.38 degrees in the lip bumper group, compared to 0.75 degrees of mesial tipping in the control group. This difference of 4.13 degrees (95% CI −6.09 to −2.17) favoured the lip bumper group (Analysis 1.6).
Harms
No harms were reported.
Other outcomes
Time to alignment and ligation time were not relevant for this comparison.
Upper incisors to maxilla, self‐esteem, participant satisfaction and jaw joint problems were not reported.
Comparison 2: Cervical pull headgear versus minor interceptive procedures (control)
We assessed Finland 2004 as being at overall high risk of performance and attrition bias.
Crowding
Finland 2004 investigated lower incisor crowding, in millimetres, measured at baseline, two, four, eight and 13 years post‐treatment. At the one‐year recall, only 53 per cent of participants were included, meaning that there was high attrition bias. In total, 64 participants began the study and their data were used for this outcome for up to four years; 54 participants provided data for the eight‐year recall; but only 34 returned for the final recall at 13 years. There was no baseline imbalance in the characteristics of participants in each group.
The study found no evidence of a difference in the amount of lower incisor crowding between the two groups at any time point or comparing the change in crowding from baseline (Analysis 2.1; Analysis 2.4)
Arch length
Finland 2004 reported on maxillary and mandibular arch length change, in millimetres, over an eight‐year period. Arch length was measured at baseline, two years and eight years and the changes occurring between these time points and baseline were reported.
For maxillary arch length, between baseline and the two‐year recall, arch length increased more in the headgear group (MD 1.98 mm) compared to the control group (95% CI 1.80 to 2.16: P < 0.00001). At the eight‐year recall, the results still favoured the headgear group (MD 2.28 mm, 95% CI 2.05 to 2.15mm; P < 0.001; Analysis 2.2).
For mandibular arch length, between baseline and the two‐year recall, arch length increased more in the headgear group compared to the control group (MD 1.3 mm, 95% CI 1.17 to 1.43 mm; P < 0.001), and was greater at 8 years (MD 1.52 mm) compared to the control group (95% CI 1.3 to 1.74; P < 0.001; Analysis 2.3).
Lower incisors to mandible
Finland 2004 reported on the lower incisor inclination, in degrees, over a two‐year period. The time points at which the change in lower incisor inclination was measured were baseline, baseline to one year and baseline to two years. In total, 64 participants were included in the analysis.
The characteristics of participants in the headgear and control groups were balanced at baseline with no evidence of a difference between the proclination of the lower incisors (P = 0.47). There was more proclination of the lower incisors (MD 2.3 degrees) in the headgear group compared to the control group at one year (95% CI 0.67 to 3.93; P = 0.006); however, at two years, this difference was lost (MD 1.4 degrees, 95% CI ‐0.42 to 3.22; P = 0.13; Analysis 2.4).
Upper incisors to maxilla
Finland 2004 reported on the upper incisor inclination, in degrees, over a two‐year period. The time points at which the upper incisor change was measured were baseline to one year and baseline to two years. In total, 64 participants were included in the analysis.
The groups were balanced at baseline with no evidence of a difference between their upper incisor inclination (P = 0.10).
Between baseline and one year, there was more proclination of the upper incisors in the headgear group compared to the control group (MD 4 degrees, 95% CI 1.97 to 6.03; P = 0.01). This difference was maintained at two years (MD 4.5 degrees, 95% CI 1.36 to 7.64; P < 0.001; Analysis 2.5).
Harms
No harms were reported.
Other outcomes
The study did not measure the relationship of the lower molars to mandible, self‐esteem, participant satisfaction or jaw joint problems.
Time to alignment and ligation time were irrelevant for this comparison.
Comparison 3: Lower lingual arch versus no active treatment (control)
We assessed Rebellato 1997 as being at overall high risk of bias as it was not possible to blind personnel and participants; the method of randomisation was also unclear.
Crowding
This outcome was not reported.
Arch length
Rebellato 1997 investigated arch length change in the mandible, in millimetres, up to a one‐year follow‐up period. Crowding was measured at baseline and at 10 to 12 months post‐treatment. In total, data from 30 participants were used for this outcome.
The arch length increased more in the lower lingual arch appliance (LLA) group (MD 2.61 mm; 95% CI 1.83 to 3.39; P < 0.001; Analysis 3.1).
Lower incisors to mandible
Rebellato 1997 reported on the lower incisors to the mandibular plane, in degrees and in millimetres, for up to a one‐year follow‐up period.
The lower incisors moved mesially by 0.32 mm in the LLA group, compared to a 0.34 mm distal movement in the control group, a clear difference of 0.66 mm (95% CI 0.46 to 0.86, P < 0.001; Analysis 3.2).
The lower incisors proclined by 0.73 degrees in the LLA group, compared to 2.28 degrees of retroclination in the control group and this difference of 3.01 degrees was clearly different (95% CI 1.71 to 4.31, P < 0.001; Analysis 3.3).
Lower molars to mandible
Rebellato 1997 reported on the lower molar to the mandibular plane, in degrees and in millimetres, for up to a one‐year follow‐up period.
The lower molar moved mesially by 0.33 mm in the LLA, compared to 1.44 mm in the control group and this difference of −1.11 mm was clearly different (95% CI −1.51 to −0.71, P < 0.001; Analysis 3.4).
The lower molars tipped distally by 0.54 degrees in the LLA, compared to 2.19 degrees of mesial tipping in the control group and this difference of −2.73 degrees was clearly different (95% CI −4.29 to −1.17, P < 0.001; Analysis 3.5 ).
Harms
No harms were reported.
Other outcomes
Time to alignment and ligation time were not relevant for this comparison.
Upper incisors to maxilla, harms, self‐esteem and participant satisfaction were not reported.
Comparison 4: Self‐ligating brackets versus conventional brackets
Five studies assessed this comparison, all of which we assessed as being at high risk of bias (Aras 2018; Atik 2014; Miles 2010; Pandis 2011; Songra 2014).
Crowding
One study investigated incisor crowding in the anterior maxilla, in millimetres, for a 10‐week period (Miles 2010). Crowding was measured at baseline and 10 weeks into treatment. We assessed this study as being at overall high risk of bias as although blinding of participants was carried out, blinding of personnel was not possible due to the type of intervention. The study states that participants were randomly allocated but no further details on the methods used were given. Additionally, there were dropouts in the conventional ligation group, so analysis was not performed on two of the self‐ligating group participants. In total, 68 participants provided baseline information and 60 (88.2%) were analysed at follow‐up.
There was no evidence of baseline imbalance between the groups with regards to the pre‐treatment degree of crowding (MD ‐0.17 mm, 95% CI ‐1.49 to 1.15; P = 0.8; Analysis 4.1).
There was no evidence of a difference in lower incisor crowding between the self‐ligating and conventional groups at 10 weeks (MD −0.40 mm, 95% CI −0.93 to 0.13; P = 0.14; Analysis 4.1).
Time to alignment
Two studies reported on time to alignment, in days (Pandis 2011; Songra 2014). The time points reported were the mean number of days it took for alignment in each group. Alignment is described as the point at which a rectangular (0.019 inch x 0.025 inch) copper nickel‐titanium (Pandis 2011), or stainless steel (Songra 2014), archwire could be placed passively. The studies were considered to be at a high overall level of bias as it was not possible to blind participants and personnel as to which bracket type each participant received. In total, data from 148 participants were used for this outcome.
There was no evidence of a difference in time to alignment between the groups (MD 89.64 days; 95% CI −45.89 to 225.17; P = 0.19; Analysis 4.2). However, there was definite heterogeneity (I2 = 94%) in the treatment effect, which can be explained by the difference in the point at which alignment was assessed.
Ligation time
One study reported on the time to tie, ligate and untie six brackets, in seconds (Miles 2010). This study was assessed as being at overall unclear risk of bias, as the methods of randomisation and allocation concealment were not described; the participants were blinded but the clinicians were not; and not all the participants who completed the study were analysed, in order to keep the groups equal in size at the follow‐up. In total, data from 68 participants were used for the outcome of the time taken to untie, and data from 60 participants were used for the outcome of the time taken to ligate six brackets.
Untying was quicker (MD −22.3 seconds) in the self‐ligating group (95% CI −25.83 to −18.77, P < 0.001; Analysis 4.3).
Ligation was quicker (MD −78.8 seconds) in the self‐ligating group (95% CI −81.86 to −75.74, P < 0.001; Analysis 4.3).
Lower incisors to mandible
Atik 2014 reported on the lower incisors to the mandibular plane, in degrees until the stage of treatment when a 0.019” x 0.025” stainless steel archwire was placed. We assessed Atik 2014 as being at overall high risk of bias as neither the participants nor the clinicians were blinded and the entire sample consisted of female participants. A total of 33 participants' data were used for the outcome of lower incisor inclination.
There was no evidence of baseline imbalance in lower incisor inclination despite there being 3.38 degrees less proclination in the conventional bracket group (95% CI −0.04 to 6.80; P = 0.05).
Post‐treatment, the change in lower incisor inclination in the conventional bracket group was 1.29 degrees less than the self‐ligating group, but no clear difference between the groups was seen (95% CI −1.77 to 4.35; P = 0.41; Analysis 4.4).
Harms
Atik 2014 and Miles 2010 reported on discomfort. Atik 2014 reported on plaque index, gingival index and probing depth. Aras 2018 reported on root resorption of the maxillary incisors.
Atik 2014 described discomfort using a 100 mm VAS over the first month. The participants were asked to keep a diary and record discomfort in the maxilla and mandible at 4 hours, 24 hours, 3 days, 1 week, and 1 month using the terms “very comfortable” and “very uncomfortable” at the ends of the scale. No evidence of a difference in discomfort scores between self‐ligating and conventional brackets, was found.
Miles 2010 described discomfort using a 7‐point Likert scale for the first week. The participants were given a questionnaire and asked to record discomfort in the upper arch at 4 hours, 24 hours, 3 days and 1 week. Again, no evidence of a difference for discomfort scores between self‐ligating and conventional brackets, was found.
