人牙本质泊松比的测定

本文报道人牙本质试件在拉车状态下的泊松比。用成年人的新鲜切牙、尖牙、双尖牙和磨牙制作１０个试件进行测试，测得人牙本质的泊松比为０．２８－０．３８，平均值μ＝０．３３，标准差０．０３。同时测得人牙本质的弹性模量为１７．２－２１．４ＧＰａ，Ｅ＝１９．８８ＧＰａ，标准差１．３８ＧＰａ。     

牙本质唾液酸焦磷酸蛋白和牙本质

在牙本质,两个编码I型胶原蛋白基因的突变会导致成骨发育不全。除了胶原蛋白,在牙本质还有一定数量的非胶原蛋白。在牙本质非胶原蛋白编码的基因中,只有牙本质唾液酸焦磷酸蛋白(dentin sialophosphoprotein,DSPP)的突变引起遗传性牙齿畸形。DSPP的突变会引起牙本质发育不全(dentinogenesis imperfecta,DGI)Ⅰ型、Ⅱ型和牙本质发育异常(dentin dysplasia,DD)Ⅱ型。DSPP由成牙质细胞表达并分泌。分泌之后,DSPP由多个细胞外蛋白酶酶切成小片。DSPP被蛋白酶酶切为三个主要部分:牙本质涎蛋白(dentin sialoprotein,DSP),牙本质糖蛋白(dentin glycoprotein,DGP)和牙本质磷蛋白(dentin phosphoprotein,DPP)。本文就这三种蛋白的最新进展进行回顾。     

牙本质发育异常和牙本质发育不全分子遗传学的研究进展

最近,牙本质疾病的进展非常迅速。这些疾病主要分为2类,并带有不同的亚型。一类为牙本质发育异常（dentin dysplasia,DD）Ⅰ型和Ⅱ型,另一类为牙本质发育不全（dentinogenesis imperfecta,DGI）Ⅰ型、Ⅱ型和Ⅲ型。遗传连锁分析证明了DD-Ⅱ、DGI-Ⅱ和DGI-Ⅲ的关键位点位于4号染色体长臂上,这些位点包括了分泌型焦磷酸蛋白（SPP1）、骨唾液酸蛋白（BSP）、细胞外基质磷酸化糖蛋白（MEPE）、牙本质基质蛋白1（DMP1）和牙本质唾液酸焦磷酸蛋白（DSPP）基因。目前,只有DSPP的突变被证实。现将最新进展做一综述。     

牙本质保护膜对牙本质小管的封闭作用**

背景：有临床研究报道牙本质保护膜在用于烤瓷全冠牙体预备后牙本质面的保护处理后,能有效降低基牙敏感度。 目的：体外实验观察牙本质保护膜封闭牙本质小管的效果。 方法：将20颗完好离体人前磨牙分为3组：空白对照组牙本质表面不作任何处理,对照组牙本质表面涂布格鲁玛脱敏剂,实验组牙本质表面涂布牙本质保护膜,在扫描电镜下观察牙本质小管口封闭情况。 结果与结论：扫描式电子显微镜观察显示,实验组牙本质小管口密度和直径均明显低于对照组与空白对照组(P < 0.05),牙本质小管口相对面积明显低于空白对照组(P < 0.01)。表明牙本质保护膜在减小牙本质小管的密度和直径方面的作用优于格鲁玛脱敏剂。     

年龄与位置对牙本质力学性质的影响

目的研究人牙本质弹性模量和硬度随年龄和位置的变化情况。方法采集下颌无龋坏第3磨牙,按照年龄分为青年、中年、老年3组。采用纳米压痕对牙本质切片的多个位置进行力学测试。结果外层和中层牙本质的弹性模量和硬度大于内层牙本质的弹性模量和硬度;随着年龄的增长,各个区域的牙本质弹性模量和硬度都增大。结论牙本质具有梯度力学特性,外层和中层牙本质具有很高的刚度,其抵抗变形的能力要强于内层牙本质。同时,随着年龄增长牙本质弹性模量和硬度增大。     

