【作者】 汪昆；

【导师】 刘宝林； 李德华； 刘彦普；

【作者基本信息】 第四军医大学 ， 口腔临床医学， 2010， 博士

【摘要】 研究背景:Br?nemark教授于上世纪60年代中后期创立的骨结合理论在现代牙种植技术发展史上具有里程碑式意义,他给骨结合下的定义为:负载状态下牙种植体表面与活的骨组织之间发生的结构上和功能上的直接连接,此概念有两层含义,即一方面强调骨结合种植体与骨组织之间为直接的紧密连接,在光镜水平下两者之间没有纤维组织的介入,另一层含义为即使在负载状态下这种紧密连接仍能维持其长期稳定性,而不会受到破坏。Br?nemark教授在提出骨结合理论的同时,根据其长期临床实践经验制定出了一套严格的操作规范用于保证骨结合种植体的长期稳定性,其中的一条操作规范就是延期负载,即种植体植入后,需经过3～6月的无负载愈合,种植体-骨界面实现骨结合才可进行上部修复体的连接;而过早负载会发生纤维性愈合,导致种植体松动、失败。大量研究证实延期负载有利于种植体-骨界面的早期愈合,是提高种植体成功率的有效措施。然而,延期负载的缺点却也非常突出:延期负载延长了疗程,手术次数多,增加了医患双方的负担。随着牙种植技术的发展,人们逐渐对延期负载的必要性提出了质疑,牙种植体的即刻负载被尝试性地用于临床。即刻负载是指在种植体植入后立即进行上部结构修复的种植治疗方法,与延期负载相比,此法疗程明显缩短,可为患者立即恢复美观和咬合功能,受到了患者和医生的欢迎,目前即刻负载已成为牙种植研究的重点和热点。目前认为初期稳定性是决定即刻负载种植体成败的关键因素,将种植体-骨界面微动控制在一定范围,即刻负载种植体即可实现骨结合。而种植体初期稳定性与下列三方面因素密切相关:种植手术技巧、种植体相关因素和颌骨的质与量。在临床实际操作中,即刻负载的成功却在很大程度上取决于临床医师判断测量种植体初期稳定性的能力和连续监测负载种植体稳定性变化的能力。目前,常用的种植体稳定性评价方法有:临床扪诊、植入扭矩法、旋出扭矩法、Periotest法和共振频率法(RFA: Resonance frequency analysis)等。前四种方法存在明显缺点,如:临床扪诊属主观测量法,不能定量,不同测量值之间可比性差;植入扭矩和旋出扭矩法属于定量测量,但是前者只能在植入种植体时测量,不能连续监测种植体的稳定性,后者因存在伦理禁忌,是不能用于临床研究的;Periotest法属定量测量方法,但是许多因素可干扰Periotest仪测量值的准确性,其测量重复性受到较多质疑。相反,共振频率法被认为是目前相对理想的定量测量种植体稳定性的方法,组织刚性(stiffness)和有效长度(effective length)被认为是影响种植体RFA值的两个因素,大量研究对这两个因素的作用进行了深入研究,而很少有研究对其它可能影响种植体RFA值的因素进行过研究。目前种植领域对下列问题尚存在疑问:除组织刚性和有效长度外,还有没有其它因素(如双皮层植入、种植体尺寸和传感器设计等)会影响RFA值?如果有,它们的作用到底如何?目的:在本质上,种植体的共振频率就是其固有频率(NF: Natural Frequency),而有限元软件的一个基本功能就是可直接计算出给定结构的固有频率。因此,本课题拟建立牙种植体-局部骨块三维有限元系列模型;该系列模型可用于种植体固有频率分析,通过有限元软件分析双皮层植入、种植体尺寸(长度和直径)和传感器设计等参数对种植体共振频率值的影响。阐明上述相关因素对牙种植体共振频率值的影响,有助于正确解释共振频率值的含义,为共振频率法在即刻负载领域的应用提供理论基础。方法:(1)建立实体模型:采用计算机建模法,即用三维绘图软件画出螺纹型牙种植体、局部骨块实体模型,模型为立体模型。(2)将实体模型导入ANASYS有限元分析软件,定义材料力学性能,建立有限元模型,其中的研究因素为:双皮层植入、种植体尺寸(长度和直径)和传感器设计。双皮层植入分为:下颌颊侧穿皮层和上颌种植体根尖穿皮层两类,其中下颌模型为磨牙区骨块,通过将种植体逐渐向颊侧密质骨板移动并实现接触来模拟颊侧双皮层植入,上颌模型为包含上颌窦底的局部骨块,通过增加种植体长度实现种植体根尖接近并接触窦底密质骨板来模拟根尖穿皮层,两类穿皮层模型中的骨质类型分为三类:D2、D3和D4骨质类型;在进行上述两类双皮层研究中,改变种植体直径(3.75mm、4.0mm、4.5mm、5.0mm和5.5mm)和长度(10.0mm、11.0mm、12.0mm、13.0mm和13.5mm),研究尺寸变化对固有频率值的影响;传感器分为两类:L型传感器和铝杆传感器,L型传感器为目前最为常用的传感器类型,大体呈L外形,为钛材质,使用时需要用螺丝固定于种植体上端,而铝杆传感器为最新一代传感器,为铝材设计,大体呈圆柱状,其下方有小螺杆设计,可直接拧入种植体上口。(3)有限元分析:在本质上,种植体一阶弯曲振动模态(BM: Bending Mode)下的固有频率与RFA仪测量的共振频率相同,因此本研究直接采用有限元软件计算不同参数条件下种植体-骨块复合体的一阶固有频率,包括一阶BM值和一阶垂直向振动模态(AM: Axial Mode)下的固有频率,前者反映的是种植体水平向稳定性,后者反映的是种植体垂直向稳定性。(4)对所得固有频率值进行统计描述和分析,寻找其中的规律,总结得出相应结论。结果:(1)建立了种植体-下颌磨牙区骨块三维有限元模型,种植体直径分为5个等级,模拟了不同等级的颊侧双皮层植入,种植体位于骨块中央设为对照。①0.5mm双皮层接触(种植体伸入密质骨内0.5mm)可增加种植体BM和AM固有频率值10.5～42.3%(平均24.3%),从0mm(种植体表面刚刚接触密质骨)至0.5mm双皮层,种植体固有频率值持续增加,从0.5mm至1.0mm双皮层,种植体固有频率值进入坪台期或有轻微下降。②在0.5mm和1.0mm双皮层模型中,增加种植体直径可引起频率值小幅增加,增幅在2.9～7.3%之间;在对照模型和0mm双皮层模型中,种植体固有频率值随直径增加而有升有降,变化幅度较小,其中各模型组最大值与最小值相比的平均增幅为5.5%。(2)建立了种植体-上颌后牙区骨块三维有限元模型,种植体长度和直径分别为2个及5个等级,模拟了种植体根尖穿上颌窦底密质骨之双皮层植入。①与10.0 mm相比,11.0 mm种植体的BM值有轻度增高,平均增幅2.4%;然而,12.0mm、13.0mm和13.5mm种植体却拥有显著的BM增幅,在D2骨质模型中(13.0mm和13.5mm种植体穿窦底皮层),这3种长度的增幅范围:29.0～30.1%,D3骨质时的增幅范围(13.5mm种植体穿窦底皮层):14.9～17.5%,D4骨质时(13.5mm种植体穿窦底皮层),13.0mm和13.5mm种植体的增幅范围高达:83.0～86.7%,平均值85.0%,12.0mm种植体的增幅为22.6%(3.75mm直径)和16.2%(5.5mm直径)。②大多数情况下,种植体直径由3.75mm变为5.5mm会引起BM和AM频率值的轻微下降,BM值的下降百分比平均8.6%,AM值的平均下降百分比为3.3%。(3)建立了种植体-传感器-下颌后牙区局部骨块(L型和铝杆传感器两类)三维有限元模型。①L型传感器模型种植体的BM值在3763～4464Hz之间(平均4235Hz),而铝杆传感器模型种植体的BM值在9192～10002Hz之间(平均9708Hz)。②骨质由D4变为D2时,L型传感器模型种植体的BM值增加百分比在12.7～16.7%之间(平均14.9%),铝杆传感器种植体的BM值增加百分比在7.4～8.5%之间(平均7.9%)。③对于L型传感器而言,长度增加BM值逐渐增加,14.0mm与8.0mm相比,BM值平均增幅为3.2%,对于铝杆传感器而言,D3骨质模型的频率值随长度增加而增加,在D4和D2骨质条件下,频率值呈先升后降(变化幅度较小)。④在D3骨质情况下,L型传感器测量值和铝杆传感器测量值之间存在线性相关,具有显著性(Pearson相关系数r=0.996,P=0.004);在D4骨质情况下,L型传感器测量值和铝杆传感器测量值之间存在负相关关系,但是没有统计意义(r=-0.846,P>0.05);在D2骨质情况下,两组数值存在正相关关系,但同样没有统计意义(r=0.736,P>0.05)。结论:(1)颊侧双皮层植入可显著增加种植体BM和AM固有频率值,随着双皮层厚度的增加,固有频率值会随之相应增加,然而当双皮层厚度超过某个最有效值(位于0.5mm和1.0mm之间)后,再额外增加双皮层厚度也不能引起固有频率的明显增加。在颊侧双皮层植入情况下,增加种植体直径可引起固有频率值有限的增加,其幅度远低于双皮层植入所增加的幅度。在对照模型和0mm双皮层模型中,种植体固有频率值随直径增加而有升有降,变化幅度较小。(2)种植体长度增加可增加种植体BM值,随长度进一步增加,种植体根方逐渐接近上颌窦底密质骨板、穿入密质骨(实现双皮层植入)会显著增加种植体BM值,但是实现双皮层后额外增加长度并不能引起固有频率值的明显增加。种植体直径增加可引起BM和AM值的轻度下降。(3)在相同骨质类型、相同种植体尺寸条件下,L型传感器模型的BM值远小于铝杆传感器模型的BM值;L型传感器反映骨质变化的灵敏度高于铝杆传感器;在D3骨质条件下,两种传感器均能反映出测量值随长度增加而增加这一趋势。更多还原