Atik 2014 described the periodontal and gingival health of all 24 maxillary and mandibular teeth and estimated the mean value per participant. They did not find evidence of differences in any of the scores between self‐ligating and conventional brackets, from the baseline measurement to the end of the study.
Aras 2018 measured the amount of root resorption of the maxillary incisors using cone beam computed tomography (CBCT) scans for 32 participants before treatment and nine months into treatment. There was no evidence of differences in root resorption between self‐ligating and conventional brackets.
Other outcomes
Lower molars to mandible, upper incisors to maxilla, arch length, self‐esteem, participant satisfaction and jaw joint problems were not reported.
Comparison 5: Active versus passive self‐ligating brackets
Two studies assessed this outcome (Pandis 2010a; Songra 2014), and we considered both as being at overall high risk of bias because it was not possible to blind personnel and participants. However, in Pandis 2010a, there was evidence of a difference between groups, in the amount of baseline crowding.
Crowding
Pandis 2010a investigated baseline upper anterior crowding in millimetres. In total, data from 70 participants were used for this outcome.
There was evidence of a difference in crowding at baseline between the two bracket groups (P = 0.04), putting the study at a high risk of bias.
Time to alignment
Both studies (Pandis 2010a; Songra 2014), reported on this outcome. Pandis 2010a considered alignment complete when the maxillary incisors were visually regarded as aligned whereas for Songra 2014, it was when a rectangular (0.019 inch x 0.025 inch) stainless steel archwire could be placed passively. In total, 144 participants completed the study and their data were used for this outcome.
There was no evidence of a difference in the time to alignment between the two bracket groups (MD −13.11 days, 95% CI −28.76 to 2.53; P = 0.10; Analysis 5.2).
Harms
No harms were reported.
Other outcomes
Ligation time, arch length, lower incisors to mandible, lower molars to mandible, upper incisors to maxilla, self‐esteem, patient satisfaction and jaw joint problems were not reported.
Comparison 6: Copper nickel‐titanium versus nickel‐titanium archwires
Three studies assessed this comparison (Aydin 2018; Ong 2011; Pandis 2009). We assessed Aydin 2018 and Ong 2011 as being at high risk of bias and Pandis 2009 as being at an unclear risk of bias overall.
Crowding
All three studies reported baseline mandibular anterior crowding in millimetres. We combined them in a meta‐analysis and found no difference in baseline crowding between the groups (MD −0.34 mm, 95% CI −1.27 to 0.58; P = 0.47; 254 participants; Analysis 6.1).
Aydin 2018 reported Little's Irregularity Index in millimetres at 2, 4, 6, 8, 10 and 12 weeks. Data after 12 weeks' treatment are reported and showed evidence of a difference favouring nickel‐titanium (NiTi )(MD 0.49 mm, 95% CI 0.35 to 0.63; P < 0.00001; Analysis 6.2).
Time to alignment
We combined two studies in a meta‐analysis to assess time to alignment in days (Ong 2011; Pandis 2009). Data from 191 participants were analysed and revealed that overall, there was no evidence of a difference in time to alignment based on either the copper NiTi or NiTi archwire sequence (MD −2.63 days, 95% CI −14.50 to 9.24; P = 0.66; Analysis 6.3).
Harms
One study investigated the discomfort experienced on a 7‐point Likert scale (Ong 2011). The participants were given a questionnaire and asked to record discomfort in the upper arch at four hours, 24 hours, three days and one week after each archwire was changed. There was no evidence of a difference in the overall discomfort levels between the copper NiTi and NiTi archwire sequences.
Other outcomes
Ligation time was not relevant to this comparison. Arch length, lower incisors to mandible, lower molars to mandible, upper incisors to maxilla, self‐esteem, participant satisfaction and jaw joint problems were not reported.
Comparison 7: Coaxial nickel‐titanium versus nickel‐titanium archwires
We assessed Sebastian 2012 as being at overall high risk of bias as they did not carry out blinding of personnel and participants; in addition, the sample consisted of female participants only.
Crowding
One study investigated lower anterior crowding in millimetres for up to eight weeks (Sebastian 2012). The time points at which reduction in crowding, or tooth movement was reported were 4, 8 and 12 weeks. In total, data from 24 participants were used for this outcome.
There was baseline equivalence in crowding between coaxial nickel‐titanium (NiTi) and NiTi groups (MD 0.10 mm, 95% CI −1.14 to 1.34; P = 0.87).
More tooth movement, or reduction in crowding, was found in the coaxial NiTi group compared to the NiTi group at 4, 8 and 12 weeks. The greatest difference was seen at 12 weeks (MD 6.77mm, 95% CI 5.55 to 7.99; P < 0.001; Analysis 7.2), with the difference having clearly increased over time from 4 to 12 weeks (P < 0.001).
Harms
No harms were reported.
Other outcomes
Ligation time was not relevant to this comparison. Time to alignment, arch length, lower incisors to mandible, lower molars to mandible, upper incisors to maxilla, self‐esteem, participant satisfaction and jaw joint problems were not reported.
Comparison 8: Nitinol versus titinol archwires
We assessed O'Brien 1990 as being at overall high risk of bias as they did not report blinding of personnel and participants.
Crowding
O'Brien 1990 investigated baseline upper anterior crowding in millimetres for up to 37 days. In total, data from 40 participants were used for this outcome.
There was baseline equivalence in the amount of crowding between nitinol and titinol groups (MD 3.31 mm, 95% CI −0.73 to 7.35; P = 0.11).
There was no evidence of a difference in the change in crowding between the nitinol and titinol groups (MD −0.28 mm, 95% CI −0.89 to 0.33; P = 0.37; Analysis 8.1).
Harms
No harms were reported.
Other outcomes
Ligation time was not relevant to this comparison. Time to alignment, arch length, lower incisors to mandible, lower molars to mandible, upper incisors to maxilla, self‐esteem, participant satisfaction and jaw joint problems were not reported.
Comparison 9: Nickel‐titanium versus multistranded stainless steel archwires
We deemed both Gravina 2013 and Sandhu 2013 at high risk of bias as they did not report blinding of participants and personnel. Gravina 2013 was also potentially under‐powered.
Crowding
Gravina 2013 investigated the change in mandibular crowding in millimetres from baseline to eight weeks. In total, data from 25 participants were used for this outcome. They found that there was no difference between the two archwires (MD 1.60, 95% CI −22.16 to 25.36; P = 0.90).
Harms
Sandhu 2013 reported on pain perception during the initial levelling and aligning phase of orthodontic treatment between nickel titanium archwires and multistranded stainless steel archwires. They found no evidence of a difference for overall pain. However, participants did definately experienced more pain with nickel titanium archwires at 12 hours and during day 1 in the morning, afternoon and at bedtime, when compared to those with the multistranded stainless steel archwires.
Other outcomes
Time to alignment, arch length, lower incisors to mandible, lower molars to mandible, upper incisors to maxilla, self‐esteem, participant satisfaction and jaw‐joint problems were not reported. Ligation time was not relevant to this comparison.
Comparison 10: Nickel‐titanium versus stainless steel archwires
We deemed Gravina 2013 at a high risk of bias as they did not report blinding of participants and personnel. The study was also potentially underpowered.
Crowding
Gravina 2013 investigated the change in mandibular crowding in millimetres from baseline to eight weeks. In total, data from 24 participants were used for this outcome. They found that there was no difference between the two archwires (MD −16.80, 95% CI −42.79 to 9.19; P = 0.21).
Harms
No study in this subgroup presented data in a way that facilitated assessment of this outcome.
Other outcomes
Ligation time was not relevant to this comparison. Time to alignment, arch length, lower incisors to mandible, lower molars to mandible, upper incisors to maxilla, self‐esteem, participant satisfaction and jaw joint problems were not reported.
Comparison 11: Multistranded stainless steel versus stainless steel archwires
We deemed Gravina 2013 at a high risk of bias as they did not report blinding of participants and personnel. The study was also potentially underpowered.
Crowding
Gravina 2013 investigated the change in mandibular crowding in millimetres from baseline to eight weeks. In total, data from 23 participants were used for this outcome. They found that there was no difference between the two archwires (MD −18.40, 95% CI −47.12 to 10.32; P = 0.21).
Harms
No study in this subgroup presented data in a way that facilitated assessment of this outcome.
Other outcomes
Ligation time was not relevant to this comparison. Time to alignment, arch length, lower incisors to mandible, lower molars to mandible, upper incisors to maxilla, self‐esteem, participant satisfaction and jaw joint problems were not reported.
Comparison 12: Lacebacks with fixed appliances versus fixed appliances only (control)
We assessed Irvine 2004 as being at high risk of bias.
Crowding
Irvine 2004 reported the amount of lower labial segment crowding at the time when the fixed appliances were placed and when sufficient levelling had taken place with a 0.018" stainless steel archwire. This was done by comparing the amount of available space and the combined mesio‐distal widths of the teeth. In total, data from 62 participants were analysed.
No evidence of baseline imbalance between the two groups was reported. There were no differences in the mean change in the amount of crowding between the fixed appliance only and the fixed appliance with lacebacks groups, at six months (MD −0.33 mm, 95% CI −5.90 to 5.24; P = 0.91; Analysis 12.1).
Arch length
Irvine 2004 also reported on the change in arch length between the two groups. They measured this bilaterally as a straight line between the marginal ridge of the lower first molar and the mesio‐incisal edge of the most prominent central incisor and added the two values together.
There was no evidence of a difference in the arch length between the fixed appliance only and the fixed appliance with lacebacks groups (MD 0.83 mm, 95% CI −6.41 to 8.07; P = 0.82; Analysis 12.2).
Harms
No harms were reported.
Other outcomes
Time to alignment, ligation time, lower incisors to mandible, lower molars to mandible, upper incisors to maxilla, self‐esteem, participant satisfaction and jaw‐joint problems were not reported.
