Investigating the effect of amalgam restoration on shear bond strength of orthodontic tubes

Adult patients who require orthodontic treatment usually have amalgam restorations at the buccal surface of the posterior teeth. Research has shown that bond strength to amalgam is less than the bond strength to enamel.The aim of this study is to determine the effect of amalgam restorations extension on shear bond strength of orthodontic tubes.

The 70 extracted molar teeth were randomly divided into 7 groups of 10 and orthodontic tubes of specimens were bonded by Transbond XT Adhesive Paste and Single Universal Bonding and/or by Transbond XT Adhesive Bond.  The specimens were subjected to 1000 thermo cycles between 10 - 50 ° C, and then the shear bond strength was measured by the Universal Testing Machine.

The results showed that the mean shear bond strength of bonded orthodontic tubes on amalgam restoration is lower than the shear bond strength on the enamel. The results indicated that when Single Bond Universal and Transbond XT Adhesive paste were used for bonding of orthodontic tubes the mean shear bond strength of increased, compared to when, only the transbond XT adhesive was used, thought this increase was not statistically significant.

The amount of enamel around amalgam restorations is one of the most important factors in the degree of bond strength of orthodontic attachments. As the amount of bonding surface on the enamel margin is higher than that of the amalgam bond, we can expect more bond strength.