Purpose: The wear properties of o five materials used in the primary dentition must be compatible with primary tooth wear. The purpose of this study was to investigate the wear rate of primary teeth opposing composite resin and different prefabricated crown materials. Methods: The study specimens were divided into four groups: (1) composite resin (CR) group; (2) stainless steel group (5.5); (3) monolithic zirconia (MZ) group; and (4) fiberglass (FG) group. Ten specimens were prepared from each group, and primary canines were used as antagonist teeth. The wear test was conducted with a vertical loud of 50 N and 240,000 cycles using a chewing simulator. The volume losses of antagonist teeth and the weight losses of restorative materials were calculated with microcomputed tomography and a digital scale, respectively. The worn surfaces of restorative materials were examined via scanning electron microscopy. Results: The amount of enamel wear was highest in the MZ group (1.551 +/- 0.859 [standard deviation] mm(3)) group, followed by the FG group (1.028 +/- 0.854 mm(3)), SS group (0.480 +/- 0324 mm(3)), and CR group (0310 +/- 0341 mm(3)). The volume losses in the MZ group were significantly greater than those in the SS and CR groups (P<0.05). The weight loss amount of restorative materials was highest in the CR group (81.2 mg), followed by the FG (6 +/- 3 mg), SS (4 +/- 3 mg), and MZ (2 +/- 1 mg) groups. Conclusions: Prefabricated monolithic zirconia crowns caused greater wear on opposing primary teeth. The amount of weight loss in the composite resins was highest while causing minor primary tooth wear.