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Materials for retrograde filling in root canal therapy

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Abstract

This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:

To examine the relative effectiveness of different materials used for retrograde (root end) obturation (filling) in patients for whom orthograde root canal filling or retreatment is ineligible and periapical surgery is used to save the tooth.

Background

Root canal therapy has shown satisfactory results for patients, but failures do occur with a rate of 10% to 15% (Wong 2004). The main contributory factor for the endodontic failure is microbial infection persistent in the root canal system and the periapical region. Chemical and mechanical preparation may not reach every corner of the complex root canal system. Bacteria in isthmuses, ramifications, irregularities and dentinal tubules may persist and some necrotic tissue substance may also remain. Bacteria may gain access to the periapical region if complete sealing is not obtained, leading to pathological lesions (Lin 1991; Siqueira 2001).

According to the Appropriateness of Care and Quality Assurance Guidelines (AAE 1998) of the American Association of Endodontists, when such failures happen, retreatment of the root canal is the choice. With the introduction of new technologies, such as ultrasonic instruments, the dental operative microscope and nickel titanium instruments, some cases which could not be handled with conventional root canal therapy as a result of the complexity of the root canal system, inadequate instrumentation, or presence of a physical barrier, can now be treated satisfactorily. When teeth cannot be treated appropriately by root canal treatment or retreatment, periapical surgery (which usually consists of periapical curettage, root end resection, root end preparation and root end filling (Gutmann 2004) is needed to save the teeth. el‐Swiah and Walber (el‐Swiah 1996) classified reasons for such a surgery into three kinds: biological (teeth with periapical lesions that do not respond to proper endodontic therapy, calcified canals etc.), technical (teeth that have a crown or a post etc.) and a combination of the two.

The aims of the periapical surgery are to remove the pathogenic agents and establish an environment facilitating the regeneration of the wounded tissue. In a retrospective study (Harty 1970), it was reported that the apical seal was the single most important factor in achieving success in such surgery. Root end filling materials are used to establish the barrier between the root canal system and the surrounding supportive tissue (Gutmann 1991). An ideal material to seal the root end cavities should be non toxic, non carcinogenic, biocompatible and bioconductive as well as having good sealing ability (Andreasen 1993; Gartner 1992).

For many years, amalgam has been accepted as the material of choice for root end filling. It has the advantage of being easily available, inexpensive and easy to handle. The clinical application has shown reasonable success. However in recent years, the appropriateness of amalgam for its initial marginal leakage, corrosion, moisture sensitivity, mercury contamination of periapical tissue, especially mercury hazard (Eley 1993; Gartner 1992), has been questioned. The disadvantages associated with amalgam led to the use of alternative materials. Gutta‐percha, zinc oxide engerol (super EBA and IRM), polymers, glass ionomer cements, composite resin and MTA have been employed and several cases have been reported (Hauman 2003). However in most studies the sample size was small and some of the results were conflicting (Dalal 1983; Jesslen 1995).

A systematic review has been conducted by Niederman (Niederman 2003) for an evaluation of various materials used in retrograde (root end) obturation (filling). There are however some restrictions to this review. The languages of the included articles were limited to only English, German and French. The search strategy was not specific or sensitive enough to retrieve all relevant articles and the inclusion criteria were not precise, the systematic review included all articles which had an experiment and a control group without demanding root end filling materials be used in both groups. In fact, the included articles which compared orthograde (occlusal to apical) filling with retrograde (apical to occlusal) filling were not addressing the question: which material is more suitable for root end filling?

In light of the variability in clinical practice and some conflicting study results, a comprehensive systematic review is needed to integrate the small sample size trials and clarify the effectiveness of different materials for retrograde filling in root canal therapy.

Objectives

To examine the relative effectiveness of different materials used for retrograde (root end) obturation (filling) in patients for whom orthograde root canal filling or retreatment is ineligible and periapical surgery is used to save the tooth.

Methods

Criteria for considering studies for this review

Types of studies

This review will include randomised controlled trials (RCTs). The authors of the identified clinical controlled trials in which the treatment assignment method was not stated clearly, will be contacted for clarification. Trials which were not randomised, or for which this is still unclear will be excluded.

