Israel Lewinstein1, Nitzan Fuhrer, Naama Churaru, Harold Cardash. 1. Department of Oral Rehabilitation, The Maurice and Gabriela Goldshleger School of Dental Medicine, Universeity of Tel Aviv, Tel Aviv, Israel. lewins@post.tau.ac.il
Abstract
STATEMENT OF PROBLEM: Bleaching of teeth by "in-office" or "home" bleaching techniques are popular methods of whitening teeth. However, bleaching may reduce the surface hardness of enamel and dentin. PURPOSE: The purpose of this study was to evaluate (1) the effect of different concentrations of 2 "in-office bleaching" and 2 "home bleaching" agents applied for different time periods on the hardness of enamel and dentin and (2) the effect of subsequent immersion in a low-concentration fluoride solution on the hardness of bleached enamel and dentin. MATERIAL AND METHODS: The enamel and dentin of 12 extracted intact human molar teeth were sectioned lengthwise, ground, polished, embedded in acrylic resin and divided into 4 groups each (n=12). An area of approximately 5 x 5 mm of enamel and dentin tested for Knoop hardness number (KHN; kg/mm 2 ) at a load of 100 g for 20 seconds (baseline). The specimens were stored in distilled water for 1 hour and the microhardness testing repeated as a control group. The groups were bleached as follows: Group OX and Group OQ were bleached "in office" with Opalescence Xtra (35% hydrogen peroxide) and Opalescence Quick (35% carbamide peroxide), respectively, for 5, 15, or 35 minutes and retested for KHN at the end of each time period. "Home bleaching" products Opalescence F (15% carbamide peroxide) and Opalescence (10% carbamide peroxide) were applied in 14-hour applications at 24-hour intervals to Groups OF and O, respectively, which were then tested for KHN. Specimens were immersed in 0.05% fluoride solution (Meridol) for 5 minutes and retested for KHN. The hardness values were analyzed by 2-way ANOVA and Scheffe post hoc test (alpha=.05). Comparisons of KHN between each time and the baseline measurement for each group were of interest. RESULTS: Significant decreases in KHN of enamel and dentin were found after bleaching for all test groups, dependent on the accumulated bleaching time. Group OX showed a 25% KHN reduction for enamel and 22% for dentin after 35 minutes bleaching (P < .0001). Group OQ showed a 13% KHN reduction (P < .0001) for enamel and 10% for dentin after 35 minutes (P < .005). Group OF showed a KHN reduction of 14% for enamel (P < .05) and 9% for dentin (P < .0001) after 14 hours bleaching, and Group O showed an 18% reduction in enamel (P < .0001) and 13% in dentin (P < .0001) for the same period. Fluoridation completely restored the softened dental tissues. CONCLUSION: The "in-office" bleaching technique reduced the hardness significantly more than the "home" bleaching technique. Low-concentration fluoride mouth rinse (Meridol) restored the softened dental tissues.
STATEMENT OF PROBLEM: Bleaching of teeth by "in-office" or "home" bleaching techniques are popular methods of whitening teeth. However, bleaching may reduce the surface hardness of enamel and dentin. PURPOSE: The purpose of this study was to evaluate (1) the effect of different concentrations of 2 "in-office bleaching" and 2 "home bleaching" agents applied for different time periods on the hardness of enamel and dentin and (2) the effect of subsequent immersion in a low-concentration fluoride solution on the hardness of bleached enamel and dentin. MATERIAL AND METHODS: The enamel and dentin of 12 extracted intact human molar teeth were sectioned lengthwise, ground, polished, embedded in acrylic resin and divided into 4 groups each (n=12). An area of approximately 5 x 5 mm of enamel and dentin tested for Knoop hardness number (KHN; kg/mm 2 ) at a load of 100 g for 20 seconds (baseline). The specimens were stored in distilled water for 1 hour and the microhardness testing repeated as a control group. The groups were bleached as follows: Group OX and Group OQ were bleached "in office" with Opalescence Xtra (35% hydrogen peroxide) and Opalescence Quick (35% carbamide peroxide), respectively, for 5, 15, or 35 minutes and retested for KHN at the end of each time period. "Home bleaching" products Opalescence F (15% carbamide peroxide) and Opalescence (10% carbamide peroxide) were applied in 14-hour applications at 24-hour intervals to Groups OF and O, respectively, which were then tested for KHN. Specimens were immersed in 0.05% fluoride solution (Meridol) for 5 minutes and retested for KHN. The hardness values were analyzed by 2-way ANOVA and Scheffe post hoc test (alpha=.05). Comparisons of KHN between each time and the baseline measurement for each group were of interest. RESULTS: Significant decreases in KHN of enamel and dentin were found after bleaching for all test groups, dependent on the accumulated bleaching time. Group OX showed a 25% KHN reduction for enamel and 22% for dentin after 35 minutes bleaching (P < .0001). Group OQ showed a 13% KHN reduction (P < .0001) for enamel and 10% for dentin after 35 minutes (P < .005). Group OF showed a KHN reduction of 14% for enamel (P < .05) and 9% for dentin (P < .0001) after 14 hours bleaching, and Group O showed an 18% reduction in enamel (P < .0001) and 13% in dentin (P < .0001) for the same period. Fluoridation completely restored the softened dental tissues. CONCLUSION: The "in-office" bleaching technique reduced the hardness significantly more than the "home" bleaching technique. Low-concentration fluoride mouth rinse (Meridol) restored the softened dental tissues.
Authors: R R Moraes; J L M Marimon; L F J Schneider; L Correr Sobrinho; G B Camacho; M Bueno Journal: Clin Oral Investig Date: 2005-11-16 Impact factor: 3.573
Authors: Alessandra B Borges; Carlos R G Torres; Paulo A B de Souza; Taciana M F Caneppele; Luciana F T F Santos; Ana Carolina Magalhães Journal: Int J Dent Date: 2012-10-30