The purpose of this in vivo study was to evaluate the marginal integrity of composite resin buildups after full crown preparation, and to identify possible changes during the provisional phase of the manufacturing process of the final restorations. Two test groups were determined for the use of an autocuring (Clearfil New Bond, Kuraray) and a light-curing (Optibond FL, Kerr) dentin adhesive. After rubber-dam application, both dentin adhesives were used with the total-etch technique. Then, an autocuring composite resin was applied for the core buildup. Impressions of the built-up teeth were taken directly after preparation and before cementation of the final restorations. During the provisional phase, which lasted from 7 to 28 days, the prepared teeth were restored with cemented provisional crowns. Replicas of the built-up teeth were manufactured and examined with a scanning electron microscope. For the autocuring dentin adhesive, only one buildup showed a gap 10 µm wide and 100 µm long. For the light-curing dentin adhesive, two samples revealed gaps that were 10 µm wide and had lengths of 100 µm and 75 µm, respectively. No change could be perceived when comparing the state of the composite/tooth interface after preparation and before final cementation. The results show that when using an autocuring composite resin in combination with dentin adhesives, nearly gap-free margins of composite buildups can be achieved and therefore might serve as a sound basis for the final restoration. Keywords: composite resin buildup, marginal fit, clinical study