Preformed metal crowns for decayed primary molar teeth
Abstract
This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:
(1) To evaluate the clinical outcome of primary teeth restored with PMCs compared with those restored with conventional filling materials such as amalgam, composite, glass ionomer, resin modified glass ionomer, compomers.
(2) To determine whether the extent of decay has an effect on the clinical outcome of primary teeth restored with PMCs compared with those restored with conventional filling materials.
(3) To report any adverse effects associated with PMCs or conventional fillings such as periodontal (gum) problems, temporomandibular disorders (TMD), phobia as a result of undergoing restorative treatment, alteration in age at exfoliation. We recognise that these side effects may not be well reported in studies where an assessment of efficacy is the main outcome.
The following null hypothesis will be tested:
There is no difference in the clinical outcome of primary molar teeth restored with PMCs when compared to those where conventional fillings have been placed.
Background
Dental decay in children's teeth is a significant public health problem, affecting 60% to 90% of school children in industrialised countries (WHO Report 2003).
In Scotland, the National Dental Inspection Programme (NDIP 2003) showed that over half of 5‐year old children had decayed primary teeth, with the average number of decayed teeth in these children being five. Untreated decay in primary teeth may lead to pain, abscess formation and possible loss of the tooth, and 15% of the 5 year olds in this sample had already had at least one tooth extracted. This large burden of treatment need has implications both for individual patients, and on a public health agenda basis.
Currently accepted best practice is to treat dental decay in primary teeth by removing all the decayed tissue, before restoring the tooth with a filling material. However, this process usually leaves the tooth structurally weak, both through loss of the decayed tissue and through unavoidable loss of sound tissue necessary to gain access to the decay to allow its removal. Re‐establishing the original form of primary molar teeth with a filling material can cause problems, particularly with multi‐surface cavities, where the increased occlusal loading that these larger fillings are subjected to, often leads to premature restoration failure. In view of this, current guidelines recommend placing a preformed metal crown (PMC) over primary molar teeth affected with moderate to severe dental caries involving two or more surfaces, in order to provide a more durable restoration than simply placing a filling (Fayle 2001).
Fitting a PMC can be more demanding both of clinical skill and child co‐operation than placing a filling. In addition, there are considerable variations in opinion as to when to place PMCs and when a filling would be more clinically appropriate. In a prescribed case scenario (Blinkhorn 2003) requesting which restoration dentists would place on a decayed primary molar, 88% of USA dentists would place a PMC compared to 4% of UK respondents. In fact, PMCs are not popular amongst UK dentists, and made up only 0.7% of restorations placed in children in the year 2001/2002 (Scottish Dental Practice Board figures).
To date, there has only been one systematic review comparing the durability of PMCs with filling materials (Randall 2002). This review supported the increased efficacy of PMCs compared with amalgam restorations in primary molars. However, the review was criticised by Ismail and Sohn (Ismail 2002), who suggested that a significant problem was that it comprised 10 studies with differing designs and inclusion criteria. No analysis for heterogeneity of the data was carried out, and a fixed‐effect analysis model was used. When the data were checked for the level of heterogeneity, this was found to be significant, and the authors argued that the data would have been more accurately analysed in a random‐effects model. When the authors carried out this analysis, they found less of a difference between the improved performance of PMCs compared with fillings. This review also focused on comparing PMCs to amalgam fillings. However, this material is being used less in primary teeth with the advent of more aesthetic, adhesive materials and it would be more appropriate now, to compare the performance of PMCs with these newer and more commonly used materials.
Dental caries has a significant impact on the lives of children and there is a clear need to base the effective management of the disease on the best available evidence. Current guidelines encourage the use of PMCs and this protocol will review the clinical outcome of PMCs compared with currently used filling materials.
Objectives
(1) To evaluate the clinical outcome of primary teeth restored with PMCs compared with those restored with conventional filling materials such as amalgam, composite, glass ionomer, resin modified glass ionomer, compomers.
(2) To determine whether the extent of decay has an effect on the clinical outcome of primary teeth restored with PMCs compared with those restored with conventional filling materials.
