Evidence is lacking on adhesive bonding for amalgam fillings


c. Spectrum Family Dentistry, under CC Licence

Tooth decay is a common problem affecting both children and adults. Cavities form in the teeth by the action of acid produced by bacteria present in dental plaque or biofilm. A number of techniques and a variety of materials can be used to restore or fill teeth affected by decay. One of the most commonly used and comparatively cheap filling materials is dental amalgam (a mixture of mercury and metal alloy particles). The review authors sought to evaluate the added benefit of using an adhesive to bond amalgam to tooth structure to see if bonded fillings would last longer and perform better.

What was the research?

A systematic review of the evidence to find out if adding adhesive designed to bond dental amalgam fillings to teeth make the fillings perform better and last longer than fillings without it

Who conducted the research?

The research was conducted by a team led by Anirudha Agnihotry from UCLA School of Dentistry, on behalf of the Cochrane Oral Health Group. Zbys Fedorowicz and Mona Nasser were also on the team.

What evidence was included in the review?

One randomised controlled trial with 31 participants (21 male, 10 female) who received 113 restorations, was included. The study took place in the UK in a university dental hospital environment. Participants were chosen who were suitable for routine dental treatment. The comparison made was between teeth in the same person on opposite sides of the mouth, one treated with the bonded technique, the other without.

What did the evidence say?

Only one study, which provided limited information, showed that for medium sized fillings there was no difference in sensitivity between the bonded and non-bonded fillings after their placement and that bonding of amalgam to tooth did not have any effect on the survival of the filling over a two-year period. In view of the lack of evidence on the additional benefit of adhesively bonding amalgam in comparison with non-bonded amalgam, it is important that clinicians are mindful of the additional costs that may be incurred. There is a wide range of bonding agents developed over a number of years that are available for use by dentists. It is therefore very disappointing that there is such a lack of suitable trials of their effectiveness.

How good was the evidence?

There was only one included study and it provides insufficient evidence that adhesively bonded amalgam restorations perform any better than non-adhesively bonded amalgam restoration when followed up for two years. The quality of the evidence is low. In addition, the university dental clinic setting may mean that the participants are not representative of the general population and the treatment offered not typical of that in general dental practice. The results may not be generalisable.

What are the implications for dentists and the general public?

There is no evidence to either claim or refute a difference in survival between bonded and non-bonded amalgam restorations. This review only found one under-reported trial. This trial did not find any significant difference in the in-service performance of moderately sized adhesively bonded amalgam restorations, in terms of their survival rate and marginal integrity, in comparison to non-bonded amalgam restorations over a two-year period. In view of the lack of evidence on the additional benefit of adhesively bonding amalgam in comparison with non-bonded amalgam, it is important that clinicians are mindful of the additional costs that may be incurred.

What should researchers look at in the future?

Following the realisation that dental amalgam may be adhesively bonded to enamel and dentine, there was a need to investigate the clinical performance of bonded amalgams. With subsequent developments in minimal intervention dentistry and enhanced durability and longevity of tooth-coloured alternatives to dental amalgam, the need for further investigations of the efficacy of adhesively bonded restorations of dental amalgam has diminished. Given the available evidence and the decreasing use of dental amalgam internationally, further clinical investigations on adhesively bonded dental amalgams would be difficult to justify. The bonding process is expensive in terms of the cost of the adhesive materials and in terms of the extra time taken to place the fillings. Extended treatment times and additional cost which add little (if anything) to clinical outcomes cannot be supported.


Agnihotry A, Fedorowicz Z, Nasser M. Adhesively bonded versus non-bonded amalgam restorations for dental caries. Cochrane Database of Systematic Reviews 2016, Issue 3. Art. No.: CD007517. DOI: 10.1002/14651858.CD007517.pub3.

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