Fracture toughness of seven resin composites evaluated by three methods of mode I fracture toughness (KIc).

This study compared the fracture toughness values of seven resin composites and analyzed the consistency of data values using three methods: compact tension, three point and four point bending for Mode I failure. Seven resin composites were selected: Estellite Sigma Quick, Esthet X HD, Filtek Supreme XTE, Heliomolar, Ice, Rok, and Vit-l-escence. For each material, 18 specimens (n=6 for each test) were prepared. Maximum load to failure was recorded using a universal testing machine and fracture toughness was calculated. There was a direct significant correlation among all tested methods. Rok showed the highest and Estelite the lowest KIc values. SEM of the fractured surface of compact tension method showed propagation of the cracks from stresses concentrating at the corner of the notch and the surface of the sample. Four-point test gave the largest range in KIc and was a simple method to discriminate between the resin composite values of KIc.