Effects of New Formulas of Bleaching Gel and Fluoride Application on Enamel Microhardness: An In Vitro Study

Abstract

©Operative Dentistry, 2007, 32-6, 589-594 JB da Costa • RF Mazur Clinical RelevanceThe results of this study suggest that tooth bleaching may lead to a reduction in enamel microhardness. Nonetheless, the application of a high concentration fluoride post-bleaching treatment may increase enamel microhardness and may restore enamel hardness to a level similar to non-bleached enamel, if the bleaching formula contains fluoride, potassium or ACP. SUMMARYThis in vitro study evaluated the new formulas of bleaching products and the effect of subsequent applications of fluoride on the hardness of enamel during and after tooth bleaching. The crowns of 60 extracted intact human molars were sectioned longitudinally; the buccal part was embedded in acrylic resin, the occlusal part was ground flat, exposing enamel and dentin, and then polished. Baseline Knoop microhardness (KHN) of enamel was determined. The specimens were then randomly divided into six groups of 10 specimens, and each group was assigned to a specific 10% carbamide peroxide (CP) bleaching agent. A: Opalescence, B: Opalescence PF (3% potassium nitrate and 0.11% fluoride), C: Nite White Excel 3 (ACP), D: Opalescence + F (acidulated phosphate fluoride 1.23%), E: Opalescence PF + F, F: Nite White Excel 3 + F. The teeth were bleached for eight hours; after each procedure, the specimens were stored in artificial saliva at 37°C. Immediately after day 21 of bleaching, the specimens in groups D, E and F received fluoride 1.23% for five minutes. KHN tests were performed before (baseline=control), during (14, 21) and two weeks (35 days) after the bleaching procedure and were statistically compared using ANOVA/Tukey's t-test (α<0.05). The statistical analysis revealed no significant difference among the bleaching materials (p=0.123). A significant enamel KHN reduction (p<0.001) was observed for all bleaching materials, with no difference among them. Two weeks after bleaching, all the groups that received fluoride showed a significant increase in microhardness. For the new bleaching formulas, the enamel was restored to a value similar to baseline.

Effect of Delaying Toothbrushing During Bleaching on Enamel Surface Roughness: An In Vitro Study

“…[21][22][23][24] However, some studies have reported significant increases in enamel surface roughness subsequent to the use of bleaching agents. 8,9 Some of the complications of applying bleaching agents in tooth hard tissues are changes in tooth chemical structure, demineralization and decreases in the mineral content including calcium and phosphate, 14,25,26 decreases in the fluoride content of enamel, 11 and changes in the micromorphology of enamel. 9,27,28 However, other studies have reported different results with no statistically significant differences in tooth hard tissue characteristics, including enamel and dentin surface roughness, after bleaching with 10% and 15% carbamide peroxide.…”

“…2 On the other hand, using a fluoride varnish or mouthwash after exposing the teeth to carbamide peroxide can remineralize the enamel. [11][12][13] Because use of saliva or artificial saliva in laboratory studies can also have a role in the remineralization of teeth, 2,7,14 the present study attempted to evaluate changes in enamel surface roughness subsequent to bleaching and brushing at three time intervals and storing the specimens in artificial saliva during the study period. The null hypothesis was that enamel surface roughness is not influenced by when toothbrushing is initiated after bleaching (immediately, at one hour, and at two hours after bleaching).…”

“…Some studies have demonstrated surface deterioration, formation of defects on the surface and porosity in electron microscope studies, and decreases in enamel hardness. [3][4][5][6][7][8][9][10][11] Therefore, the patient's oral hygiene procedures during the bleaching period can have a substantial role in creating subsequent complications, including tooth hypersensitivity. One study demonstrated that brushing teeth bleached with 10% carbamide peroxide using abrasive toothpastes increases enamel surface roughness.…”

In Vitro Evaluation of the Effect of Delaying Toothbrushing With Toothpaste on Enamel Microhardness Subsequent to Bleaching the Teeth With 15% Carbamide Peroxide

“…6 On the other hand, saliva or other remineralizing agents can create an environment to help remineralize the teeth following bleaching. [7][8][9][10] Enamel microhardness is a property that can be influenced by a combination of the above-mentioned factors.…”

Particularités du collage aux dents qui ont subi un éclaircissement

“…Da Costa et coll. (2007) ont constaté que l'émail éclairci avec le peroxyde de carbamide à 10 %, associé au nitrate de potassium à 3 % et au fluor à 0,11 %, a une micro-dureté similaire à celle de l'émail non éclairci [42]. Cependant, Tschoppe et coll.…”