Composite Inlays Vs. Composite Fillings For Restoring Class V Cavities With Proximal Margins In Dentin B. Bott*, M. Hannig (Clinic Of Operative Dentistry And Periodontology, University Of Kiel, Germany) The aim of this in vitro study was to analyse the marginal adaptation of composite resin inlays in comparison to direct composite resin restorations placed in Class II cavities with proximal margins located in dentin. Thirty-six standardized mesio-occlusal cavities were prepared in extracted human molars. Gingivo-proximal margins of the cavities were located 1 mm beyond the cemento-enamel junction. The teeth were randomly divided to six groups with six teeth each and restored with composite resin inlays (Groups Ii , IIi, IIIi ) or directly placed composite resin fillings (Groups If , IIf , IIIf). After application of an insulating gel to the cavity walls composite resin inlays were fabricated from Charisma Group (Ii) or Ecusit (Groups IIi and IIIi) and light-cured by use of the ADT 1000 PAC curing unit. The inner surfaces of the composite inlays were treated by air-abrasion (KCP 1000, 27 µm aluminum oxide particles) and silanization (Monobond S) before adhesive luting. In Groups I and II the enamel margins were etched with phosphoric acid and the dentin was conditioned by application of Denthesive II (Group I) or Ecusit Primer AB Mono (Group II). In Group III a self-etching/self-priming bonding agent (Resulcin AquaPrime) was applied to enamel and dentin without phosphoric acid etching.   Composite resin inlays were adhesively luted by use of dual-curing composite resin materials (Microfill Pontic in Group Ii , Ad-Cem in Group IIi , Dualcement in Group IIIi). Direct composite resin restorations were placed according to the incremental technique using the fine hybrid composite materials Charisma (Group If) or Ecusit (Group IIf and IIIf). Marginal adaptation was evaluated by quantitative SEM analysis after thermocycling (2,500 cycles, 5°C- 55°C) and mechanical loading (500,000 cycles, 100 N) using replica models. After in vitro loading the inlay restorations (Groups Ii , IIi , IIIi) were characterized by high percentages (more than 97%) of gap-free marginal adaptation at the gingivo-proximal margins located in dentin. However, the directly placed composite resin restorations revealed significantly (H-test, U-test; p < 0.01) lower levels of gap-free marginal adaptation (0.9% in Group If , 52.5% in Group IIf , and 76.3% in Group IIIf) at the proximal filling-dentin interfaces. In conclusion, the results of this in vitro study demonstrate the benefits of the composite resin inlay technique as compared to directly placed composite fillings in providing a stable load-resistant marginal adaptation at the proximal dentinal margins of Class II composite resin restorations.