# Wear of enamel antagonist to gradient zirconia vs full strength monolithic zirconia: a randomized clinical trial

## TL;DR

This study compares how two types of zirconia crowns affect enamel wear and finds that one causes more wear over time.

## Contribution

The study provides new clinical evidence on enamel wear caused by gradient versus full-strength monolithic zirconia crowns.

## Key findings

- Gradient zirconia caused significantly more enamel wear than full-strength zirconia after 6 months and 1 year.
- Restoration wear was comparable between the two zirconia types at both follow-up periods.
- The difference in enamel wear increased over time with gradient zirconia.

## Abstract

Monolithic zirconia restorations have emerged as a viable alternative to veneered zirconia restorations, eliminating the risk of veneer chipping due to their superior strength, fracture resistance, and aesthetics. New types of monolithic zirconia are becoming widely available, making it essential to clinically assess their wear behaviour and the effect on opposing enamel.

To evaluate the wear of enamel opposed by gradient monolithic zirconia compared to full-strength monolithic zirconia, and to assess the wear of both restorations.

Twenty-six patients aged 21 to 35 years requiring a crown for endodontically treated molars were randomly divided into two groups. The comparator group (Zolid HT; Monolithic zirconia) included patients receiving full-strength monolithic zirconia crowns, while the intervention group (ZirCAD Prime; Multilayer zirconia) included patients receiving gradient monolithic zirconia crowns. After final cementation, a baseline direct scan was obtained for both arches, followed by additional scans at 6 months and 1 year post-treatment. These scans were imported into 3D software for superimposition to calculate the wear that occurred throughout the follow-up period for both restorations and the opposing enamel.

At the 6-month follow-up, the root mean square (RMS) values for Multilayer zirconia showed significantly higher wear of opposing enamel (75.6 μm) compared to Monolithic zirconia (61.18 μm), with a p-value of 0.0119. At the 1-year follow-up, Multilayer zirconia also exhibited significantly higher wear of opposing enamel (97.2 μm) compared to Monolithic zirconia (68.77 μm), with a p-value of 0.0046. Regarding restoration wear, RMS values at 6 months were comparable between Monolithic zirconia (82.65 μm) and Multilayer zirconia (72.16 μm), with a p-value of 0.6294. Similarly, at the 1-year follow-up, the RMS values remained statistically similar between Monolithic zirconia (89.47 μm) and Multilayer zirconia (73.57 μm), with a p-value of 0.4889.

Gradient monolithic zirconia restorations were associated with greater enamel wear compared to Monolithic zirconia restorations, and the difference in wear depth became statistically significant over time. In terms of restoration wear, both types exhibited comparable material wear.

This study was registered on clinicaltrials.gov with ID no. NCT04798300 on 28/1/2021.