Evaluation ofthe microleakage under orthodontic brackets bonded with four different bondingtechniques and aged with thermal cyclus and chewing simulation protocols

The microleakage caused by the shrinkage of the adhesive related to the polymerization reaction causes weakening of the connection between the bracket and the tooth surface and leads to the penetration of bacteria. Increased microleakage in the shrinkage zone causes also decalcification, enamel coloring, corrosion and secondary decays. The adhesives used to bond brackets are subjected to the chewing forces and their physical integrty is affected by the thermal changes in the mouth environment. Chewing forces are transmitted directly to the teeth or indirectly through brackets and adhesives or the arch wire. Structural deterioration may occur on the adhesive because of the chewing forces. There are studies showing that these microcracks allow penetration of the oral fluids. In thepresent study, the efficiency on microleakage of asid etch, self etch and two different laser methods was evaluated in comparison. In our study, the enamel surface of 160 extracted teeth was etchedwith acid, self etch adhesives, Er:YAG laser and X-Runner handpiece appliactions. After bondingthe brackets to the specimens, 0.016X0.022 inch nickel titanium arch wire was ligatureted, samples were embedded in autopolymerizing acrylic blocks with imitated periodontal ligament. The specimens were aged with either chewing simulator and thermal cyclingor only thermal cycling procedures. Microleakage amount in milimeters between enamel-adhesive and adhesive-bracket surfaces was recorded for occlusal and gingival sections in each specimen. The median and mean values of microleakage were evaluated with Kruskall Wallis and Mann Withney tests respectively, (p <0.05). Microleakage measured in the gingival part of enamel and adhesive surfaces of the samples aged with chewing simulator was significantly higher. The half of the samples was aged with chewing simulator and thermal cycling procedures while the other half was aged only with thermal cycling. The microleakage values were found to be higher in samples aged with chewing simulator and thermal cycling procedures. The correct simulation of the oral conditions can be crucial to assess and understand the performance of the adhesive materials in laboratory tests.