【作者】 安晶涛；

【导师】 张斌；

【作者基本信息】 哈尔滨医科大学 ， 口腔临床医学， 2017， 博士

【摘要】 背景及目的正畸治疗过程中,牙齿移动与牙槽骨改建密切相关。研究表明:在接受正畸治疗的成人患者,特别是绝经后的老年患者中,由于雌激素缺乏和增龄变化导致其出现不同程度的骨密度降低和骨质疏松,进而影响牙周组织在正畸力作用下骨吸收和骨生成的正常平衡机制,成为严重制约中老年患者正畸治疗的关键因素。对正畸过程中牙槽骨显微结构,即骨小梁显微结构的研究,有利于探究正畸牙齿移动的生物力学机制。本研究旨在通过三维有限元法分析大鼠磨牙正畸受力情况下,牙根表面的应力分布特点,进而应用显微CT(Micro-Computed Tomography,Micro-CT)研究去卵巢大鼠在正畸牙齿移动过程中牙槽骨显微结构的动态变化和磨牙的位移情况,探讨骨质疏松状态下牙槽骨骨小梁显微结构的变化和牙齿移动的规律,为正畸临床治疗提供理论参考。方法通过Micro-CT扫描大鼠上颌第一磨牙和周围牙槽骨,建立三维有限元模型,在模型的牙颈部,沿近中根和远中颊根的中心,分别模拟加载25 g和75 g指向近中的拉力,测定不同加载力值情况下,牙根表面的应力分布特点。选取健康雌性Wistar大鼠140只,随机平均分为双侧卵巢切除组(Ovariectomy,OVX组)和假手术组(sham组)。在分别施行OVX手术和假手术后3个月,从两组中各随机选取60只大鼠,安放正畸牙齿移动装置,施加牵引力近中移动上颌左侧第一磨牙。根据施加牵引力值的不同,每组又分为轻力亚组(30只,25 g)和重力亚组(30只,75 g)。分别在装置安放后的第3天,第7天和第14天,从各亚组中随机选取10只大鼠,包括两组中没有被安放移动装置的20只大鼠,在麻醉下处死并分离左侧上颌骨作为实验标本。使用Micro-CT对标本进行扫描,计算第一磨牙远中颊根近中侧牙槽骨的骨小梁显微结构的各项参数,同时测量磨牙近中移动的距离,并进行统计学分析。结果通过Micro-CT扫描结合三维有限元法能够较好地模拟大鼠上颌第一磨牙受载时的应力分布情况;两种不同力值作用下,牙根表面的应力分布情况相似;随着加载力值的增大,牙根表面相应部位的应力值均增大。在大鼠上颌第一磨牙的五个牙根中,近中颊根远中侧的颈1/3表面的应力值最大;对于牙根体积相对粗大的远中颊根而言,其近中侧的颈1/3表面的应力值最大。近中颊根远中侧;远中颊根和近中根远中侧的颈、中1/3;远中舌根远中侧的中1/3均为应力分布区域。同时位于舌侧的近中舌根和远中舌根,其应力值均明显小于位于颊侧的近中颊根和远中颊根。四个亚组大鼠在加力前至加力后第3天各项参数均无明显变化(P>0.05);从加力后第3天至第7天骨矿密度(Bone Mineral Density,BMD)、骨体积分数(Bone Volume/Total Volume,BV/TV)和骨小梁厚度(Trabecular Thickness,Tb.Th)均明显减少(P<0.05),骨小梁间隙(Trabecular Separation,Tb.Sp)和结构模型指数(Structure Model Index,SMI)均明显增加(P<0.05);不同之处表现在加力后第7天至第14天:sham轻力亚组BMD、BV/TV和Tb.Th明显增加(P<0.05),Tb.Sp和SMI明显减少(P<0.05);sham重力亚组各项参数均无明显变化(P>0.05);虽然OVX轻力亚组各项参数的变化也无统计学意义(P>0.05),但BMD、BV/TV和Tb.Th明显呈现减少趋势,Tb.Sp和SMI明显呈现增加趋势;而OVX重力亚组BMD、BV/TV和Tb.Th继续明显减少(P<0.05),Tb.Sp和SMI继续明显增加(P<0.05)。在相同牵引力值作用下,OVX组大鼠磨牙在不同时间点的近中移动距离均大于sham组(P<0.05);但在两个组内,重力亚组在加力后第3天和第7天的移动距离仅轻微大于轻力亚组,差异均无统计学意义(P>0.05),只有在第14天明显大于轻力亚组(P<0.05)。结论大鼠上颌第一磨牙远中颊根近中侧颈1/3对应的牙槽骨是观测正畸牙齿移动过程中牙槽骨改建的最适合部位。雌激素缺乏可加速大鼠的牙齿移动,但易导致牙槽骨的过度吸收。虽然轻力作用下的大鼠牙齿移动距离小于重力,但相对更安全。更多还原

