活髓牙修复的实验室探讨

龋病修复体的长寿耐用不仅要求洞型兼顾抗力型和固位型,还要考虑修复体对牙体组织的力学影响。本实验模拟活髓牙下颌第一磨牙颌面Ｉ类洞采用三维有限元法建立数值模型,用八节点等参三维实体单元进行离散,利用ＳＡＰ８４（Ｖ４．２）程序。计算并作一系列力学分析寻求活髓牙修复时垫底材料与修复材料最佳厚度比的力学模型。实验结果表明应力曲线的峰值主要出现在不同材料交界面附近,因此该处的修复应尽量采用圆弧过度。另外基底材     

两种较新的复合型材料修复楔状缺损的临床疗效比较

目的:比较两种较新型的复合材料(光固化复合树脂材料和树脂加强型玻璃离子水门汀材料)修复楔状缺损的临床疗效.方法:对210例楔状缺损患牙,分别用树脂加强型玻璃离子水门汀材料和光固化复合树脂材料应用修复,观察1～2年的修复效果.结果:两种材料修复1年成功率都高于85％,树脂加强型玻璃离子水门汀材料修复楔状缺损2年成功率(82.9％)略高于光固化复合树脂(77.1％).结论:两种新型材料都是修复楔状缺损是口腔门诊值得推荐的方法,其中树脂加强型玻璃离子水门汀材料长期效果略好一些.     

两种树脂修复上颌切牙缺损的疗效分析

目的:对比分析需酸蚀和非酸蚀的树脂材料修复上颌切牙缺损的疗效。方法:门诊选择136颗缺损的上颌切牙分别用Dyract复合体(非酸蚀组)和普通光固化树脂(酸蚀组)充填治疗,随访1a,分析临床效果。结果:两组树脂固位效果无显著性差异(p>0.05),但在深龋充填过程中对牙髓刺激性两组间有显著性差异(p<0.05),即非酸蚀组显著小于酸蚀组。结论:非酸蚀型树脂材料具有对牙髓刺激小、粘接性强、操作方便等优点,更适合临床应用。     

纤维桩树脂核用于老年残根残冠修复的效果及对生活质量的影响

目的:探讨老年残根残冠应用纤维桩树脂核修复的临床效果及对病人生活质量的影响。方法:抽选我院行纤维桩树脂核修复的79例(86颗)老年残根残冠患者,对其进行3年随访,观察总体及不同牙位修复成功率和修复前、后生活质量的变化。结果:修复后进行3年随访,86颗残根残冠修复总成功率为95.3%,不同牙位修复成功率无显著差异(P0.05),均在94%以上,86颗牙失败4颗(其中2颗并发牙周炎、2颗牙纤维桩脱落,均未出现牙桩折断);修复后患者生活质量总分及各维度评分均明显优于修复前(P0.05)。结论:纤维桩树脂核是一种极为理想的残冠残根修复材料,能显著提高老年患者术后的生活质量,值得临床推广。     

非线性光学偶氮染料SiO2/（TiO2）杂化材料的合成初探

近年来,随着科学技术的发展,单一性质的材料已不能满足人们的需求,无机-有机杂化材料越来越凸显出它本身的优势,所以非线性光学偶氮染料SiO2/(TiO2)杂化材料的合成问题尤为重要。溶胶-凝胶法是制备非线性偶氮染料杂化材料的方法之一,与其他制备方法相比,溶胶-凝胶法具有反应条件温和、样品均匀性好、光学透明性高、兼具有机-无机材料的优势等优点。本文分别研究了pH、乙二醇和浓硫酸的比例对前驱体非线性光学有机染料的影响,非线性有机染料、四乙氧基硅烷(TEOS)/钛酸正丁酯(TBT)、水三者的比例对终产物的影响。还利用红外图谱和X-射线的方法,推断产物的结构,从而确定最佳的反应条件。结果表明重氮化反应的pH值应<3,为强酸性,联偶反应中pH值应控制在7~8的弱碱性条件。乙二醇和浓硫酸比例在6:1时产率最佳,水钛和水硅比在4:1时,杂化材料的质量最好。     

