表面官能团作用下的牙釉质原位再矿化研究

采用酸蚀后的牙釉质作为早期龋缺损模型,在缺损牙釉质表面修饰-SO3-功能基团,分别在人工唾液和含氟人工唾液中进行原位再矿化的研究。利用X-射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、能谱仪(EDS)、选区电子衍射(SAED)研究原位再矿化晶体的组成和结构。结果表明,在人工唾液和含氟人工唾液中,表面修饰的官能团均可有效促进牙釉质再矿化。在含氟人工唾液中生成了沿c轴取向生长的具有较大长径比的棒状氟羟基磷灰石(FHA),这种FHA晶体具有类牙釉质的成分和结构,对修复早期龋有重要的意义。     

分级结构类釉质氟磷灰石的原位仿生再矿化合成

以酸蚀牙釉质为模板,在仿生条件下进行原位釉质再矿化,合成了具有分级结构的类釉质样晶体.利用扫描电子显微镜(SEM)、X射线衍射(XRD)、X射线能谱(EDS)和傅里叶变换红外光谱(FTIR)分析及机械性能检测等手段对再矿化层晶体的形貌、化学组成、硬度和生物相容性等性质进行了表征,并将其与水热条件下合成的类釉质样结构晶体进行比较.结果表明,2种方法均可获得类似于天然牙釉质釉柱及釉间柱样分级结构,所得晶体主要为氟磷灰石.在仿生条件下得到的类釉质晶体更接近于天然牙釉质釉柱及釉间柱样分级结构,在形貌、结构组成及硬度上均优于水热条件下得到的晶体.     

用XPS和SEM研究氟化物对牙釉质早期脱矿和再矿化的影响

用光电子能谱和扫描电镜分析体外人牙釉质片经含不同浓度氟化物的脱矿液和再矿化液处理后釉质化学成分和形态学变化。结果发现，脱矿液中单独加入低浓度氟化物不能有效抑钙和磷溶解，在有外源性钙和磷存在时，才能获得再矿化而抑制钙和磷溶解，脱矿环境中有高浓度氟，通过局部沉积氟化钙而抑制酸与牙的反应，氟促进再矿化主要表现在加速钙的沉积，同时本身参以形成氟磷灰石，提高了牙齿的耐酸能力。     

缺钙对儿童牙齿发育有何影响

首先，让大家了解一下牙齿的构造。每个牙齿都有牙冠和牙根两部分，露出在121腔的部分为牙冠，埋在牙齿周围组织里的部分为牙根。牙齿由牙釉质、牙本质、牙骨质和牙髓质构成，牙齿的主体是牙本质，冠部表面被覆着一层牙釉质，根部被覆着一层牙骨质。这3种组织是经过钙化的硬组织，其主要成分与骨骼一样，是羟磷灰石。牙齿硬组织的中央有一空腔，其中含有牙髓。牙髓是软组织，由血管、神经、淋巴管及结缔组织所组成，为牙齿提供营养。     

缺钙为什么会引起龋齿

龋齿俗虫蛀牙，是儿童的多发病。乳牙患龋率高峰在5岁左右，恒牙患率高峰在15岁左右。椐上海市1976--1778年调查材料证实，4岁儿童患龋率达66．14％，9岁高达90％。龋齿的发生与细菌、饮食、牙齿本身和唾液均有关系，牙釉质是牙齿最外层的一层光亮、乳白色的物质，是人体最坚硬的物质，耐腐蚀、耐腐蚀、耐摩擦，具有保护整个牙齿的作用。缺钙可造成牙釉质钙化不全，使牙本质失去了保护层，同时牙釉质和牙本质的致密度降低，抗龋能力下降，一些细菌和变形链球菌、乳酸杆菌等乘虚而入，分解食物中的碳水化合物而产生酸性物质，使牙齿硬组织脱钙，软组织崩解，逐层破坏牙釉质、牙本质，在牙上形成小洞。当小洞接近牙髓中的神经时，冷、热等刺激和食物嵌入洞内，可引起疼痛。如果儿童因为缺钙致使牙齿的钙化程度降低，就会使细菌产酸脱钙过程加快，龋齿的发展也随之加快。另外，缺钙也使唾液中的含钙量减少，促使龋齿更易发生。所以预防儿童龋齿，在注意口腔卫生的同时，还要保证充足的钙营养。     

类牙釉状丝胶蛋白/羟基磷灰石复合材料的合成及表征

采用化学沉淀法合成了丝胶蛋白(SS)/羟基磷灰石(HAP)复合材料, 并研究了矿化时间对复合材料的影响. X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)、透射电镜(TEM/HRTEM)和扫描电镜(SEM)表征结果表明: 在较短的矿化时间内, 合成的SS/HAP为直径约20 nm的复合颗粒; 随着矿化时间的延长, 这些复合颗粒能够沿轴方向组装并融合成类牙釉结构的较大晶体. 文章讨论了其可能的组装机制.     

