Effect of microwave disinfection on physical and mechanical properties of acrylic resins

Rafael Leonardo Xediek Consant,Wilson Batista Mendes,Marcelo Ferraz Mesquita,Erica Brenoe Vieira,João Neudenir Arioli-Filho

doi:10.1590/s0103-64402008000400011

Abstract

This study evaluated the effect of microwave energy on the hardness, impact strength and flexural strength of the Clássico, Onda-Cryl and QC-20 acrylic resins. Aluminum die were embedded in metallic or plastic flasks with type III dental stone, in accordance with the traditional packing technique. A mixing powder/liquid ratio was used according to the manufacturer's instructions. After polymerization in water batch at 74 degrees C for 9 h, boiling water for 20 min or microwave energy at 900 W for 10 min, the specimens were deflasked after flask cooling at room temperature, and submitted to finishing. Specimens non-disinfected and disinfected by microwave irradiation were submitted to hardness, impact and flexural strength tests. Each specimen was immersed in distilled water and disinfected in a microwave oven calibrated to 650 W for 3 min. Knoop hardness test was performed with 25 g load for 10 s, impact test was carried out using the Charpy system with 40 kpcm, and 3-point bending test with a crosshead speed of 0.5 mm/min until fracture. Data were submitted to statistical analysis by ANOVA and Tukey's test (alpha=0.05). Disinfection by microwave energy decreased the hardness of Clássico and Onda-Cryl acrylic resins, but no effect was observed on the impact and flexural strength of all tested resins.

Highlights

Treatments in dental clinics use instruments and prosthetic materials that should be properly disinfected or sterilized to avoid cross-contamination among dentists, patients, assistants and technicians in the dental prosthetic laboratory
An important clinical implication regarding hardness of acrylic resins is the possibility of abrasion over time during denture use [11]
In the present study, when Knoop hardness was analyzed under no-disinfection and microwave-disinfection conditions (Table 1), the KHN values obtained for Clássico, QC-20 and OndaCryl acrylic resins differed significantly from each other

Summary

Introduction

Treatments in dental clinics use instruments and prosthetic materials that should be properly disinfected or sterilized to avoid cross-contamination among dentists, patients, assistants and technicians in the dental prosthetic laboratory. Prosthetic materials sent from the dental clinics to the dental laboratories are contaminated by pathogenic bacteria, which could be transferred to the technicians by means of direct contact or during the finishing and polishing procedures [1]. A previous study showed that microorganisms found in pumice slurry were originated from contaminated prosthetic pieces, which were polished without prior disinfection or cleanness. Unde these conditions, these pathogens can be transferred to other prostheses and prosthetic pieces during laboratory procedures [2]

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