【Abstract】 Background: The theory of osseointegration, which was proposed by professor Br?nemark, was regarded as a milestone in the history of dental implantology. Osseointegration was originally defined as a direct structural and functional connection between ordered living bone and the surface of a load-bearing implant. This definition has two meanings. One is that no scar tissue, cartilage or ligament fibers are present between the bone and implant surface, and the other is that the status of osseointegration could be maintained under functional loading.Application of loads to implants at the time of surgical placement or shortly thereafter is called immediate implant loading, and this loading protocol is becoming more common with acceptable success rates. Immediate loading has been the focus of much research. In addition to the establishment of the theory of osseointegration, Br?nemark set some recommendations ensuring durable osseointegration of dental implants. The most important recommendation was using a stress-free healing period of 3～6 months before loading, which was also considered as the delayed loading protocol. Early /immediate loading was identified as the dominating risk factor for osseointegration by Br?nemark et al. The rationale for such a long delayed loading period was that premature loading may lead to fibrous tissue encapsulation instead of direct bone apposition. The main disadvantage of this delayed loading protocol is that the treatment time is lengthened. The discomfort, inconvenience, and anxiety associated with waiting period remain challenges to both patients and clinicians.However, the necessity of waiting to load an implant was not scientifically but rather clinically based. It is therefore justifiable to question whether this healing period is an absolute prerequisite for obtaining osseointegration. In this background, immediate loading of dental implants was put forward, and received good results. The protocol, under which the prosthesis is attached to the implants the same day the implants are placed, is defined as immediate loading. The use of such protocols has obvious advantages for the patient, because, for example, treatment time and the number of surgical interventions are reduced.According to most researchers, primary implant stability is the most important determining factor on the success of immediate loading, which is related to bone qualities and quantities, implant dimensions/designs, and surgical techniques. It is thought that the success of immediate loading, to a great extent, is dependent on clinicians’ability to detect and monitor implant stability. Presently, various methods have been suggested to define implant stability: tapping test (percussion of the implant with a mirror handle), insertion torque analysis, removal torque analysis, and the Periotest method. However, these methods have many disadvantages. The tapping test is empirical and not sensitive enough to monitor different degrees of implant stability. But the insertion torque analysis can only be used during implant placement. For the removal torque analysis, non-physiologic forces usually are used. So it is not suitable