生物活性牙科复合树脂的研究进展

牙科复合树脂由于色泽美观,在口腔临床上具有广泛的应用。但其仍然存在边缘缝隙的问题,从而导致继发龋的发生。再矿化复合树脂中的生物活性填料会释放能够再矿化的钙、磷离子,促使材料表面形成矿化层,能够抑制二次龋的发生。本文介绍了不同种类、含量、粒径大小和表面改性的生物活性填料对复合树脂物理、机械性能的影响,分析了再矿化复合树脂的再矿化行为,提出了再矿化复合树脂亟待解决的问题和研究难点,展望了复合树脂的研究方向。     

组合脱胺对β沸石酸性和结构的影响

利用ＴＰＤＥ、ＴＰＤ和ＸＲＤ等手段研究了低温恒温脱胺后再程序升温脱胺的组合脱胺法．结果表明，不同组合脱胺工艺均可调变β沸石的表面酸性，适当选择组合脱胺温度可大幅度调变β沸石的表面酸性，其中２７０℃和２９０℃下分别恒温脱胺后再程序升温脱胺，β沸石表面除出现传统脱胺的两个酸性位外，还出现了一个中等强度的酸性位，且酸量很大，可调变性较强．晶相测定可知，低温脱胺后再程序升温脱胺有利于β沸石结晶度的保持．此外，还对β沸石的脱胺过程和脱胺后β沸石的吡啶脱附过程的动力学行为进行了初步的研究．     

二级脱附反应TPD谱图剖析

程序升温脱附(TPD)技术在固体表面化学和催化等研究领域中已得到广泛的应用.但由于缺乏有力的理论处理手段,对TPD谱图所提供的信息利用率不高,甚至仍在运用某些错误的处理方法.为此,作者曾对一级脱附反应TPD谱图作过理论分析.本文进一步对二级脱附反应(均匀表面、无再吸附过程)TPD谱图作理论分析.     

丙烯在Fe-Sb-W-O/SiO2催化剂上氧化机理的研究Ⅰ.氧和丙烯的吸附

通过氧和丙烯在铁锑氧化物催化剂上吸附的研究,认为丙烯在铁锑氧化物催化剂上的氧化是在表面活性晶格氧参与下的还原-再氧化循环过程,弱结合的晶格氧的活性比强结合的高,优先参加反应。通过催化剂表面还原和再氧化速度的研究,并和钼系催化剂相比较,证明铁锑氧化物催化剂不仅易被还原,而且还原表面上的产物较难脱附,故认为在选择氧化反应中铁锑氧化物催化剂上的积炭可能是由表面还原引起的。     

Relationship between microhardness and fluorine contents on tooth enamel determined by PIGE analysis

The remineralization effect of fluoride has been measured by surface microhardness on tooth enamel. The purpose of this study was to investigate the relationship between microhardness and fluorine concentration on tooth enamel. Twelve sound bovine enamel specimens were prepared and immersed in 0.05% NaF solution for 1, 3, 6, 24 and 36 hours, respectively. The concentration of fluorine in specimens were measured by PIGE analysis and surface microhardness of each specimen was measured by surface microhardness tester. Fluorine concentration was increased by immersing time. There was no change in microhardness of each specimen by fluorine content. The results of this study suggest that there was no relationship between the fluorine concentration and surface microhardness in sound tooth enamel. PIGE analysis can be used effectively to assess the remineralization effect of fluorine content in tooth enamel.     

Determination of some trace elements in human tooth enamel

Determination of seven elements (Cu, Fe, Mg, Mn, Pb, Sr and Zn) in whole enamel and surface layers of extracted non-carious human teeth by FAAS, ETA AAS, ICP-AES and ICP-MS (Pb) is demonstrated. Techniques are described for obtaining whole enamel and its acid dissolution. Fifty microm width enamel layers from outer enamel surface to a 200 microm depth were successively etched in 1 mL of 3 M HClO4 for 3 min dissolution periods. Enamel samples were analyzed for populations under and over 20 years of age and enamel from Bronze Age teeth. Concentrations of microelements in the whole enamel and in the first surface layer (50 microm depth) were compared. With exception of Sr and Mg, all elements show significantly higher concentrations in the first layer than in whole enamel and higher concentration in teeth of individuals over 20 years, which demonstrate the cumulative effect of these elements. The Cu, Fe, Mn, Pb and Zn concentrations in four layers of erupted and non-erupted teeth decreased while Mg and Sr concentrations increased toward enamel-dentine junction. The concentrations of most elements were almost constant as they approached the 150 microm layer. This concentration gradient may result from interaction between saliva and teeth and supports the hypothesis that the surface de- and re-mineralization process is effective at most to 150 microm from the enamel surface.     

Reactions of dental enamel with superficially applied fluorides: electron spectroscopic investigations

Electron spectroscopy combined with argon ion etching was applied for studying reactions of fluoride with dental enamel. Using this assembly to alternately record the spectra and etch the surface, depth profiles of topmost surface enamel can be obtained. The hyperfine depth resolution of the technique provided new information on the distribution of fluoride and its reaction products in the outermost layers of dental enamel.     