男性青少年脂肪组织分布与相对骨龄的关系——Fels追踪研究

本文对Fels追踪研究中8—17岁男性青少年的相对骨龄与脂肪分布类型之间的关系做了分析。按体重/身高~2调整后,如用每个年龄的三种皮褶厚度(ST)指数的均值表示脂肪分布类型的话,8—12岁时,脂肪分布类型呈外周型分布,但13岁后开始朝向心型发展呈全身性分布。如用肩胛下ST/(肩胛下ST+肱三头肌区ST)的比例表示的话,那么14—17岁时,相对骨龄早者(简称早组)与相对骨龄晚者(简称晚组)相比,前者有较明显的向心型分布倾向。13—14岁时,早组的上述比值的年增长明显大于晚组。但是,按脂肪分布类型指数等级的基线和体重/身高~2调整之后,7、11或14岁时的相对骨龄不能预测17岁时的脂肪分布类型指数的等级。所以,我们可以得出这样的结论:如按本文的比例指数加以定量的话,脂肪分布类型与男性青少年的相对骨龄只有微弱的关系。他们的脂肪分布类型可能与其它成熟指征(如男性青春期的第二性征)有明显的关系。     

Embrace树脂和LuxaCoreZ-Dual树脂在纤维桩全冠修复牙冠严重缺损的效果对比

目的:比较Embrace树脂和Luxa Core Z-Dual树脂在纤维桩全冠修复牙冠严重缺损的效果。方法:将116颗牙冠严重缺损的患牙行根管治疗后随机分为两组,A组60颗(前牙39颗,后牙21颗)采用Embrace树脂及纤维桩全冠修复。B组56颗(前牙33颗,后牙23颗)采用Luxa Core Z-Dual树脂及纤维全冠修复,比较两组患牙的修复效果。结果:对所有患者随访3-12月,A组58颗牙修复体完好,失败2颗,成功率为96.66%,其中前牙失败2颗,成功率为94.87%,而后牙成功率为100%;B组54颗牙修复体完好,2颗失败,成功率为96.43%,其中前牙失败2颗,成功率为93.94%,而后牙成功率为100%,两组患牙修复体成功率比较差异无统计学意义(P0.05),4颗修复体的失败均因纤维桩松动脱落所致。结论:Embrace树脂和Luxa Core Z-Dual树脂在纤维桩全冠修复牙冠严重缺损时均具有良好的临床疗效,但Embrace树脂临床操作上更简便。     

一种新型瓷嵌体修复用树脂粘接材料生物安全性评价

目的:初步评价一种新型瓷嵌体修复用树脂粘接材料的生物安全性。方法:按照国标GB16886.5-1997,医药行业标准YY/T0268-2001、YY/T0279-1995、以及YY/T 0244-1996所规定的方法对本院材料科新研制的复合树脂粘接材料的生物安全性进行评价,内容包括短期急性全身毒性试验,粘膜刺激实验,细胞毒性试验。结果:此种新型瓷嵌体修复用树脂粘接材料无细胞毒性,无短期全身毒性,对口腔黏膜无刺激。结论:此种新型瓷嵌体修复用树脂粘接材料具有良好的生物安全性,可以进行进一步安全性检测。     

聚合物脂质纳米球的制备优化

目的:制备粒径均一且稳定、载药率和包埋率较高的聚合物脂质纳米球。方法:将HSPC(氢化大豆卵磷脂)与PLGA(聚乳酸-羟基乙酸共聚物)两种材料结合,利用超声复乳法制备聚合物脂质纳米球,采用响应面法优化最佳制备工艺;以HSPC(氢化大豆卵磷脂)与PLGA(聚乳酸-羟基乙酸共聚物)的比例、PVA浓度、超声功率为条件优化制备参数,以粒径为响应值。结果:优化后的最佳工艺参数为:HSPC与PLGA的比例为1:10,PVA浓度为0.66%,超声功率为51.34%(205.36 W)。结论:按最优工艺制备出的聚合物脂质纳米粒的粒径为230 nm左右,多分散系数(PDI)值为0.057,与预测值偏差较小,且粒径分布均一,可作为蛋白及多肽类药物的递送载体。     

钉与桩在后牙冠缺损修复中的应用

牙科学所关注的一个重要问题是关于修复性材料与牙齿结构之间的连接。通过钉与桩等中间体,连接牙齿与修复体是基本固位原理的应用形式之一。钉(pin)是能正好钻入离开牙髓腔的牙本质槽内的一种小杆状物。桩(dowel)是指一种圆柱或圆锥体,能进入预备好的牙根管内固位,它与术语post(桩)或根管桩是同义的。在牙冠大部缺损修复时,借助桩紧密地连接冠与根两部分,而桩通常是一种垂直的柱状体,用以在离开其基底一段距离的地方负重。钉与桩在后牙大面积缺损修复中的合理应用,具有极其重要的临床意义。     