for long-term clinical stability assessing. On the other hand, these two methods also have the disadvantages of invasiveness and inaccuracy. Periotest is less invasive and more accurate, but many clinical studies indicated that lack of resolution, poor sensitivity, and susceptibility to operator variables limited the use of Periotest in measuring implant stability.The method of resonance frequency analysis (RFA) has been introduced into the oral field to quantitatively monitor dental implants’stability and is considered as an ideal technique. It has been shown that RFA is able to measure the changes in implant stability over time, and can discriminate between successful implants and clinical failures. In vitro and in vivo investigations have revealed that the RFA technique is non-invasive, easy to use, and capable of analyzing the degree of osseointegration. According to previous studies, RFA values of dental implants are mainly associated with the stiffness of the implant-bone system (bone qualities, stiffness of implant components), and the effective length (the distance from the upper bone surface to the shoulder of the implant + the length of the abutment). However, effects of bi-cortical anchorages, implant dimensions and transducer types on the RFA values remain unknown.Objectives:①To generate 3-dimensional models of dental implants for finite element analysis (FEA) by computer.②To caculate the effects of bi-cortical anchorages, implant dimensions and transducer types on RFA values by modal analysis.Methods:①Using the ANSYS software, 3-D models of dental implants and alveolar bone segments were generated, which had 3 different bone qualities (D2, D3 and D4). Then the models were meshed, and material properties were defined. The interfacial contact of bone and the implants was simulated as a frictional contact.②In fact, the resonance frequency of an implant is equal to its natural frequency. Therefore this study used the modal analysis to caculate implants’natural frequency values (NF values). By the modal analysis, NF values of implant-bone complexes were computed and the effects of bi-cortical anchorages, implant dimensions and transducer types on NF values were analyzed. Two types of bi-cortical anchorages were simulated: buccal and apical type. In the two bi-cortical anchorage models, different implant diameters (3.75mm, 4.0mm, 4.5mm, 5.0mm and 5.5mm) and lengths (10.0mm, 11.0mm, 12.0mm, 13.0mm and 13.5mm) were modelled and effects of these dimension parameters on NF values were analyzed. The L-shaped transducer and the aluminum peg transducer were modelled and their effects on NF values were analyzed. The L-shaped transducer is of titanium poperty, which is connected to the implant by the fixing screw. But the peg transducer is made of aluminum, which is connected to the implant by its tip screw. The peg transducer is in cylindrical shape, but the L-shaped transducer is designed as a L-shaped cantilever.③When studying the effects of bi-cortical anchorages, NF values of two vibrating modes were computed and they were the bending mode (BM) and axial mode (AM). The BM values are same to measurements of the RFA device.Results:①3-D FEA models of implant-bone complexes were successfully created on the computer. Different degrees of buccal bi-cortical anchorages were simulated by buccally displacing implants to contact compact bone. The results showed that buccal bi-cortical anchorages significantly enhanced bending and axial NF values. The increasing rates resulting from 0.5mm engagement ranged from 10.5 to 42.3%, with a mean of 24.3%. From 0 to 0.5mm engagement, the NF values maintained an increasing trend, and from 0.5 to 1.0mm engagement, the values levelled off or even decreased. In 0.5 and 1.0mm engagement models, increasing implant diameter resulted in small increases of NF values. In the control and 0mm engagement models, increasing implant diameter resulted in small fluctuations of NF values.