The purpose of this ongoing prospective long-term study was to evaluate the clinical performance of Ormocer restorative material in combination with a self-conditioning adhesive. Five operators at five clinics placed 356 restorations (48 class I, 150 class II, 63 class III, 32 class IV, and 63 class V) in 117 patients aged 17 to 65years. All fillings were placed with cotton roll isolation and clear matrix bands for class III and IV restorations, and metal matrix bands and an incremental placement technique were used for class II restorations. In follow-up examinations after 6 and 12months, modified Ryge criteria were recorded on all restorations. With 33 randomly selected class I and II restorations, measurements of occlusal wear (via 3D laser scanner) and qualitative and quantitative marginal analysis (via scanning electron microscope) were performed using a replica technique. After placing the fillings, patients reported postoperative hypersensitivity corresponding to B scores in 19 cases and to C scores in four cases. At 12-month recall, 328 restorations were available for evaluation. Losses in the five cavity classes (I, II, III, IV, V) numbered 0, 2, 0, 1, and 6, respectively. The percentages of retained restorations for clinical parameters in four categories (Alpha, Beta, Charlie, Delta) were: 94.7, 5, 0.3, and 0 (marginal integrity), 81.2, 18.8, 0, and 0 (marginal discoloration), 75.2, 24.8, 0, and 0 (anatomic form), and 95, 4.7, 0.3, and 0 (fracture), respectively. Marginal analysis showed 48.7% continuous margin initially and 17.7% at 12months (difference statistically significant, P=0.05). The occlusal wear at 12months was 10.0m (SD 11.6) for premolars and 22.0m (SD 24.1) for molars. Over the 12-month observation period, the Ormocer restorative was clinically effective in combination with a self-conditioning adhesive, and concern persists related to the marginal quality and retention of class V restorations.