The Influence of Post Bleaching Treatments in Stain Absorption and Microhardness

Abstract

Objectives:This study investigated the effects of post bleaching treatments to prevent restaining and the change of enamel surface microhardness after dental bleaching in vitro.Methods:Sixty intact human incisor teeth were stained in tea solution and randomly assigned into four groups (n=15). Then samples were bleached for two weeks (8 hours daily) by 15% carbamide peroxide. Tooth color was determined both with a spectrophotometer and visually before bleaching (T1) and immediately after bleaching (T2). Next, it was applied in group 1 fluoride (Naf 2%) gel for 2 minutes, and in group 2 a fractional CO2 laser (10 mJ, 200 Hz, 10 s), and in group 3, nanohydroxyapatite gel for 2 minutes. The bleached teeth in group 4 remained untreated (control group). Then teeth placed in tea solution again. Color examinations were repeated after various post bleaching treatments (T3) and restaining with tea (T4) and color change values recorded. The microhardness was measured at the enamel surface of samples. Data was analyzed using ANOVA, Tukey HSD test and Dunnett T3 (α = 0.05).Results:Directly after bleaching (ΔE T3-T2), the treatment with nanohydroxyapatite showed significantly the least color lapse in colorimetric evaluation. In experimental groups, the color change between T3 and T4 stages (ΔE T4-T3) was significantly lower than control group (P < 0.05). Different methods of enamel treatment caused a significant increase in surface microhardness compared to control group (P < 0.05).Significance:Application of fluoride, fractional CO2 laser and nanohydroxyapatite as post bleaching treatments are suggested for prevention of stain absorption and increasing the hardening of bleached enamel.

Influence of three treatment protocols for dental fluorosis in the enamel surface: an in vitro study

“…One possible factor that may have contributed to the reduction of enamel microhardness was the contact time of fluoride free bleaching gel with enamel surface which may have disrupted the balance between demineralization caused by the bleaching agent and the remineralization caused by artificial saliva. 27,33,34 These findings are in agreement with our SEM analyses, where was observed an irregular surface with depressions, porosity, and increased depth of enamel grooves. 13 Other studies also observed these alterations and the enamel microhardness decrease when low carbamide peroxide (10 or 15%) concentrations were used for long treatment times.…”

“…Several aspects related to bleaching agents might influence the enamel surface microhardness, such as peroxide concentration, time of application, pH or the incorporation of fluoride in bleaching agents. 25,[32][33][34][35] The bleaching agent used has a pH of 5.8 and this pH could not have contributed significantly to enamel demineralization. One possible factor that may have contributed to the reduction of enamel microhardness was the contact time of fluoride free bleaching gel with enamel surface which may have disrupted the balance between demineralization caused by the bleaching agent and the remineralization caused by artificial saliva.…”

“…13 Other studies also observed these alterations and the enamel microhardness decrease when low carbamide peroxide (10 or 15%) concentrations were used for long treatment times. 25,27,33,34 Additionally, the in situ effects of low concentrated bleaching agents on human enamel surface demonstrated no morphologic or chemical changes. This may be attributed to the protective effects of saliva, which provided dilution, buffering capacity, and supply Ca and P ions for tooth remineralization.…”

The effect of different biomimetic materials as a remineralization protocol on microhardness and ultramorphology of bleached enamel

“…In an aqueous environment, this material undergoes a series of reactions, resulting in the formation of a surface layer made of hydroxy-apatite and/ or hydroxycarbonate apatite. (21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33) However, the remineralization potential of bioactive glass has so far not been evaluated.…”

The effects of fractional CO2 laser, Nano-hydroxyapatite and MI paste on mechanical properties of bovine enamel after bleaching

“…The loss of mechanical properties of enamel after the use of bleaching agents could be regained by the incorporation of agents that can compensate for the mineral loss ( 7 ). Several types of lasers, with different parameter settings, have been used for enamel reinforcement ( 8 ). The CO2 laser (9.3, 9.6, 10.3 and 10.6 μ wavelengths), however, should be considered the mainstay in enamel hardening, because the absorption bands of phosphate, carbonate and hydroxyl groups of enamel and dentin structures are within 9.0 to 11.0 μ region which coincide well with the wavelengths of the CO2 laser ( 8 ).…”