Conservative techniques for improving the appearance of discolored teeth have become popular in the past decade. These include: in-office bleaching with 30% hydrogen peroxide, which is applied on etched enamel with a gauze pad and then exposed to a bleaching light; home bleaching with a mild form of peroxide, such as 10% carbamide peroxide, which is applied on the tooth surface with custom-made mouthguards; and enamel micro-abrasion with 18% hydrochloric acid, which is applied in a pumice slurry. In this study, the in-office bleaching and enamel micro-abrasion techniques were performed on extracted teeth for investigation of their microscopic effects on the surface enamel. Specimens treated only with 37% phosphoric acid showed an enamel loss of 5.7 +/- 1.8 microns. The specimens treated with 37% phosphoric acid followed by 30% hydrogen peroxide showed enamel loss of 5.3 +/- 1.6 microns; this loss was probably not caused by the hydrogen peroxide, but rather by the etching with 37% phosphoric acid which preceded the hydrogen peroxide application. A direct application of 18% hydrochloric acid for 100 s resulted in a loss of 100 +/- 47 microns. The extent of enamel loss was much greater when the 18% hydrochloric acid was applied in a pumice slurry for the same period of time (360 +/- 130 microns), and the effect was time-dependent. Thus, the pumice and rotary prophy cup used in conjunction with the 18% hydrochloric acid contributed markedly to the loss of surface enamel, enhancing the non-selective stain-removing action of the hydrochloric acid. Therefore, the hydrochloric acid-pumice technique must be used clinically with caution.
Serial sections (each from 150 to 200 μm thick) of porcine molar tooth germs within their bony crypts, rodent incisor teeth (in situ), and human extracted teeth were cut with a thin rotating diamond-impregnated disc, without prior embedding. Some specimens were cut unfixed, at room temperature (21°C) or frozen (-70°C), some in fixative, and others cut after fixation. A variety of routine fixatives has been tried, and in general the preservation of hard/soft tissue interfaces is best achieved when fixation precedes cutting. Several histological and histochemical methods have also been tried successfully. The damaged surface layers of the specimens brought about by the cutting disc can be removed after staining, if the section is embedded in a thin sheet of Epon and then thinned by being polished. The method provides a novel way of studying hard/soft tissue junctions.
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