Effects of bonding agent types and incremental techniques on minimizing contraction gaps around resin composites

In this in vitro study, large rectangular cavities were prepared on the proximal surfaces of human premolars with cervical margins placed beyond the cemento-enamel junction. Before the insertion of resin composite, the cavity walls were treated with Bowen's system, Scotchbond, or Gluma combined with different bonding agents. Various incremental techniques were tested. The contraction gap was determined by use of the resin impregnation technique: After polymerization shrinkage, a low-viscosity resin with a fluorescent additive was applied to the cervical and occlusal margins to penetrate the contraction gap. After being ground, the width of fluorescent resin could be measured with a microscope. All combinations of materials and techniques produced contraction gaps at the cervical wall. The range for mean width of the impregnated gap at the cervical wall was from 5 to 13 microns. The lowest mean value was obtained for Gluma in combination with Clearfil Bonding Agent. Placement of the composite in two increments significantly reduced the gap width. No reduction was achieved when a three-step insertion technique was used.