| ObjectivePolymethylmethacrylate(PMMA) has been used widely in clinic as a denture base material because of its good physical and chemical properties, mechanical properties and biological properties. Resin base denture which usually consists of PMMA resins and artificial teeth, has a smooth and glassy surface and is capable of matching the natural appearance of soft tissues and teeth. Therefore, it can attain esthetic effect. However, great color change has been found on the surface of base resin and artificial teeth, which may result in patient dissatisfaction. The purpose of this study was to determine color stability of the PMMA resins with different surface roughness degree and five brands of artificial teeth by subjecting them to three beverages (coffee, tea, vinegar) and distilled water as a means of control.MethodsSixty-four specimens (20mm*20mm*5mm) made of heat-cured base resin were fabricated, divided into four groups randomly, and then produced different surface roughness degree for different group. Five brands of artificial teeth used widely in clinic(Endura anterio、Heraeus three-color synthetic resin teeth、Synthetic resin teeth、 EFUCERA-A、Kaifeng synthetic resin teeth) were prepared. A surface roughness tester was used to measure Ra along3tracks on specimens’surface. The specimens in the same group were respectively immersed in three solutions(coffee、tea and vinegar) as well as distilled water for a control. Solutions were placed in the37℃incubator and freshened once every day. Color measurements of specimen were performed by using a spectrophotometer. Color differences were characterized using the CIE L*a*b*color space. The color value of each specimen was recorded before immersion and after1day,1week,2weeks, and4weeks of immersion. Total color difference(△E) is expressed by the following formula:△E=(△L*2+△a*2+△b*2)1/2. To relate the amount of color change(△E) recorded by the spectrophotometer to a clinical environment, the data were converted to National Bureau of Standards units (NBS units) through the equation:NBS units=△E*0.92. Both color differences and surface roughness were statistically analyzed using SPSS19.0. Results1.For both PMMA resin and artificial teeth, there were no statistically significant differences between the mean△E values before immersion and after one day of immersion in the three staining solutions(P>0.5).However, when comparison was made between the mean△E values after one week of immersion in three solutions and before immersion, there were statistically significant differences (P<0.05). And the degree of staining increased with longer immersion time.2. After four weeks of immersion, the color stability of the heat-cured base resin specimens and artificial teeth specimens in coffee and tea were significantly affected by the immersion solutions(P<0.05),and the higher color change(△E) was observed in coffee than that in tea (P<0.05). There were no statistically evident color change in water and vinegar (P>0.05)3.When comparing the PMMA resin specimens with different surface roughness in same solution, there were statistically significant differences between the mean AE values (P<0.05).And those with greatest surface roughness demonstrated the highest color change (P<0.05). Except the group whose Ra was0.052μm,for other PMMA resin specimens immersed in coffee and tea, the mean AE values were more than3.3.4.When comparing the five artificial teeth specimens in same solution, there were statistically significant differences between the mean△E values (P<0.05). The Kaifeng synthetic resin teeth group demonstrated significantly less color change than the other brands of artificial teeth tested. The highest color difference in this study was observed for specimens in the EFUCERA-A group. However, for all artificial teeth specimens immersed in three solutions, the mean△E values were less than3.3.Conclusion1. Extrinsic pigment could make both PMMA resin and artificial teeth stain, such as coffee and tea. In contrast, vinegar had no effect on their color stability. Moreover, coffee stained more than tea.2. The color change was found when PMMA resin and artificial teeth were immersed in the coloring agents after one week. And the degree of staining increased with longer immersion time.3. The surface roughness of PMMA resin could affect its color stability, and the rough surface could increase the staining susceptibility of them. In order to ensure the color stability of PMMA resin in the process of clinical use, it was required perfect polishing and that Ra should be less than0.1μm.4. The staining susceptibility of five brands of artificial teeth was varying, which had some connection with both surface roughness and filler type. But they all accorded with clinical standard. Of those brands Endura anterio and Kaifeng synthetic resin teeth were good choice. |
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