Comparison of direct and indirect composite resin restorations effect on the fracture resistance of maxillary premolars (An in vitro study)

One of the problems involved in the restoration of extensive cavities is loss of the fracture resistance of the remaining tooth structure to withstand masticatory forces. But possible reinforcement of remaining tooth structure has been increased by the use of adhesive restorative materials. Tooth reinforcement may be affected by the different physical properties of direct and indirect composite resin restorations.So, theaim of this study was tocompare direct and indirect composite resin restorations effect on the fracture resistance of maxillary premolars with mesio-occluso distal (MOD) cavities. In this experimental (in vitro) study, 24 human maxillary premolars free of any caries, restoration or crack, which had been extracted in a 6 month period, were selected and MOD cavities with the bucco-lingual extension equal to two third of intercuspal distance were prepared on them all. The teeth were divided randomly in 3 groups including A (8 teeth & direct restoration group), B (8 teeth & indirect restoration group) and C (8 teeth &preparation without restoration group) and were undergone fracture test with universal testing machine.Variance and Tukey tests were used for analysis of results; the level of significance was set at 0.05. The mean fracture resistance was1314.75 ± 332.26, 1192.25 ± 352.45 and 382.45 ± 142.51 for direct restoration, indirect restoration and preparation withoutrestoration groups,respectively. There was no significant difference between A & B groups (P=0.60), whereas the differences were significant between A&C groups (P=0.00) and also B&C groups (P=0.00). According to the present study, both direct and indirect composite restorations cause increase in the fracture resistance of teeth and so can have an important role in extensive cavities.