Gluma脱敏剂对牙本质黏结强度影响的系统评价

BACKGROUND: Desensitization agent is widely used to relieve tooth sensitivity after tooth preparation. However, some components in the desensitization agent for certain affect the dentin bond strength between prosthesis and dentin. Given this, choosing a proper desensitization agent is under discussion. OBJECTIVE: To investigate the influence of Gluma desensitizing agents on bond strength to dentin by Meta-analysis. METHODS: A computer-based retrieval of PubMed, EMbase, EBSCO EDLINE, The chrane Library, ScienceDirect, Web Of Science, OVID, CBMbase, CJFD, CqVip and WanFang databases combined with manual searching was performed for randomized controlled trials or controlled clinical trials about effect of desensitizing agents on dentin bond strength. The retrieval time ranged from the creation date to June 18, 2016, without region and language limits. In accordance with inclusion/exclusion criteria, related data were extracted, and the qualitative and quantitative analysis of the included studies was performed by two researchers independently, and then the Meta-analysis was conducted using RevMan 5.2 software. RESULTS AND CONCLUSION: There was no significant difference in the shear bond strength of self-etching or total-etching adhesive to dentin between two groups, and the same results were found when comparing the shear bond strength of self-etching and total-etching adhesive to dentin. The Gluma had a beneficial effect on the shear bond strength of self-adhesive. These results indicate that when Gluma used as the desensitizing agent, self-adhesive materials are the first choice, and secondly the self-etching or total-etching adhesive materials containing acid or able to dissolve protein crystals are preferred.     

枸橼酸酸蚀牙本质的最佳浓度和时间

背景：虽然目前枸橼酸溶液已被逐渐运用于制作牙本质敏感模型方面的研究,但仍未得出一个有效的统一浓度及酸蚀时间。 目的：观察不同浓度枸橼酸酸蚀牙本质盘不同时间的效果,以获得研究牙本质敏感症的可靠体外实验模型。 方法：选取30颗前磨牙并制作成牙本质盘,经碳化硅水磨砂纸抛光、枸橼酸酸蚀处理,扫描电镜观察牙本质盘表面酸蚀后的形态学特征,测量牙本质小管的直径,比较分析不同浓度枸橼酸溶液(5%,10%,15%)分别酸蚀不同时间(30,60,120,180 s)对牙本质样本表面玷污层的去除效果、开放牙本质小管的能力。 结果与结论：枸橼酸溶液具有较强的酸蚀作用,其去除玷污层的能力随着酸蚀时间延长及溶液浓度的增加而加强。5%枸橼酸溶液酸蚀各时间组、10%和15%枸橼酸溶液酸蚀30 s或60 s时去除玷污层能力有限,仍有牙本质小管受到不同程度的玷污层覆盖;10%、15%浓度组各酸蚀120,180 s均可使表面玷污层去除,暴露牙本质小管。15%枸橼酸酸蚀120,180 s组的牙本质小管直径较10%浓度组大(P < 0.05),而10%枸橼酸酸蚀120,180 s组的牙本质小管直径差异无显著性意义   (P > 0.05)。提示10%枸橼酸溶液酸蚀牙本质样本120 s是去除玷污层,暴露牙本质小管的最佳方法。关键词：牙本质敏感模型;枸橼酸;牙本质;扫描电镜;牙本质小管直径 doi:10.3969/j.issn.1673-8225.2012.16.026     

牙本质发育不全的硬组织研究与进展◆

背景：牙本质发育不全是一种牙本质发育异常的常染色体显性遗传病,目前的研究大多集中在致病基因和临床治疗上,硬组织方面的研究相对较少。 目的：就牙本质发育不全的硬组织研究进展做一综述。 方法：以“牙本质发育不全,表面形态,动物模型,釉牙本质界,牙本质小管”为关键词,应用计算机检索1999/2011 CNKI数据库、PubMed数据库,OVID数据库。 结果与结论：多数学者研究发现牙本质发育不全的釉质结构正常,病变主要表现在釉牙本质界和牙本质。其釉牙本质界大多表现为直线型外观,牙本质结构紊乱,钙化不规则,牙本质小管数目减少,胶原纤维形态和排列异常。这些异常结构的成因尚不清楚,有待深入研究。     

基于PDMS微结构的气道平滑肌舒张药物评测装置

本研究设计并制备了一种基于PDMS微弦结构的细胞力学测量装置.将平滑肌微组织培养在该柔性微型传感器上,通过检测PDMS微结构因微组织牵拉作用而产生的形变,实现了对其收缩力动态的测量.利用临床抗哮喘药物,我们验证了该装置的灵敏度和可靠性.该方法的建立将将有助于未来筛选平滑肌舒张作用药物.     

