This randomized trial evaluated the 12-month clinical performance of nanofill, a nanohybrid, and a microhybrid composite in restorations in occlusal cavities of posterior teeth. This study utilized 41 patients, each of whom had three molars affected by primary caries or the need to replace restorations. All restorations were performed in accordance with the manufacturer's recommendations and evaluated in accordance with U.S. Public Health Service-modified criteria. Based on the results of the present study, the material investigated demonstrated acceptable clinical performance after 12 months of clinical service. Long-term re-evaluations are necessary for a more detailed analysis of these composites.