Magister Chirurgiae Dentium - MChD / The purpose of this study was to evaluate in vitro, the tensile bond strengths of some conventional and light cured resins, to study the effects of etchants on polished and ground enamel using the scanning electron microscope, and to the resin/etched enamel examlne electron interface by scanning microscopy This study was divided into: 1) laboratory tensile bond strength study of 'four composite resin materials. 2) a scanning electron microscopic study of the effect of four etchants on enamel. 3) the S.E.M. examination of the interfacial zone after the application of a demineralizing agent. The tensile bond strength study consisted of testing the bond strengths of two macrofilled and two microfilled resins in common use. These resins were applied directly to the etched enamel surfaces of extracted human teeth by utilizing newly developed perpex stubs which allowed a uniform surface area and for light curing of the resin. In this laboratory study the extracted teeth and the composite filled stubs were stressed to failure of the material bond to tooth in an Instron Machine. Bond strengths were recorded and tabulated in Newtons/mm2. The application of statistical analysis by Analysis of Variance and Duncans Multiple Range Test showed that there was a significant difference in the bond strengths of some of the four materials. The scanning electron microscope study consisted of an examination of etched enamel, either polished or ground using the etchants supplied by the two manufacturers i.e. 3 M Dental Company and J&J Dental Company. The interfacial zones of the resin/tooth interface systems were examined, using the two macrofilled and the two microfilled resijs in the stUdY.! Differences were found to exis.t at this zone.