Marginal adaptation of inlay-retained adhesive fixed partial dentures after mechanical and thermal stress: An in vitro study

Statement of problem. There are no studies that analyze the long-term durab ility of minimally invasive fixed partial dentures (FPDs) by comparing diff erent methods of adhesive bonding. Purpose. This in vitro study examined the influence of cavity design and op erative technique on the marginal adaptation of resin-bonded composite FPDs . Material and methods. Slot-inlay tooth preparations with cavity margins loc ated in enamel were prepared in 18 maxillary canines and 18 maxillaxy first molars designated as abutments. The specimens were divided equally into 3 experimental groups. In all groups, butt joint tooth preparations were crea ted in canines and molars. In group 2, canines were prepared additionally w ith 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 pr ostheses were inserted with Tetric Ceram with use of an ultrasonic-supporte d, high-viscosity technique. Restorations were selectively bonded to cavity finish lines in groups 1 and 2 ("selective bonding"). In group 3, restorat ions were bonded totally to the whole cavity surface ("total bonding"). The restorations were stressed in a computer-controlled masticator. Marginal q uality was examined with an SEM at x200. 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 a nd 86.4%+/-3.2% for molars. The marginal quality for molars inserted with t otal bonding was significantly lower (P<.05). Conclusion. Within the limitations of this study, the selective bonding tec hnique for slot inlay-retained fixed partial dentures resulted in a negligi ble loss of marginal quality after extensive mechanical and thermal stress. The selective bonding technique is recommended for box-shaped cavity prepa rations.