Comparison 13: Vibrational appliance versus no vibrational appliance (control)
Crowding
Three studies investigated mandibular anterior crowding in millimetres and but we combined only two of them in a meta‐analysis (Miles 2012; Woodhouse 2015). We assessed Miles 2016 as being at overall high risk of bias and we were unable to obtain appropriate data for this outcome. Woodhouse 2015 was also at a high risk of bias, mainly as they did not blind the clinicians and participants to the intervention, and Miles 2012 was at a high risk of bias as they could not blind participants and they reported on discomfort using a 100 mm VAS. In total, data from 119 participants were used for the outcome of the change in crowding. There was no evidence of baseline imbalance in irregularity between the two groups in each study and between the studies (P = 0.7; Analysis 13.1).
Overall, there was no evidence of a difference in the change in crowding in either group as reported in Miles 2012 and Woodhouse 2015 (MD 0.24, 95% CI −0.81 to 1.30; P = 0.65). There was no heterogeneity (I2= 0%; Analysis 13.2).
Time to alignment
We combined results from Miles 2016 and Woodhouse 2015 in a meta‐analysis that showed that there was no evidence of a difference between the two groups for the time to alignment (MD −3.70, 95% CI −26.29 to 18.89; P = 0.75). There was no heterogeneity (I2 = 0%; Analysis 13.3).
Harms
Two studies reported on discomfort using a 100 mm VAS over the first week (Miles 2012; Miles 2016). The participants were asked to keep a diary and record discomfort at four time points: bond‐up, six to eight hours after appliance placement, one day after, three days after and seven days after at the appliances were placed. There was no clear difference in discomfort scores between those participants in the vibrational appliance and those in the control groups.
Woodhouse 2015 reported pain intensity using a 100 mm VAS over the first week following insertion of fixed appliances, as well as analgesia consumption. Recordings were taken at bond‐up, four hours, 24 hours, 72 hours and at one week. The use of a vibrational appliance made no clear difference in the pain intensity experienced by the participants or the amount of analgesics they took.
Root resorption
Woodhouse 2015 also reported orthodontically‐induced inflammatory root resorption by taking a long‐cone periapical radiograph of the upper right central incisor for 81 participants at the start of treatment and at the end of alignment when a 0.019 x 0.025‐inch stainless steel archwire was placed. For the 72 participants included in the analysis, the study found that using a vibrational appliance did not affect the amount of root resorption when compared to the control.
Other outcomes
Time to alignment, arch length, lower incisors to mandible, lower molars to mandible, upper incisors to maxilla, self‐esteem, participant satisfaction and jaw‐joint problems were not reported. Ligation time was not relevant to this comparison.
Removable appliances and auxiliaries
Comparison 14: Schwarz appliance versus no active treatment (control)
We assessed Tai 2010 as being at overall high risk of bias as it was not possible to blind personnel and participants.
Crowding
Tai 2010 investigated lower arch crowding, in millimetres, over a nine‐month post‐treatment follow‐up period. Time‐points measured were baseline and nine months after expansion of the arches with a Schwarz appliance for six months. In total, 28 participants were included in this study.
There was no evidence of baseline imbalance in the degree of crowding between the Schwarz appliance and control groups (P = 0.48).
There was more reduction in lower arch crowding (MD −2.14 mm) in the Schwarz appliance group at the nine‐month follow‐up (95% CI −2.79 to −1.49, P < 0.00001; Analysis 14.1).
Arch length
Tai 2010 reported mandibular arch length, in millimetres, as reported above. Twenty‐eight participants were included in this analysis.
There was evidence of imbalance in baseline arch length (MD 1.86 mm) with the Schwarz appliance group having a longer pre‐treatment arch length than the control group (95% CI 0.23 to 3.49; P = 0.03).
There was no evidence of a difference in the change in arch length (MD 0.11 mm) between baseline and the nine‐month follow‐up between the Schwarz appliance group and the control (95% CI −0.46 to 0.68; P = 0.71; Analysis 14.2).
Lower incisors to mandible
Tai 2010 reported on lower incisor position, in millimetres. The time points at which lower incisor position was measured are as above. In total, 28 participants were included in the analysis.
There was no evidence of baseline imbalance in the lower incisor position of the groups (P = 0.89).
There was evidence of a difference in the change in lower incisor position relative to the mandible (MD 0.39 mm; 95% CI 0.11 to 0.67; P = 0.006) with the lower incisors being more advanced in the Schwarz appliance group (Analysis 14.3).
Upper incisors to maxilla
Tai 2010 reported on upper incisor position, in degrees. The time points and risk of bias have been discussed earlier. In total, 28 participants were included in the analysis.
There was no evidence of baseline imbalance, between the groups, in the incisor inclination (P = 0.94).
There was no evidence of a difference between the Schwarz appliance group and the control group in the change in upper incisor inclination at the nine‐month follow‐up (MD 0.33 degrees, 95% CI −2.26 to 2.92; P = 0.8; Analysis 14.4).
Harms
No harms were reported.
Other outcomes
Time to alignment and ligation time were not relevant for this comparison.
Lower molars to mandible, self‐esteem, participant satisfaction and jaw joint problems were not reported.
Comparison 15: Eruption guidance appliance versus no active treatment (control)
We assessed Myrlund 2015 as being at overall high risk of bias as it was not possible to blind personnel and participants.
Crowding
Myrlund 2015 investigated incisor crowding in the maxilla and the mandible, in millimetres, for a one‐year follow‐up period. They measured crowding at baseline and one‐year post‐treatment. In total, 46 participants began the study and their data were used for this outcome.
There was no evidence of baseline imbalance in crowding between the eruption guidance appliance (EGA) and the control groups for maxillary (upper) and mandibular (lower) anterior crowding (P = 0.15 in maxilla; P = 0.26 in mandible).
In the maxilla, there was no evidence of a difference in the number of children with crowding between the EGA and control groups at one‐year post‐treatment (OR 0.82 mm, 95% CI 0.25 to 2.63; P = 0.74; Analysis 15.1).
In the mandible, there were fewer children with crowding in the EGA group than the control group at one‐year post‐treatment (OR 0.19, 95% CI 0.05 to 0.68; P = 0.01; Analysis 15.2).
Lower incisors to mandible
Myrlund 2015 reported on lower incisor inclination to the mandible, in degrees, for a one‐year follow‐up in the EGA group. No data for the control group were reported for the one‐year post‐treatment follow‐up.
Upper incisors to maxilla
Myrlund 2015 reported on upper incisor inclination to the maxilla, in degrees, for a one‐year follow‐up in the EGA group. No data for the control group were reported for the one‐year post‐treatment follow‐up.
Harms
No harms were reported.
Other outcomes
Ligation time was not relevant. Arch length, lower molars to mandible, self‐esteem, participant satisfaction, jaw joint problems, and time to alignment were not reported.
Extractions
Comparison 16: Extraction of lower deciduous canines versus no active treatment (control)
We assessed Kau 2004 as being at overall high risk of bias as it was not possible to blind the assessors and there was a definate difference in the amount of dental crowding at baseline.
Crowding
Kau 2004 investigated lower incisor crowding in millimetres at baseline and one to two years post‐treatment. In total, 97 participants began the study and their data were used for the outcome of crowding at baseline, and 85 (85.6%) participants attended the recall appointment.
At baseline, there was evidence of less lower incisor crowding (1.8 mm) in the non‐extraction group (95% CI 0.39 to 3.21; P = 0.01).
The reduction in lower incisor crowding in the extraction group, between baseline and 1 to 2 years post‐treatment, was greater than in the control group (MD −4.76 mm, 95% CI −6.24 to −3.28; P = 0.00001; Analysis 16.1).
Arch length
Kau 2004 reported on arch length, in mm, at one to two years post‐treatment. The change in arch length was measured at baseline and one year post‐treatment. In total, data from 97 participants were used for the outcome of arch length at baseline and 83 participants presented at the one‐year recall.
There was a greater reduction in arch length in the extraction group compared to the non‐extraction group (MD −2.73 mm, 95% CI −3.69 to −1.77, P < 0.001; Analysis 16.2).
Lower incisors to mandible
Kau 2004 reported on lower incisor inclination, in degrees, for up to one year post‐treatment. The change in lower incisor inclination was measured at baseline and one year post‐treatment. In total, 97 participants began the study and their data were used for the outcome of crowding at baseline and 83 participants presented at the one‐year recall.
There was no evidence of a difference in the change in lower incisor inclinational between baseline and one year post‐treatment, between the extraction and the non‐extraction groups (MD 0.08 degrees, 95% CI −0.55 to 0.71; P = 0.8; Analysis 16.3).
Harms
No harms were reported.
Other outcomes
Time to alignment and ligation time were not relevant for this comparison.
Lower molars to mandible, upper incisors to maxilla, self‐esteem, participant satisfaction and jaw joint problems were not reported.
Comparison 17: Extraction of third molars versus no active treatment (control)
We assessed Harradine 1998 as being at a high risk of bias due to a high number of dropouts and participants and personnel not blinded due to the nature of the intervention.
Crowding
Harradine 1998 reported the amount of crowding using Little's Irregularity Index. For the 77 participants who completed the study, no baseline imbalances were reported. There was no evidence of a difference in the change in the amount of crowding between the two groups (MD −0.30 mm, 95% CI −1.30 to 0.70; P = 0.56; Analysis 17.1).
Arch length
Harradine 1998 also reported the change in arch length between the two groups as the sum of the distances measured bilaterally between the mesial contact of the first molars and the midline contact point. There was evidence of a clear difference between the two groups (MD 1.03, 95% CI 0.56 to 1.50, P < 0.0001) with a greater decrease in arch length for the non‐extraction group (Analysis 17.2).
Harms
No harms were reported
Other outcomes
Time to alignment, ligation time, lower incisors to mandible, lower molars to mandible, upper incisors to maxilla, self‐esteem, participant satisfaction and jaw‐joint problems were not reported.
Discussion
Summary of main results
We included 24 RCTs with 1512 participants, of whom 1314 were analysed in this review. The studies evaluated 17 comparisons. We were able to perform meta‐analyses for four comparisons.
