Cementogenesis is inhibited under a mechanical static compressive force via Piezo1

Objective:To investigate whether Piezo1, a mechanotransduction gene mediates the cementogenic activity of cementoblasts under a static mechanical compressive force.Materials and Methods:Murine cementoblasts (OCCM-30) were exposed to a 2.0 g/cm² static compressive force for 3, 6, 12, and 24 hours. Then the expression profile of Piezo1 and the cementogenic activity markers osteoprotegerin (Opg), osteopontin (Opn), osteocalcin (Oc), and protein tyrosine phosphataselike member A (Ptpla) were analyzed. Opg, Opn, Oc, and Ptpla expression was further measured after using siRNA to knock down Piezo1. Real-time PCR, Western blot, and cell proliferation assays were performed according to standard procedures.Results:After mechanical stimulation, cell morphology and proliferation did not change significantly. The expression of Piezo1, Opg, Opn, Oc, and Ptpla was significantly decreased, with a high positive correlation between Opg and Piezo1 expression. After Piezo1 knockdown, the expression of Opg, Opn, Oc, and Ptpla was further decreased under mechanical stimulation.Conclusions:Cementogenic activity was inhibited in OCCM-30 cells under static mechanical force, a process that was partially mediated by the decrease of Piezo1. This study provides a new viewpoint of the pathogenesis mechanism of orthodontically induced root resorption and repair.     

Comparison of compressive strength between three different plates for mandibular angle fractures fixation

The present study aims to compare three types of internal fixation for fractures of the mandibular angle. Mechanical testing was performed on replicas of polyurethane hemimandibles sectioned at the angle region to simulate a fracture and fixed with three different hardwares. Fixation devices enrolled on this survey included the grid plates with and without an intermediate bar and the method described by Champy and colleagues in 1978 and the sample consisted of 10 hemimandibles for each group. Vertical loadings were applied on each hemimandible and recorded after a vertical displacement of 3 and 5 mm. Statistical analysis was made by means of the variance analysis (ANOVA) and the Duncan test with a significance level of 5%.The Champy technique showed a statistically significant increased resistance when compared to the grid plates after vertical displacements of 3 and 5 mm. The results of this survey suggest that the Champy technique, when compared to the grid plate positioned at the middle of the mandibular bone (placement site selected for this study), is more resistant than the grid plate and that the inclusion or not of an intermediate bar to the grid plates does not improve its resistance after linear vertical loadings.     

缺氧与加力在正畸骨吸收作用中的细胞学研究

目的 观察缺氧对正畸压力侧破骨细胞形成的影响,探讨缺氧、加力在正畸骨改建中各自所起的作用,并分析其在破骨细胞形成过程中的相互作用关系.方法 建立人牙周膜细胞与外周血单个核细胞接触式共培养模型,模拟正畸缺氧、加力、缺氧+加力,不同条件作用1、3、6h后培养3d,TRAP染色检测破骨样细胞的形成.Reahime PCR检测骨改建相关因子HIF-1α 、IL-1β、RANKL、OPGmRNA的表达并计算RANKL/OPG比值.结果 TRAP染色阳性细胞在缺氧+加力组各个处理时间段都有出现,缺氧组则在处理3、6h中出现,加力组仅在处理6h中出现,且缺氧+加力组的阳性细胞数目均大于单独缺氧、加力组.HIF-1α、IL-1β、RANKL、OPGmRNA的表达及RANKL/OPG比值都呈现出缺氧+加力组均大于单纯缺氧、加力组.结论 缺氧和加力分别可以诱导与人牙周膜细胞共培养的单个核细胞向破骨细胞分化,缺氧和加力相互协同、共同促进正畸牙齿移动过程中骨吸收的发生.     

