# Fit of Three-Unit Posterior Fixed Dental Prostheses Made from Tetragonal Zirconia Polycrystal by 3D Printing and Milling

## TL;DR

This study compares the fit of 3D-printed and milled zirconia dental prostheses, finding that 3D-printed ones can match milled ones but require support structures for thinner designs.

## Contribution

The study introduces the use of support structures to improve the fit of 3D-printed zirconia prostheses.

## Key findings

- Milled FDPs showed the best marginal fit with median/maximum gaps of 79/127 µm vertically and 85/171 µm tangentially.
- 3D-printed FDPs with a support frame improved fit, especially for thinner designs (0.6 mm wall thickness).
- 3D-printed FDPs had slightly higher variability in fit compared to milled ones.

## Abstract

(1) Objective: To compare the marginal and internal fit of 3D-printed and milled three-unit fixed dental prostheses (FDPs) made from tetragonal zirconia polycrystal (3Y-TZP). (2) Methods: Three-unit FDPs were designed for a typodont maxillary model with crown preparation for the second premolar and second molar. Nominal cement gap widths were set to 30 µm at the margins and 80 µm internally. A total of 40 FDPs (n = 10/group) differing in wall thickness (w = 0.6/1.0 mm) and support structures (with/without a stiffening frame) were fabricated from 3Y-TZP by 3D printing. A total of 10 milled FDPs with w = 0.6 mm served as a control group. After adhesive cementation on the respective replicated maxillary models, FDPs were sectioned and the cement gap dimension was assessed with a digital microscope. The marginal and internal fit found for the different test groups were compared using non-parametric tests. (3) Results: The best marginal fit—qualified by median/maximum marginal gap width—was given for milled FDPs (79/127 µm vertical; 85/171 µm tangential), whereas the marginal fit of 3D-printed FDPs with w = 0.6 mm and regular support structures was the worst (144/284 µm vertical; 107/198 µm tangential). Use of an additional support frame improved the marginal fit of 3D-printed FDPs, in particular FDPs with w = 0.6 mm (108/197 µm vertical; 87/161 µm tangential). (4) Conclusions: 3D-printed zirconia FDPs showed conditionally comparable marginal and internal fit as their milled counterparts, but with slightly higher scattering. When fabricating thinner 3D-printed FDPs, additional support structures are mandatory to achieve clinically well-fitting restorations.