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Effect of tooth-bleaching on the tensile strength and staining by caries detector solution on bovine enamel and
Morakot Piemjai1, Janya Surakompontorn
1Department of Prosthodontics, Faculty of Dentistry, Chulalongkorn University, Henri-Dunant Road, Pratumwon, Bangkok 10330, Thailand. tmorakot@chula.ac.th
Purpose:
To evaluate the tensile strength and staining of enamel and dentin after extracoronal or intracoronal bleaching using conventional bleaching agents.
Methods:
Extracted bovine incisors were divided into eight groups of 10 specimens. Individual groups were treated by extracoronal bleaching (E) using in-office and home techniques with different concentrations of hydrogen peroxide (H2O2) and carbamide peroxide (CP); no bleaching (EN), 35% H2O2 and 10% CP (E35H-10C), 35% H2O2 and 20% CP (E35H-20C), 35% CP and 10% CP (E35C-10C), 35% CP and 20% CP (E35C-20C). Intracoronal "walking bleaching" (I) was performed after 24 hours of root canal treatment in the three remaining groups; no bleaching (IN); sodium perborate dissolved in 35% H2O2 (ISP-35H); and sodium perborate in distilled water (ISP-W). Mini dumbbell shapes of enamel and dentin with central cross-section diameters of 1.5 x 0.5 mm and 3 x 1 mm respectively were prepared for tensile testing using an Instron machine. Fracture surfaces were examined using SEM. Bleached enamel and dentin specimens were stained and evaluated using Caries Detector solution. Staining scores were analyzed using Kruskal-Wallis H and Mann-Whitney test (P < 0.05).
Results:
Tensile strengths (mean +/- SD) of enamel and dentin respectively for each group in MPa were: EN = 30.5 +/- 3.3 and 85.4 +/- 3.0, E35H-10C = 14.8 +/- 2.3 and 58.9 +/- 2.0, E35H-20C = 10.6 +/- 2.6 and 55.5 +/- 2.2, E35C-10C = 25.4 +/- 3.4 and 70.8 +/- 2.5, E35C-20C = 20.3 +/- 4.1 and 67.2 +/- 3.3, IN = 26.5 +/- 4.1 and 85.9 +/- 2.5, ISP-35H = 13.6 +/- 3.1 and 46.7 +/- 2.3, ISP-W = 21.7 +/- 3.3 and 68.3 +/- 4.4. ANOVA and Tukey HSD test found statistically significant differences among and between groups respectively (P < 0.05). No significant difference was found between non-bleached groups (IN and EN) of enamel and dentin. Mean tensile strengths of all bleached groups were significantly lower than those of non-bleached groups. Fracture surfaces demonstrated the different morphologies for bleached and non-bleached enamel and dentin.
