The change in retentive force of magnetic attachment by abrasion

Magnets are frequently applied to removable dentures as retentive attachments. A magnet-retained removable overdenture might be slightly shifted from side to side by eccentric movement in the mouth, and the surface of magnetic attachment may be worn as a result. However, the relationship between the retentive force of magnetic attachment and its surface abrasion has not been reported. The purpose of this research is to investigate this relationship. Ten Mgfit DX 400 magnetic attachments for natural tooth roots were used for this experiment. The magnetic attachments were embedded in autopolymerizing acrylic resin, and ten pairs of specimens were fabricated. A 5-mm repeated gliding motion was applied on each pair of specimens until 30 000, 50 000, or 90 000 cycles had been achieved. The abrasion machine was under 5 kg loading, and the slide speed was 60 times/min. The retentive force of magnetic attachment was measured with a tension gauge at (1) before gliding; (2) after 30 000 gliding cycles; (3)after 50 000 gliding cycles; or (4) after 90 000 gliding cycles. The average change of retentive force of ten magnetic attachments after 30 000, 50 000, and 90 000 gliding cycles was 0.016 N, 0.003 N, and -0.008 N, respectively. The change was statistically analyzed using a paired-sample t test, which showed that the number of gliding cycles did not affect the retentive force of magnetic attachment significantly. The surface of magnetic attachment after gliding was observed by a microscope, and the abrasion of this attachment surface is clearly seen.     

稀土氧化物着色牙色四方多晶氧化锆陶瓷的烧结性能

目的 探讨添加微量稀土氧化物对以稀土氧化物作为着色剂制备的与天然牙颜色匹配的牙色四方多晶氧化锆陶瓷的烧结性能的影响。方法 采用内着色法制备6组与天然牙色匹配的四方多晶氧化锆陶瓷,通过阿基米德定律测试其烧结致密性,通过扫描电镜观察其显微结构,X射线衍射测试其相变特征。结果 6组与天然牙色匹配的四方多晶氧化锆陶瓷的相对密度达到98%;电镜观察可见氧化锆的晶粒完整、晶界清楚、晶粒大小均匀,100～300 nm,未见异常生长的晶粒,晶界处未见到第二相的杂质相;XRD图谱显示,6种牙色四方多晶氧化锆陶瓷的晶相组成均以四方相氧化锆的特征峰为主,未见明显的杂质峰。结论 微量稀土氧化物的添加对以稀土氧化物作为着色剂制备的与天然牙颜色匹配的牙色四方多晶氧化锆陶瓷的烧结性能的影响较小,最终烧结体的主晶相仍以四方相为主。     

稀土元素在口腔医学领域应用研究进展

稀土元素是一组金属元素的简称,包括镧系元素及化学性质与其相近的钪和钇2种元素。稀土元素具有拮抗内毒素、抑制炎症因子分泌、防龋、干预和调控骨的形成与再造、抗凝血、抑癌等生物学作用,已广泛应用于生物医学领域。本文主要对稀土元素在口腔医学领域内的应用研究进展做一综述。     

Methodological Aspects of Obtaining and Characterizing Composites Based on Biogenic Diatomaceous Silica and Epoxy Resins

Diatomaceous earth are sediments of unicellular algal skeletons with a well-defined hierarchical structure. Despite many tests conducted on systems using diatomaceous earth and epoxy resins, we can find many differences in the methods of acquisition and characteristics of the composite, which may considerably affect the results. In our study, we have conducted tests to verify the impact of the method of obtaining samples and the degassing of the composite on its mechanical properties and standard deviation. The samples were cast in glass moulds and silicone moulds and then subjected to testing for their mechanical and functional properties, imaging with the use of an optical microscope and a scanning electron microscope. The tests have shown that, for samples cast in glass moulds, there is no heterogeneity within the area of the tested sample, as in the case of samples cast in silicone moulds. Silicone moulds allow for quite effective self-degassing of the resin due to the large area-to-mass ratio, and the small remaining air vesicles have a limited effect on the mechanical properties of the samples. The filler used also played a significant role. For systems containing base and rinsed diatomite, it is clear that the degassing of mixtures increases the tensile strength. For treated diatomite, the elongation at break grew along with increasing filler concentration, while for base diatomite, the improvement was observed for flexural strength and impact strength. A non-modified epoxy resin shows a tensile strength at 19.91 MPa (silicone mould cast). At the same time, the degassed, glass mould-cast systems containing 12% of base and rinsed diatoms showed a tensile strength of 27.4 MPa and 44.7 MPa, respectively. We have also observed that the higher the filler concentration, the higher were the tensile strength values, which for the rinsed diatoms reached over 55.1 MPa and for the base diatoms were maximum of 43.8 MPa. The tests, therefore, constitute a set of guidelines and recommendations for testing with the use of fillers showing an extended inner structure.     

