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

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. 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 (1.2×10 cycles at 1.7 Hz/50N, 8000 cycles 5°C to 55°C) and axially loaded until failure. Data were analyzed using analysis of variance and Tukey post hoc test (α=0.05). Fracture strength was significantly affected by the type of restoration ( =0.000; statistically similar groups identified with superscript letters): LDS (3217±1052 N), P-LDS (2697±665 N), EC (2425±993 N), C (2192±752), control (1890±774 N), CP (1830±590 N), and GFRC (1823±911 N). Group GFRC obtained significantly more repairable fractures than the other groups. 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.