Fixed appliances and auxiliaries
Lower lip bumper versus no active treatment (control)
The lower lip bumper reduced crowding by 4.39 mm more than the control group and increased the arch length by 3.34 mm. Both these findings are clearly different and clinically important.
The increase in arch length for the lip bumper group appeared to be due to incisor advancement (0.69 mm) and distal movement of the molar (0.61 mm), thus potentially gaining 1.3 mm of arch length. Additionally, in the lip bumper group, the lower incisors proclined by 3.14 degrees and the molars tipped distally by 4.13 degrees more than in the control group.
These findings suggest that the lip bumper keeps the molars upright and increases arch length at the expense of lower labial segment advancement. Whilst these findings showed differences with lip bumper, their clinical importance would have to be assessed on a case‐by‐case basis. Additionally, as there was only one available study that was at high risk of bias, the evidence is of very low certainty.
These findings were similar to those resulting from treatment with the lower lingual arch. Both appliances increased the arch length by around 3 mm, resulted in lower labial segment advancement of about 0.5 mm and prevented mesial movement of the molars by causing them to tip distally compared to the control groups.
Cervical headgear versus minor interceptive procedures (control)
We found that, in the one available study, headgear increased arch length in the upper arch by up to 2.28 mm more than the control group, but this was at the expense of 2.5 degrees of upper incisor proclination, therefore resulting in anterior anchorage loss. Subgroup analysis revealed that there was no clear difference in the change in proclinations seen, between baseline and one year or between baseline and two years, so the majority of the proclination occurred in the first year.
Lower arch length also increased by up to 1.52 mm and the majority of the increase was in the first two years, as subgroup analysis did not reveal a clear difference between two and eight years. The lower incisors also initially proclined, but this effect was not maintained at two years, indicating that cervical pull headgear therapy does not result in long‐term lower incisor proclination. It was also found not to affect lower incisor crowding. Upper incisor crowding was not examined, but this would be an outcome worth investigating to determine whether cervical pull headgear does alleviate crowding and if so, whether this is by increasing the maxillary arch length by incisor proclination, by distal movement of the buccal segments or a combination of both.
Lower lingual arch (LLA) versus no active treatment (control)
The LLA is traditionally passive so is used to maintain arch length and maintain leeway space following the loss of deciduous molar(s). Our analysis, from the one available study, revealed that the LLA prevented mesial movement (1.11 mm) and tipping (2.73 degrees) of the molar compared with the control group. The clinical importance of these findings may be limited. More detailed analysis revealed that the LLA only permitted 0.33 mm of mesial movement of the molar and resulted in 0.54 degrees of distal tipping, which would be 0.66 mm for the entire lower arch. In comparison, the control group had 1.44mm of mesial movement, giving a total of 2.88 mm for the arch and 2.19 degrees of mesial inclination.
Anteriorly, in the LLA group, the lower incisors advanced by 0.66 mm and 3.01 degrees more than the control group, which can be interpreted as anterior anchorage loss. However, upon closer inspection, the advancement in LLA was only 0.32 mm and by 0.73 degrees. In contrast, the control group had retroclination and distal movement of the anterior teeth, so whilst there was a difference, it may not be clinically important.
Overall, it seems that the LLA keeps the molars upright and preserves space, despite a small amount of anterior anchorage loss, compared to the control group, who had mesial movement of the lower molars and retroclination of the lower incisors. These findings were confirmed by the clear difference in the arch lengths: the LLA increased mandibular arch length by 0.07 mm, whereas the control group had a 2.54 mm reduction. The 2.61 mm difference may be clinically important.
The LLA could be considered a method of preserving the leeway space and helping to prevent crowding in the mixed dentition from being perpetuated into the permanent dentition. This may be even more relevant if deciduous molars are lost early and could be the focus of future clinical studies. However, the evidence is of very low certainty with only one available study at a high risk of bias.
Brackets
Self‐ligating versus conventional brackets
Our analysis, of three studies, revealed that there was no evidence of a difference in the relief of crowding (Analysis 4.1), or time to alignment (Analysis 4.2), between the self‐ligating and conventional brackets (Miles 2010; Pandis 2011; Songra 2014). However, there was significant heterogeneity (I2 = 94%) in the time to alignment with the time taken being much longer in Songra 2014. This can be explained by the difference in the point at which alignment was assessed. Pandis 2011 took the point to be when a rectangular (0.019" x 0.025") copper nickel‐titanium archwire was inserted passively whereas for Songra 2014, it was when a rectangular (0.019" x 0.025") stainless steel archwire was placed.
Whilst the lower incisors definitely appeared to show more proclination in the self‐ligation group, no difference was found between the two groups in the periodontal index, gingival index or pocketing depths, from the start to end of the study. However, this could be attributed to differences between the groups at baseline, with the self‐ligation group already having greater incisor proclination (Atik 2014). Further confirmation was provided by no difference being found in the change in inclination of the lower incisors, between the groups.
There was, however, a clear and clinically important difference between self‐ligating and conventional brackets, in the time taken to ligate and untie the brackets (Miles 2010). Overall, self‐ligating brackets saved over a minute and a half per treatment episode (where we assume a participant has an archwire change and so requires untying and ligation). If this is extrapolated to 30 patients, which is an estimation of the number of patients seen in an orthodontic practice per day, this is potentially a saving of approximately 45 minutes per day. This is clinically significant as this time could be used to see more patients, take a break or undertake other activities; however, the increased cost of the self‐ligating bracket systems also needs to be considered.
No evidence of a difference was found in the discomfort experienced by participants, with each of the two types of brackets, from four hours to one month after bond‐up (Atik 2014; Miles 2010).
No evidence of a difference found between the periodontal index, gingival index or pocketing depths between both groups of participants between the start and end of the study (Atik 2014).
There was also no difference in the amount of root resorption between the two groups measured between the start of treatment and nine months into treatment (Aras 2018).
These data suggest that self‐ligating brackets have no clinical advantages; however, they did result in some time saving, which has to be balanced against their increased cost. However, the evidence is of very low certainty and based on three available studies at a high risk of bias.
Active versus passive self‐ligating brackets
Two studies contributed data to this comparison (Pandis 2010a; Songra 2014). Our analysis showed that there was no evidence of a difference in the time to alignment between active and passive self‐ligating brackets. The results were consistent (I2 = 0%). The lack of significance may be attributed to the studies having relatively small sample sizes and relatively large SDs and wide CIs (Analysis 5.2). Additionally, in Pandis 2010a, there was evidence of less crowding (MD −1.0 mm; 95% CI −1.96 to −0.04; P = 0.04) in the active self‐ligation group at baseline, so alignment in this group may have been quicker, causing the difference in treatment effect to have been overestimated.
Archwires
Copper nickel‐titanium versus nickel‐titanium
We combined data from three studies in meta‐analyses to assess differences in baseline crowding and time to alignment (Aydin 2018; Ong 2011; Pandis 2009). This revealed that overall, there was baseline equivalence with regards to pre‐treatment crowding (Analysis 6.1).
For crowding at 12 weeks, a difference between groups was found in favour of the nickel‐titanium sequence (Analysis 6.2).
For time to alignment, no evidence of a difference was found between the groups in the meta‐analysis (Analysis 6.3). There was very limited heterogeneity with I2 statistic at 2%.
When investigating discomfort, there was no difference found between the archwire groups for up to one week after the archwire was changed (Ong 2011).
Coaxial nickel‐titanium versus nickel‐titanium
One study provided evidence that there is greater resolution of crowding with coaxial NiTi than NiTi and that the treatment effect increases over time for up to 12 weeks, which was the end point of the study (Sebastian 2012). However, all the participants were female so the results of the study may not be generalisable.
Titanol versus Nitinol
After demonstrating baseline equivalence in crowding between the groups, one study found no difference in the relief in crowding between the archwires (O'Brien 1990). Again, this would suggest that there is no advantage to using one wire or the other for faster alignment of the teeth; however, the level of certainty of the evidence is very low.
Nickel‐titanium versus multistranded stainless steel
We assessed one study for this comparison and found no difference in the change in crowding over time; however, this could potentially be a false negative due to the small sample size (Gravina 2013). Sandhu 2013 demonstrated that there was no difference in overall pain experience; however, NiTi archwires did cause significantly more pain at 12 hours and during day 1, than the multistranded stainless steel. The study was deemed to be at a high risk of bias.
Nickel‐titanium versus stainless steel
We assessed one study for this comparison and found that whilst initially there appeared to be a benefit to using NiTi between baseline and eight weeks, there was no clear difference in the change in crowding over time, however the study was small and likely to be under‐powered (Gravina 2013).
Multistranded stainless steel versus stainless steel
Gravina 2013 showed that there was no difference in the change in the amount of mandibular incisor crowding between the two archwires from baseline to eight weeks, but this may again be attributed to this study being small and potentially under‐powered.
Lacebacks and fixed appliances versus fixed appliances only (control)
Irvine 2004 reported that there were no clear differences in the amount of crowding or arch length between the two groups. In both groups, the lower incisors retroclined and extruded. The mandibular first molar, however, migrated mesially in the laceback group by 0.75 mm compared to the non‐laceback group, which moved distally by 0.08 mm. This mean difference of 0.83 mm could be deemed clinically significant in terms of anchorage control and space closure.
Therefore, while the use of lacebacks may not affect crowding, arch length or the position of the lower labial segment, they may be useful if anchorage loss, by mesial migration of the first permanent molars, is required posteriorly. However, This is based on one study and the evidence is of low certainty.
Vibrational appliances with fixed appliances versus fixed appliances only (control)
Two studies were identified for this comparison and combined in a meta‐analysis (Miles 2012; Woodhouse 2015).
Baseline equivalence of crowding was demonstrated (Analysis 13.1). No difference in the change in irregularity between the start and at 8 to 10 weeks (Analysis 13.2, or any subgroup differences were found between the vibrational appliance group and the control group (Analysis 13.2); however, the studies were potentially under‐powered. Additionally, there was no clear difference in the time to alignment (Analysis 13.3), reduction in discomfort or root resorption when using the vibrational appliances, so overall they provided no benefit with regards to relief of crowding, analgesia consumption, pain reduction or root resorption.
