Tensile bond strength and flexural modulus of resin cements--influence on the fracture resistance of teeth restored with ceramic inlays.

PURPOSE: This in vitro study tested tensile bond strength to enamel and dentin and the flexural modulus of three resin cements. It also determined the influence of these properties on the fracture resistance of teeth restored with ceramic inlays.

MATERIALS AND METHODS: Initially, 10 standard ceramic discs were bonded to enamel using the following resin cements: Enforce (E), RelyX ARC (RX) and Fill Magic Dual Cement (FM). After seven days of storage, the specimens were subjected to tensile forces at a crosshead speed of 0.5 mm/minute until fracture. The enamel was then ground and the ceramic disks were bonded to dentin. The flexural modulus of each type of resin cement was calculated based on the straight-line tension-deformation curve using the three-point flexure method. For resistance to fracture, 40 sound maxillary premolars were randomly divided into four groups (n = 10). Three groups were submitted to preparations and restored with ceramic inlays bonded with the same resin cements used during the tensile test (n = 10). Intact teeth were used as the control group. The specimens were subjected to compressive axial loading at 0.5 mm/minute using a 10-mm steel ball until fracture.

RESULTS: Statistical analysis revealed that, for all cements, the bond strength to enamel was significantly higher (p < 0.05) than that obtained in dentin. In both substrates, RX and FM showed higher bond strengths than that obtained for E (p < 0.05). In relation to flexural modulus, FM had the lowest and E the highest flexural modulus; whereas, RX differed from the other two (p < 0.05). The teeth with inlays that were bonded using RX, and E had a significantly higher (p < 0.05) fracture resistance than those where the inlays were bonded with FM but without recovering the resistance observed for the control group (intact teeth).

CONCLUSION: The three resin cements had different mechanical properties. A higher flexural modulus usually resulted in improved resistance to fracture for the ceramically restored teeth.