Effect of 10% Carbamide Peroxide Bleaching Gel on Enamel Microhardness, Microstructure, and Mineral Content

Abstract

The effect of 10% carbamide peroxide on human enamel subsurface layers was examined. Microhardness, microstructure, and mineral content were studied in such a manner that control and test side were located on the same tooth. Longitudinally sectioned samples were obtained from six teeth and Vickers microhardness of the enamel was measured. Enamel microstructure was analyzed using a scanning electron microscope and subjected to electron probe microanalysis for chemical analysis of calcium (Ca) and phosphorus (P). The concentration of Ca in the bleaching gel was measured spectrophotometrically and the concentration of P was measured photometrically. Results showed that a bleaching gel of 10% carbamide peroxide did not significantly affect the microhardness of the enamel. Scanning electron microscopic analysis showed local changes in enamel microstructure similar to those of initial caries. Electron probe microanalysis showed lowered concentrations of Ca and P; in addition the Ca:P ratio was lowered. There was some Ca and P in the bleaching gel after use. It is concluded that 10% carbamide peroxide causes local microstructural and chemical changes in enamel that are likely not clinically significant.

The effect of bleaching on enamel susceptibility to acid erosion and demineralisation

“…Again, no evidence was provided within this report that bleaching, or activation of the CP, took place. Similar results were reported by Potocnik and colleagues, 20 again using 10% CP. One study, by researchers at Procter and Gamble, used a colorimeter to prove bleaching effects and then undertook surface hardness measurements.…”

“…20 No other study was found within the literature that assessed the demineralisation effects of bleached enamel. A study undertaken by Amaechi et al 22 examined the effects of differing methods of enamel sterilisation prior to employment in situ models.…”

Effect of Different Fluoridation Regimes on the Microhardness of Bleached Enamel

“…7,9,13,[19][20] However, other studies reported that 10% carbamide peroxide gel did not affect enamel surface hardness. [21][22][23] These contradictory findings among different studies might be due to differences in method, such as frequency and time of bleaching treatment, storage media or the use of human or bovine teeth.…”

In vitro colorimetric evaluation of the efficacy of various bleaching methods and products

“…While numerous in vitro studies were designed to assess the effect of bleaching techniques on tooth composition and microstructure, [21][22][23][24][25][26] little was undertaken to measure their effects on tooth color or specific lightening potential. Staining techniques were developed to assess the lightening effect of different bleaching techniques but mainly for nonvital teeth.…”

“…58,60,63,64 However, in the later clinical trials, measurements were performed at the end of the treatment, which does not take into consideration the rebound effect observed within the forthcoming days and weeks. 65 It has been shown that bleaching induces enamel and dentin demineralization, as measured by changes in microhardness values, which is followed by a remineralization process [21][22][23][24][25][26] ; this likely explains changes in tooth appearance such as the short-term higher enamel brightness and opacity. It therefore appears mandatory to assess the clinical efficacy of bleaching not only immediately after completion of the treatment but also after a few months at least, so that an objective comparison of treatment modalities can be performed.…”