Sir, I must commend Dr Worskett for undertaking his research into bonded amalgams within a general dental practice setting (BDJ 2013; 214: E19). However, the title should surely have been something more like A comparison between NHS lathe cut amalgam and private high Cu spherical amalgam.

By using two completely different amalgams there is no relevance to whether or not bonding agents were used. Surely the editorial board should have pointed this out and asked for revision of the paper?

Dr Paul Worskett responds: I must thank Dr Neill for his comments but the comparison was not intended to be between NHS and private amalgams. The study was between non-bonded amalgams, which happened to be carried out under NHS regulations, and bonded amalgams. Dr Neill appears to make the incorrect assumption that the amalgam used for NHS amalgams was a low copper lathe cut alloy. The precise alloy used for non-bonded amalgams was not known but it is very likely it would have been Gs-80 as this has been used in the practice for many years going back to the late nineties and is still used today. Gs-80 is a high copper, non-gamma2, admix alloy marketed by SDI. However, I was not certain enough to be able to quote this alloy in the paper. If the amalgam used was not Gs-80 it would have been of similar quality.

The theoretical advantages of bonded amalgams have been verified in many in vitro studies and these were reviewed in the article. Of course, it is very difficult to eliminate all the variables in a study, especially retrospective studies carried out in general practice. I had tried to discuss many of the variables ofthe study in the article. Also, in the discussion part of the paper, a comparison was made of the results of this study compared with other amalgam studies, including those carried out in academic settings which found an average failure rate of 3.3% for non-bonded amalgam restorations across all types of alloys.1 In my study, the failure rate of bonded amalgams was between 1.5% and 2.5% per year over five years.

Although there were acknowledged limitations of the study, the conclusion was that amalgams placed by the bonding and non-bonding techniques, using the methods described, yielded significantly different results. It is for the reader to decide the relevance of the findings in the light of the methodology used and the limitations of the study.