Abstract
Although visible light-polymerized acrylic resins have been used in removable partial dentures, it is not clear whether the presence of a metal framework could interfere with their polymerization, by possibly reflecting the light and affecting important properties, such as roughness and hardness, which would consequently increase biofilm accumulation. The aim of this study was to compare the roughness and Knoop hardness of a visible light-polymerized acrylic resin and to compare these values to those of water-bath- and microwave-polymerized resins, in the presence of a metal framework. Thirty-six specimens measuring 30.0 × 4.0 ± 0.5 mm of a microwave- (Onda Cryl), a visible light- (Triad) and a water-bath- polymerized (Clássico) (control) acrylic resins containing a cobalt-chromium metal bar were prepared. After processing, specimens were ground with 360 to 1000-grit abrasive papers in a polishing machine, followed by polishing with cloths and 1μm diamond particle suspension. Roughness was evaluated using a profilometer (Surfcorder SE 1700) and Knoop hardness (Kg/mm2) was assayed using a microhardness tester (Shimadzu HMV 2000) at distances of 50, 100, 200, 400 and 800 μm from the metal bar. Roughness and Knoop hardness means were submitted to two-way ANOVA and compared by Tukey and Kruskal Wallis tests at a 5% significance level Statistically significant differences were found (p<0.05) for roughness and Knoop hardness, with light-polymerized resin presenting the highest values (Ra = 0.11 μm and hardness between 20.2 and 21.4 Kg/mm2). Knoop values at different distances from the metal bar did not differ statistically (p>0.05). Within the limitations of this in vitro study, it was concluded that the presence of metal did not influence roughness and hardness values of any of the tested acrylic resins.
Highlights
Water-bath polymerization is extensively used to process polymethylmethacrylate (PMMA), new resins and processing methods are often proposed to obtain better physical and esthetic properties and simplify the technique . 1,6,8,11,14 Two relatively new polymerization methods are microwaving and visible light polymerization[7,9].One of the advantages of microwave and visible light polymerization methods is the shorter processing time they offer in comparison to water bath
While denture base acrylic resins polymerized by microwave irradiation and conventional water bath curing systems are composed of PMMA6,8, visible lightpolymerized resins are similar to composites, having an organic instead of an inorganic filler content
Light-polymerized resins have been used in removable partial dentures, it is not clear whether the presence of a metal framework could interfere with their polymerization, by possibly reflecting the light and affecting important physical properties, such as surface roughness and hardness
Summary
1,6,8,11,14 Two relatively new polymerization methods are microwaving and visible light polymerization[7,9]. One of the advantages of microwave and visible light polymerization methods is the shorter processing time they offer in comparison to water bath. While denture base acrylic resins polymerized by microwave irradiation and conventional water bath curing systems are composed of PMMA6,8, visible lightpolymerized resins are similar to composites, having an organic instead of an inorganic filler content. Light polymerization occurs by exposure to quartz halogen lamps in the shorter blue 400 to 500 nm wavelength spectrum of visible light. This exposure results in 5 to 6-mm-deep polymerization . This exposure results in 5 to 6-mm-deep polymerization . 7,9,13
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