The effect of placement technique on marginal adaptation of posterior resins

Polymerization shrinkage of posterior resin restorations leads to margins that pull away from the tooth, or to cracks in the material itself. The purpose of this study was to determine the effect of three different placement techniques on the marginal adaptation (or in effect the amount of polymerization shrinkage) of posterior resin restorative materials. Three posterior resin materials, namely, Distalite, Heliomolar and P30 were included in this study. Each of these materials were placed by means of three different placement techniques (Bulk pack, Horizontal layering and Vertical layering) into class II cavities in extracted human molars. No dentine bonding agents were used. The samples were light cured, the teeth sectioned longitudinally and stored dry before examination in a Scanning Electron Microscope. Results showed polymerization shrinkage with all three techniques, with the poorest the bulk pack technique where large marginal discrepancies were visible. No significant differences were detected between the horizontal and vertical placement techniques, but the two microfilled resins Heliomolar and Distalite showed significantly poorer marginal adaptation than the small particle conventional resin, P30. All three materials had better adaptation on the occlusal margins than on the margins situated along the floor of the cavity or the gingival margins of the proximal box of the cavity. It can be concluded that the bulk pack technique should be avoided as this leads to large contraction gaps at most of the margins of the restoration.