Fatigue behavior and crack initiation of CAD/CAM resin composite molar crowns

•Fatigue behaviour of CAD/CAM resin composite molar crowns was assessed.•Crack initiation of CAD/CAM resin composite molar crowns was analysed.•Fracture loads of CS and KA were significantly greater than that of HC.•Fracture probabilities at 120,000 cycles of KA were the lowest.•CAD/CAM resin composite crowns could be used as an alternative to ceramics. The aim of this study was to evaluate long-term fatigue behavior using an in vitro step-stress accelerated life test (SSALT), and to determine the crack initiation point using in silico finite element analysis for computer-aided designed and manufactured (CAD/CAM) molar crowns fabricated from three commercial CAD/CAM resin composite blocks: Cerasmart (CS; GC, Tokyo, Japan), Katana Avencia Block (KA; Kuraray Noritake Dental, Niigata, Japan), and Shofu Block HC (HC; Shofu, Kyoto, Japan). Fifty-one mandibular first molar crowns luted on a resin core die were embedded in acrylic resin and covered with a polyvinyl chloride tube. Single compressive tests were performed for five crowns. SSALT was conducted for 36 crowns using three profiles and reliabilities at 120,000 cycles, and a Weibull analysis was conducted. The maximum principal strain of each CAD/CAM resin composite crown model was analyzed by three-dimensional finite element analysis. Fracture loads of CS and KA (3784±144N and 3915±313N) were significantly greater than that of HC (2767±227N) (p