Types of participants

Patients for whom orthograde root canal filling or retreatment is ineligible and periapical surgery is used to save the tooth. There will be no age or gender limitations.

Types of interventions

Experimental group: retrograde obturation with any material (other than amalgam).
Control group: retrograde obturation with any other material (including amalgam).

Types of outcome measures

Primary outcomes

Clinical symptoms and signs: pain, pain on percussion or palpation, tenderness, increased tooth mobility, sinus tract formation or any other subjective discomfort. Any of those symptoms or signs will claim the failure of the treatment.
Radiographic outcomes: the status of periapical bone regeneration and apical absorption.

Secondary outcomes

The relationship between the follow‐up period and the outcome changes. If any adverse effect was reported, it will also be recorded and analysed.

Any other outcome measures used in articles will also be recorded. They will be converted by the review authors for better comparison if the conversion is possible and appropriate.

Search methods for identification of studies

The search strategy developed by the Trials Search Co‐ordinator of the Cochrane Oral Health Group will be adopted for searching The Cochrane Library (seeAppendix 1).

The Cochrane Oral Health Group Trials Register, EMBASE, Ovid MEDLINE, and the Chinese Biomedical Disk (CBMDisk) will be searched based on the aforementioned strategy, but revised appropriately. Each database will be searched from its starting date to the end of March 2005.
The reference lists from each identified article, review and related textbook will also be searched. The authors of eligible studies will be contacted to see if there are any additional published or unpublished studies. Relevant studies will be identified irrespective of languages.
Related manufacturers of different materials will be contacted to identify if there are any unpublished trials on the material.
Related Chinese journals will be identified and searched by hand to make sure any eligible trials are included.

Data collection and analysis

Study selection

Titles and abstracts (if available) of the articles identified by the search will be reviewed independently and in duplicate by two review authors to locate articles that meet the inclusion criteria. If it is not possible to assess eligibility from only the title and abstract, the full text article will be obtained and reviewed further. Any disagreement will be resolved by discussion between the two review authors.
Non‐English and non‐Chinese papers will be translated.

Quality assessment

The quality assessment will be made by two review authors, also independently and in duplicate, according to the guidelines in the Cochrane Handbook for Systematic Reviews of Interventions (Green 2005), as a part of data extraction.

Four main quality criteria will be examined.
(1) Randomisation, recorded as:
(A) true
(B) unclear.

(2) Allocation concealment, recorded as:
(A) adequate
(B) unclear
(C) inadequate.

(3) Blind outcome assessment, recorded as:
(A) yes
(B) no
(C) unclear
(D) not possible.

(4) Completeness of follow up (was there a clear explanation for withdrawals and drop outs in each treatment group?), recorded as:
(A) no drop outs
(B) yes
(C) no.

Definition of inclusion/exclusion criteria, comparability of control and treatment groups at entry, and adequate definition of the outcome measures will be assessed too.
Any disagreement will be resolved by discussion.

Data extraction

Two review authors will independently extract the data from relevant articles with the help of a data extraction form which will be designed specifically for this study. These forms will be piloted on several papers and modified as required before use.
For each study, the following data will be recorded:
Date of the study, year of publication, country of origin, inclusion and exclusion criteria, characteristics of the participants, sample size, allocation, characteristics of the interventions (instruments used, cavity form prepared, and material used), outcome measures and detailed follow‐up information.
Any disagreement will be resolved by discussion. The author will be contacted for clarification if necessary. Studies that do not have enough information will be excluded and recorded.

Data synthesis

For dichotomous outcomes, the estimate of effect of an intervention will be expressed as risk ratios together with 95% confidence intervals, for continuous outcomes, means and standard deviations will be used to summarise the data for each group.
Clinical heterogeneity will be assessed, and only if there are studies of similar comparisons reporting the same outcomes, will a meta‐analysis be carried out. A random‐effects model will be used throughout. Risk ratios will be combined for dichotomous data and mean differences for continuous data. 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 analysis will be performed on the basis of effect of randomisation, allocation concealment and blind outcome assessment. The effect of including unpublished literature on the review's findings will also be explored.