Effect of artificial toothbrushing on wear, surface roughness and hardness of additively manufactured and milled resin-based restorative materials: an in vitro study

Abstract

BACKGROUND: Recently introduced milled and 3D-printed resin dental restorations are designed for long-term use. They must endure the mechanical stresses of chewing in the oral environment. This study aimed to evaluate the effect of artificial toothbrushing on wear, surface roughness and hardness of additive-manufactured and milled ceramic filled resin restorative materials. MATERIALS AND METHODS: Thirty bar-shaped specimens (15 mm x 4 mm x 1.5 mm) were divided into three groups (n = 10): 3D printed CROWNTEC Saremco permanent resin (CT), 3D printed Flexcera Smile Ultra+ (FSU), and CAD-CAM BRILLIANT Crios (BC). All groups underwent the same finishing protocol using a composite polishing kit. The specimens baseline weight was first measured using a sensitive electronic balance, then tested for surface microhardness using the Vickers hardness test (VHN), and for surface roughness using confocal laser scanning microscopy (CLSM). Wear testing was conducted using an artificial toothbrushing machine. Specimen wear was calculated by evaluating weight loss. The Vickers hardness test and surface roughness test were then repeated. Differences in wear and hardness were analyzed using one-way ANOVA followed by Tukey's post hoc test with Bonferroni correction. Changes before and after artificial toothbrushing were assessed using a paired t-test. The Kruskal-Wallis test, followed by Dunn's post hoc test with Bonferroni adjustment, was employed to analyze surface roughness values. The Wilcoxon signed-rank test was used to assess changes in surface roughness after toothbrushing. RESULTS: Flexcera Smile Ultra+ demonstrated the least wear reduction, CROWNTEC the middle, and BRILLIANT Crios the most. All groups had significant change in hardness before and after intervention. BRILLIANT Crios changed least, CROWNTEC somewhat, and Flexcera Smile Ultra+ most. Using One Way Analysis of Variance ANOVA, significant wear and hardness differences were found between groups before and after the intervention (p < 0.0001). The Kruskal-Wallis test showed significant surface roughness changes between groups before and after intervention (p < 0.0001). The intervention reduced surface roughness differently across materials, with Flexcera Smile Ultra+ showing the largest consistent reduction. CONCLUSIONS: All materials that were tested exhibited notable variations in terms of wear, hardness, and surface roughness both prior to and following an artificial toothbrushing, which depended on their respective qualities. Regarding wear, FSU exhibited the least reduction, CT showed a moderate reduction, and BC experienced the most significant reduction. In terms of hardness, BC underwent the least change, CT displayed a moderate change, while FSU experienced the greatest change. Milled resin was found to have the lowest surface roughness, whereas 3D printed resin demonstrated the highest surface roughness.