Objective: The purpose of this study was to evaluate the effect of finish line design and cement space thickness on the marginal accuracy of monolithic zirconia crowns. Materials and methods: Thirty crowns were fabricated from translucent zirconia (inCoris TZI) using Cerec in-Lab system and divided into three main groups (10 each) according to the finish line type of the die (knife-edge, chamfer, and shoulder). Every group was divided into two subgroups (5 each) according to cement space thickness (20 and50μm). Optical impressions were taken for the dies using the Cerec scanner and cement space was set twice for every finish line design; 20 and 50 μm. The completed crowns were cemented to the dies and the marginal gap was evaluated. The collected data was statistically analyzed using Mann-Whitney U test and Kruskal-Wallis test and the significance level was set at P ≤ 0.05. Results: Regarding the marginal gap; there was no statistically significant difference between different finish line designs or between different cement space thicknesses. Conclusion: Neither finish line design nor cement space thickness has an effect on the marginal gap of inCoris TZI crowns.KeywordsCement space; Finish line; Marginal fit; Monolithic zirconia.

This study aimed to evaluate the internal adaptation of three different computer-aided design/computer-aided manufacturing (CAD/CAM) ceramic crowns. The internal adaptation of a polymer-infiltrated ceramic network material (Vita Enamic [VE]) was compared to two machinable glass-ceramics; Zirconia-reinforced lithium silicate (Vita Suprinity [VS]) and a lithium disilicate glass-ceramic (IPS e.max. CAD). Thirty human premolars of average size were prepared (n=10 each group) by computer numerical control to fulfill the criteria of all-ceramic crown design. Optical impressions were taken for each tooth preparation using the CAD/CAM scanner. Thirty crowns were fabricated using CAD/CAM system and divided into three groups (IPS e.max, VE, and VS). To assess the internal fit of tested crowns, the gap between the intaglio of each crown and the corresponding tooth surface was evaluated using a 3D digital scanner using the Triple-scan Protocol. One-way ANOVA followed by Tukey Post Hoc statistical tests were used to statistically analyze results of the internal fit. There was a statistically significant difference for all groups at the four axial walls (p = 0.000002). For total internal fit between groups, comparisons showed a statistically significant difference between all tested groups (p=0.000002). When each pair of groups was statistically compared with each other, all pair comparisons showed a statistically significant difference. IPS e.max CAD had the best internal fit, followed by Vita Enamic, then Vita Suprinity. For all ceramics tested, values of internal fit of all ceramics tested were within the clinically acceptable range.

Purpose: This study was designed to evaluate the dimensional accuracy of different impression techniques of implant-supported fixed dental prosthesis. Materials and Methods: Thirty impressions were made upon a specialized stainless-steel mold containing two parallel implant analogues. The impressions were divided into three groups according to implant impression technique used ten each; group (I) closed tray technique (C), group (II) open tray technique (O) and group (III) splinted open tray technique (OS). After taking impressions, they were poured with type IV dental stone and left for one day before analysis with a stereo microscope. Results: Regarding impression accuracy, there was no statistically significant difference between open tray and splinted open tray technique within the master mold while there was statistically significant difference between closed tray technique within the master mold. There was no statistically significant difference between open tray and splinted open tray technique while there was statistically significant difference between closed tray technique within the other two techniques. Conclusion: Closed tray technique showed more deviation in comparison to the master mold and the other two techniques that affect the final accuracy of multiple implant impression while no significant difference with the open tray technique of both types.