(3) To report any adverse effects associated with PMCs or conventional fillings such as periodontal (gum) problems, temporomandibular disorders (TMD), phobia as a result of undergoing restorative treatment, alteration in age at exfoliation. We recognise that these side effects may not be well reported in studies where an assessment of efficacy is the main outcome.
The following null hypothesis will be tested:
There is no difference in the clinical outcome of primary molar teeth restored with PMCs when compared to those where conventional fillings have been placed.
Methods
Criteria for considering studies for this review
Types of studies
Randomised controlled trials (RCTs) and controlled clinical trials (CCTs) that assess the effectiveness of preformed metal crowns compared with conventional fillings or where there has been no treatment.
Types of participants
Children who have untreated tooth decay in one or more primary molar tooth. Where possible, the caries risk status of the participants will be recorded.
Exclusion criteria
Studies investigating filling materials not currently advocated for the restoration of primary teeth will be excluded e.g. cermets, temporary restorative materials.
PMCs are not routinely used in the restoration of permanent teeth, therefore where studies present data for permanent and primary teeth, only the results from primary teeth will be included. Where these data cannot be separated, studies will be excluded.
Types of interventions
Caries removal followed by placement of a conventional filling in one tooth compared with caries removal followed by placement of a preformed metal crown.
Types of outcome measures
The main outcome measures for children and carers are long‐term freedom from the main symptom of dental decay/pain.
Primary outcome measures
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Freedom from clinical or radiographic signs or symptoms of pulp pathology including pain/pulp infection/discharging sinus/swelling.
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Time until filling or crown needs to be replaced or requires further intervention.
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Proportion of filled or crowned teeth retained until appropriate age of shedding.
Other measures of success to be recorded and analysed:
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absence of clinical or radiographic evidence of secondary caries;
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other clinical signs of pathology (fracture of tooth or filling, wear of crown, inflammation of gingival (gum) tissue);
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patient satisfaction;
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costs to patient and provider;
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adverse events.
Search methods for identification of studies
For the identification of studies included or considered for this review, detailed search strategies will be developed for each database to be searched. These will be based on the search strategy developed for MEDLINE but revised appropriately for each database.
The MEDLINE search strategy will be combined with phases 1 and 2 of the Cochrane Sensitive Search Strategy for Randomised Controlled Trials (RCTs) as published in Appendix 5b of the Cochrane Handbook for Systematic Reviews of Interventions (updated May 2005) and amended by the Cochrane Oral Health Group to include research design terms particular to oral health trials.
MEDLINE via OVID
(Controlled vocabulary terms (MeSH) are presented in uppercase text, free text terms in lowercase.)
1. CROWNS (single term MeSH)
2 crown$
3 ((1 or 2) and ("preformed metal$" or "pre‐formed metal$" or "stainless steel" or "nickel chromium crown$" or "NiCr crown$"))
4 TOOTH DECIDUOUS (explode all trees MeSH)
5 ((deciduous or primary or milk or first or baby or natal) and (teeth or tooth or dentition))
6 (4 or 5)
7(3 and 6)
Databases to be searched
The Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library (current issue))
MEDLINE (1966 to present)
EMBASE (1980 to present)
SIGLE (System for Information on Grey Literature in Europe) (1976 to present).
Language
The search will attempt to identify all relevant studies irrespective of language. An effort will be made to translate all foreign language articles via the Cochrane Oral Health Group.
Reference list searching
The reference lists of review articles, and standard clinical textbooks will be checked for additional studies. The reference lists of included studies will also be checked for additional studies.
Handsearching
The following journals have been identified as being important to be handsearched for this review:
British Dental Journal
International Journal of Paediatric Dentistry.
Those issues not covered as part of the Cochrane worldwide handsearching programme (www.cochrane.org) will be handsearched.
Unpublished studies
Requests for information about unpublished studies/studies published in the 'grey literature' will be sent to relevant companies, relevant investigators and relevant professional organisations.