【Abstract】 Background and PurposeDuring orthodontic treatment,tooth movement was closely related to alveolar bone remodeling.Due to estrogen deficiency and aging,orthodontic treatment,especially for postmenopausal women,could result in the decline of bone mineral density（BMD）and osteoporosis（OP）,which would further affect the balance of bone resorption and formation in periodontal tissues and pose a crucial factor hindering orthodontic treatment to senior patients.In this study,stress distribution of root surface of rat molar was analyzed under orthodontic force loading by means of finite element method（FEM）.And micro-computed tomography（Micro-CT）system was used to develop a new approach to evaluate the dynamic changes of alveolar bone and distance for mesial movement of the molar in ovariectomized rats during orthodontic tooth movement,and explore the change pattern of the trabecular bone microstructure in alveolar bone and orthodontic tooth movement under osteoporosis conditions so as to provide theoretical reference for orthodontic clinic treatment.MethodsA three dimensional finite element model of maxillary first molar and its support tissues of rat was established by means of FEM and Micro-CT system.Different force magnitudes（25 g and 75 g）were exerted simulatly on the tooth cervix of model passing the centers of mesial root and distobuccal root,and Von Mises stress was determined under different force loading.140 female Wistar rats were randomly divided into ovariectomy（OVX）group and sham group of equal number.Three months after surgery,60 rats were selected randomly from each group and orthodontic appliances with force loading were installed to simulate the orthodontic tooth movement.Each group was divided into25-g subgroup and 75-g subgroup of equal number according to diferent force loading.On the 3^rd,7^th and 14^th day after the installation of the orthodontic appliances,three batches of 10 rats from each group being randomly picked and 20 rats which were not installed the appliances as control were anesthetized to death respectively.Their left maxillary bones as samples were separated and scanned using Micro-CT system,microstructural parameters for trabecular bone mesial to the distobuccal root were evaluated.Meanwhile,distance for mesial movement of the molar was measured.ResultsThree dimensional finite element model of maxillary first molar of rat which was established by combining Micro-CT system had satisfactory geometric and mechanical comparability.The characteristics of stress distribution of root surface were similar under 25 g and 75 g force loading.The stress became larger with force loading increased.Among five roots of the maxillary first molar,the stress of distal region to the cervical third of the mesiobuccal root was largest.And to distobuccal root which volume was relative bigger,the stress of mesial region to the cervical third of it was largest.Stress distribution of root surface also included:the distal region of mesiobuccal root,distal region to the cervical and middle third of the distobuccal and mesial roots,distal region to the middle third of the distolingual root.Moreover,the stress of mesiolingual and distolingual roots which lied in lingual side were smaller than that of mesiobuccal and distobuccal roots which lied in buccal side significantly.Microstructural parameters for trabecular bone of four subgroups showed no significant changes from day 0 to day 3（P>0.05）;from day 3 to day 7,BMD,BV/TV and Tb.Th decreased significantly（P<0.05）,whereas Tb.Sp and SMI increased significantly（P<0.05）;the differences lied in that:from day 7 to day 14,in sham 25-g subgroup,BMD,BV/TV and Tb.Th increased significantly（P<0.05）,while Tb.Sp and SMI decreased significantly（P<0.05）.And in sham 75-g subgroup,changes of parameters did carry any statistical significance（P>0.05）.Correspondingly,the various parameters of OVX 25-g subgroup were no obvious change,while the significant increase of BMD,BV/TV and Tb.Th and the significant decrease of Tb.Sp and SMI were found.Meanwhile,in OVX 75-g subgroup,BMD,BV/TV and Tb.Th decreased significantly（P<0.05）,whereas Tb.Sp and SMI increased significantly（P<0.05）.In addition,under the same force magnitudes,the distance for mesial movement in OVX group was larger than that in sham group at different time points（P<0.05）.But in each group,the 75-g subgroup showed larger distance than 25-g subgroup only at day 14（P<0.05）.ConclusionsMesial region to the cervical third of the distobuccal root was most suitable for study region in term of alveolar bone remolding during orthodontic tooth movement.Lack of estrogen could affect alveolar bone remolding and accelerate tooth movement.Apparently,the fast tooth movement at the expense of excessive alveolar bone resorption was not ideal.Even the distance for mesial movement of molar under light force loading was less than that of under heavy force loading,but orthodontic tooth movement was safty.更多还原