Removable appliances and auxiliaries
Schwarz appliance versus no active treatment (control)
Our analysis found that the Schwarz appliance reduced lower arch crowding by 2.14 mm more than in the control group. However, there were clear differences in baseline arch lengths, favouring the Schwarz group, and overall, no difference was seen in the change in arch length. There was also no difference in maxillary incisor advancement, but subgroup analysis revealed that the change in mandibular incisor advancement was double in the Schwarz appliance group compared to the control group. However, whilst there was a difference in the amount of advancement seen, (P = 0.006), at only 0.39 mm, it was not thought to be clinically important and could also be attributed to tracing error.
While the available evidence suggests that the Schwarz appliance is an effective treatment option for the alleviation of crowding in the mandibular arch in the short‐term, the evidence is of very low certainty with only one available study that was deemed at high risk of bias. Also, there was no follow‐up beyond nine months so it is not possible to say whether this improvement in crowding was maintained into the permanent dentition.
Eruption guidance appliance versus no active treatment (control)
The eruption guidance appliance (EGA) improved crowding in the lower labial segment with an odds ratio of 0.19, so that the likelihood of remaining crowded in the control group was 5.3 times more than in the treatment group. This was also confirmed by subgroup analysis that demonstrated a clear difference in crowding levels post‐treatment, despite baseline equivalence. However, the treated group also had 4.1 degrees of lower incisor proclination post‐treatment, which would suggest that resolution of crowding was, in part, due to the space gained from proclination. As the control group’s incisor inclination was not reported, we are unable to determine if this effect is due to the appliance.
In the maxilla, the appliance made no difference to crowding or to upper incisor proclination.
Further research, with data for the control group and long‐term follow‐up, is required for this appliance. There is a very low level of certainty in the results because they were based on one available study, which was at a high risk of bias.
Extractions
Extraction of lower deciduous canines versus no active treatment (control)
Extracting the lower deciduous canines definitely reduced crowding of the lower incisors by 4.76 mm more, but the arch length was reduced by 2.73 mm when compared to the observation group. There was no difference in the inclination of the lower incisors between the extraction and observation groups, so relief of crowding did not occur by proclination of the lower labial segment and was more likely to be as a direct result of alignment into the extraction space. However, as arch length was also reduced in the extraction group, this would imply that space is then lost for either the permanent canines or the premolars, thus transferring and increasing the crowding into the adult dentition.
The study, Kau 2004, discusses the impact of the crowding in more detail; crowding was considered to have improved if there was a 50% reduction, or if there was an irregularity score of less than 2.5 mm at the end of the study. In the extraction group, only 28% of cases demonstrated an improvement against these criteria. In fact, when arch length loss was considered alongside the crowding, only 6% of cases showed an improvement, meaning that overall there was only a 5% chance of improving crowding by extracting the lower deciduous canines.
These results should be interpreted with caution, as there was a definite difference in baseline crowding between the groups, with the extraction group having more crowding pre‐treatment. This suggests that the treatment effect may have been overestimated, as the more severely crowded teeth were able to align into the available space.
Extraction of third molars versus no active treatment (control)
Extraction of the third molars did not affect the amount of lower incisor crowding that developed; the difference between the extraction and non‐extraction groups was only 1.1 mm, which was not thought to be clinically significant. The study also reported that there were no clear differences between the two groups for upper arch crowding (Harradine 1998).
Extraction of the third molars did significantly affect the mandibular arch length, with a greater decrease in the non‐extraction group of 2.1 mm compared to the extraction group of 1.1 mm. Harradine 1998 discussed that they looked back at the study models as they could not understand why the arch length was significantly affected but not the level of crowding; they found that 23 cases had some residual space where they had had premolar extractions, despite absence of space being part of the inclusion criteria. However, when they further analysed the data by excluding these cases, they found that there was still not definate difference in crowding but that the difference in arch length was still clearly different. The study discussed that this disparity may be due to third molars having a greater impact on arch form, rather than anterior alignment.
These results should be interpreted carefully due to the high dropout rate, with only 47% of the original recruited participants completing this study. The results suggest that while extraction of wisdom teeth may have some effect on mandibular arch length, it does not significantly affect anterior crowding.
Overall completeness and applicability of evidence
Overall, we found 24 studies that investigated orthodontic interventions used to prevent or correct crowding of teeth in children.
Twenty studies compared the use of fixed appliances and auxiliaries to a control, including the use of a lower lip bumper, cervical pull headgear, lower lingual arch, different types of brackets, different types of archwire, lacebacks and vibrational appliances. Two studies compared the use of removable appliances to a control, including the Schwarz appliance and eruption guidance appliance. Two studies compared extracting teeth to a control, including extracting deciduous canines and third molars.
Two studies had high levels of attrition (Finland 2004; Harradine 1998), and four studies were potentially under‐powered (Gravina 2013; Miles 2012; Miles 2016; Woodhouse 2015). We assessed 23 studies as being at a high risk of bias and one study as being at an unclear risk of bias. The results for most outcomes were of very low certainty and therefore their results should be interpreted with caution.
We included only RCTs in this review, which we recognise is only a fraction of the total available body of evidence investigating interventions to prevent and correct dental crowding in children. However, it does represent the most reliable evidence for treatment of this clinical condition (Baumgartner 2014; Gibson 2011).
This review aimed to assess the different interventions used to prevent and correct dental crowding in children; hence we included only studies where at least 80% of participants were aged 16 years old or younger.
Most orthodontic treatment is carried out in high street private practices. Some countries may have state‐funded care, however, the criteria for patients to be deemed eligible for this care, is variable. While some of the studies included in this review were carried out in private practice, most were carried out in a university or hospital setting and therefore may have limited external validity. Additionally, while some of the interventions may require input from clinicians with specialist training, some may be appropriate for general dental practitioners to provide for their patients.
Quality of the evidence
We assessed 23 studies as being at high risk of bias and one study as being at unclear risk of bias. However, most of the studies that we deemed to be at high risk of bias, were assessed as such because, due to the nature of the interventions, participants and personnel could not be blinded, which is the same for most orthodontic interventions.
Whilst many different treatment options were identified for both the prevention and correction of crowding, there was a lack of good‐quality RCTs available for each comparison. This meant that, in many instances, there was only one study included per comparison. There was also a variety of outcome measures reported, making it difficult to draw parallels between the outcomes of different comparisons. As a result, we carried out only four meta‐analyses, with each including two studies.
Several studies had small sample sizes or had not carried out a priori sample size calculations, or both (Gravina 2013; Ong 2011; Pandis 2009; Pandis 2010a). Four studies were also potentially under‐powered (Gravina 2013; Miles 2012; Miles 2016; Woodhouse 2015). Additionally, two studies suffered high levels of dropouts, which led to attrition bias (Finland 2004; Harradine 1998).
Overall, the evidence was deemed to have a very low level of certainty, and therefore the results and conclusions should be interpreted with caution.
Potential biases in the review process
The original protocol for the review was published before the year 2000 and since then treatment modalities have changed and additional outcomes have been considered relevant. Additionally, as this review was carried out over a long period of time, three review teams have been involved over its duration, with one consistent link (JH).
Agreements and disagreements with other studies or reviews
We found seven other reviews that reported on similar comparisons and outcomes to this review (Chen 2019; El‐Angbawi 2015; Fleming 2016; Papageorgiou 2019; Wang 2018; Wazwaz 2021; Yu 2013). It was difficult to compare most of them with this review as they had no upper age limit whereas our review considers treatment for children (80% participants aged 16 years old or younger).
Chen 2019 investigated the use of a lower lingual arch to treat mandibular incisor crowding and the effects on arch dimensions and also assessed Rebellato 1997. They found that a lower lingual arch was useful to relieve mandibular incisor crowding without any significant changes in the arch dimensions. Our review showed that arch length does significantly increase, but at the expense of proclination of the lower incisors.
El‐Angbawi 2015 investigated non‐surgical adjunctive interventions for accelerating tooth movement in people undergoing fixed orthodontic treatment and also assessed Miles 2012. They also found that there was no clear difference between the two groups.
Fleming 2016 investigated non‐pharmacological interventions for alleviating pain during orthodontic treatment and assessed Miles 2012 as part of their review. They agreed with our findings that vibrational appliances do not reduce discomfort or pain at any of the time points investigated.
Papageorgiou 2019 investigated the evidence of the use of myofunctional appliances and also assessed Myrlund 2015 as part of their review. They agreed with our findings that appliances such as the eruption guidance appliance can help to treat dental crowding; however, the crowding is often alleviated by proclination of the lower incisors.
Wang 2018 evaluated initial archwires for alignment during orthodontic treatment with fixed appliances and compared stabilised NiTi against superelastic NiTi. As part of this comparison, they assessed O'Brien 1990 and agreed with our findings: there was no definite difference between nitinol and titinol in terms of tooth movement. Additionally, Wang 2018 compared single‐stranded NiTi against other types of NiTi and concluded that there was very weak evidence from one study (Sebastian 2012), that coaxial NiTi produces greater tooth movement than single‐stranded NiTi. Again, this is in agreement with our findings.
Wazwaz 2021's main outcome was time to alignment rather than crowding. Twenty of their included studies were not eligible for this review due to the age of the participants, two assessed surgical interventions, one was not an RCT and two of the interventions were not relevant to this review; we had eight studies in common but their meta‐analysis was difficult to compare to ours. It also included studies involving older participants.
Yu 2013 investigated interventions for managing relapse of the lower front teeth after orthodontic treatment and did not find any relevant studies during their searches.
