Marginal Adaptation Of Compomer/Composite "Sandwich" Fillings In Class II Cavities M. Kahl*, B. Bott, M. Hannig (Clinic Of Operative Dentistry And Periodontology, University Of Kiel, Germany) The purpose of this in vitro study was to analyse the marginal adaptation of Class II „sandwich“ restorations using low-viscosity compomers in combination with composite resins (according to the CbC-technique; Hannig et al. 1997). Thirty Class II cavities with the proximal box ending 1 mm beyond the CEJ were prepared in extracted human molars and randomly assigned to five groups with six teeth each. The following dentin bonding agents / low-viscosity compomer materials were applied up to the level of the cemento-enamel junction: Ecusit Primer AB -Mono / Prima Flow (Group I), Syntac sprint / Compoglass Flow (Group II), Syntac classic after total etching of the cavity with phosphoric acid / Compoglass Flow (Group III), Syntac classic / Compoglass Flow (Group IV), and NRC, Prime & Bond NT / Dyract Flow (Group V).   Subsequently, all cavities were filled with a fine-hybrid composite resin (Ecusit) using the incremental technique. SEM-analysis of the marginal adaptation of the restorations after thermocycling (5-55 °C, 2,500 cycles) and mechanical loading (100 N, 500,000 cycles) revealed that excellent, gap-free marginal integrity (mean / median percentages) was achieved in 87.2% / 89.0% (Group I), 57.2% / 53.0% (Group II), 62.0% / 55.0% (Group III), 70.0% / 92.5% (Group IV), and 55.8% / 54.0% (Group V) of the marginal areas located in dentin.   Statistical analysis (H-test according to Kruskal and Wallis; p < 0.05) did not indicate significant differences in percentages of gap-free marginal adaptation between the various groups. Results indicate that use of the material combination tested in Groups I and IV provided high levels of perfect marginal adaptation in Class II cavities with proximal margins located in dentin. However, a completely gap-free marginal seal at the critical dentinal margins of Class II cavities could not be obtained with the low-viscosity compomer / composite "sandwich“ restorations evaluated in this study.