3 种不同弹性模量钛合金股骨假体在羊股骨置换模型中应力分布的三维 有限元分析

目的:通过三维有限元分析方法来观察并比较3种不同弹性模量钛合金股骨假体在羊股骨置换模型中von-Mises应力分布的情况。方法:采用64排螺旋CT对一健康成年羊的下肢股骨进行全长的CT扫描,扫描层厚为0.5 mm,扫描所得的数据存储为DICOM文件。将得到的DICOM文件导入到CT图像分析软件Mimics 10.0,然后利用Mimics 10.0软件来生成股骨的骨质点云数据,再将生成的骨质点云数据导入到Simpleware分析软件,通过机械加工反求中的复杂曲面造型技术建立起精确的三维实体模型。对三维实体模型进行网格划分,确定了髓腔的形状,并根据羊下肢股骨髓腔的形状设计了作者实验用的羊股骨假体模型,然后在ANSYS 12.1软件中进行网格划分。给予加载缓慢行走载荷以及扭转载荷,分析并比较羊股骨以及3种不同弹性模量钛合金股骨假体在股骨置换模型中von-Mises应力分布的情况。结果:在缓慢行走载荷以及扭转载荷条件下,3种不同弹性模量钛合金股骨假体von-Mises应力分布变化趋势一致,假体的柄颈结合部以及假体柄上1/3为应力集中区域。3种不同弹性模量的最大应力集中点均位于柄颈结合部,60 GPa弹性模量的股骨假体植入后假体的最大应力最小(37.8 MPa、29.1 MPa),股骨的最大应力最大(12.6 MPa、24.5 MPa);80 GPa的次之,假体的最大应力(38.4 MPa、33.4 MPa),股骨的最大应力(12.5 MPa、24.5 MPa);110 GPa的股骨假体植入后假体的最大应力最大(38.9 MPa、38.1 MPa),股骨的最大应力最小(12.3 MPa、24.5 MPa)。60 GPa弹性模量的股骨假体植入后的假体最大位移和相对位移均最小(缓慢行走载荷下假体最大位移为0.551 mm、相对位移为0.008 mm,扭转载荷下假体最大位移为0.730 mm、相对位移为0.011 mm)。结论:较低弹性模量的钛合金股骨假体(60 GPa)由于其弹性模量更接近于骨组织的弹性模量,股骨假体与股骨间的"应力遮挡"效应较小,更有利于应力在股骨假体及股骨间的传递,增加了股骨假体的早期稳定性,延长了其临床寿命。     

Collagen fibril diameters increase and fibril densities decrease in skin subjected to repetitive compressive and shear stresses

Understanding microstructural changes that occur in skin subjected to repetitive mechanical stress is crucial towards the development of therapies to enhance skin adaptation and load tolerance in patients at risk of skin breakdown (e.g. prosthesis users, wheelchair users). To determine if collagen fibril diameter, collagen fibril density, dermal thickness, epidermal thickness, basement membrane length, and dermal cell density changed in response to repetitive stress application, skin subjected to moderate cyclic compressive and shear stresses for 1 h/d, 5 d/week, for 4 week was compared with skin from an unstressed contralateral control. The lateral aspects of the hind limbs of 12 Landrace/Yorkshire pigs were used. Skin from under the stressed site and a contralateral control site was processed for electron microscopy and light microscopy analysis. Electron microscopy results demonstrated significant (p<0.01) increases in collagen fibril diameter of 15.9%, 22.4%, and 22.9% for the upper, mid, and lower layers of the dermis, respectively, for the stressed skin compared with the control skin. Collagen fibril density (fibrils/unit cross-sectional area) decreased significantly for stressed vs. control by 19.8%, 29.2%, and 31.8% for the upper, mid, and lower layers, respectively. Light microscopy results demonstrated trends of a decrease in dermal thickness and an increase in cell density for stressed vs. control samples, but the differences were not significant. Differences in epidermal thickness and basement membrane length were not significant. These results demonstrate that quantifiable changes occur in collagen fibril architecture but not in the gross tissue morphology following in vivo cyclic loading of pig skin.     