髁突手术对其压缩力学性能及骨密度的影响

目的 探讨不同术式后髁突力学性能的变化及与材料特性之间的关系。方法 采用压缩力学性能测试技术和双能Ｘ线吸收法,定量分析１２例正常、６例髁突高位切削术及６侧关节重建术的成年杂种犬髁突的压缩力学性能和骨矿含量。结果 髁突的载荷与位称呈非线性关系。其弹性极限负荷及位移、最大负荷及位移以正常组为最高,而刚度及骨矿含量则以切削组为最高,减径组各项指标均最低。３组髁突弹性极限负荷、最大负荷及刚度与骨密度之间均     

正畸移动牙齿牙周膜细胞ERK通路的表达变化研究

目的探讨正畸牙齿移动牙周组织改建中细胞外信号调节激酶(ERK)通路调节的分子机制。方法体外培养因阻生或正畸需要拔除的牙齿无菌条件下刮取根中1/3的牙周膜组织,采用组织块法进行原代培养,所培养的细胞经免疫细胞化学检测Vimentin,Ck(pan)。接种塑料培养板,细胞加力0、1、6、12、24、48 h后收集细胞。Western Blot检测pERK蛋白表达。结果原代人牙周膜成纤维细胞(HPDLCs)组织块培养细胞生长缓慢,传代后细胞生长旺盛,细胞形态为纺锤形或成纤维样,胞浆透明,状态良好。Vimentin染色呈阳性,Ck(pan)染色呈阴性。加力后细胞多呈长梭形,胞浆透亮均匀,排列整齐。细胞加力后pERK在1 h无明显变化,pERK表达水平随加力作用时间延长而增高,组间比较差异有统计学意义(P<0.01),12 h后pERK的蛋白表达水平下降。结论ERK在一定压力下,参与了机械力在HPDLCs的信号转导过程,其磷酸化程度随着时间点不同产生波动。     

正畸热压膜材料力学性能及矫治力测量的研究进展

随着隐形矫治技术的产生和发展,热压膜材料逐渐成为正畸研究领域关注的热点.本文回顾了国内外对于正畸热压膜材料力学性能的研究,表明材料的力学性能直接影响其正畸矫治力.矫治力测量包括理论力学分析和实验力学分析.实验力学分析中应变电测法最常用,可以用于研究隐形矫治力学机制,未来的研究将更多集中在口内测量矫治力.矫治器材料特性、厚度、移位量、环境条件等均可影响隐形矫治力大小.     

Aging stimulates cyclooxygenase-2 expression and prostaglandin E2 production in human periodontal ligament cells after the application of compressive force

BACKGROUND AND OBJECTIVES: Some clinical studies show that alveolar crestal bone loss is higher in adults than in young patients during orthodontic treatment, but the causes of such a phenomenon have not been elucidated. It is known that prostaglandin E2 (PGE2) is a proinflammatory agent and one of the potent osteoclast-inducing factors, and is produced by human periodontal ligament cells in response to orthodontic force. The aim of this study was to investigate age-related change in the biosynthetic capacity of PGE2 and its regulatory gene, cyclooxygenase 2 (COX-2) from periodontal ligament cells in response to mechanical stress. METHODS: Compressive force of 2 g/cm2 was applied for 3-48 h to periodontal ligament cells obtained from human donors aged 9-50 years, and COX-2 mRNA expression in and PGE2 production by the periodontal ligament cells in response to the compressive force were examined. RESULTS: Application of a compressive force of 2 g/cm2 for 3-48 h significantly stimulated these factors in both time- and age-dependent manners. Furthermore, these increases were dramatically larger in periodontal ligament cells obtained from donors over the age of 35. CONCLUSIONS: Periodontal ligament cells obtained from old donors have significantly greater COX-2 expression and PGE2 production in response to compressive force than those from younger donors. The turning point of aging, where significantly larger amounts of theses factors begin production, appears to be around the age of 35. These results may be positively related to the acceleration of alveolar crestal bone loss during orthodontic treatment in adult patients.     

Effects of mechanical properties of thermoplastic materials on the initial force of thermoplastic appliances

