Monday, July 17, 2017

Influence of scanner, powder application, and adjustments on CAD-CAM crown misfit


Statement of problem

The manufacturers of computer-aided design and computer-aided manufacturing (CAD-CAM) systems emphasize that new technologies can improve the marginal fit of dental crowns. However, data supporting this claim are limited.


The purpose of this in vitro study was to investigate the differences among the following fabrication methods on the marginal discrepancy of dental crowns: intraoral optical scanners, powder application, and adjustments of intaglio surface.

Material and methods

A single human premolar was fixed on a typodont and prepared to receive crowns prepared by the CEREC CAD-CAM system. Three fabrication techniques were used: digital impressions using the CEREC Bluecam scanner with titanium dioxide powder (TDP), digital impressions using the CEREC Omnicam scanner without TDP, and digital impressions using the Omnicam scanner with TDP. Five experimental groups (n=10) were designated: Bluecam (group B), Bluecam with adjustments (group BA), Omnicam (group O), Omnicam with adjustments (group OA), and Omnicam with TDP (group OP). The specimens were scanned using microcomputed tomography to measure the vertical, horizontal, and internal fit and volumetric 3-dimensional (3D) internal fit values of each luting space. The paired t test was used to evaluate mean marginal fit change after adjustments within the same group. One-way analysis of variance and post hoc tests were used to compare groups B, O, and OP (α=.05).


Mean vertical fit values ±standard deviations of group B=29.5 ±13.2 μm; BA=26.9 ±7.7 μm; O=149.4 ±64.4 μm; OA=49.4 ±12.7 μm; and OP=33.0 ±8.3 μm. Adjustments in the intaglio surface and TDP application statistically influenced the vertical fit of group O (P<.001). The percentage of vertical fit values <75 102.5="" 77.5="" 85.8="" 91.4="" and="" b="" ba="" different="" em="" fit="" for="" from="" group="" groups="" horizontal="" in="" m="" mean="" o="" oa="" of="" op.="" op="92.0%." other="" results="" significantly="" test="" the="" those="" values="" were="">P
<.05). The percentages of horizontal misfit were 61.2% in group B; 73.5% in group BA; 88.1% in group O; 92.4% in group OA; and 85.0% in group OP. Volumetric 3D internal fit values in group B were 9.4 ±1.3 mm3; 10.7 ±1.0 mm3 in group BA; 11.8 ±2.1 mm3 in group O; 11.0 ±1.3 mm3 in group OA; and 9.6 ±0.9 mm3 in group OP. The overall results from groups B and OP were better than those of group O, with regard to vertical misfit and volumetric 3D internal fit.


Different intraoral optical scanners, powder application, and internal adjustments influenced the marginal discrepancy of crowns. Crowns fabricated using the Omnicam system had significantly higher vertical discrepancy and volumetric 3D internal fit than those fabricated using the Bluecam scanner with TDP. Adjustments of the intaglio surface improved the vertical fit of crowns made using the Omnicam scanner; however, TDP application before Omnicam scanning improved the vertical fit as well as the volumetric 3D internal fit value of the luting space of crowns

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