The vital tooth bleaching is impossible by the cloudiness of the tooth enamel outer layer

过氧化脲和过氧化氢是牙齿漂白的主要试剂。在这项研究中，牛牙釉质在不同的时间浸泡在不同浓度的过氧化物中，以阐明过氧化物处理的影响。研究了其对截面形貌和力学性能的影响。除去冠状牙骨质的牛牙釉质表面涂上指甲油，除了唇表面有一个3x5毫米的窗口。然后将标本浸泡在10%或30%过氧化脲（CP）或过氧化氢（HP）中30或180分钟（每种情况n=5）。然后将标本包埋在环氧树脂中，并在距离牙齿切缘7mm处以垂直于牙轴的角度切割。最后用0.05 gm氧化铝悬浮液抛光截面搪瓷。采用纳米压痕系统测定纳米硬度。在扫描电镜下进行观察。两种过氧化物处理的牙釉质在最外表面以下2μm处纳米硬度降低，但在50 μm处没有降低。较高浓度的过氧化物在最外表面以下5μm处造成侵蚀，较低浓度的过氧化物在最外表面以下5μm处造成侵蚀。

Carbamide peroxide and hydrogen peroxide are used as the main agent in vital tooth bleaching. In this study, bovine enamel was immersed in different concentrations of peroxide over differing periods of time to clarify the influence of peroxide treatment. Its influence on cross-sectional morphology and mechanical properties was investigated.Bovine enamel surfaces, from which coronal cementum was removed, were covered with nail varnish, except for a 3x5-mm window on the labial surface. Specimens were then immersed in 10% or 30% carbamide peroxide (CP) or hydrogen peroxide (HP) for 30 or 180 min (n=5, each condition). The specimens were then embedded in epoxy resin and cut at an angle perpendicular to the tooth axis 7 mm from the incisal edge of the tooth. Sectional enamel was finally polished with a 0.05-gm alumina suspension. Nanohardness was determined by using a nanoindentation system. Observation was carried out under scanning electron microscopy. The nanohardness of the enamel treated with either peroxide decreased at 2μm below the outermost enamel surface, but no decrease was observed at 50 tm. Higher concentrations of peroxides caused erosion to a depth of 5μm below the outermost surface, which was deeper than that with a low concentration of peroxide.