A comparative study on the effect of the composite type and restoration method on fracture resistance of composite restorations

The purpose of this study was to evaluate the fracture resistance of premolars with mesio-occluso-distal (MOD) preparations restored with two different resin composites along with three placement methods.Method and materials: In this in vitro study, sixty human sound maxillary premolars mounted in acrylic resin were randomly divided into two groups according to the type of composite restoration (Filtek P60, Nulite F). Each group was further subdivided into three subgroups according to the type of placement methods namely Bulk, Centripetal and Fibre Insert (n = 10). The same adhesive system; Single Bond, was used for composite bonding following manufacturer's instructions for all teeth. Specimens in groups 1, 2 and 3 were restored with Filtek P60 resin composite while in groups 4, 5 and 6 Nulite F was applied. After 24 hours storage in 37°C, a 4 mm diameter steel sphere in Universal Testing Machine was contacted the buccal and lingual cusps of the tested teeth at a crosshead speed of 5 mm/min until fracture occurred. Data were subjected to analysis of variance and Duncan tests (p value < 0.05). Groups 3 and 6 showed a higher fracture resistance than other groups (P = 0.001). Among the placement methods, Fibre insert showed a significant result (P = 0.0001) but the type of composite was insignificant (P = 0.791). It seems that on MOD cavities, contrary to the type of materials used, the insertion method, largely influences fracture resistance of premolar teeth restored with resin composite.