Stress corrosion cracking of NiTi in artificial saliva.

OBJECTIVES: This paper aimed to study the mechanism of the cracking of orthodontic NiTi wire. METHODS: Two orthodontic NiTi wires were subjected: (1) optical and scanning electron microscopy (SEM) to observe the fracture surface; (2) energy dispersive X-ray spectroscopy to determine the composition of the surface product; (3) anodic polarization to remove the surface product. Samples of NiTi alloy were subjected to the constant loading test to study the stress corrosion cracking (SCC) behavior of NiTi shape memory alloy in artificial saliva. RESULTS: The results showed that there were three typical areas at the fracture surface of NiTi orthodontic wire. Area '1' was a tool-made notch. Crack initiated from the root of this notch and propagated to form Area '2', which was perpendicular to the wire axis and covered by surface film. This film consisted of Na, K, Cl, P, S and O except Ni and Ti. The cracking process of NiTi alloy under the constant loading test depended on the pH of saliva and applied stress. The crack length was about 262microm, the longest at 300MPa and pH 3.0. SIGNIFICANCE: A tool-made notch in orthodontic NiTi wires can cause SCC. At high stress and low pH, this NiTi alloy was most sensitive to cracking.     

种植义齿系统工程的概念及修复环节在其中的位置

种植义齿治疗是一个系统工程，需要医学专家、理工专家和患者的共同努力。其中，修复专家占有重要地位。他们需要根据患者的意愿和条件确定种植义齿是否可行，以及是否能给患者带来最大的利益。需要设计植入体的数量、部位和植入角度。需要根据种植体界面的特殊条件在义齿的设计制作中作相应的处理。还需要对患者作咨询教育，使之对种植义齿抱有合理的期望并遵医嘱执行保健措施。     

漂白剂对牙颈部硬组织影响的扫描电镜研究

目的：观察漂白剂直接作用于牙颈部后牙的结构变化。方法：选用几种不同的漂白剂，直接作用于牙颈部，应用扫描电镜观察漂白剂引起的牙本质、釉质、牙骨质的结构变化。结果：牙颈部的牙骨质、牙本质均有结构上改变，釉质变化不明显。结论：提出预防牙颈部外吸收的措施，使临床上能安全、有效地应用漂白技术     

单个下颌磨牙缺失种植修复体尺寸对骨界面应力分布的影响

目的：分析单个下颌磨牙缺失采用种植修复时，种植体尺寸对骨界面的应力分布的影响。方法：采用三维有限元法，模拟单个种植体及双种植体修复单个缺失下颌第一磨牙的情况，在保证其它因素不变的条件下，分析种植体尺寸(包括种植体长度和直径)对种植体一骨界面应力分布的影响。结果：不论单种植体修复或双种植体修复单个缺失磨牙时，种植体直径变化对种植体一骨界面应力影响较大，斜向载荷时更为明显；而种植体长度对骨界面应力影响较小。结论：建议临床尽量采用直径较大的种植体修复单个缺失下颌磨牙。     

腭心面综合征研究进展

腭心面综合征（velo-cardio-facial syndrome,VCFS）是人类常见的染色体缺失综合征之一,缺失基因大多定位于22q染色体长臂的22q11.21～q11.23区。其复杂临床表现集中体现在颅面、心脏、免疫、腺体等方面的发育性畸形,作者就其临床表现、发病机制、候选基因及其相关作用通路的最近研究进展做一综述。     

球形二氧化硅和碳酸钙2种磨擦剂牙膏对牙本质影响的体外对比研究

目的：评价球形二氧化硅(SiO2)和碳酸钙(CaCO3)磨擦剂牙膏对牙本质的影响。方法：采用光镜、扫描电镜和放射活性方法检测牙本质磨损(RDA)，观察SiO2和CaCO3磨擦剂牙膏体外对牙本质表面磨损的影响，以及对牙本质的氟吸收量和牙本质再矿化的影响。结果：使用CaCO3磨擦剂牙膏刷牙造成了牙本质的明显磨损；SiO2牙膏的RDA值分别是98．61和86．17，而CaCO3牙膏的RDA值分别是222．85和253．84；相应也观测到CaCO3磨擦剂尖锐的形态；CaCO3牙膏牙本质的氟吸收量为7．28，SiO2牙本质的氟吸收量为21．65；扫描电镜观察证明，SiO2能明显促进牙本质的再矿化。结论：在体外试验中，CaCO3牙膏较SiO2牙膏更易造成牙本质的磨损。     

