Fracture Resistance of Maxillary Premolars Restored with Direct and Indirect Adhesive Techniques

Objective: To evaluate the fracture resistance of teeth restored using 2 intracoronal direct and indirect adhesive techniques.Methods: Forty maxillary premolars were divided randomly into 4 groups of 10: group 1, intact teeth; group 2, mesio-occlusodistal (MOD) cavity preparation associated with endodontic therapy (unrestored); group 3, MOD cavity preparation and restoration with direct composite resin (Z100, 3M ESPE); and group 4, MOD cavity preparation and restoration with indirect ceramic inlay (IPS Empress, Ivoclar-Vivadent). Specimens were subsequently submitted to an axial compression test, using an 8-mm diameter steel ball at a loading speed of 0.5 mm per minute, until their fracture.Results: The average compression force causing cuspal fracture in the 4 experimental groups was group 1, 138.4 kg; group 2, 49.0 kg; group 3, 105.4 kg; and group 4, 82.7 kg. ANOVA analysis and Tukey tests showed that cavity preparation significantly weakened the remaining tooth structure.The fracture resistance of teeth restored using direct composite resin was not significantly different from that of teeth restored with ceramic inlays (p > 0.05). None of the materials tested was able to restore completely the fracture resistance lost during cavity preparation.Conclusions: Cavity preparation significantly weakens the remaining tooth structure. Direct and indirect intracoronal adhesive restorations can partly restore fracture resistance of teeth weakened by wide cavity preparation.