年龄变化对人牙本质裂纹扩展升阻能力的影响

目的通过有限元数值计算的方法研究年龄变化对牙本质断裂力学行为的影响。方法根据典型的紧凑拉伸试件形式建立有限元模型,采用内聚力模型分别模拟裂纹在年轻和老龄牙本质中稳态扩展的过程,并进行比较。结果老龄牙本质的扩展断裂韧度和断裂韧度趋于恒定时的值分别为0.51、1.19 MPa.m1/2,显著小于年轻牙本质的相应值(7.48、1.71 MPa.m1/2);然而,这两者之间的初始断裂韧度相差比较微小,年轻和老龄牙本质的初始断裂韧度分别为0.51和0.38 MPa.m1/2。结论随着年龄的增长,牙本质抵抗裂纹扩展的能力发生了明显的减弱。基于内聚力模型的数值方法能够很好地预测牙本质等力学性能与年龄相关的生物硬组织材料的裂纹扩展行为。     

Non-invasive assessment of aortic mechanical properties

Echocardiography and sphygmomanometry were used to noninvasively assess the changes in aortic mechanical properties associated with aging. Fifty normal individuals were examined and were divided into three groups: young (<35 years of age), middle-aged (35–55), and old (>55). Experimental measurements indicated that elastic aortic stiffness in the circumferential direction increased with increased age. It was concluded that this was consistent with increased deposition of circumferentially oriented collagen within the media. Associated with increased elastic aortic stiffness in the circumferential direction was a decrease in the ability of the aorta to act as an auxiliary pump. The average work per unit length recovered from aortas of older individuals was only 44% of that recovered from the aortas of individuals in the young group. These studies suggest that increased elastic aortic stiffness results in decreased aortic pumping efficiency and may lead to a compensating increase in blood pressure. The authors would like to acknowledge grant support from the Whitaker Foundation and the National Institutes of Health (GMS 30425). Dr. Tsipouras is the recipient of a Clinical Investigator Award AM-01224 from the NIADDKD. We would also like to thank Dr. John Kostis for use of the echocardiographic equipment in the cardiodynamics unit of the Department of Medicine, Middlesex General Hospital, New Brunswick, New Jersey.     

A novel combinatorial approach for understanding microstructural evolution and its relationship to mechanical properties in metallic biomaterials

The new generation of metallic biomaterials for prosthesis implantation (orthopedic and dental) typically have a Ti base with fully biocompatible alloying additions such as Nb, Ta, Zr, Mo, Fe and Sn. While the binary Ti-Ta and the ternary Ti-Nb-Ta systems are promising, the large composition space afforded by these systems offers tremendous scope in terms of alloy design via optimization of alloy composition and thermomechanical treatment. In the present paper a novel combinatorial approach has been developed for rapidly exploring the microstructural evolution and microstructure-microhardness (or elastic modulus) relationships in these systems. Using directed laser deposition, compositionally graded alloy samples have been fabricated and subsequently heat-treated to affect different microstructures in terms of the volume fraction and distribution of the alpha phase in the beta matrix as a function of composition. Subsequently, composition-specific indentation-based hardness and modulus information has been obtained from these graded samples, and the resulting data have been used to develop relationships between the composition, microstructure and mechanical properties. Such rapid combinatorial assessments can be very useful in optimizing not only the alloy composition but also the desired microstructure for achieving the best combination of properties for specific orthopedic or dental applications.     

The role of heat treatment on microstructure and mechanical properties of Ti-13Zr-13Nb alloy for biomedical load bearing applications

The suitability of heat treated Ti–13Zr–13Nb (TZN) alloy for biomedical load bearing applications has been investigated. Depending upon the heat treatment conditions, the microstructure of TZN alloy mainly consists of α, β or α” martensite phases. In general, for all the deformation and solution treatment temperatures the variation of the hardness and tensile strength with cooling rate is similar. The elastic modulus of TZN alloy decreases with an increase in cooling rate from the solution treatment temperature. Relatively fine α+β microstructure increases the hardness and tensile strength. The presence of martensite and/or retained β in the microstructure decreases the hardness and elastic modulus and increases the ductility substantially whereas higher amount of α phase in the matrix increases the elastic modulus. Decomposition of martensite and retained β into α phase during aging increases the hardness, elastic modulus and tensile strength and decreases the ductility. Among the samples studied, the aged TZN sample, which was deformed and solution treated at 800 °C followed by water quenching, is a promising candidate for the application as implant material.     

Experimental method for determining the 2-dimensional mechanical properties of living human skin

An experimental method for obtaining the 2-dimensional skin tension/extension-ratio characteristics of living human skin is described. This method incorporates a strain-gauged pretension device used to determine the naturally existing tension and deformation fields in a specific skin area and a suction-cup system that applies a homogeneous, plane strain field to the skin at controlled straining rates. A series of experiments conducted to validate the use of the method for obtaining quantitative measures of the mechanical behaviour of skinin vivo is also presented. This method is being used to investigate the variation of mechanical properties with such factors as age, sex, hormonal change, ultraviolet radiation and various disease states.     

