Fracture Strength of Various Types of Large Direct Composite and Indirect Glass Ceramic Restorations

Introduction: The objective of this study was to investigate the mechanical behavior of severely compromised endodontically treated molars restored by means of various types of composite buildups, full-contour lithium disilicate crowns (with or without post) or a lithium disilicate endocrown. Methods and Materials: One hundred five sound molars were endodontically treated and randomly assigned to 1 control group (endodontic access cavity only) and 6 experimental groups (n=15): glass fiber reinforced composite (GFRC group), direct microhybrid composite (C group), direct microhybrid composite restoration with glass fiber post (CP group), composite buildup and full-contour lithium disilicate crown (LDS group), additional glass fiber post (P-LDS group), and endocrown (EC group). Molar crowns in the treatment groups were removed 1 mm above the cementoenamel junction and restored. All specimens were thermomechanically aged (1.2x10(6) cycles at 1.7 Hz/50N, 8000 cycles 5 degrees C to 55 degrees C) and axially loaded until failure. Data were analyzed using analysis of variance and Tukey post hoc test (alpha=0.05). Results: Fracture strength was significantly affected by the type of restoration (p=0.000; statistically similar groups identified with superscript letters): LDSB (3217 +/- 1052 N), P-LDSAB (2697 +/- 665 N), ECAB (2425 +/- 993 N), C-A (2192 +/- 752), control(A) (1890 +/- 774 N), CPA (1830 +/- 590 N), and GFRC(A) (1823 +/- 911 N). Group GFRC obtained significantly more repairable fractures than the other groups. Conclusions: Significant differences in fracture strength were obtained between LDS, the composite restorations, and control group. Direct composite restorations showed similar fracture strength as P-LDS and EC. Incorporating a glass fiber reinforced composite resulted in significantly more repairable failures.