The aim of this article was to report the results of an 18-month longitudinal randomized clinical trial that evaluated the clinical performance of microhybrid, packable and nanofilled resin composite restorations placed in Class I cavities of molar teeth. Three Class I resin composite restorations were placed in each of 35 patients. Each patient received one microhybrid ('Point 4'; Kerr, Orange, CA, USA), one packable ('Packable Premise'; Kerr, Orange, CA, USA) and one nanofilled ('Nanofilled Premise'; Kerr, Orange, CA, USA) resin composite restoration. Clinical evaluation was performed at baseline (2 weeks after placement), and after 6, 12 and 18 months after placement using modified Ryge criteria. No patients were lost from the study. At the final appointment (after 18 months), 95.4%, 93.7% and 96.2% respectively of the microhybrid ('Point 4'), packable ('Packable Premise' and nanofilled ('Nanofilled Premise') resin composite restorations received Alfa ratings. Regardless of the type of restorative material, no significant changes were observed in the modified Ryge criteria at the baseline and 18-month recalls (P
10.1111/j.1365-2842.2010.02073.x