An in vitro investigation of human enamel wear by restorative dental materials

A radiometric method was applied to assess enamel wear by another enameland by restorative materials. The radioactive enamel was submitted to wearin a machine which allows sliding motion of an antagonistic surface in contactwith the radioactive enamel. The enamel wear was evaluated by measuring thebeta-activity of ³²P transferred to water from this irradiatedtooth. Results obtained indicated that dental porcelains cause pronouncedenamel wear when compared with that provoked by another natural enamel orby resin materials. Resin materials caused less enamel wear than another naturalenamel. Vickers microhardness data obtained for antagonistic materials showeda correlation with the wear caused to the enamel.     

Peptidomic analysis of human acquired enamel pellicle

Human acquired enamel pellicle is the result of a selective interaction of salivary proteins and peptides with the tooth surface. In the present work, the characterization of the peptides as well as the type of interactions established with the enamel surface was performed. Peptides from in vivo bovine enamel implants in the human oral cavity were sequentially extracted using guanidine and trifluoroacetic acid solutions and the fractions obtained were analysed by LC-MS and LC-MS/MS. Based on the LC-MS data, six phosphorylated peptides were identified in an intact form, strongly adsorbed to the enamel surface. Data from the LC-MS/MS analyses allowed us to identified 30 fragment peptides non-covalently bonded to enamel [basic proline-rich proteins, histatins (1 and 3) and acidic proline-rich protein classes]. The tandem mass spectrometry experiments showed the existence of a pattern of amide bond cleavage for the different identified peptide classes suggesting a selective proteolytic activity. For histatins, a predominance of cleavage at Arg, Lys and His residues was observed, while for basic proline-rich proteins, cleavage at Arg and Pro residues prevailed. In the case of acidic proline-rich proteins, a clearly predominance of cleavage of the Gln-Gly amide bond was evident.     

The Early Stages of Native Enamel Dissolution Studied with Atomic Force Microscopy

Food-induced demineralization (erosion) is one of the key factors in surface structural changes of tooth enamel, with soft drinks being a significant etiological agent. The objective of this study was to measure early stages of enamel loss with high accuracy on native enamel surfaces combined with qualitative observations of changes in the surface morphology using the atomic force microscope (AFM). Native unerupted third molar surfaces were partly covered with a gold reference layer. Samples were imaged with the AFM before dissolution (at baseline) and after exposure to three different drinks (mineral water, a "toothkind" blackcurrant drink, and a lemon and lime juice drink) at five different exposure times (15 min, 30 min, 1 h, 2 h, and 3 h). The changes in the surface morphology were investigated qualitatively as well as quantitatively. This study showed that the maximum material loss occurred at the aprismatic parts of the enamel close to the perikymata. The maximum enamel loss was greatest for the lemon and lime juice drink and lowest for water. A two-way ANOVA of the transformed data, employing the natural logarithm, showed a statistically significant difference between both the drinks and the exposure time at a 95% confidence level (P=0.000). This demonstrates that the AFM is a suitable tool for measuring early stages of enamel demineralization. Copyright 2000 Academic Press.     

Microscopic and electron spectroscopic characterization of dental enamel surfaces

 The effects of surface pretreatment on the topography and composition of dental enamel surfaces of extracted bovine teeth have been investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. Surface pretreatment with a solution of benzoic acid in acetone does not change the topography of the surface; it leads to enrichment of calcium and, to a lesser extent, phosphorus at the enamel surface. The higher adhesion strength reported between enamel surfaces pretreated with benzoic acid in acetone and glass ionomer cement might be explained in terms of a greater number of chemical bonding sites due to the enrichment of calcium and phosphorus at the surface. Received: 6 November 1998 Accepted in revised form: 3 December 1998     

龋病人牙釉质表面硬度及抗磨损性能测试

采用人工方法制成人牙釉质浅龋及使用抗龋措施的龋损釉质样本，分别测量各组釉质表面显微硬度，并以微动摩擦磨损试验机测试其抗磨性能，试验结果表明：各组实验组釉质较对照组表面硬度都有不同程度下降，氟化钠前处理会使釉质表达硬度显著下降，人工浅龋牙釉质的抗磨损性能不如正常釉质，使用两种抗龋措施对其抗磨性能没有明显改善。     

Anisotropic demineralization and oriented assembly of hydroxyapatite crystals in enamel: smart structures of biominerals

It is interesting to note that the demineralization of natural enamel does not happen as readily as that of the synthesized hydroxyapatite (HAP), although they share a similar chemical composition. We suggest that the hierarchical structure of enamel is an important factor in the preservation of the natural material against dissolution. The anisotropic demineralization of HAP is revealed experimentally, and this phenomenon is understood by the different interfacial structures of HAP-water at the atomic level. It is found that HAP {001} facets can be more resistant against dissolution than {100} under acidic conditions. Although {100} is the largest surface of the typical HAP crystal, it is {001}, the smallest habit face, that is chosen by the living organisms to build the outer surface of enamel by an oriented assembly of the rodlike crystals. We reveal that such a biological construction can confer on enamel protections against erosion, since {001} is relatively dissolution-insensitive. Thus, the spontaneous dissolution of enamel surface can be retarded in biological milieu by such a smart construction. The current study demonstrates the importance of hierarchical structures in the functional biomaterials.