Objective: The purpose of this study was to use wear simulation to develop wear rates for two modern composite systems and then compare these rates with clinical studies on the same materials. Method and materials: A spring-loaded piston wear simulator was used to generate localized wear rates for P50 and Z100 at 100,000, 200,000, 300,000, and 400,000 cycles. Clinical studies on P50 and Z100 conducted at Creighton University and the Catholic University of Leuven were used for comparison of clinical wear to the laboratory values. Regression analysis was employed to define the wear rates. Results: The laboratory wear rates determined with simulation for P50 and Z100 were similar. Clinical occlusal contact area (OCA) wear for P50 and Z100 had small differences and were pooled to provide comparison with laboratory data. Wear rates determined from linear regression analysis provided equivalency factors between laboratory localized wear and clinical OCA wear that could be used for future studies. Further regression analysis comparing OCA and generalized clinical wear allowed a conversion factor of 4.5 to be determined. Conclusion: Localized wear from laboratory simulation may be a useful predictor of localized clinical wear and also clinical generalized wear using a conversion factor.