Data collection and analysis
The titles and abstracts of all reports identified by the search strategy will be scanned independently and in duplicate by two authors (Nicola Innes (NI), David Ricketts (DR)). For studies that appear to meet the inclusion criteria but where there is insufficient information in the title and abstract to be certain, the full report will be obtained and assessed independently by two authors to establish whether the study meets the inclusion criteria. Disagreements will be resolved by discussion, any disagreements that cannot be resolved, the third author (Dafydd Evans (DE)) will be consulted. All studies meeting the inclusion criteria will undergo validity assessment and the data will be extracted. Studies excluded at this or subsequent stages will be entered in the table of excluded studies with the reasons for exclusion recorded.
Quality assessment
The quality assessment of the included trials will be undertaken independently and in duplicate by two of the authors based on what is written in the articles.
Four main quality criteria will be examined.
(1) Generation of randomisation sequence, recorded as:
(A) Adequate ‐ e.g. computer generated random numbers, table of random numbers, drawing lots, coin tossing, shuffling of cards, throwing dice.
(B) Unclear.
(C) Inadequate ‐ e.g. case record number, date of birth, date of administration, alternation.
(2) Allocation concealment, recorded as:
(A) Adequate ‐ e.g. prior numbered or coded drug containers prepared by an independent pharmacy, central randomisation, sequentially numbered sealed opaque envelopes.
(B) Unclear.
(C) Inadequate ‐ e.g. open allocation schedule, unsealed or non‐opaque envelopes.
(3) Blind outcome assessment.
(A) Yes.
(B) Unclear.
(C) No.
(D) Not used/possible.
(4) Completeness of follow up (is there a clear explanation for withdrawals and drop outs in each treatment group?) assessed as:
(A) Yes, drop outs less than 10%.
(B) Yes, drop outs more than 10%.
(C) No explanation.
The agreement for the quality criteria between assessors will be determined by kappa statistics.
After taking into account the additional information provided by the authors of the trials, studies will be grouped into the following categories.
(A) Low risk of bias (plausible bias unlikely to seriously alter the results) if all criteria are met.
(B) Moderate risk of bias (plausible bias that raises some doubt about the results) if all criteria are at least partly met.
(C) High risk of bias (plausible bias that seriously weakens confidence in the results) if one or more criteria were not met as described in Section 6.7 of the Cochrane Handbook for Systematic Reviews of Interventions.
In addition to the above quality criteria, the presentation of a sample size calculation will be recorded.
Data extraction
Data will be extracted by two authors independently and in duplicate using specially designed data extraction forms. The data extraction forms will be piloted on several papers and modified as required before use. The data to be extracted will include:
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Citation details: including year of publication, country of origin, setting and source of funding.
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Details of participants: including demographic characteristics.
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Details of intervention: including type and method of restoration.
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Details of outcomes reported: including method of assessment.
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Quality issues.
Authors will be contacted for clarification and missing information. Data will be excluded until further clarification is available. In cases of disagreement, a third reviewer (DE) will be consulted to resolve the issue.
Data synthesis
For dichotomous data, the estimate of effect of an intervention will be expressed as risk ratios together with 95% confidence intervals. In addition the number needed to treat (NNT) will be calculated. For continuous outcomes, mean differences and 95% confidence intervals will be used to summarise the data for each group.
Clinical heterogeneity will be assessed by examining the types of participants (e.g. age), interventions (e.g. method of restoration) and outcomes (e.g. pain relief) in each study. Only if there are studies of similar comparisons reporting the same outcome measures will meta‐analysis be attempted. Risk ratios will be combined for dichotomous data, and standardised mean differences for continuous data, using a random‐effects model. The significance of any discrepancies in the estimates of the treatment effects from the different trials will be assessed by means of Cochran's test for heterogeneity.
Sensitivity analyses will be undertaken to examine the effect of randomisation, allocation concealment and blind outcome assessment on the overall estimates of effect. In addition, the effect of including unpublished literature on the review's findings will also be examined if data allow.
Where possible, subgroup analyses will be performed on trials involving different types of interventions; different age groups; types of service delivery and types of funding.
