Characteristics of Esthetics Coating Material and Influence on Tooth Substrate

Abstract

In cases in which tooth bleaching is difficult, esthetics can be improved by applying coating materials to the coronal area. It has been reported that the color of tetracycline teeth changes to dark brown with age, due to irradiation by ultraviolet rays. Therefore, if the irradiation of teeth by ultraviolet rays in natural light can be decreased by applying coating materials to tetracycline teeth, such color changes to dark brown with age can be suppressed. In this study, using two types of coating materials (White Coat™ shade OB0 (WOB), opaque (WOP), and Beauti Coat shade BW3 (BBW) , shade WO (BOP)), composite resin (UniFil® LoFlo Plus shade AO3 (UAO)), glassionomer cement (Fuji Ionomer® Type II shade YB (FYB)), and enamel, disk specimens of 0.1, 0.3, 0.5, and 1.0 mm in thickness were produced, and the light transmissivity of each specimen was measured. As the control group, disk specimens of human tooth enamel of 0.3, 0.5, and 1.0 mm were produced, and the light transmissivity was measured. After producing tetracycline discoloration models by mixing tetracycline solution with dental apatite cements, the models were covered with each disk specimen of 0.3 mm in thickness, and they were irradiated with artificial sunlight containing ultraviolet rays for 7 days. Color changes (ΔE*ab) after irradiation were measured, and the results were evaluated using one-way layout analysis of variance and Tukey's test (p<0.05). Furthermore, when coating materials are employed for suppressing the progression of tetracycline tooth color changes, they require long-term durability. Therefore, marginal leakage at the interface of coating materials (WOB, BBW) and enamel was observed by the dye-penetration method after 24 hours, and 500 and 1,000 repetitions of thermal-cycling (TC500 and TC1000, respectively) for 30 seconds at 5 and 55℃. The results obtained were evaluated using Mann-Whitney's U test (p<0.05). Also, to investigate the influence of the repeated application and removal of coating materials on the enamel surface, SEM observation of the specimens in which coating materials were removed 24 hours after application (24-hour removal), those in which coating materials were removed after TC500 (TC500 removal), and those in which the removal of coating materials was repeated 3 times after TC500 (TC500×3 removal), was performed. The following results were obtained: 1. Regarding the 0.3-mm-thick specimens, the light transmissivity was below 0.5% in WOB, WOP, and BOP, at wavelengths of around 400 nm and over, showing ultraviolet ray absorption effects. 2. Regarding the 1.0-mm-thick specimens, although the light transmissivity was below 0.5% in BBW, UAO, and FYB, at wavelengths of around 400 nm and over, suggesting ultraviolet ray absorption effects, this thickness is not suitable for clinical application. 3. Color changes of the discoloration models were significantly lower with WOB, WOP, and BOP, compared with those of enamel. These findings suggested that WOB, WOP, and BOP suppressed the progression of discoloration in tetracycline teeth. 4. In the dye-penetration test, marginal leakage was not present after 24 hours. However, since dye-leakage was found after TC500 and TC1000, it was suggested that marginal leakage would occur after long-term application of coating materials. 5. SEM observation of the enamel surface after removing coating materials showed that the coating materials were abraded at their interface with enamel in the cases of 24-hour removal, TC500 removal, and TC500×3 removal, suggesting that the influence of the repeated application and removal of coating materials on the enamel surface was low.