Different materials and techniques are used in dental wear restoration with the objective of increasing teeth resistance, and providing an aesthetic appearance. The aim of this study was to compare the fracture resistance of amalgam and posterior composite in abrasioned premolar and molar teeth. In this study, 60 carries and restoration- free human permanent mandibular premolar and molar teeth, freshly extracted because of orthodontic, periodontal and surgery reasons, were used. Cusps of teeth were removed with a horizontally cut, and were randomly divided into four groups of 15 teeth each. Groups 1 and 2 received class II restorations with posterior composite and amalgam, respectively in 15 premolar teeth. Groups 3 and 4 had class II restorations with posterior composite and amalgam, respectively in 15 molar teeth. After finishing and polishing, all samples were subjected to 1.000 times thermocycling with a dwell time of 30 s at 5 ± 2 oC, and 55 ± 2 oC. Then, teeth were mounted in acrylic resin to a depth of 2 mm apical to the cemento-enamel junction, and force was applied to all samples in a universal testing machine until fracture occurred. The results obtained after fracture were analyzed using the Shapiro-wilk and one-way ANOVA tests. According to these results, the difference between groups 1-2, 1-3, 1-4, 2-3 and 2-4 was statistically significant (P< 0.05). The results of this study showed that posterior composite may be used in molar teeth which have suffered abrasion. In premolar teeth, the selection of restorative material must be made taking aesthetic expectations into consideration.