A numerical analysis of the backflow between the leaflets of a St Jude Medical cardiac valve prosthesis

Clinically significant, unexplained hemolysis has been reported to occur in St Jude Medical (SJM) cardiac valve prostheses. The leakage phase of backflow is identified as having the most hemolytic potential, when compared with the other phases of the cardiac cycle. A two-dimensional, laminar, constant fluid property finite element analysis (FEA) is used to calculate the peak shear stress obtained in the flow through the narrow slit formed by the closed leaflets of an idealized size 29 mm (tissue annulus diameter) SJM cardiac valve prosthesis, during the leakage phase of backflow. The flow geometry was such that the simple laminar flow theory (SLFT) could be used to model the flow through the region of peak shear stresses with reasonable accuracy. The SLFT predicts that the maximum shear stress depends upon the thickness of the clearance space and the average velocity through that space. These results suggest that the magnitude of the peak shear stress is of the order of 700-1000 Pa for a duration of the order of 0.5-0.4 ms for pressure drops across the valve of 150-300 torr. This suggests that hemolysis is possible for certain unfortunate combinations of clearances and pressure conditions. However, further research is needed before this flow phenomenon can be associated with the reported clinical hemolysis.     

Three-dimensional finite element analysis of the composite and compomer onlays in primary molars

Resin onlay restoration is an esthetic alternative technique used for restoring extensively damaged primary molars. Understanding the behavior of materials under repeated functional stress and how the stress is transmitted to the remaining tooth structure is important. The aim of this study was to compare stresses in primary molars restored with indirect composite and compomer onlay. 3D frame models of the right mandibular and maxillary primary molars and the alveolar bone were created using computerized tomography images of a six-year-old girl. The enamel and dentine layers above the cement layer were unified to generate onlay restoration, and composite and compomer were used as restorative materials. The vertical occlusal load (100?N) was applied to the teeth in the occlusal contact areas. The von Mises stress distributions and normal stress distributions of the y-axis (parallel to the long axis of tooth) were evaluated. The occlusal stress is transmitted to the cervical part of healthy teeth by spreading it through the enamel layer. The composite and compomer restorative materials exhibited similar stress distribution patterns. An indirect technique creates a structure similar to the original morphological form, and it allows restorations to distribute high occlusal stresses and to minimize possible breakages.     

Analysis of a femoral hip prosthesis designed to reduce stress shielding

The natural stress distribution in the femur is significantly altered after total hip arthroplasty (THA). When an implant is introduced, it will carry a portion of the load, causing a reduction of stress in some regions of the remaining bone. This phenomenon is commonly known as stress shielding. In response to the changed mechanical environment the shielded bone will remodel according to Wolff's law, resulting in a loss of bone mass through the biological process called resorption. Resorption can, in turn, cause or contribute to loosening of the prosthesis. The problem is particularly common among younger THA recipients. This study explores the hypothesis that through redesign, a total hip prosthesis can be developed to substantially reduce stress shielding. First, we describe the development of a new femoral hip prosthesis designed to alleviate this problem through a new geometry and system of proximal fixation. A numerical comparison with a conventional intramedullary prosthesis as well as another proximally fixed prosthesis, recently developed by Munting and Verhelpen (1995. Journal of Biomechanics 28(8), 949–961) is presented. The results show that the new design produces a more physiological stress state in the proximal femur.     

Design parameters dependences on contact stress distribution in gait and jogging phases after total hip arthroplasty

We have developed a mathematical model to calculate the contact stress distribution in total hip arthroplasty (THA) prosthesis between the articulating surfaces. The model uses the clearance between bearing surfaces as well as the inclination and thickness of the Ultra High Molecular Weight Poly-Ethylene (UHMWPE) cup to achieve this. We have used this mathematical model to contrast the maximal force during normal gait and during jogging. This is based on the assumption that the contact stress is proportional to the radial deformation of the cup. The results show that the magnitude of the maximal contact stress remains constant for inclination values in the range of [0-35 degrees ] and increase significantly with the cup clearance and liner thickness for inclination values in the range of [35-65 degrees ]. A major use for this model would be the calculation of spatial contact stress distribution during normal gait or jogging for different couples of bearing surfaces.     