Objective:To measure the forces delivered by thermoplastic appliances made from three materials and investigate effects of mechanical properties, material thickness, and amount of activation on orthodontic forces.Materials and Methods:Three thermoplastic materials, Duran (Scheu Dental), Erkodur (Erkodent Erich Kopp GmbH), and Hardcast (Scheu Dental), with two different thicknesses were selected. Values of elastic modulus and hardness were obtained from nanoindentation measurements at 28°C. A custom-fabricated system with a force sensor was employed to obtain measurements of in vitro force delivered by the thermoplastic appliances for 0.5-mm and 1.0-mm activation for bodily tooth movement. Experimental results were subjected to several statistical analyses.Results:Hardcast had significantly lower elastic modulus and hardness than Duran and Erkodur, whose properties were not significantly different. Appliances fabricated from thicker material (0.75 mm or 0.8 mm) always produced significantly greater force than those fabricated from thinner material (0.4 mm or 0.5 mm). Appliances with 1.0-mm activation produced significantly lower force than those with 0.5-mm activation, except for 0.4-mm thick Hardcast appliances. A strong correlation was found between mechanical properties of the thermoplastic materials and force produced by the appliances.Conclusions:Orthodontic forces delivered by thermoplastic appliances depend on the material, thickness, and amount of activation. Mechanical properties of the polymers obtained by nanoindentation testing are predictive of force delivery by these appliances.     

灯盏花联合机械牵张力对成骨细胞OPG和RANKL蛋白表达的影响

目的：研究灯盏花、机械牵张力以及灯盏花与机械牵张力联合作用下对体外培养的成骨细胞OPG和RANKL蛋白表达的影响,探讨灯盏花对正畸骨改建的作用机理。方法：体外培养成骨样细胞株MG63细胞,细胞的机械牵张力刺激采用SXG4201型四点弯曲细胞力学加载仪。分别单用机械牵张力刺激（2000 μstrain,0.5Hz）、单用灯盏花（1mg/mL）干预、以及机械牵张力（2000 μstrain,0.5Hz）和灯盏花（1mg/mL）联合干预MG63细胞不同时间（3h,6h,12h,24h）后,提取细胞总RNA和蛋白质,用Western blot方法检测MG63细胞OPG蛋白和RANKL蛋白的表达。结果：单用机械牵张力刺激MG63细胞后OPG蛋白表达上调,且呈时间依赖性,而RANKL蛋白表达无明显变化;单用灯盏花干预MG63细胞后OPG蛋白表达下调,RANKL蛋白表达增加;两者联合干预MG-63细胞后,OPG蛋白表达量减少,RANKL蛋白表达显著增加。结论：灯盏花能拮抗机械牵张力对成骨细胞OPG分泌的刺激作用,促进机械牵张力对成骨细胞RANKL分泌的刺激作用。     

间充质干细胞在拉力作用下的大鼠皮下成骨能力研究

目的 构建一个简易、有效的体内加力动物模型,研究大鼠骨髓间充质干细胞(rBMSC)在大鼠皮下受拉力作用下的成骨能力.方法 将成骨诱导后的rBMSC与聚乳酸-羟基乙酸共聚物(PLGA)支架材料复合构建骨移植材料,再运用澳丝弯制成加力装置与该移植材料复合,实验分为细胞-材料-加力装置复合物(A组)和细胞-材料复合物(B组,对照组)2组,分别植入12只SD雄性大鼠皮下,术后4w、8w取材,分别行micro-CT扫描、苦味酸-品红染色、骨钙素免疫组化染色,采用SPSS19.0进行统计学处理.结果 micro-CT扫描可见与低密度的支架材料形成明显对比的高密度影像,且成骨量A组＞B组,2组间存在明显差异.组织学评分表明A组与B组之间的差异具有统计学意义(P＜0.05).结论 相比较不受力条件,受到拉力作用的rBMSC在体内的成骨量更多,本研究建立的大鼠皮下加力动物模型有效、可靠.     

机械牵张力对人牙周膜细胞成骨样细胞功能的影响

目的 观察机械力作用下牙周膜细胞成骨样细胞特性的改变，以深入探讨正畸牙齿移动的机理。方法 利用自行研制的细胞加力装置对体外培养的人牙周膜细胞施加间歇性机械牵张力，检测其成骨样细胞表型蛋白碱性磷酸酶（alkaline phosphotase,ALP)、骨桥蛋白（osteopontin,OPN)和骨钙素（osteocalcin,OCN)表达的改变。结果 人牙周膜细胞在受到机械牵引力刺激后表现为ALP分泌活性的影响，而且24h的时段内波动，2、4h和24h出现2个显著增高期（P＜0．01）；OCN受机械牵张力影响出现较缓慢和晚期的表达增强，加力4h后缓慢增高，在12h最为明显（P＜0．05）；非分泌型ALP、OPN随观察时间延长蛋白表达水平，如ALP、OCN和OPN都增强，具有时序性。提示人牙周膜细胞在机械力诱导下向成骨样细胞分化成熟，从而可能在机械力介导的骨改建中起作用。     