稀土粉尘作业工人接触剂量与X线胸片改变关系探讨

本文根据剂量-反应关系,对有系列X线胸片的379例轻稀土粉尘作业工人进行了累积接尘量计算,并用寿命表方法分析了接尘量与胸片O~+累计发生率的关系。结果表明,按工人工作30年计,O~+发生率在1%时,稀土粉尘浓度为3.3mg/m~3(几何均值),或4.3mg/m~3(算术均值)。     

稀土对小鼠卵母细胞成熟和孤雌活化的影响

目的　探讨稀土对小鼠卵母细胞发育、成熟和孤雌活化的影响 ,以评价稀土的生殖毒性。方法　以不同剂量的混合稀土连续 10d腹腔注射 ,超数排卵处理后收集小鼠卵母细胞 ,氯化锶孤雌活化处理 ,倒置显微镜下观察统计。结果　 4 0 0mg/ (kg·d)以上的稀土处理对超排卵数、活卵数、成熟卵数和孤雌活化率均存在不同程度的影响。 结论　一定剂量的稀土对小鼠卵母细胞发育、成熟和孤雌活化具有明显抑制作用 ,提示稀土可能对动物和人的生殖细胞发育和受精等产生毒性。     

混合稀土对恒河猴的急性毒性研究

本文研究了混合稀土经消化道和静脉注射对恒河猴的急性毒性作用。结果表明,混合稀土硝酸盐灌胃可引起动物呕吐,半数有效量为68.1mg/kg。500mg/kg/d掺入饲料喂饲可使动物拒食和大便硬结。静脉注射混合稀土可产生溶血(急性阈浓度为2mg/kg)、抗凝作用(阈浓度为1mg/kg)剂量达20mg/kg时,具有肝、肾损害及影响钙、磷代谢。     

儿童稀土暴露的健康效应研究

目的　探讨稀土暴露与儿童健康的关系。方法　选择与稀土效应有关的生长发育水平、免疫功能以及智能发育作为儿童稀土暴露健康效应的指标。在江西省某稀土矿区和对照区对 7～ 10岁儿童进行生长发育有关指标测量。采用免疫消浊比色法、化学免疫发光法、流式细胞仪技术对儿童血清中IgA、IgG、IgM和补体C3、C4、IgE以及血中淋巴细胞亚群CD+3 、CD+4 、CD+8、CD+4 CD+8及NK细胞进行测定 ;采用绘人智能法对儿童进行智商测定 ;并采用ELAN - 5 0 0 0型号的电感藕合等离子体质谱仪对儿童进行血中稀土元素总量和分量测定 ,同时用简单回归、多元逐步回归等方法分析稀土暴露情况与儿童健康之间的关系。结果　儿童血样中 15种稀土元素均可检出 ,且稀土暴露区儿童血稀土总含量 (2 18± 1 0 8)ng g ,比对照组 (1 2 6± 0 35 )ng g高出 1 73倍 (P <0 0 1)。稀土暴露组儿童肺活量、血压较对照组低 ;稀土暴露区儿童体液免疫有所改变 ,稀土暴露组IgM比对照组显著降低 (P <0 0 5 ) ,儿童T淋巴细胞亚群测定结果显示 ,CD+3 、CD+8、CD+4 CD+8有明显改变 (P <0 0 5 ) ,稀土暴露组儿童血中CD+3 和CD+8比对照组CD+3 、CD+8明显降低 ,而CD+4 CD+8比值则有所升高。稀土暴露区儿童智商得分显著低于对照组儿童 ;高智能儿童比     

新型含硫酰基吡唑啉酮席夫碱稀土配合物的合成与结构表征

目的 :含硫席夫碱配合物的研究。方法 :在无水溶剂中 ,通过溶解、回流合成了未见报道的吡唑啉酮席夫碱两种稀土金属配合物。对所合成的配体和配合物进行了元素分析、电子光谱、红外光谱、差热—热重 ,并辅电导测定 ,从而初步确定了它们的分子结构式。结果 :通过分析可以基本得到稀土配合物的分子式和结构 :ML3(NO- 3) 3.3H2 O。结论 :得到所合成配合物。