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

活体牙齿漂白以过氧化脲和过氧化氢为主要漂白剂。在本研究中，将牛牙釉质浸泡在不同浓度的过氧化氢中不同时间，以明确过氧化氢处理的影响。去除冠状牙骨质的牛牙釉质表面除唇侧表面有3×5 mm的窗口外，其余表面均涂有指甲油。然后将样品浸泡在10%或30%过氧化脲(CP)或过氧化氢(HP)中30或180分钟(n=5，每种条件)。然后将标本包埋在环氧树脂中，以垂直于牙轴的角度切割，距离牙齿切缘7 mm。最后用0.05克氧化铝悬浮液抛光分节牙釉质。使用纳米压痕系统测定了纳米硬度。扫描电子显微镜下观察。在牙釉质最外表面以下2μm处，两种过氧化氢处理后牙釉质的纳米硬度均下降，但在50 tm处未见降低。当过氧化氢浓度较高时，腐蚀深度达5μm，低于低浓度过氧化氢的腐蚀深度。

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.