Magnitude and direction of mechanical stress at the osseointegrated interface of the microthread implant

Background: The mechanism by which the microthread implant preserves peri‐implant crestal bone is not known. The objective of this research is to assess the effect of microthreads on the magnitude and direction of the stress at the bone–implant interface using finite element analysis modeling. Methods: Three‐dimensional finite element models representing the microthreaded implant (microthread model) and smooth surface implant (smooth model) installed in the mandibular premolar region were created based on microscopic and computed tomography images. The mesh size was determined based on convergence tests. Average maximum bite force of adults was used with four loading angles on the occlusal surface of the prosthesis. Results: Regardless of the loading angle, principal stresses at the bone–implant interface of the microthread model were always perpendicular to the lower flank of each microthread. In the smooth model, stresses were affected by the loading angle and directed obliquely to the smooth interface, resulting in higher shear stress. The interfacial stresses decreased gradually in the apical direction in both models but with wavy pattern in the microthread model and smooth curve for the smooth model. Although peak principal stress values were higher around the microthread implant, peri‐implant bone volume exhibiting a high strain level >4,000 μ was smaller around the microthread implant compared to the smooth implant. Conclusion: Stress‐transferring mechanism at the bone–implant interface characterized by the direction and profile of interfacial stresses, which leads to more compressive and less shear stress, may clarify the biomechanical aspect of microthread dental implants.     

Sexual dimorphism of murine masticatory muscle function

OBJECTIVE: To determine if gender distinctions of force generating capacity existed in murine masticatory muscles. DESIGN: In order to investigate the effect of sex on force generating capacity in this muscle group, an isolated muscle preparation was developed utilising the murine anterior deep masseter. Age-matched male and female mice were utilized to assess function, muscle fibre type and size in this muscle. RESULTS: Maximum isometric force production was not different between age-matched male and female mice. However, the rate of force generation and relaxation was slower in female masseter muscles. Assessment of fibre type distribution by immunohistochemistry revealed a three-fold decrease in the proportion of myosin heavy chain 2b positive fibres in female masseters, which correlated with the differences in contraction kinetics. CONCLUSIONS: These results provide evidence that masticatory muscle strength in mice is not affected by sex, but there are significant distinctions in kinetics associated with force production between males and females.     

张应力刺激下Wnt/β-catenin信号通路对成牙骨质细胞Runx2表达调控的体外研究

目的 研究张应力刺激下Wnt/β-catenin信号通路对成牙骨质细胞Runx2表达的调控。方法 以成牙骨质细胞样细胞OCCM30为研究对象,应用FX4000T应力加载装置对其加载张应力,时间为0、3、6、12 h,然后分别使用不同质量浓度的Dikkopf-1（DKK1）处理48 h,采用Western blot法检测β-catenin蛋白的表达水平,实时荧光定量聚合酶链反应法（RT-PCR）检测Runx2 mRNA的表达水平。选取最佳作用时间点（12 h）和最佳阻断剂质量浓度（150 ng•mL-1）,将样本分为A、B、C、D共4组,A组不加力不加阻断剂,B组加力加阻断剂,C组加力不加阻断剂,D组不加力加阻断剂,测量β-catenin蛋白和Runx2 mRNA的表达水平。结果 1）张应力加载3、6、12 h后,Runx2 mRNA表达水平和β-catenin蛋白水平与对照组相比均明显升高,差异有统计学意义（P<0.05）。2）不同质量浓度DKK1处理后,细胞内Runx2 mRNA的表达量呈下降趋势。3）未加载张应力的情况下,DKK1明显抑制了β-catenin蛋白的表达,Wnt/β-catenin通路被抑制;加载张应力情况下,DKK1处理组β-catenin蛋白表达低于未加DKK1处理组;不加阻断剂的情况下,张应力刺激增强了β-catenin蛋白的表达;阻断剂作用后,应力刺激组β-catenin蛋白表达相对较高。结论 机械应力刺激下Wnt/β-catenin信号通路可正向调控成牙骨质细胞Runx2基因的表达。