Composites And Compomers Marginal Adaptation In Class II Restorations After Cariogenic Treatment C. Prati, M. Muratori*, S. Chersoni, G. Valdre’, R. Mongiorgi, G. Montanari (University Of Bologna, Italy) Purpose: The aim of this study was to evaluate the morphology and the interproximal marginal adaptation of Class II cavities restored with different procedures and materials.   Materials and Methods: Class II OM and OD restorations (n= 30) were prepared in vitro at CEJ in 15 extracted third molars. Bonding systems selected was Scotchbond 1 (3M, MN, USA). Fifteen cavities were filled with compomer F 2000 (Group A) and Z 250 while 15 cavites were filled with only Z 250. After finishing with SofLex PopOn (3M, USA) discs, each margin was polished for 1 mins with diamond polishing paste and then treated with 2.5 % NaOCl for 60 secs to remove polishing debris and uninfiltrated collagen and then stored in acid lactic solution (pH 4.5; 37°C) for 7 days (daily sobstitued). SEM analysis was performed on each sample.   Results: Enamel marginal adaptation resulted gap-free in all the observed samples but with many enamel fractures 10-50 microns parallel to the marginal interface. In all samples perimarginal enamel was more demineralized that buccal enamel. The typical demineralization morphology of perimarginal area was characterized by the removal of prism cores and by the presence of unaffected interprismatic enamel matrix. Enamel fractures were frequently observed along the margin of the restorations. No morphological differences were observed between the compomer and composite restorations.   Conclusions: Lactic acid-cariogenic solution caused an area of demineralization with many enamel porosities and demineralization alterations that can increase perimarginal microleakage. The combination of etching procedures and lactic acid increase the risks for caries along the interproximal enamel margins. This in vitro model may be suitable to investigate the demineralization mechanisms of secondary caries.