Effect of preparation angles on the precision of zirconia crown copings fabricated by CAD/CAM system

Abstract

The aim of this in vitro study was to evaluate the effects of different preparation angles on the precision of fit of zirconia crown frameworks. Dies were fabricated with three different preparation angles: 4, 8, and 12 degrees total taper. Ten copings were fabricated for each angle by a laboratory and a milling-center CAD/CAM system. After cementation, cross-sections were obtained and cement gaps were measured. Preparation angle (ANOVA, p<0.01) and measurement location (ANOVA, p<0.01) exhibited statistically significant influence on the precision of fit. On the other hand, no statistically significant influences were detected between copings prepared using the laboratory and milling-center CAD/CAM systems (ANOVA, p=0.92). All groups showed marginal openings ranging between 36.6 and 45.5 μm. In light of the results obtained in this study, a preparation angle of 12 degrees is hence recommended with the confidence that the marginal gap will be consistently less than 50 μm.

Multifactorial analysis of the impact of different manufacturing processes on the marginal fit of zirconia copings

“…Confl icting results have been reported regarding the effect of the milling system on the marginal accuracy of fabricated crowns. Beuer et al 18) found no signifi cant differences in the marginal fi t of single zirconia copings manufactured by an in-laboratory milling unit relative to those manufactured by a milling center 18) . Kohorst et al demonstrated a better marginal accuracy for FPD retainers produced in a milling center compared to restorations fabricated by a CAM process with manual modeling of the framework 26) .…”

“…Evaluation of the mean marginal gaps (calculated by 20 copings per sample series ×24 measurement points per coping) was performed according to the literature 11,18,26,30) as well as by considering the averaged maximum marginal gap within one system or parameter (calculated only by the maximum values of each coping within one sample series). Data are expressed as means with standard deviations and 95% confi dence intervals.…”

“…In in vitro studies of marginal adaptation, taper angles varied between 6 and 20°1 5) . Previous in vitro studies revealed that the best marginal accuracies of zirconia copings produced by CAD/CAM systems occurred when the angles of the axial walls were prepared with a 12-degree axial taper 18,19) . Other studies have shown that the retention forces on abutments, especially for conventionally luted restorations, are signifi cantly higher when the axial walls are prepared such that they are nearly parallel to each other (convergence angles≤5°) 20,21) .…”

The Accuracy of Optical Scanning: Influence of Convergence and Die Preparation

“…Our study showed that convergence does not affect the data acquisition and modeling for 3D scanners as long as the TOC is larger than 58. 20,21 Because convergence angles between 68 and 128 appear to be optimum for tooth crown preparation, our results showed that optimal preparation will not be affected by visual interferences. Thus extraoral scans have less limitation than intraoral systems.…”

In vitro analysis of residual tooth structure of maxillary anterior teeth after different prosthetic finish line preparations for full-coverage single crowns

“…Dentalfarm Srl, Torino, Italy). The total occlusal convergence (TOC) angle was set and controlled at 10° to slightly taper the axial walls (15,22,24,25). The following preparation protocols were adopted: SHO finish line preparation: diamond cylindrical bur with rounded angles, ø 2.1 mm (ISO 314141534021, 100-µm granulometry, shape n° 881, Intensiv SA, Grancia, Switzerland); a half bur was used to measure and control the amount of tooth reduction.…”