Adhesively or non-adhesively bonded amalgam restorations for dental caries

Review question

Does adding adhesive designed to bond dental amalgam fillings to teeth make the fillings perform better and last longer than fillings without it?


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.

Study characteristics

The evidence in this review, carried out by authors from the Cochrane Oral Health Group, is up to date as of 21 January 2016. One 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. At two years no difference was found.

Key results

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.

Quality of 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 so the results may not be generalisable.

Authors' conclusions: 

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.

Read the full abstract...

Dental caries (tooth decay) is one of the commonest diseases which afflicts mankind, and has been estimated to affect up to 80% of people in high-income countries. Caries adversely affects and progressively destroys the tissues of the tooth, including the dental pulp (nerve), leaving teeth unsightly, weakened and with impaired function. The treatment of lesions of dental caries, which are progressing through dentine and have caused the formation of a cavity, involves the provision of dental restorations (fillings). This review updates the previous version published in 2009.


To assess the effects of adhesive bonding on the in-service performance and longevity of dental amalgam restorations.

Search strategy: 

We searched the Cochrane Oral Health Group Trials Register (to 21 January 2016), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2015, Issue 12), MEDLINE via Ovid (1946 to 21 January 2016) and EMBASE via Ovid (1980 to 21 January 2016). We also searched the US National Institutes of Health Trials Registry ( and the WHO International Clinical Trials Registry Platform ( (both to 21 January 2016) for ongoing trials. No restrictions were placed on the language or date of publication when searching the electronic databases.

Selection criteria: 

Randomised controlled trials comparing adhesively bonded versus traditional non-bonded amalgam restorations in conventional preparations utilising deliberate retention, in adults with permanent molar and premolar teeth suitable for Class I and II amalgam restorations only.

Data collection and analysis: 

Two review authors independently screened papers, extracted trial details and assessed the risk of bias in the included study.

Main results: 

One trial with 31 patients who received 113 restorations was included. At two years, 50 out of 53 restorations in the non-bonded group survived, and 55 of 60 bonded restorations survived with five unaccounted for at follow-up. Post-insertion sensitivity was not significantly different (P > 0.05) at baseline or two-year follow-up. No fractures of tooth tissue were reported and there was no significant difference between the groups or matched pairs of restorations in their marginal adaptation (P > 0.05).