Fracture toughness comparison of six resin composites

Objectives: This study investigated the Mode I and II fracture toughness values of resin composites used for the restorations of anterior teeth by the Brazilian disk test method. Methods: The Brazilian disk test was performed on six commercially available dental resin composites, VenusTM (hybrid resin composite), Durafill^® (micro-filled resin composite), GradiaTM (micro-filled/hybrid resin composite), Point 4TM (hybrid resin composite), SupremeTM (nano-particle resin composite) and Filtek Z250™ (resin composite with zirconia particles). Five resin composite disks of 25 mm in diameter and 2 mm in thickness with chevron notches were prepared for each fracture mode per material. The specimens were stored in distilled water for 24 h at 37 °C, and then tested by a Zwick testing machine under compression mode with a constant crosshead speed of 0.25 mm/min at room temperature. The stress intensity factors under combined Modes I and II fracture toughness were calculated by the formula presented by Atkinson et al. The fracture patterns of two specimens randomly selected from each test group were examined using a scanning electron microscope. A one-way analysis of variance (ANOVA) was performed for the statistical evaluations followed by the post-hoc Tukey's Student Range (HSD) test. Results: The highest mean Mode I and II fracture toughness values were found in Filtek Z250™ and Filtek™ Supreme and they were significantly higher than other materials (comparisons significant at the 0.05 level). The intermediate group consisted of Point4TM, VenusTM and GradiaTM ANTERIOR, whereas Durafill^®, statistically, had the lowest mean value for fracture toughness. Significance: Fracture toughness values of hybrid and nano-particle resin composites are significantly higher than those of micro-filled resin composites. This suggests that the latter should be used for non-stress bearing areas.