Study flow diagram
Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies
Risk of bias summary: review authors' judgements about each risk of bias item for each included study
Comparison 1: Lower lip bumper versus no active treatment (control), Outcome 1: Change in mandibular crowding
Comparison 1: Lower lip bumper versus no active treatment (control), Outcome 2: Change in arch length
Comparison 1: Lower lip bumper versus no active treatment (control), Outcome 3: Change in mandibular incisor A‐P position
Comparison 1: Lower lip bumper versus no active treatment (control), Outcome 4: Change in mandibular incisor inclination
Comparison 1: Lower lip bumper versus no active treatment (control), Outcome 5: Change in mandibular molar A‐P position
Comparison 1: Lower lip bumper versus no active treatment (control), Outcome 6: Change in mandibular molar inclination
Comparison 2: Cervical pull headgear versus minor interceptive procedures (control), Outcome 1: Mandibular incisor crowding (pre‐treatment, 2 years, 4 years, 8 years, 13 years)
Comparison 2: Cervical pull headgear versus minor interceptive procedures (control), Outcome 2: Change in maxillary arch length
Comparison 2: Cervical pull headgear versus minor interceptive procedures (control), Outcome 3: Change in mandibular arch length
Comparison 2: Cervical pull headgear versus minor interceptive procedures (control), Outcome 4: Change in lower incisor to mandibular plane (0‐1 years and 0‐2 years)
Comparison 2: Cervical pull headgear versus minor interceptive procedures (control), Outcome 5: Change in upper incisor to maxillary plane
Comparison 3: Lower lingual arch versus no active treatment (control), Outcome 1: Change in mandibular arch length
Comparison 3: Lower lingual arch versus no active treatment (control), Outcome 2: Change in mandibular incisor A‐P position
Comparison 3: Lower lingual arch versus no active treatment (control), Outcome 3: Change in mandibular incisor inclination
Comparison 3: Lower lingual arch versus no active treatment (control), Outcome 4: Change in mandibular molar A‐P position
Comparison 3: Lower lingual arch versus no active treatment (control), Outcome 5: Change in mandibular molar inclination
Comparison 4: Self‐ligating brackets versus conventional brackets, Outcome 1: Maxillary incisor crowding (pre‐treatment and 10 weeks)
Comparison 4: Self‐ligating brackets versus conventional brackets, Outcome 2: Time to alignment
Comparison 4: Self‐ligating brackets versus conventional brackets, Outcome 3: Ligation time
Comparison 4: Self‐ligating brackets versus conventional brackets, Outcome 4: Change in lower incisor to mandibular plane
Comparison 5: Active self‐ligating brackets versus passive self‐ligating brackets, Outcome 1: Maxillary incisor crowding (pre‐treatment)
Comparison 5: Active self‐ligating brackets versus passive self‐ligating brackets, Outcome 2: Time to alignment
Comparison 6: Copper nickel‐titanium versus nickel‐titanium archwires, Outcome 1: Mandibular incisor crowding (pre‐treatment)
Comparison 6: Copper nickel‐titanium versus nickel‐titanium archwires, Outcome 2: Little's Irregularity Index at 12‐weeks
Comparison 6: Copper nickel‐titanium versus nickel‐titanium archwires, Outcome 3: Time to alignment
Comparison 7: Coaxial nickel‐titanium versus nickel‐titanium archwires, Outcome 1: Mandibular incisor crowding (pre‐treatment)
Comparison 7: Coaxial nickel‐titanium versus nickel‐titanium archwires, Outcome 2: Total amount of tooth movement
Comparison 8: Titanol versus nitinol archwires, Outcome 1: Change in maxillary incisor crowding
Comparison 9: Nickel‐titanium versus multistranded stainless steel archwires, Outcome 1: Change in mandibular incisor crowding
Comparison 10: Nickel‐titanium versus stainless steel archwires, Outcome 1: Change in mandibular incisor crowding
Comparison 11: Multistranded stainless steel versus stainless steel archwires, Outcome 1: Change in mandibular incisor crowding
Comparison 12: Lacebacks with fixed appliances versus fixed appliances only (control), Outcome 1: Change in mandibular incisor crowding
Comparison 12: Lacebacks with fixed appliances versus fixed appliances only (control), Outcome 2: Change in mandibular arch length
Comparison 13: Vibrational appliances with fixed appliances versus fixed appliances only (control), Outcome 1: Mandibular incisor crowding (pre‐treatment and after initial alignment)
Comparison 13: Vibrational appliances with fixed appliances versus fixed appliances only (control), Outcome 2: Change in mandibular incisor crowding
Comparison 13: Vibrational appliances with fixed appliances versus fixed appliances only (control), Outcome 3: Time to alignment
Comparison 14: Schwarz appliance versus no active treatment (control), Outcome 1: Change in mandibular incisor crowding
Comparison 14: Schwarz appliance versus no active treatment (control), Outcome 2: Change in mandibular arch length
Comparison 14: Schwarz appliance versus no active treatment (control), Outcome 3: Change in lower incisor to APog
Comparison 14: Schwarz appliance versus no active treatment (control), Outcome 4: Change in upper incisor to SN
Comparison 15: Eruption guidance appliance versus no active treatment (control), Outcome 1: Maxillary incisor crowding (pre‐treatment and 1 year)
Comparison 15: Eruption guidance appliance versus no active treatment (control), Outcome 2: Mandibular incisor crowding (pre‐treatment and 1 year)
Comparison 16: Extraction lower deciduous canines versus no active treatment (control), Outcome 1: Change in mandibular incisor crowding
Comparison 16: Extraction lower deciduous canines versus no active treatment (control), Outcome 2: Change in mandibular arch length
Comparison 16: Extraction lower deciduous canines versus no active treatment (control), Outcome 3: Change in mandibular incisor inclination
Comparison 17: Extraction of third molars versus no active treatment (control), Outcome 1: Change in mandibular incisor crowding
Comparison 17: Extraction of third molars versus no active treatment (control), Outcome 2: Change in mandibular arch length
Comparison 17: Extraction of third molars versus no active treatment (control), Outcome 3: Change in maxillary incisor crowding
| Fixed appliances and auxiliaries versus other treatment or no treatment to prevent or correct dental crowding in children | ||||||
|---|---|---|---|---|---|---|
| Population: children or adolescents, or both (age ≤ 16 years) having treatment to prevent or correct dental crowding Settings: Australia, Brazil, Finland, India, Turkey, UK, USA Intervention: fixed appliances and auxiliaries (lip bumper, headgear, lower lingual arch, brackets, archwires, lacebacks, vibrational appliances) Comparison: control (brackets, archwires, fixed appliances only, minor interceptive procedures, no active treatment) | ||||||
| Outcomes | Illustrative comparative risks* (95% CI) | Relative effect
| Number of participants | Certainty of the evidence | Comments | |
| Assumed risk | Corresponding risk | |||||
| Control | Fixed appliances and auxiliaries | |||||
| Lower lip bumper ‐ lower lip bumper versus no active treatment (control) | ||||||
| Change in the amount of crowding at 6 months | Mean change −0.7 mm | Mean change −5.09 mm ± 0.97 mm |
| 34 (1) | ⊕⊝⊝⊝ Very lowa,b | There was less crowding in the lip bumper group (MD −4.39 mm, 95% CI −5.07 to −3.71). |
| Headgear ‐ cervical pull headgear versus minor interceptive procedures (control) | ||||||
| Amount of crowding at 2 years | Mean change 2.45 mm | Mean change 2.78 mm ± 1.91 mm |
| 64 (1) | ⊕⊝⊝⊝ Very lowa,b | There was no difference between groups in the amount of crowding at 2 years (MD 0.33 mm (95% CI −0.60 to 1.26). There was also no difference at 13 years follow‐up of the remaining 34 participants (MD 0.26, 95% CI −1.35 to 1.87). |
| Lower lingual arch ‐ lower lingual arch versus no active treatment (control) | ||||||
| Amount of crowding | Not measured | |||||
| Brackets ‐ self‐ligating brackets versus conventional brackets | ||||||
| Amount of crowding at 10 weeks | Mean amount of crowding 2.7 mm | Mean amount of crowding was 0.40 mm less (0.93 mm less to 0.13 mm more) |
| 60 (1) | ⊕⊝⊝⊝ Very lowa,b | There was no difference between groups in the amount of crowding. |
| Archwires ‐ coaxial nickel‐titanium archwire versus nickel‐titanium archwire | ||||||
| Amount of tooth movement at 12 weeks | Mean amount of tooth movement 3.1 mm | Mean amount of tooth movement was 6.77 mm more (5.55 mm to 7.99 mm more) |
| 24 (1) | ⊕⊝⊝⊝ Very lowa,b | There was more tooth movement with the coaxial nickel‐titanium archwire than the nickel‐titanium archwire. |
