Evaluation of the Effect of Brushing on Vickers Microhardness of Acrylic Denture Base Resins Polymerized by Different Techniques

Abstract

Objectives: In selecting a denture base material, different polymerization techniques might be considered to avoid adverse effects of brushing on the microhardness of the acrylic resin. The purpose of this study was to evaluate the brushing effect on Vickers microhardness of acrylic denture base resins polymerized by different techniques. Material and Methods: One hundred disk-shaped specimens (15 mm in diameter and 2 mm thick) were fabricated from each acrylic resin (Integra and FuturaJet). Five different polymerization techniques were tested (n=20): conventional water-bath polymerization, short autoclave polymerization (60°C for 30 minutes, then 130°C for 10 minutes), long autoclave polymerization (60°C for 30 minutes, then 130°C for 20 minutes), injection-molding polymerization and auto-polymerization. Half of the specimens were subjected to simulated brushing in an automatic brushing machine using 54 000 brush strokes for each specimen. All specimens were then submitted to Vickers hardness test with a 300-g load for 15 s. Mann Whitney U test and Kruskal-Wallis test followed by Dunn’s post-hoc test were used for results analysis, which were statistically significant at p < 0.05. Results: A statistically significant difference was observed between the control and brushing groups in all polymerization techniques (p < 0.05). Autopolymerized acrylic resin group showed significantly lower microhardness values than water bath, short and long autoclave polymerized resins in control and brushing groups (p < 0.05). Conclusions: Autopolymerization technique might has some disadvantages on avoid adverse effects of brushing on the microhardness, therefore tehniques of polymerization should be considered as microhardness of acrylic denture base resins.