# Comparative evaluation of fracture resistance force of three different posterior aesthetic crowns and occlusal wear of antagonist primary teeth – An in vitro study

## TL;DR

This study compares the strength and wear effects of three types of crowns for children's decayed back teeth, finding that PMMA crowns are a strong and cost-effective option.

## Contribution

The study introduces a comparative in vitro evaluation of PMMA and 3D printable resin crowns as alternatives to zirconia crowns for primary molars.

## Key findings

- Milled zirconia crowns showed the highest fracture resistance force (1,712.488 N), followed by PMMA (1,326.522 N) and 3D printable resin crowns (877.212 N).
- PMMA crowns caused minimal occlusal wear on opposing primary teeth.
- Zirconia and 3D printed crowns showed significant occlusal wear differences after simulation.

## Abstract

Aesthetic restorations for managing severely carious primary molars pose a clinical challenge, particularly regarding limited treatment options and the importance of aesthetics to parents. While zirconia crowns are commonly used for posterior teeth due to their aesthetic appeal, advancements in digital technology have introduced alternative options such as polymethylmethacrylate (PMMA) crowns and 3D printable photopolymer resin crowns, which offer cost-effective alternatives. This in vitro study aimed to comparatively evaluate the fracture resistance force (FRF) and occlusal wear of three types of posterior aesthetic crowns: milled zirconia crowns, PMMA crowns, and 3D printable photopolymer resin crowns.

A universal mechanical testing machine was employed to measure the FRF, while occlusal wear was assessed by subjecting five samples from each group to chewing simulation with opposing natural teeth. Preoperative and post-operative 3D scan measurements were obtained.

The average force required to fracture 3D printable photopolymer resin crowns was 877.212 N, compared to 1,326.522 N for PMMA crowns and 1,712.488 N for milled zirconia crowns. Significant differences in occlusal wear were observed in the zirconia (p-value= 0.005) and 3D printed crown groups (p-value= 0.010) when comparing pre-operative and post-operative measurements.

This study suggests that PMMA crowns exhibit clinically acceptable fracture resistance force and cause minimal occlusal wear on opposing primary teeth. These findings support the potential long-term clinical use of PMMA crowns as an alternative to zirconia crowns in aesthetic restorations for severely decayed primary molars.

Key words:Zirconia crowns, polymethylmethacrylate crowns, Photopolymer resin crowns, Primary teeth.