| Archwires ‐ copper nickel‐titanium archwire versus nickel‐titanium archwire | ||||||
| Amount of crowding at 12 weeks | Mean amount of crowding 6.33 mm | Mean amount of crowding was 0.49 mm more (0.35 mm to 0.63 mm more) |
| 66 (1) | ⊕⊝⊝⊝ Very lowa,b | There was less residual crowding with the nickel‐titanium archwire than the copper‐nickel titanium archwire. |
| Archwires ‐ Titanol versus Nitinol | ||||||
| Change in the amount of crowding up to 37 weeks | Mean change 1.42 mm ± 0.79 mm | Mean change 1.7 mm ± 1.15 mm |
| 40 (1) | ⊕⊝⊝⊝ Very lowa,b | There was no difference between groups in the change in the amount of crowding (MD −0.28 mm, 95% CI −0.89 to 0.33). |
| Archwires ‐ nickel‐titanium archwire versus multistranded stainless steel archwire | ||||||
| Change in the amount of crowding at 8 weeks | Mean change −29.2 mm | Mean change −27.6 mm ± 26.5 mm |
| 25 (1) | ⊕⊝⊝⊝ Very lowa,b | There was no difference between groups in the overall change in the amount of crowding (MD 1.60 mm, 95% CI −22.16 to 25.36). |
| Archwires ‐ nickel‐titanium archwire versus stainless steel archwire | ||||||
| Change in the amount of crowding at 8 weeks | Mean change −10.8 mm | Mean change −27.6 mm ± 26.5 mm |
| 24 (1) | ⊕⊝⊝⊝ Very lowa,b | There was no difference between groups in the overall change in the amount of crowding (MD 16.80 mm, 95% CI −42.79 to 9.19). |
| Archwires ‐ multistranded stainless steel archwire versus stainless steel archwire | ||||||
| Change in the amount of crowding at 8 weeks | Mean change −10.8 mm | Mean change −29.2 mm ± 33.4 mm |
| 23 (1) | ⊕⊝⊝⊝ Very lowa,b | There was no difference between groups in the overall change in the amount of crowding (MD −18.40 mm, 95% CI −47.12 to 10.32). |
| Lacebacks ‐ lacebacks and fixed appliances versus fixed appliances only (control) | ||||||
| Change in the amount of crowding at 6 months | Mean change −2.67 mm | Mean change −3.00 mm ± 8.94 mm |
| 62 (1) | ⊕⊝⊝⊝ Very lowa,b | There was no difference between groups in the change in the amount of crowding (MD −0.33 mm, 95% CI −5.90 to 5.24). |
| Vibrational appliances ‐ vibrational appliances with fixed appliances versus fixed appliances only (control) | ||||||
| Change in the amount of crowding at 10 to 30 weeks | Mean change −0.7 mm | Mean change ranged from 4.0 mm to 5.5 mm |
| 119 (2) | ⊕⊝⊝⊝ Very lowc,d | There was no difference between groups in the change in the amount of crowding (MD 0.24, 95% CI −0.81 to 1.30). |
| *The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; MD: mean difference; mm: millimetre | ||||||
| GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect. | ||||||
| aDowngraded one level as study at high risk of bias. | ||||||
| Removable appliances and auxiliaries to prevent or correct dental crowding in children | ||||||
| Population: children or adolescents (age ≤ 16 years) having treatment to prevent or correct dental crowding Setting: Japan, Norway Intervention: removable appliances, e.g. Schwarz appliance Comparison: fixed appliances only, no treatment | ||||||
| Outcomes | Illustrative comparative risks* (95% CI) | Relative effect | Number of participants | Certainty of the evidence | Comments | |
| Assumed risk | Corresponding risk | |||||
| Control | Experimental | |||||
| Schwarz appliance ‐ Schwarz appliance versus no active treatment (control) | ||||||
| Change in the amount of crowding at 9 months (after 6 months treatment) | Mean change −0.66 mm | Mean change −2.80 mm ± 1.14 mm |
| 28 (1) | ⊕⊝⊝⊝ Very lowa,b | Use of a Schwarz appliance reduced crowding (MD −2.14, 95% CI −2.79 to −1.49). |
| Eruption guidance appliance (EGA) ‐ EGA versus no active treatment (control) | ||||||
| Number of children with crowding after 1 year | 14 out of 22 children | 6 out of 24 children | OR 0.19 (95% CI 0.05 to 0.68) | 46 (1) | ⊕⊝⊝⊝ Very lowa,b | Use of an EGA reduced the number of children with dental crowding after a year. |
| *The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval;MD: mean difference; mm: millimetre; OR: odds ratio | ||||||
| GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect. | ||||||
| aDowngraded as study at high risk of bias. | ||||||
| Extractions to prevent or correct dental crowding in children | ||||||
| Population: children or adolescents (age ≤ 16 years) having treatment to prevent or correct dental crowding Settings: Italy, Germany, Wales, UK Intervention: extraction of wisdom teeth or deciduous canines Comparison: no active treatment | ||||||
| Outcomes | Illustrative comparative risks* (95% CI) | Relative effect | Number of participants | Quality of the evidence | Comments | |
| Assumed risk | Corresponding risk | |||||
| Control | Experimental | |||||
| Extraction of wisdom teeth ‐ extraction of wisdom teeth versus no active treatment (control) | ||||||
| Change in the amount of crowding at 5 years | Mean change 1.1 mm | Mean change 0.8 mm ± 1.23 mm |
| 77(1) | ⊕⊝⊝⊝ Very low | There was no difference between extracting wisdom teeth and not extracting them in terms of the mean change in the amount of crowding (MD −0.30 mm (95% CI −1.30 to 0.70). |
| Extraction of deciduous canines ‐ extraction of deciduous canines versus no active treatment (control) | ||||||
| Change in the amount of crowding at 1‐2 years | Mean change −1.27 mm | Mean change −6.03 mm ± 4.44 mm |
| 83(1) | ⊕⊝⊝⊝ Very low | There was a greater change in the amount of crowding when lower canines were extracted compared to when they were not (MD −4.76 mm (95% CI −6.24 to −3.28). |
| *The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; MD: mean difference; mm: millimetre | ||||||
| GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect. | ||||||
| aDowngraded one level as study at high both studies were at unclear risk of bias. | ||||||
| 1. Relationship of the top front teeth (incisors) to the upper jaw (maxilla) | |
|---|---|
| U1‐CT (°) | Angle formed between the upper incisor axis and the CT horizontal plane |
| U1–Vp | Distance from the vertical plane to the upper incisor crown tip |
| U1–CT | Distance from the CT horizontal plane to the upper incisor crown tip |
| 2. Relationship of the top back teeth (molars) to the upper jaw (maxilla) | |
| U6–CT (°) | Angle formed between the upper first molar axis and the CT horizontal plane |
| U6d–Vp | Distance from the vertical plane to the upper first molar distal point |
| U6–CT | Distance from the CT horizontal plane to the upper first molar mesiobuccal crown tip |
| A‐P: antero‐posterior; APog: A‐point to pogonion line; SN: sella‐nasion | |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 1.1 Change in mandibular crowding Show forest plot | 1 | 34 | Mean Difference (IV, Random, 95% CI) | ‐4.39 [‐5.07, ‐3.71] |
| 1.2 Change in arch length Show forest plot | 1 | 34 | Mean Difference (IV, Fixed, 95% CI) | 3.34 [2.71, 3.97] |
| 1.3 Change in mandibular incisor A‐P position Show forest plot | 1 | 34 | Mean Difference (IV, Fixed, 95% CI) | 0.49 [0.09, 0.89] |
| 1.4 Change in mandibular incisor inclination Show forest plot | 1 | 34 | Mean Difference (IV, Fixed, 95% CI) | 3.14 [1.73, 4.55] |
| 1.5 Change in mandibular molar A‐P position Show forest plot | 1 | 34 | Mean Difference (IV, Fixed, 95% CI) | ‐0.91 [‐1.58, ‐0.24] |
| 1.6 Change in mandibular molar inclination Show forest plot | 1 | 34 | Mean Difference (IV, Fixed, 95% CI) | ‐4.13 [‐6.09, ‐2.17] |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 2.1 Mandibular incisor crowding (pre‐treatment, 2 years, 4 years, 8 years, 13 years) Show forest plot | 1 | Mean Difference (IV, Fixed, 95% CI) | Subtotals only | |
| 2.1.1 Pre‐treatment | 1 | 64 | Mean Difference (IV, Fixed, 95% CI) | ‐1.09 [‐2.53, 0.35] |
| 2.1.2 2 years | 1 | 64 | Mean Difference (IV, Fixed, 95% CI) | 0.33 [‐0.60, 1.26] |
| 2.1.3 4 years | 1 | 64 | Mean Difference (IV, Fixed, 95% CI) | ‐0.03 [‐0.86, 0.80] |
| 2.1.4 8 years | 1 | 54 | Mean Difference (IV, Fixed, 95% CI) | 0.52 [‐0.35, 1.39] |
| 2.1.5 13 years | 1 | 34 | Mean Difference (IV, Fixed, 95% CI) | 0.26 [‐1.35, 1.87] |
| 2.2 Change in maxillary arch length Show forest plot | 1 | Mean Difference (IV, Fixed, 95% CI) | Subtotals only | |
| 2.2.1 2 years | 1 | 64 | Mean Difference (IV, Fixed, 95% CI) | 1.98 [1.80, 2.16] |
| 2.2.2 8 years | 1 | 54 | Mean Difference (IV, Fixed, 95% CI) | 2.28 [2.05, 2.51] |
| 2.3 Change in mandibular arch length Show forest plot | 1 | Mean Difference (IV, Fixed, 95% CI) | Subtotals only | |
| 2.3.1 2 years | 1 | 64 | Mean Difference (IV, Fixed, 95% CI) | 1.30 [1.17, 1.43] |
| 2.3.2 8 years | 1 | 54 | Mean Difference (IV, Fixed, 95% CI) | 1.52 [1.30, 1.74] |