②3-D FEA models of the apical type of bi-cortical anchorages were produced. In the D2 bone models, 13.0 and 13.5mm impants were bi-cortically anchoraged, but in D3 and D4 models, only implants of 13.5mm length were bi-cortically stabilized. Regardless of implant diameter, increasing implant length resulted in increases of BM values. Compared with the 10.0mm implants, BM values of 11.0mm implants had a mean increasing rate of 2.4%. However, the increasing rates of 12.0, 13.0, and 13.5mm implants were notable, which ranged from 29.0 to 30.1% under the D2 bone quality, and from 14.9 to 17.5% under the D3 bone quality. In the D4 models, the increasing rates of 13.0 and 13.5mm implants ranged from 83.0 to 86.7% with a mean of 85.0%, and the increasing rates of 12.0mm implants were 22.6% (3.75mm diameter) and 16.2% (5.5mm diamter). In most cases, 5.5mm diameter implants had slightly lower BM and AM values compared to 3.75mm diameter implants, with the mean decreasing rates were 8.6% (BM) and 3.3%( AM).③3-D FEA implant-bone models of the two transducers were generated, and only BM values of implants were computed in this section. In general, BM values of implants connected with the L-shaped transducer had a range of from 3763 to 4464 Hz, which was much less than the range of from 9192 to 10002 Hz generated in implants connected with the aluminum peg transducer. When bone quality increased from D4 to D2, BM values of the L-shaped transducer models went to higher levels with increasing rates ranging from 12.7 to 16.7% (mean: 14.9%), however BM values of the aluminum peg transducer models increased by a range of from 7.4 to 8.5% (mean: 7.9%). In the L-shaped transducer models, increasing implant length resulted in higher BM values, with a mean increasing rate of 3.2%. In the aluminum peg transducer models, increasing implant length brought about higher BM values only when bone quality was D3. And in D3 bone quality models, a linear correlation was found between BM values of the two transducers models (r = 0.996,P=0.004). In D3 and D4 models, linear correlations were also found between BM values of the two transducers models, but without no statistical significance.Conclusions:①Buccal bi-cortical anchorages could significantly increase both bending and axial NF values of dental implants, but extra-buccal cortical bone engagement could not produce considerable incremental increases of NF values as anticipated. Increasing implant diameter could result in limited increases of NF values in case of implants being bi-cortically anchored.②An increase of the implant length could enhance BM values, and moreover, closer approach of fixture ends to the sinus floor and bi-cortical anchorages, resulted from using longer implants, could remarkably enhance BM values. Implant diameter has slightly negative effects on BM and AM values.③BM values of the L-shaped transducer models were much less than those of the aluminum peg transducer models. The L-shaped transducer seems to be more sensitive to bone quality changes than the aluminum peg transducer. Only in D3 bone quality models, the two transducers measure smilar varying trends of implant BM values.更多还原