Effects of fibre reinforcement on the mechanical properties of brushite cement

In this study the effect of structure and amount of polyglactin fibre incorporation into a brushite forming calcium phosphate cement system and the effect of mechanical compaction on the fibre modified system were investigated. In comparison the effect of resorbable polycaprolactone surface coating of cement specimens was investigated. The results showed that, apart from the mechanical properties of the reinforcing material, the structure of the incorporated fibres, regular or random, is crucial for the resulting flexural strength and modulus of elasticity. Fibre reinforcement could also be combined with mechanical compaction of the cement/fibre composite paste leading to a possible 7-fold increase in flexural strength or an almost 5-fold increase in modulus of elasticity. Reinforcement of the tensile surface of cement grafts may ultimately improve strength where required, especially in conjunction with bone fixation devices.     

Changes in the mechanical properties or rat tail tendon during postnatal ontogenesis

Summary The ultimate tensile strength, elasticity modulus and ultimate elongation of tail tendon in rats aged 1–18 months were measured with an Instron tensile apparatus. An increase in all these parameters was observed during the period of maturation, with a later levelling off of the tensile strength and the ultimate elongation. The value of the elasticity modulus attained a maximum during sexual maturation, and then decreased and stabilized.     

Effects of postcuring and water sorption on the mechanical properties of composite dental restorative materials

Four commercial dental restorative composites with different filler contents, were tested for the effects of postcuring and water sorption on elastic modulus, compressive strength and ultimate strain. Large variations in mechanical properties were seen; water sorption plasticizes the matrix, causing loss of low molecular weight substances.     

Noninvasive assessment of mechanical properties of peripheral arteries

An ultrasound examination was used to noninvasively determine the changes in mechanical properties associated with age for the common carotid, brachial, popliteal, femoral, and tibial arteries. Forty-two normal male subjects, ranging in age from 8 to 60 years of age, were examined. The subjects were placed in one of three age groups: <29 years of age, 29 to 38, and >38. Mechanical properties including percentage variation in diameter, pressure-strain, and circumferential elastic modulus were determined from changes in wall thickness and pulse pressure. Percentage variation in diameter (PVD) was seen to decrease with age for all arteries except the brachial, which remained relatively constant. Pressure-strain (Ep) and circumferential elastic moduli (Eo) were seen to increase with age in all arteries except the brachial, which remained relatively constant. Values of Ep and Eo were normalized into a stiffness index by dividing by the value found for the brachial artery. Stiffness indexes for the common carotid and femoral arteries were observed to increase more rapidly with age than the indexes obtained for the popliteal and tibial arteries. It is proposed that the stiffness index and changes in this parameter that occur with age may be useful in noninvasively assessing the progression of atherosclerosis.     

Effects of crosslinking on the mechanical properties,drug release and cytocompatibility of protein polymers

Recombinant elastin-like protein polymers are increasingly being investigated as component materials of a variety of implantable medical devices. This is chiefly a result of their favorable biological properties and the ability to tailor their physical and mechanical properties. In this report, we explore the potential of modulating the water content, mechanical properties, and drug release profiles of protein films through the selection of different crosslinking schemes and processing strategies. We find that the selection of crosslinking scheme and processing strategy has a significant influence on all aspects of protein polymer films. Significantly, utilization of a confined, fixed volume, as well as vapor-phase crosslinking strategies, decreased protein polymer equilibrium water content. Specifically, as compared to uncrosslinked protein gels, water content was reduced for genipin (15.5%), glutaraldehyde (GTA, 24.5%), GTA vapor crosslinking (31.6%), disulfide (SS, 18.2%) and SS vapor crosslinking (25.5%) (P < 0.05). Distinct crosslinking strategies modulated protein polymer stiffness, strain at failure and ultimate tensile strength (UTS). In all cases, vapor-phase crosslinking produced the stiffest films with the highest UTS. Moreover, both confined, fixed volume and vapor-phase approaches influenced drug delivery rates, resulting in decreased initial drug burst and release rates as compared to solution phase crosslinking. Tailored crosslinking strategies provide an important option for modulating the physical, mechanical and drug delivery properties of protein polymers.     

介入治疗用支架力学性能的研究方法综述

介入治疗用支架是治疗管腔梗阻的新兴医疗器械,植入管腔狭窄部位后起支撑管腔和提高管腔畅通性的作用。理想的支架必须具备可靠的力学性能,而目前对支架力学性能的研究方法有理论分析、数值模拟和实验测试3种。对测定支架力学性能的各种分析方法及局限性进行详细地阐述和总结,并对支架后期的研究进行展望。