STATEMENT OF PROBLEM: There are no studies that analyze the long-term durability of minimally invasive fixed partial dentures (FPDs) by comparing different methods of adhesive bonding. PURPOSE: This in vitro study examined the influence of cavity design and operative technique on the marginal adaptation of resin-bonded composite FPDs. MATERIAL AND METHODS: Slot-inlay tooth preparations with cavity margins located in enamel were prepared in 18 maxillary canines and 18 maxillary first molars designated as abutments. The specimens were divided equally into 3 experimental groups. In all groups, butt joint tooth preparations were created in canines and molars. In group 2, canines were prepared additionally with a 1.5-mm wide palatal bevel in enamel. After pretests with modification spaces of 11 and 17 mm (length), 2 missing premolars were replaced by the ceromer Targis and reinforced with the glass-fiber material Vectris. The prostheses were inserted with Tetric Ceram with use of an ultrasonic-supported, high-viscosity technique. Restorations were selectively bonded to cavity finish lines in groups 1 and 2 ("selective bonding"). In group 3, restorations were bonded totally to the whole cavity surface ("total bonding"). The restorations were stressed in a computer-controlled masticator. Marginal quality was examined with an SEM at x 200. RESULTS: The percent area of optimal margins after thermomechanical loading between composite and enamel in each group was as follows: group 1, 86.2% +/- 12.3% for canines and 95.5% +/- 3.5% for molars; group 2, 95.3% +/- 2.1% for canines and 96.2% +/- 2.7% for molars; and group 3, 95% +/- 0.9% for canines and 86.4% +/- 3.2% for molars. The marginal quality for molars inserted with total bonding was significantly lower (P< or =.05). CONCLUSION: Within the limitations of this study, the selective bonding technique for slot inlay-retained fixed partial dentures resulted in a negligible loss of marginal quality after extensive mechanical and thermal stress. The selective bonding technique is recommended for box-shaped cavity preparations.