Topological optimization in hip prosthesis design

With particular interest on total hip arthroplasty (THA), optimization of orthopedic prostheses is employed in this work to minimize the probability of implant failure or maximize prosthesis reliability. This goal is often identified with the reduction of stress concentrations at the interface between bone and these devices. However, aseptic loosening of the implant is mainly influenced by bone resorption phenomena revealed in some regions of the femur when a prosthesis is introduced. As a consequence, bone resorption appears due to stress shielding, that is to say the decrease of the stress level in the implanted femur caused by the significant load carrying of the prosthesis due to its higher stiffness. A maximum stiffness topological optimization-based (TO) strategy is utilized for non-linear static finite element (FE) analyses of the femur–implant assembly, with the goal of reducing stress shielding in the femur and to furnish guidelines for re-designing hip prostheses. This is accomplished by employing an extreme accuracy for both the three-dimensional reconstruction of the femur geometry and the material properties maps assigned as explicit functions of the local densities.     

Ontogenesis of glomerular basement membrane: structural and functional properties

Protein A-gold immunocytochemistry was applied in combination with morphometrical approaches to reveal the alpha 1(IV), alpha 2(IV), and alpha 3(IV) chains of type IV collagen as well as entactin on renal basement membranes, particularly on the glomerular one, during maturation. The results have indicated that a heterogeneity between renal basement membranes appears during the maturation process. In the glomerulus at the capillary loop stage, both the epithelial and endothelial cell basement membranes were labeled for the alpha 1(IV) and alpha 2(IV) chains of type IV collagen and entactin. After fusion, both proteins were present on the entire thickness of the typical glomerular basement membrane. At later stages, the labeling for alpha 1(IV) and alpha 2(IV) chains of type IV collagen decreased and drifted towards the endothelial side, whereas the labeling for the alpha 3(IV) chain increased and remained centrally located. Entactin remained on the entire thickness of the basement membrane during maturation and in adult stage. The distribution of endogenous serum albumin in the glomerular wall was studied during maturation, as a reference for the functional properties of the glomerular basement membrane. This distribution, dispersed through the entire thickness of the basement membrane at early stages, shifted towards the endothelial side of the lamina densa with maturation, demonstrating a progressive acquisition of the permselectivity. These results demonstrate that modifications in the content and organization of the different constituents of basement membranes occur with maturation and are required for the establishment of the filtration properties of the glomerular basement membrane.     

Stress distribution on the cusps of a polyurethane trileaflet heart valve prosthesis in the closed position.

In this paper, a finite element analysis of the stress distribution on the cusps of a polyurethane trileaflet heart valve prosthesis in the closed position is presented. The geometry of the valve was modified from a relationship proposed by Ghista and Reul (J. Biomechanics 10, 313-324, 1977). The effects of variations in stent height, leaflet thickness and coaptation area on the stress distribution were also analyzed. Analyses were performed with both rigid and flexible stents for the trileaflet valve in order to delineate the effect of stent flexibility on the leaflet stress distribution. The results showed that regions of stress concentration were present near the commissural attachment similar to those predicted with the bioprostheses. The stresses on the leaflets were reduced by increasing the stent height with both rigid and flexible stents. Selectively increasing the leaflet thickness near the commissures and also increasing the coaptation area did not prove to reduce the leaflet stresses when the stent flexibility was taken into account. The possible effect of high stresses on the structural integrity of polyurethane leaflets and its relationship with calcification is yet to be investigated.     

Basement Membrane Formation in Transfilter Tooth Culture and Its Relation to Odontoblast Differentiation

The mesenchymal cells of the developing tooth differentiate into odontoblasts as a result of an epithelio-mesenchymal interaction. Odontoblast differentiation was studied in vitro by cultivating dental mesenchyme and epithelium with interposed filters. Separation of the two components by enzyme treatment resulted in removal of the basement membrane. When the epithelium was grown alone, or transfilter from killed lens capsule, the basement membrane was not restored. Transfilter cultivation with dental mesenchyme resulted in basement membrane formation, but only if the filter pores allowed penetration of cytoplasmic processes. Hence, a close association between the epithelial and the mesenchymal cells seems to be a prerequisite for the restoration of the basement membrane. Differentiation of odontoblasts took place only in explants in which a basement membrane was formed. Differentiation did not occur when contact of the mesenchymal cells with the basement membrane was prevented by small pore size filters. Further experiments demonstrating an intact basement membrane suggested that membrane contacts between the epithelial and the mesenchymal cells are not needed for odontoblast differentiation. Hence, we suggest that differentiation of odontoblasts is triggered via contact of the mesenchymal cells with the basement membrane.