# Verification of extraoral versus intraoral scanning techniques: fit accuracy implications for 3D printed and milled zirconia crowns (An in-vitro study)

## TL;DR

This study compares the accuracy of extraoral and intraoral scanners in measuring the fit of 3D printed and milled zirconia crowns.

## Contribution

The study provides new insights into the accuracy of scanning techniques for zirconia crown fit assessment.

## Key findings

- Extraoral scanners showed significantly lower gap values than intraoral scanners for both milled and printed zirconia crowns.
- Both scanning methods showed significant differences in internal fit compared to the reference standard.
- Extraoral scanners matched stereomicroscope results for marginal fit accuracy.

## Abstract

Marginal and internal fit significantly influence the longevity of fixed restorations. This study aims to evaluate the accuracy of extraoral and intraoral scanning techniques for assessing gaps of 3D printed and milled zirconia crowns.

Milled (n = 12) and 3D printed zirconia crowns (n = 12) were fabricated. Triple scan protocol was implemented for each specimen in both groups using extraoral and intraoral scanners to determine marginal and internal fit. The marginal fit was compared to predetermined marginal gap identified using stereomicroscope, whereas the internal fit was assessed in relation to a reference standard of cement space set at 70 μm during the crown design process. Comparisons between different scanners were conducted using an independent t-test for internal fit and one-way ANOVA for marginal fit.

Superimposition scans obtained from extraoral scanner revealed significantly lower gap values both internally and marginally when compared to the intraoral scans for both milled (P < 0.001, P = 0.04) and printed (P < 0.001, P < 0.001) zirconia. The values from both methods showed significant differences in internal fit compared to the reference standard (P < 0.001). The extraoral scanner showed no significant difference in marginal fit values when compared to stereomicroscope.

The type of scanner used and the fabrication technique both influenced the accuracy of marginal and internal fit measurements. This verification provides an insight into the accuracy of extraoral and intraoral scanners in the assessment of internal and marginal fit of monolithic zirconia restorations fabricated by milling and 3D printing to aid in improving restoration retention and longevity of the fixed prostheses.