Notchless Triangular Prism Fracture Toughness of CAD/CAM Resin Blocks

Objectives: Hybrid resin blocks for CAD/CAM are known as useful material for clinical use. Last year, CAD/CAM hybrid resin crowns for molar teeth have been approved by Japanese national insurance and we launched new product CERASMART300 in only Japanese market. Fracture toughness is an important property that describes the ability of a material against crack extension. Notchless triangular prism (NTP) fracture toughness test has been paid attention as an effective method for measuring fracture toughness of hybrid resin. The aim of this study was to evaluate the NTP fracture toughness of CERASMART300.
Methods: Four products were selected for analysis, 1) CERASMART300 (GC Corp.), 2) CERASMART270 (GC Corp.), 3) CERASMART (GC Corp.) and 4) Lava Ultimate (3M ESPE). Blocks were milled and fabricated to triangular prism (6×6×6×12 mm) and polished for NTP fracture toughness test (n=5). NTP fracture toughness test was conducted with a crosshead speed of 0.5 mm/min (AG-I, SHIMADZU). Fracture toughness, K_IC was calculated by following equation, K_IC = Pmax*Ymin / (D*W^0.5) where Pmax = the maximum load at fracture (N), D = the specimen diameter (12mm), W = the specimen length (10.5mm), and Ymin = the minimum of the dimensionless stress intensity factor coefficient (= 28). The data were analyzed by one-way ANOVA and Tukey’s test (p<0.05).
Results: The results of NTP fracture toughness test are shown below and same letter indicates no significant difference. CERASMART300 shows significantly higher NTP fracture toughness than any other materials tested.
Conclusions: CERASMART300 exhibit highest NTP fracture toughness, and it is suggested that CERASMART300 is not easily fractured. Therefore, it is expected that CERASMART300 is durable material and may have clinical advantage.