ABSTRACT
Background : Microwave postpolymerization has been suggested as a method to improve the flexural strength of an autopolymerizing denture reline resin. However, the effect of microwave postpolymerization on the residual monomer content and its influence on flexural strength have not been investigated. Objectives : This study analyzed the effect of microwave postpolymerization on the residual monomer content and its influence on the flexural strength of an autopolymerizing reline resin (Denture Liner). Materials and Methods : A total of 70 specimens (64 Χ 10 Χ 3.3 mm) were polymerized according to the manufacturer's instructions and divided into 7 groups (n = 10). Control group specimens were not subjectedto any further processing. Before testing, the specimens were subjected to postpolymerization in a microwave oven using different power (550 and 650 W) and time (3, 4, and 5 min) settings. Two specimens of each group were then manually ground into fine powder and samples extracted from the specimens using reflux method. The samples were then subjected to gas chromatography for residual monomer determination in area%. Eight specimens were subjected to a three-point bending device with a span of 50 mm and crosshead speed of 5 mm/min, and the flexural strength was determined in MPa. Data analyses included Student's t-test and one-way analysis of variance. Results : For the Denture Liner reline resin, the residual monomer content decreased and the flexural strength increased significantly with the application of microwave irradiation using different time/power combinations. The specimens with the lowest residual monomer content were the similar specimens which presented with the highest flexural strength. Conclusion : Microwave postpolymerization irradiation can be an effective method for increasing the flexural strength of denture liner (at 650 W for 5 min) by reducing the residual monomer content by further polymerization at free radical sites.
Subject(s)
Acrylic Resins/chemistry , Acrylic Resins/radiation effects , Analysis of Variance , Dental Materials/chemistry , Dental Materials/radiation effects , Denture Liners , Denture Rebasing , Methacrylates/chemistry , Methacrylates/radiation effects , Microwaves , Pliability/radiation effects , Statistics, NonparametricABSTRACT
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 74ºC 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 (?=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.
Este estudo verificou o efeito da desinfecção por microondas sobre a dureza, impacto e resistência à flexão das resinas acrílicas Clássico, Onda-Cryl e QC-20. Matrizes de alumínio foram incluídas em muflas metálica ou de plástico com gesso pedra tipo III, de acordo com a técnica de inclusão tradicional. A proporção polímero/monômero foi de acordo com as recomendações dos fabricantes. Depois da polimerização em água à temperatura de 74ºC por 9 h, água em ebulição por 20 min ou por energia de microondas a 900 W por 3 min, os corpos-de-prova foram demuflados após esfriamento da mufla em temperatura ambiente e submetidos ao polimento convencional. Testes de dureza, impacto e resistência à flexão foram feitos nos corpos-de-prova submetidos ou não à desinfecção por microondas. Cada corpo-de-prova foi submetido individualmente à desinfecção por microondas em forno doméstico com 900 W de potência por 3 min, imersos em 150 mL de água destilada. O teste de dureza Knoop foi realizado com carga de 25 g por 10 s, a de impacto pelo sistema Charpy com 40 kpcm e o de flexão por três pontos com velocidade de 0,5 mm/min até fratura. Os dados foram submetidos à análise de variância e ao teste de Tukey (?=0,05). A desinfecção simulada por microondas diminuiu a dureza Knoop das resinas Clássico e Onda-Cryl e não promoveu nenhum efeito nas resistências ao impacto e à flexão das resinas estudadas.