Effect of Core Thickness and Porcelain Sintering on Marginal Adaptation

Marginal adaptation affects the long-term success of full-coverage restorations. This study aimed to assess the effect of porcelain sintering and zirconia core thickness on the marginal adaptation of all-ceramic restorations. In this in-vitro experimental study, a standard brass die, 7 mm in length and 5 mm in diameter, was fabricated using a milling machine. A classic chamfer finish line with the depth of 0.8 mm was prepared with 10-degree tapered walls. Copings were fabricated on the die using the computer aided design/computer aided manufacturing (CAD/CAM) system and were divided into three groups (n=10) with 0.3-mm (group 1), 0.5-mm (group 2), and 0.7-mm (group 3) core thicknesses. The copings were placed on the dies and randomly coded. The vertical gap was measured at 10 points on the margin under a scanning electron microscope (SEM). After porcelain sintering, the crowns were placed again on the dies, and the vertical gap was measured again at the same points. Data were analyzed using analysis of variance (ANOVA) and paired t-test. There was a significant difference among the three groups in marginal gap (P<0.05). The comparison of marginal gaps before and after porcelain sintering showed no significant changes with 0.3-mm and 0.5-mm thicknesses (P>0.05) but the difference was statistically significant with 0.7-mm core thickness (P<0.05). It may be concluded that by increasing the zirconia core thickness, the marginal gap of all-ceramic crowns decreases. Regarding 0.3-mm and 0.5-mm core thicknesses, porcelain sintering had no effect on marginal gap but regarding 0.7-mm core thickness, marginal gap increased after sintering.[U1] [U1]5