| 2.4 Change in lower incisor to mandibular plane (0‐1 years and 0‐2 years) Show forest plot | 1 | Mean Difference (IV, Fixed, 95% CI) | Subtotals only | |
| 2.4.1 0 to 1 year | 1 | 64 | Mean Difference (IV, Fixed, 95% CI) | 2.30 [0.67, 3.93] |
| 2.4.2 0 to 2 years | 1 | 64 | Mean Difference (IV, Fixed, 95% CI) | 1.40 [‐0.42, 3.22] |
| 2.5 Change in upper incisor to maxillary plane Show forest plot | 1 | Mean Difference (IV, Fixed, 95% CI) | Subtotals only | |
| 2.5.1 0 to 1 year | 1 | 64 | Mean Difference (IV, Fixed, 95% CI) | 4.00 [1.97, 6.03] |
| 2.5.2 0 to 2 years | 1 | 64 | Mean Difference (IV, Fixed, 95% CI) | 4.50 [1.36, 7.64] |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 3.1 Change in mandibular arch length Show forest plot | 1 | 30 | Mean Difference (IV, Fixed, 95% CI) | 2.61 [1.83, 3.39] |
| 3.2 Change in mandibular incisor A‐P position Show forest plot | 1 | 30 | Mean Difference (IV, Fixed, 95% CI) | 0.66 [0.46, 0.86] |
| 3.3 Change in mandibular incisor inclination Show forest plot | 1 | 30 | Mean Difference (IV, Fixed, 95% CI) | 3.01 [1.71, 4.31] |
| 3.4 Change in mandibular molar A‐P position Show forest plot | 1 | 30 | Mean Difference (IV, Fixed, 95% CI) | ‐1.11 [‐1.51, ‐0.71] |
| 3.5 Change in mandibular molar inclination Show forest plot | 1 | 30 | Mean Difference (IV, Fixed, 95% CI) | ‐2.73 [‐4.29, ‐1.17] |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 4.1 Maxillary incisor crowding (pre‐treatment and 10 weeks) Show forest plot | 2 | Mean Difference (IV, Fixed, 95% CI) | Subtotals only | |
| 4.1.1 Pre‐treatment | 2 | 166 | Mean Difference (IV, Fixed, 95% CI) | ‐0.17 [‐1.49, 1.15] |
| 4.1.2 10 weeks | 1 | 60 | Mean Difference (IV, Fixed, 95% CI) | ‐0.40 [‐0.93, 0.13] |
| 4.2 Time to alignment Show forest plot | 2 | 148 | Mean Difference (IV, Random, 95% CI) | 89.64 [‐45.89, 225.17] |
| 4.3 Ligation time Show forest plot | 1 | Mean Difference (IV, Fixed, 95% CI) | Subtotals only | |
| 4.3.1 Untying | 1 | 68 | Mean Difference (IV, Fixed, 95% CI) | ‐22.30 [‐25.83, ‐18.77] |
| 4.3.2 Ligating | 1 | 60 | Mean Difference (IV, Fixed, 95% CI) | ‐78.80 [‐81.86, ‐75.74] |
| 4.4 Change in lower incisor to mandibular plane Show forest plot | 1 | Mean Difference (IV, Fixed, 95% CI) | Subtotals only | |
| 4.4.1 Change | 1 | 33 | Mean Difference (IV, Fixed, 95% CI) | 1.29 [‐1.77, 4.35] |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 5.1 Maxillary incisor crowding (pre‐treatment) Show forest plot | 1 | 70 | Mean Difference (IV, Fixed, 95% CI) | ‐1.00 [‐1.96, ‐0.04] |
| 5.1.1 Pre‐treatment | 1 | 70 | Mean Difference (IV, Fixed, 95% CI) | ‐1.00 [‐1.96, ‐0.04] |
| 5.2 Time to alignment Show forest plot | 2 | 144 | Mean Difference (IV, Fixed, 95% CI) | ‐13.11 [‐28.76, 2.53] |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 6.1 Mandibular incisor crowding (pre‐treatment) Show forest plot | 3 | 254 | Mean Difference (IV, Random, 95% CI) | ‐0.34 [‐1.27, 0.58] |
| 6.2 Little's Irregularity Index at 12‐weeks Show forest plot | 1 | 66 | Mean Difference (IV, Fixed, 95% CI) | 0.49 [0.35, 0.63] |
| 6.3 Time to alignment Show forest plot | 2 | 191 | Mean Difference (IV, Random, 95% CI) | ‐2.63 [‐14.50, 9.24] |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 7.1 Mandibular incisor crowding (pre‐treatment) Show forest plot | 1 | 24 | Mean Difference (IV, Fixed, 95% CI) | 0.10 [‐1.14, 1.34] |
| 7.2 Total amount of tooth movement Show forest plot | 1 | Mean Difference (IV, Fixed, 95% CI) | Subtotals only | |
| 7.2.1 4 weeks | 1 | 24 | Mean Difference (IV, Fixed, 95% CI) | 3.33 [2.72, 3.94] |
| 7.2.2 8 weeks | 1 | 24 | Mean Difference (IV, Fixed, 95% CI) | 5.07 [4.16, 5.98] |
| 7.2.3 12 weeks | 1 | 24 | Mean Difference (IV, Fixed, 95% CI) | 6.77 [5.55, 7.99] |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 8.1 Change in maxillary incisor crowding Show forest plot | 1 | 40 | Mean Difference (IV, Fixed, 95% CI) | 0.28 [‐0.33, 0.89] |
| 8.1.1 Change in maxillary incisor crowding | 1 | 40 | Mean Difference (IV, Fixed, 95% CI) | 0.28 [‐0.33, 0.89] |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 9.1 Change in mandibular incisor crowding Show forest plot | 1 | 25 | Mean Difference (IV, Fixed, 95% CI) | 1.60 [‐22.16, 25.36] |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 10.1 Change in mandibular incisor crowding Show forest plot | 1 | 24 | Mean Difference (IV, Fixed, 95% CI) | ‐16.80 [‐42.79, 9.19] |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 11.1 Change in mandibular incisor crowding Show forest plot | 1 | 23 | Mean Difference (IV, Fixed, 95% CI) | ‐18.40 [‐47.12, 10.32] |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 12.1 Change in mandibular incisor crowding Show forest plot | 1 | 62 | Mean Difference (IV, Fixed, 95% CI) | ‐0.33 [‐5.90, 5.24] |
| 12.1.1 Amount of crowding (mean change) | 1 | 62 | Mean Difference (IV, Fixed, 95% CI) | ‐0.33 [‐5.90, 5.24] |
| 12.2 Change in mandibular arch length Show forest plot | 1 | 62 | Mean Difference (IV, Fixed, 95% CI) | 0.83 [‐6.41, 8.07] |
| 12.2.1 Arch length (mean change) | 1 | 62 | Mean Difference (IV, Fixed, 95% CI) | 0.83 [‐6.41, 8.07] |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 13.1 Mandibular incisor crowding (pre‐treatment and after initial alignment) Show forest plot | 2 | Mean Difference (IV, Fixed, 95% CI) | Subtotals only | |
| 13.1.1 Irregularity at baseline | 2 | 122 | Mean Difference (IV, Fixed, 95% CI) | ‐0.42 [‐2.54, 1.70] |
| 13.1.2 Irregularity at initial alignment | 2 | 119 | Mean Difference (IV, Fixed, 95% CI) | 0.42 [‐0.05, 0.90] |
| 13.2 Change in mandibular incisor crowding Show forest plot | 2 | 119 | Mean Difference (IV, Fixed, 95% CI) | 0.24 [‐0.81, 1.30] |
| 13.3 Time to alignment Show forest plot | 2 | 94 | Mean Difference (IV, Fixed, 95% CI) | ‐3.70 [‐26.29, 18.89] |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 14.1 Change in mandibular incisor crowding Show forest plot | 1 | 28 | Mean Difference (IV, Fixed, 95% CI) | ‐2.14 [‐2.79, ‐1.49] |
| 14.1.1 Change in mandibular incisor crowding | 1 | 28 | Mean Difference (IV, Fixed, 95% CI) | ‐2.14 [‐2.79, ‐1.49] |
| 14.2 Change in mandibular arch length Show forest plot | 1 | 28 | Mean Difference (IV, Fixed, 95% CI) | 0.11 [‐0.46, 0.68] |
| 14.2.1 Change in mandibular arch length | 1 | 28 | Mean Difference (IV, Fixed, 95% CI) | 0.11 [‐0.46, 0.68] |
| 14.3 Change in lower incisor to APog Show forest plot | 1 | Mean Difference (IV, Fixed, 95% CI) | Subtotals only | |
| 14.3.1 Change in lower incisor to APog | 1 | 28 | Mean Difference (IV, Fixed, 95% CI) | 0.39 [0.11, 0.67] |
| 14.4 Change in upper incisor to SN Show forest plot | 1 | 28 | Mean Difference (IV, Fixed, 95% CI) | 0.33 [‐2.26, 2.92] |
| 14.4.1 Change in upper incisor to SN | 1 | 28 | Mean Difference (IV, Fixed, 95% CI) | 0.33 [‐2.26, 2.92] |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 15.1 Maxillary incisor crowding (pre‐treatment and 1 year) Show forest plot | 1 | Odds Ratio (M‐H, Fixed, 95% CI) | Subtotals only | |
| 15.1.1 Pre‐treatment | 1 | 46 | Odds Ratio (M‐H, Fixed, 95% CI) | 2.40 [0.73, 7.92] |
| 15.1.2 1 year post‐treatment | 1 | 46 | Odds Ratio (M‐H, Fixed, 95% CI) | 0.82 [0.25, 2.63] |
| 15.2 Mandibular incisor crowding (pre‐treatment and 1 year) Show forest plot | 1 | Odds Ratio (M‐H, Fixed, 95% CI) | Subtotals only | |
| 15.2.1 Pre‐treatment | 1 | 46 | Odds Ratio (M‐H, Fixed, 95% CI) | 2.02 [0.60, 6.83] |
| 15.2.2 1 year post‐treatment | 1 | 46 | Odds Ratio (M‐H, Fixed, 95% CI) | 0.19 [0.05, 0.68] |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 16.1 Change in mandibular incisor crowding Show forest plot | 1 | 83 | Mean Difference (IV, Fixed, 95% CI) | ‐4.76 [‐6.24, ‐3.28] |
| 16.1.1 Change between baseline and 1 year | 1 | 83 | Mean Difference (IV, Fixed, 95% CI) | ‐4.76 [‐6.24, ‐3.28] |
| 16.2 Change in mandibular arch length Show forest plot | 1 | 83 | Mean Difference (IV, Fixed, 95% CI) | ‐2.73 [‐3.69, ‐1.77] |
| 16.3 Change in mandibular incisor inclination Show forest plot | 1 | 83 | Mean Difference (IV, Fixed, 95% CI) | 0.08 [‐0.55, 0.71] |
| 16.3.1 LR1 Incisor change | 1 | 83 | Mean Difference (IV, Fixed, 95% CI) | 0.08 [‐0.55, 0.71] |
| Outcome or subgroup title | No. of studies | No. of participants | Statistical method | Effect size |
| 17.1 Change in mandibular incisor crowding Show forest plot | 1 | 77 | Mean Difference (IV, Fixed, 95% CI) | ‐0.30 [‐1.30, 0.70] |
| 17.2 Change in mandibular arch length Show forest plot | 1 | 77 | Mean Difference (IV, Fixed, 95% CI) | 1.03 [0.56, 1.50] |
| 17.3 Change in maxillary incisor crowding Show forest plot | 1 | 77 | Mean Difference (IV, Fixed, 95% CI) | 0.44 [‐0.52, 1.40] |
