Influence of dentin and enamel on the fracture resistance of restorations at several thicknesses

Purpose: To investigate the effect of substrate and thickness on the fracture resistance of bonded dental restorative materials. Methods: Cylindrical restorations (d = 4.0 mm) of resin composites Filtek Supreme XTE, Clearfil AP-X, Lava Ultimate and glass-ceramic IPS e.max CAD were fabricated at thicknesses of 0.5 mm, 1.0 mm and 2.0 mm respectively (n = 10 per group) and adhesively bonded to bovine enamel or dentin. The load to failure (LtF in N) of all specimens was determined in a universal testing machine and two one-way ANOVAs with a post hoc LSD tests and separate independent samples t-tests, performed at a significance level of 5%. Results: At 0.5 and 1.0 mm, direct resin composites bonded to dentin showed a higher LtF than when bonded to enamel, while the indirect materials showed reversed results (P< 0.05). At 2.0 mm there was no difference except for LU. A direct relationship between LtF and increasing thicknesses on enamel was found, while on dentin the LtF of direct resin composite restorations was less dependent on the thickness.