The Influence of Total Convergence of Abutment and Cement Layer Thickness on Marginal Adaptation of Lithium Disilicate Glass-Ceramic Crown Restorations Manufactured by CAD/CAM

Abstract

Purpose of present in vitro study is to evaluate the effect of convergence angle and cement layer thickness on the marginal adaptation of lithium disilicate glass-ceramic crown restorations fabricated by CAD/CAM. Total thirty-six standardized lower left second premolar lithium disilicate glass-ceramic crowns were fabricated with six parameters; three convergence angles (6°, 12°, and 20°) each with two cement layer thicknesses (20 and 40µm). Marginal adaptation was assessed to measure marginal gaps or absolute marginal discrepancy by direct viewing measurement method. For Statistical analysis, one-way ANOVA was performed using Tukey’s (HSD) test for homogeneous groups whereas Tamhane-T2 tests for non-homogeneous variance groups (? =0.05). The range of means of marginal gaps was from 37.62 to 93.63µm. The differences elaborated from statistical analysis of marginal gap between the groups had 6°, 12°, and 20° convergence angles were found significant, regardless of cement layer thickness. The 40µm cement layer thickness group exhibited statistical significant smaller marginal gaps than the 20µm group for all three convergence angles. Within the barriers of the current study, the marginal gap shrinks while enlarges the convergence angle of abutment. The cement layer thickness might influence the marginal adaptation of lithium disilicate glass-ceramic crown restorations. The marginal adaptation of lithium disilicate glass-ceramic crowns was within the clinically suggested range.