Abstract
The aim of this study was to evaluate the following acrylic resins: Clássico, QC-20 and Lucitone, recommended specifically for thermal polymerization, and Acron MC and VIPI-WAVE, made for polymerization by microwave energy. The resins were evaluated regarding their surface nanohardness and modulus of elasticity, while varying the polymerization time recommended by the manufacturer. They were also compared as to the presence of water absorbed by the samples. The technique used was nanoindentation, using the Nano Indenter XP, MTS. According to an intra-group analysis, when using the polymerization time recommended by the manufacturer, a variation of 0.14 to 0.23 GPa for nanohardness and 2.61 to 3.73 GPa for modulus of elasticity was observed for the thermally polymerized resins. The variation for the resins made for polymerization by microwave energy was 0.15 to 0.22 GPa for nanohardness and 2.94 to 3.73 GPa for modulus of elasticity. The conclusion was that the Classico resin presented higher nanohardness and higher modulus of elasticity values when compared to those of the same group, while Acron MC presented the highest values for the same characteristics when compared to those of the same group. The water absorption evaluation showed that all the thermal polymerization resins, except for Lucitone, presented significant nanohardness differences when submitted to dehydration or rehydration, while only Acron MC presented no significant differences when submitted to a double polymerization time. Regarding the modulus of elasticity, it was observed that all the tested materials and products, except for Lucitone, showed a significant increase in modulus of elasticity when submitted to a lack of hydration.
Highlights
For many decades, polymethylmethacrylate has been the first choice for making the base of complete dentures
As we analyzed the nanohardness of the conventional, thermally polymerized resins, which were polymerized according to the recommendations of the manufacturer, it was observed that the Clássico resin presented a significant difference when compared to QC-20® and Lucitone®, which were very similar to each other (Table 1)
The group of resins that were polymerized by microwave energy according to the standard time of polymerization presented significant differences
Summary
Polymethylmethacrylate has been the first choice for making the base of complete dentures. Activated acrylic resins have been traditionally processed by immersion in temperature-controlled water, for a specific period of time.[1] Recently, polymerization methods involving activated light and microwave energy were introduced. When dielectric materials are placed in a microwave energy field, some kind of molecular friction takes place and these materials warm up rapidly.[3] Some authors believe that physical proprieties such as hardness and transversal resistance are favored when this process polymerizes the resins,[4] others believe that the polymerization by immersion in heated water during a long cycle results in better physical properties.[2] Others still consider that the conventional and microwave energy methods are similar, such as Smith et al.[5] (1992), who submitted some materials to the existing polymerization methods: conventional (water heat diffusion), microwave energy and light, and compared properties such as hardness, surface smoothness, transversal resistance, modulus of elasticity and resistance to impact. The only difference found between the two methods was that the second showed higher values for modulus of elasticity
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