Contraction gaps in Class II restorations with self-cured and light-cured resin composites

To evaluate in vitro the cervical gap formation in composite restorations in which an increment of autopolymerizing composite was interposed between the light-cured filling material and the dentin bonding system. Two different self-cured materials and two different adhesives were used and compared.

In 40 Class II cavity preparations with the gingival margins in dentin or cementum, an increment of either of two different autopolymerizing composites, Palfique or Bisfil 2B, was interposed between the light-cured filling material (Palfique Estelite) and either of two different dentin bonding systems, All-Bond and Superbond D (20 restorations each). The specimens were immersed in toluidine blue dye. A section was taken from each specimen and examined under an optical microscope. The extent of dye penetration was measured. The specimens were then stored in water for 1-4 months and replicas of the sections were examined by SEM.

Good marginal adaptation was observed for All-Bond/Bisfil 2B in all the restorations. All-Bond/Palfique showed good adaptation in 7 out of 10 cases, the failures occurring between bonding agent and composite. Superbond D/Palfique and Superbond D/Bisfil 2B showed marginal gap formation in 8 out of 10 and in all the restorations respectively. In the latter, four gaps occurred between bonding agent and dentin. As a consequence, a very significant difference (P<0.001) was found between All-Bond and Superbond treatments; no significant difference was found between Bisfil 2B and Palfique in each group treated with either All-Bond or Superbond. After 1-4 months storage in water, hygroscopic expansion of the restorative materials reduced the total number of gaps and the efficacy of the treatments was no more significantly different.