Polymerization contraction stress in dual-cure cements and its effect on interfacial integrity of bonded inlays

Objectives. To compare the polymerization contraction stress of resin cements in dual-cure and self-cure modes, and verify its effect on microleakage and gap formation in class I cavities restored with porcelain inlays. Methods. Dual-cure cements (Calibra, Choice and RelyX ARC) were monitored for contraction stress during 30 min in the tensilometer, in the presence or absence of photo-activation. Microleakage was evaluated in porcelain inlays bonded to cavities prepared in bovine incisors, combining the same adhesive (One-Step) with each of the cements in both activation modes. Epoxy replicas of the sectioned specimens were analyzed in the SEM to determine the percentage of discontinuous margins. Results. The stress developed in dual-cure mode was higher than in self-cure mode for all cements. In self-cure mode, no significant difference in stress was found among materials. Choice and RelyX ARC showed higher microleakage in dual-cure mode than in self-cure mode. Calibra did not show a significant difference in microleakage between activation modes. Contraction gap results showed wide variations, and no significant differences were detected among the groups. Gaps occurred more often in dentin, with an overall average of 22 ± 17.5%. Conclusions. The higher stress generated in dual-cure cements subjected to photo-activation may lead to higher marginal leakage. In the confinement condition represented by the class I inlay, even the lower contraction stress of the cements in self-cure mode had enough magnitude to disrupt the bonding to dentin.