Filling materials for retreatment of failed root canals – only very low quality evidence is available from RCTs

Composite_resin_fillng_2The living part of the tooth, also known as the tooth pulp, can become irreversibly inflamed as a result of damage or bacterial infection due to tooth decay. To deal with this problem, the dentist has to drill a hole to access the inner space of the tooth or root canal system, and remove the infected tissue and toxic irritants by a combination of mechanical cleaning and irrigation. After this is done, the dentist fills the space with an inert packing material and seals the opening. This procedure is known as root canal therapy. Although results are generally good, a small number of failures do occur. This may be attributed to the complexity of the root canal system, which has many small additional pathways communicating with each other, making it difficult to completely eliminate all of the toxins and irritants. These can spread, causing the infection around the root to last indefinitely. When root canal therapy fails, a retreatment called retrograde filling is a good alternative to save the tooth. During retrograde filling the dentist cuts a flap in the gum and creates a hole in the bone to get access to the bottom tip of the root. After cutting off the tip, then thorough preparation, the apex is sealed (the apical seal) and the hole made by the dentist filled with a dental material. This sealing process is thought to be the single most important factor in achieving success in a retrograde root filling. Many materials have been developed to seal the root tip, mineral trioxide aggregate is the material of interest at present, but there is no consensus about which material is best.

What was the research?

A systematic review to examine the effects of different materials used for retrograde filling in children and adults for whom this treatment is necessary in order to save the tooth.

Who conducted the research?

The research was conducted by a team led by Xiangyu Ma from Mianyang Hospital of TCM, China; and the West China College of Stomatology, China, on behalf of Cochrane Oral Health. Chunjie Li, Liuhe Jia, Yan Wang, Wenwen Liu, Xuedong Zhou, Trevor M Johnson and Dingming Huang were also on the team.

What evidence was included in the review?

The evidence in this review is up-to-date as of 13th September 2016. Six randomised controlled trials were evaluated. 916 participants were included, who were undergoing retrograde filling using different types of filling material: mineral trioxide aggregate (MTA), intermediate restorative material (IRM), super ethoxybenzoid acid (Super-EBA), dentine-bonded resin composite, glass ionomer cement, and amalgam. 988 teeth in total were evaluated. Five studies were conducted in Europe, and one in Asia. Studies measured the success rate with clinical or radiological methods. None of the studies reported possible side effects.

What did the evidence say?

The limited evidence is insufficient to draw any conclusion as to the benefits of any one material over another, so we are not able to recommend which material is best to use in retrograde filling at present.

How good was the evidence?

The evidence presented is of very low quality due to the small amount of available studies, all at high risk of bias, results were imprecise and may not be applicable to other settings/countries.

What are the implications for dentists and the general public?

Based on the present limited evidence, we do not have sufficient evidence to determine the benefits of any one material over another.

What should researchers look at in the future?

The present results call for further research. We hope future studies could address and answer the following issues.

  • Participants: studies with a large number of participants from different races.
  • Intervention and comparison: trials focusing on the materials considered in this systematic review are still needed, and trials using new materials are also required. Many investigations have tried to use a chelating agent or accelerator to overcome the long setting time of mineral trioxide aggregate (MTA), which is its main drawback. More research into this issue in particular is needed.
  • Follow-up: increasing the follow-up period to observe the long-term effects and safety.
  • To improve the quality of future evidence, we recommend blinding the outcome assessors. Most studies only have the participants and the statistical assessor blinded.


Ma X, Li C, Jia L, Wang Y, Liu W, Zhou X, Johnson TM, Huang D. Materials for retrograde filling in root canal therapy. Cochrane Database of Systematic Reviews 2016 , Issue 12 . Art. No.: CD005517. DOI: 10.1002/14651858.CD005517.pub2 .

This post is an extended version of the review’s plain language summary, compiled by Anne Littlewood at the Cochrane Oral Health Editorial Base.