In-Vitro investigation of the effects of bleaching techniques applied at different times after debonding on enamel surface

The aim of this study is to examine the effects of different bleaching techniques applied at different times on the enamel surface after orthodontic debonding. A total of 60 teeth, consisting of 6 groups, were used in this study. The teeth were separated from their roots 1 mm below the cementoenamel junction for better manipulation and embedded in cold acrylic filled molds. The roughness values of the enamel surfaces before processing were measured by optical profilometer. Adhesive resin was bonded to the tooth surfaces and thermal cycle was applied 10.000 times between 5 and 55 ⁰C in order to simulate the oral environment in all samples. Then, the adhesive on the enamel surface was cleaned at 20000 rpm with a 6 blade tungsten carbide bur attached to the micromotor, similar to the debonding movements in the mouth. The grouping of the samples was done according to the applied procedures. The group to be used as the control group which only the debonding process was applied was called 1. group - D, the group which clinical bleaching was applied after debonding immediately with %40 hydrogen peroxide for 3 times in 20 minutes sessions was called 2. group - DKB, the group which home bleaching was applied after debonding immediately with %16 carbamide peroxide 6 hours a day for 14 days was called 3. group - DEB, the group which was stored in artificial saliva for 4 weeks was called 4. group - DT, the group which was stored in artificial saliva for 4 weeks and then bleached with %40 hydrogen peroxide for 3 times in 20 minute sessions was called 5. group - D4KB, the group which was stored in artificial saliva for 4 weeks and then bleached with %16 carbamide peroxide 6 hours a day for 14 days was called 6. group - D4EB. After the procedures were completed, the second and final measurements of the specimens were made with optical profilometer. One randomly selected sample from all groups for qualitative examination was examined with a scanning electron microscope at 500 magnification. Surface roughness increased in all samples after the treatment. After removal of the adhesive resin, the roughness was found to be maximum on the tooth surfaces which were immediatey bleached with 40% hydrogen peroxide (DKB). This was followed by the teeth surfaces which were stored in artificial saliva for 4 weeks and then bleached with %40 hydrogen peroxide (D4KB). There was no vi significant difference in surface roughness between home bleaching techniques using 16% carbamide peroxide immediately after debonding or after 4 weeks storing in artificial saliva. In all bleaching techniques using 16% carbamide peroxide, similar results were obtained with enamel surface roughness values obtained after debonding alone. The artificial saliva did not cause significant changes in the enamel surface after debonding in vitro. When the enamel surface change rates of all the study groups were compared, although the highest change rate was observed in the groups using 40% hydrogen peroxide, the difference between the final roughness values of the groups were not significant. If bleaching will be performed after orthodontic treatment, home bleaching with carbamide peroxide is recommended for bleaching treatments since the enamel roughness formed by debonding does not further increased by bleaching procedure. After orthodontic treatment, immediate bleaching with high concentrations of hydrogen peroxide should be avoided because high concentrations of hydrogen peroxide can cause increased roughness of enamel after debonding. Key Words: Enamel surface; Surface roughness, Debonding; Resin removal; Bleaching; Hydrogen peroxide; Carbamide peroxide