# Marginal Fit Evaluation of Zirconia Copings Based on Conventional and Digital Impressions Using a Tooth Section Microscopic Examination Technique

## TL;DR

This study compares the fit of zirconia dental crowns made using digital and traditional methods, finding significant differences in some measurements but not others.

## Contribution

A new tooth section microscopic examination technique is introduced to evaluate the marginal fit of zirconia copings.

## Key findings

- Digital impressions showed significantly smaller internal gaps compared to conventional methods.
- All digital impression copings were overextended, while conventional methods had some underextensions.
- No significant differences were found in marginal gap and vertical marginal discrepancy between the two methods.

## Abstract

Background/Objectives: This study compared the marginal fit of CAD/CAM zirconia copings based on digital and conventional impression techniques by using a new method of tooth section examination. Methods: Twenty premolars were prepared for an all-ceramic full crown. Ten conventional impressions using the polyether Impregum and ten digital impressions using the cara TRIOS intraoral scanner were used to fabricate zirconia copings. Slices were prepared by cutting each tooth five times. The marginal fit was microscopically analyzed using seven defined distances at 20 measuring points per tooth. The statistical analyses were carried out by using the Mann–Whitney test and the Kruskal–Wallis test (α = 0.05). Results: The median values for the copings based on the conventional (c) and digital (d) impressions showed significant differences for the internal gap (c: 56 μm (IQR = 22); d: 30 μm (IQR = 13); p < 0.001), horizontal marginal discrepancy (c: 64 μm (IQR = 59); d: 84 μm (IQR = 41); p < 0.001), absolute marginal discrepancy (c: 81 μm (IQR = 40); d: 98 μm (IQR = 50); p < 0.001) and the overextension (c: 63 μm (IQR = 48); d: 89 μm (IQR = 50); p < 0.001). All copings based on digital impressions were overextended. Underextensions only occurred with the conventional impression method with a median value of 40 μm (IQR = 64). For the marginal gap (c: 29 μm (IQR = 27); d: 31 μm (IQR = 22); p = 0.477) and the vertical marginal discrepancy (c: 34 μm (IQR = 32); d: 35 μm (IQR = 40); p = 0.944) no significant differences could be found. Conclusions: Both impression methods are suitable for the fabrication of ceramic copings. The microscopic examination of tooth sections seems to be a suitable in vitro method for the evaluation of the marginal fit of ceramic copings.