静磁场对大鼠三叉神经节中SP-mRNA作用的实验研究

目的　探讨静磁场对大鼠三叉神经节中SP-mRNA的影响。方法　将 4 4只 6～ 7周的大鼠置于静磁场中 ,在 1、2、6、1 2和 2 4h时分别将动物处死 ,取其三叉神经节 ,用原位杂交方法研究SP-mRNA在各时间点的变化。结果　在静磁场作用下三叉神经节中SP-mRNA的表达呈上调变化 ,2h时达峰值 ,各时间点与正常对照组间均存在显著性差异 (P <0 0 1 )。结论　静磁场可以使三叉神经节中的SP-mRNA呈现上调性变化。     

~(60)Co照射及低温保存对转基因细胞影响的分析

目的　观察经放射前后的转基因细胞Tca8113/TNF α的TNF α的分泌情况 ,为转基因细胞经致死剂量的放射线灭活作为“瘤苗”应用于临床前TNF α基因的有效表达提供依据。方法　利用基因转染技术 ,用逆转录病毒载体将肿瘤坏死因子基因 (TNF α基因 )转导入人舌癌Tca8113细胞 ,并获得表达 ;在此基础上 ,通过ELISA法分析转基因细胞Tca8113/TNF α在60 Co放射组及未放射组的TNF α分泌量的变化以及经液氮储存 4 8h、一周复苏后的TNF α分泌量的变化。结果　 (1) 60 Co放射组转基因细胞Tca8113/TNF α的TNF α的分泌量 (x±s) (pg/ml/ 10 6细胞 /2 4h)平均高达 (110± 5 6 2 ) ,而未转基因的Tca8113细胞的上清液中未检测到TNF α ,统计学上有明显的差异性 (P <0 0 1) ;(2 )经频率为 4 39 5cGy/min ,总剂量为 10 0 0 0cGy的60 Co放射后TNF α分泌量降低 ,但在 4～ 6d时有一分泌高峰 ;(3)转基因细胞Tca8113/TNF α经60 Co放射后在经 4 8h及一周的液氮内储存后TNF α能够分泌 ,其分泌量的变化趋势同储存前。 4 8h组和一周组之间无明显的统计学差异性。结论　转基因细胞Tca8113/TNF α作为“瘤苗”应用时 ,目的基因的表达可初步评价为有效     

Micropush-out bond strengths of gutta-percha versus thermoplastic synthetic polymer-based systems - an ex vivo study.

AIM: To compare the interfacial strength and failure mode of root fillings consisting of different technique-material combinations. METHODOLOGY: Human mandibular premolars (n = 144) instrumented to apical size 40 and .06 taper were divided into 12 experimental groups. The root canals were filled with either gutta-percha (groups 1-6) or Resilon (groups 7-12) core materials combined with AH Plus (groups 1, 4, 7, 10), Ketac-Endo (groups 2, 5, 8, 11) or Epiphany (groups 3, 6, 9, 12) using cold lateral compaction (groups 1-3, groups 7-9) or System B with Obtura II (groups 4-6, groups 10-12). Three serial 1.00 +/- 0.05-mm-thick root slices were prepared and push-out tests on the filling material were performed. Interactions amongst the compaction techniques, core materials and sealers were analysed using a three-way analysis of variance (anova) (P < 0.05). One-way anova and Duncan's Multiple Range tests were used to compare the bond strengths of the 12 groups. Fracture modes of all root slices were evaluated stereomicroscopically at x40 magnification. RESULTS: All the parameters except compaction techniques had significant interactions (P < 0.05). A significant difference was found amongst the groups (P < 0.05). Gutta-percha/Ketac-Endo/cold lateral compaction and gutta-percha/AH Plus/cold lateral compaction groups had the highest micropush-out bond strength values (P < 0.05). The number of overall cohesive failures was significantly more than that of adhesive failures (P < 0.05). CONCLUSIONS: The push-out bond strengths of Resilon/Epiphany combinations were lower than those of gutta-percha/conventional root canal sealer combinations. Core materials and sealers may affect the push-out bond strengths of root canal filling materials.     

有限元法在牙体修复研究领域的应用现状

有限元法是一种与现代计算机技术相联系的理论力学应用分析方法,其建立的模型直观、省时、结论明确,在工程技术领域广泛应用。有限元法在口腔医学应力研究中,也显示出极大的优越性。作为口腔医学研究的重要领域,牙体修复学也是有限元法应用的热点。本文就近年来有限元法在修复洞型、桩核材料、楔状缺损的成因及修复等方面的应用现状做一综述。