Effects of home-bleaching on composite resin restorative materials

• Main Authors: Mei-Chien Chen, 陳美蒨
• Other Authors: Shyh-yuan Lee
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/18579751479161919478

碩士 === 國立陽明大學 === 臨床牙醫學研究所 === 95 === Tooth bleaching has become popular in the esthetic dentistry. Previous literatures found that home-bleaching might increase degradation of composite resins. However the mechanism is still unclear. Four composite resins were enrolled in the study, including two light-polymerized hybrid composites (3M Z100 and Filtek Z250), one microfilled composite (Filtek Z350), and one polyacid-modified composite (compomer, Dyract AP). Thirty standardized disc specimens (15 x 1 mm) of each material were made and stored in distilled water for 7 days, in which 5 specimens of each material was used to measure the water sorption and solubility. Twenty specimens were randomly divided into two groups, in which one group was immersed in 10% carbamide peroxide solution for 8 hours per day for 28 days, and the other group was stored in distilled water as control. Surface properties, including Knoop microhardness, roughness and CIELab values of each specimen was measured, before bleaching treatment and repeatedly at intervals of 7, 14, 21 and 28 days, respectively. The rest specimens were used for examination under SEM and Raman spectroscope in order to investigate the surface characteristics and polymeric structures. The results showed that Z350 had higher water sorption then Z100 and DAP, while Z250 had the least. The impacts of home-bleaching on composite resin degradation were also different. DAP had the greatest degradation with the most color changes and roughness increase compared with the control group, followed by Z100, while Z350 and Z250 had the least degradation subjected to bleaching treatment. Bleaching impacts on microhardness of composite resins were material dependant. Bleached DAP and Z100 were softer than the control group, whereas bleached Z350 and Z250 were harder. With the observation of the surface of specimens under SEM, all materials tested had more degradation profile after home-bleaching compared to the control group. The Raman spectrum revealed that home-bleaching treatment changed the chemical polymeric structures of the composite resins. The aliphatic C=C bond vibration (ω = 1638 cm-1) was reduced and carbonyl bond vibration (C-O, ω = 1200 ~ 1355 cm-1) was increased in hybrid and microfilled composite resins. This denoted that oxidation reaction could be a possible mechanism of degradation of composite resins subjected to home-bleaching treatment. Meanwhile the CO2- asymmetric stretching vibration (ω = 1335 ~ 1440 cm-1) was reduced and carboxylic salts was increased in Raman spectrum of polyacid-modified composite resin. The possible reason is that home-bleaching accelerated the water diffusion and thus enhanced the acid-base neutralization of polyacid-modified composite resin. Within the limitation of this study, the degradation effects of home-bleaching on composite resins were material dependant, which might be related to the water diffusion of resin matrix, filler type and setting mechanism of these materials. SEM observation and Raman spectrum analyses seem to be good tools to evaluate the degradation of bleached composites, while microhardness of composite resins was not a good indicator. Applying the findings of this study, polyacid-modified composite resins should be avoided to restore the teeth before home-bleaching therapy, and also the discoloration and polymeric change of other composites should be anticipated, since home-bleaching could accelerate the degradation of composite resins and consequently increase the surface roughness, poor esthetics and tendency of wear.