Scanning electron microscopic study evaluating the effect of 16% carbamide peroxide bleaching gel application at different periods on enamel and dentine

ABSTRACT

Technology has introduced bleaching gels and pastes that contain carbamide peroxide as a whitening agents. The carbamide peroxide agent has been popular since its use in 1989. The crowns of fifty extracted human anterior teeth were sectioned incisally exposing the dentine and the enamel ring. The teeth were divided into four groups; one control group and three experimental groups. The control one [5 specimens] was subjected to the application of placebo gel. The experimental groups [15 specimens each] were subjected to the application of the bleaching gel. The composition of it was carbamide peroxide 16%, glycerin, buffered polycarboxylic acid and pepermint oil. The 1[st], 2[nd] and 3[rd] experimental groups were exposed to 16% carbamide peroxide bleaching gel for 8, 10, 12 hours/day for 6 weeks respectively. Following each bleaching session; the specimens were washed with deionized water and kept in artificial saliva. After the bleaching periods; the samples were prepared for examination with scanning electron microscope. X ray quantitative analysis of Calcium and Phosphorous atomic contents for enamel and dentine specimens was done at two standardized points [mesio-incisal and disto-incisal] for each; using the same scanning electron microscope. The results showed the following as regarding the enamel ultrastructure; exaggerated thickness of the prism boundaries and mild to moderate loss of hydroxyapatite crystals [erosion of the prisms] in the 1[st] and 2[nd] groups while in the 3[rd] group there was total loss of hydroxyapatite crystals leaving empty enamel rods. The dentine ultrastructure results showed blocking of some dentinal tubules in the 1[st] experimental group by a smear layer of the demineralized debris that filled the empty tubules. More narrowing of the dentinal tubules by these demineralized debris became more prominently increased from the 2[nd] to 3[rd] experimental group which appeared to be completely obliterated. The statistical results revealed an overall significant difference between the control and the three experimental groups for enamel and dentine atomic calcium and phosphorus contents. Thus, we can conclude that the effect of 16% concentration of carbamide peroxide bleaching gel was safety for enamel and dentine at 8 hours/day for 6 weeks [1[st] experimental group] and this must be considered the optimal time period for bleaching without adverse hazardous effects on enamel and dentine microstructures