RESUMO
STATEMENT OF PROBLEM: The acrylic resin used in dental prostheses, which is subject to changes in its properties caused by hygiene chemicals, brushing, and colored beverages, can benefit from mechanical polishing methods. However, studies evaluating whether such procedures can be performed continuously without damaging the prosthetic materials are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the effect of a continuous mechanical polishing protocol on the color stainability, surface roughness, microhardness, and mass of a denture base acrylic resin. MATERIAL AND METHODS: The polishing protocol was tested in specimens submitted to one of the following conditions: immersion in coffee (CF) (n=20); toothbrushing (Br, 35 600 cycles in a brushing simulation machine) (n=20); and immersion in 1% sodium hypochlorite (HYP) (n=20). For each condition, half of the specimens were polished (aluminum oxide paste and felt wheel attached to an electric motor, 3000 rpm) at simulated biweekly intervals. Two groups (n=10) of specimens were immersed in distilled water and used as the control for the immersion groups. Thus, the present study consisted of a total of 8 groups (n=80). Before and after simulated periods of 12 and 24 months, surface roughness was evaluated by using a contact profilometer; a spectrophotometer was used to calculate color changes (ΔE00); and a Knoop microdurometer and a precision balance were used to assess microhardness and mass changes. Data were compared by using 2-way mixed ANOVA. The Tukey HSD and Student t tests were used for post hoc analysis (α=.05). RESULTS: The polishing influenced surface roughness (Br, CF, HYP: P<.001) and color stainability (Br: P=.008; CF: P<.001). Significant increase in roughness was observed for the Br and HYP groups, and the polishing significantly reduced roughness under all experimental conditions. In general, the polishing did not affect the microhardness and caused minimum wear of the acrylic resin. ΔE00 values were above the clinical perceptibility threshold (ΔE00>1.30) for the Br group, exceeding the clinical acceptability threshold for the CF group (ΔE00= 2.51). Polishing reduced ΔE00 in these groups, making values similar to those found in the groups immersed in distilled water. The color in the HYP group was not influenced by polishing. CONCLUSIONS: In general, the tested polishing protocol reduced the deleterious effects of brushing and contact with 1% sodium hypochlorite and coffee, reducing surface roughness and color change without affecting microhardness and mass in any clinically relevant way.
Assuntos
Resinas Acrílicas , Polimento Dentário , Cor , Bases de Dentadura , Humanos , Teste de Materiais , Propriedades de SuperfícieRESUMO
STATEMENT OF PROBLEM: Computer-aided design and computer-aided manufacturing (CAD-CAM) has enhanced the physicomechanical stability of ceramics. However, various factors in the oral cavity may impair the longevity of restorations by negatively affecting their properties. Appropriate surface treatments such as glaze application or mechanical polishing are necessary to diminish these effects. PURPOSE: The purpose of this in vitro study was to evaluate the influence of common beverages and toothbrushing on the surface roughness, microhardness, and color stainability of a vitreous CAD-CAM lithium disilicate ceramic with a glazed or mechanically polished surface. MATERIAL AND METHODS: Specimens (N=160) were divided into 2 groups according to the surface treatment method: polishing with abrasive disks or glaze application. Each group was subdivided (n=8) according to the immersion solution and toothbrushing: distilled water and distilled water plus brushing; coffee and coffee plus brushing; black tea and black tea plus brushing; red wine and red wine plus brushing; and cola and cola plus brushing. Before and after simulating a 5-year period of immersion and toothbrushing, a contact profilometer and a Vickers microhardness tester were used to measure the surface roughness and microhardness. CIELab parameters were assessed by using a portable spectrophotometer, and color differences were calculated by using the CIEDE2000 formula (ΔE00). Data were compared by using 3-way ANOVA/Bonferroni test for post hoc analysis (α=.05). RESULTS: Surface roughness increased irrespective of solution (P=.763), being influenced by surface treatment (P<.001), with the glazed groups presenting higher values. Microhardness decrease was influenced by solutions (P<.038) and surface treatment (P<.001), and glazing was associated with lower values. Irrespective of the surface treatment, color stainability was influenced by solutions (P<.001), with ΔE00 values for red wine being above the perceptibility threshold (ΔE00>1.30). No influence of toothbrushing was found for any parameter (P>.05). CONCLUSIONS: Despite its excellent mechanical properties, CAD-CAM lithium disilicate ceramic degraded after exposure to commonly consumed beverages. Irrespective of surface treatment, beverages decreased microhardness and caused color changes. Surface roughness increased, showing higher variation for glazed groups. Toothbrushing was unable to potentiate or diminish the observed effects. In general, the results showed that proper mechanical polishing can produce a surface with desirable properties.