Effect of preparation depth differences on the marginal fit of zirconia crown copings: an in vitro study.

If optical scanning is used for crown fabrication, variability in preparation depth may be a limitation. Therefore, this preliminary laboratory study evaluated marginal fit in relation to preparation depth. Three dies with different preparation depths between the vestibular and oral regions were fabricated. Ten zirconia copings were manufactured for each die, and marginal gaps were examined. Increasing differences in preparation depth influenced the size of the marginal gap between the vestibulo-oral and mesiodistal regions significantly (P < .001). This study shows primarily that differences in preparation depth resulted in decreasing marginal precision.

Repeatability of color-measuring devices.

INTRODUCTION: The objective of this study was to evaluate the intra- and interdevice repeatability in different tooth regions using three color-measuring devices under clinical conditions. MATERIALS AND METHODS: Fifteen shade measurements (cervical, body, incisal) were recorded on 15 patients by one investigator using three color-measuring devices (VITA Easyshade compact, DeguDent Shadepilot, X-Rite ShadeVision). CIE Lab values were determined for all maxillary anterior teeth. Intraclass correlation coefficients (ICCs) were used to statistically analyze intra-and inter-device repeatability for different tooth regions. Color differences (ΔE) between measurements were also computed to evaluate the clinical acceptability of repeatability values. The data were evaluated using analysis of variance and Bonferroni's adjustment to control for multiple testing. Differences were deemed significant when P < 0.016. RESULTS: The three color-measuring devices generally exhibited high repeatability of color coordinates for all tooth regions (ICC > 0.516-0.986, ΔE < 3.03). In contrast, inter-device repeatability was lower for all tooth regions (ICC = 0.010-0.922, ΔE = 4.06-16.04). CONCLUSIONS: High intra-device repeatability of color coordinates could be achieved for all tooth regions when the same color-measuring device was used. However, because of low inter-device repeatability, results using different color-measuring devices are not comparable.