Purpose: 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.
Materials and methods: 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.
Results: 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.