Fracture load and three-dimensional internal void analysis of direct composites used to restore worn molars

This study evaluated (1) the load-bearing capacity of molars restored with direct occlusal veneers fabricated either from short-fiber-reinforced composite (SFRC) or particulate-filled composite (PFC) and the presence of internal voids within the materials, and (2) effect of water storage on the fracture load and correlation between internal voids and fracture load. Sixty human molars (n = 10/group) were prepared with flat occlusal surfaces and preserved enamel margins simulating worn teeth. Conventional molds were taken for each tooth to control the preparation depth and transparent molds to restore the teeth to their original shape. Following bonding procedure, teeth were restored with flowable SFRC, flowable PFC, or condensable PFC using either injectable or pressing technique. Restored teeth were stored in water for 1 d or 6 months before the static loading test. Fracture mode and three-dimensional internal void analyses were additionally conducted. SFRC occlusal veneers showed significantly higher fracture load (3661 ± 446 N) than both PFC materials, flowable PFC (2064 ± 372 N) and condensable PFC (2183 ± 563 N). SFRC redirected the fractures towards the periphery of the restoration. Prolonged water storage duration or single voids did not adversely affect the fracture load. The use of SFRC as occlusal veneers for restoring molars improves the fracture load and the fracture propagation.