RESUMO
One of the most important criteria for clinical acceptance and longevity of cast restorations is marginal accuracy. Marginal discrepancy causes cement layer exposure, increases risk of cement wash out leading to plaque accumulation, recurrent caries and gingival tissue inflammation. This study assessed the effect of finishing line preparation design on marginal discrepancy. In this experimental invitro study, three metal dies were prepared using simulation method with beveled shoulder, chamfer and combination of both [buccal beveled shoulder encounters palatal chamfer] that addressed groups A, B and C respectively. Seven wax patterns for each die were cast in Wiron 99 [Basemetal Alloy]. After seating the frameworks, marginal discrepancy was measured in two horizontal and vertical dimensions. The data were analyzed by one way ANOVA and Tukey multiple comparisons tests. The significant differences of horizontal marginal opening were found among three groups in buccopalatal and mesiodistal directions [P<0.003, P<0.0001]. Also, significant differences found between pair groups except to A and C in buccopalatal and A and B in mesiodistal directions. The vertical marginal opening in three groups was statistically different at mesial, distal and palatal directions [P<0.05] but not at buccal side. The vertical marginal opening differences of pair groups [A and C, B and C] at mesial, distal and palatal directions were significant [P<0.05]. Within the limitation of this study, finishing line, preparation design significantly affects the marginal discrepancy, the least and most horizontal marginal opening was produced in beveled shoulder and the combined preparation of beveled shoulder and chamfer, respectively. Chamfer preparation caused minimum vertical marginal opening while the beveled shoulder was in the next rank with no significant statistical differences