不同基台时种植体支持全瓷单冠的应力分析

目的：观察氧化铝、氧化锆全瓷基台和钛基台支持时种植体全瓷单冠各部位的应力分布情况。方法：建立种植体支持下颌第一前磨牙全瓷单冠的三维有限元模型，基台分别选用氧化铝、氧化锆和钛，采用垂直和水平加载两种方式，分析全瓷冠、基台、种植体及其周围骨组织的应力分布情况和最大应力。结果：全瓷基台和钛基台支持时应力分布基本类似，最大应力在水平加载时大于垂直加载时。全瓷冠内部应力集中在加载部位和舌侧肩台处，全瓷基台支持时最大应力无明显差异，稍低于钛基台支持时。基台内部应力集中在基台-种植体连接处的颊侧，瓷基台内部的最大应力高于钛基台，位移量小于钛基台。种植体及骨组织内部应力集中在种植体颈部皮质骨，最大应力在垂直加载条件下不同基台时无明显差异，在水平加载条件下钛基台高于全瓷基台。结论：全瓷基台支持时全瓷冠、种植体和骨组织内部应力较小；两种全瓷基台内部应力无明显差异，均高于钛基台。     

瓷基台和钛基台用于种植体支持全瓷单冠修复的临床观察

目的观察瓷基台和钛基台用于种植体支持全瓷单冠修复的美观效果以及两者对种植体周围软硬组织的影响。方法19例单颗上颌前牙缺失患者，分为瓷基台组（8例）和钛基台组（11例），行种植体支持全瓷单冠修复，随访观察2年，用改良的美国公共卫生署（United States Public Health Service，USPHS）标准评价两者的美观效果，并在修复后6、12、18和24个月测量种植体周围牙龈出血指数和骨吸收量，所得数据进行秩和检验和方差分析。结果在随访期间内未发现全瓷冠和钛基台折断，1例瓷基台在修复后15个月折断。瓷基台组和钛基台组达到USPHS标准A级的分别为8例和10例，差异无统计学意义（P〉0.05）。种植体周围牙龈组织颜色正常，无炎性反应，瓷基台和钛基台修复2年后种植体周围骨吸收量分别为0.70mm和0.77mm。统计学分析表明，瓷基台组和钛基台组两组间，以及同种基台修复后不同时间的牙龈出血指数和骨吸收量差异均无统计学意义（P〉0.05）。结论瓷基台和钛基台用于种植体支持全瓷单冠修复可取得理想的美观效果，两者均对种植体周围软硬组织无明显的不良影响。     

不同结构氧化锆瓷基台及种植体周骨壁应力的有限元分析

目的 研究不同结构氧化锆瓷基台及种植体周骨壁应力的分布情况,为临床应用提供理论指导.方法 采用建模软件Altair Hypermesh建立三维有限元模型,应用Altair Hyperview后处理软件对模型中不同载荷条件下的三种不同结构氧化锆瓷基台及种植体周骨壁应力的分布情况进行分析,并与常规钛基台进行比较.结果 Replace基台模型的种植体周骨壁应力明显小于Lifecore实心基台模型和Lifecore螺栓固定基台模型的种植体周骨壁应力,而Replace基台模型的基台等效应力明显大于Lifecore实心基台模型和Lifecore螺栓固定基台模型的基台等效应力,Replace基台模型的螺栓等效应力峰值明显大于Lifecore螺栓固定基台的模型的螺栓等效应力峰值;Lifecore实心基台模型的种植体周骨壁应力略小于Lifecore螺栓固定基台模型的种植体周骨壁应力,而Lifecore实心基台模型的基台等效应力略大于Lifecore螺栓固定基台模型的基台等效应力;氧化锆基台模型与钛基台模型比较,两者无明显差异.结论 基台与种植体连接方式的不同对氧化锆瓷基台及种植体周骨壁应力的分布有影响,提示临床上应该根据患者情况选择最合适的基台;基台材料的改变对应力分布无明显影响,从生物力学考虑可以放心使用氧化锆瓷基台.     

牙尖斜度对种植体支持全瓷单冠应力分布的影响

目的：分析不同牙尖斜度对种植体支持全瓷单冠应力分布的影响。方法：利用COSMOS 2．85参照相关文献建立5个种植体支持的下颌第一磨牙全瓷单冠三维有限元模型,全瓷冠的颊尖斜度分别设计为20°、25°、30°、35°和40°,采用垂直和水平两种加载方式,分析不同牙尖斜度对全瓷冠、基台、种植体以及周围骨组织内部的应力影响。结果：全瓷冠内部的张应力和等效应力主要集中在全瓷冠颊侧颈部,压应力主要集中在全瓷冠表面加载部位。最大张应力在垂直加载下随牙尖斜度增加而增加,水平加载下随牙尖斜度增加而减小;最大压应力和等效应力在牙尖斜度为25°时最小。基台内部的应力主要集中在种植体-基台衔接处的颊侧：种植体应力集中部位在颈部颊侧;骨组织应力集中部位在种植体颈部皮质骨,垂直加载时在颊侧,水平加载时在颊舌侧。不同牙尖斜度时基台、种植体及骨组织内部的最大等效应力在垂直加载时无明显差异,在水平加载时随牙尖斜度的增加而增大。结论：不同牙尖斜度时种植体支持全瓷单冠的应力集中部位相似,最大应力与加载方式有密切关系。     

平台转换锥形锁柱种植基台的三维有限元疲劳分析

目的:通过三维有限元法了解锥形锁柱结构平台转换种植体系统不同基台材料疲劳寿命。方法:建立平台转换连接种植体支持的下颌第一磨牙三维有限元模型,分析不同基台材料疲劳寿命。结果:不同材料平台转换连接基台的疲劳寿命均是钛基台＞氧化锆基台＞氧化铝基台。结论:钛基台、氧化铝基台和氧化锆基台的疲劳寿命均在30年以上,决定不同材料基台疲劳寿命的关键是其应力集中点,即基台与种植体连接处。     

动态载荷下双种植体单冠修复下颌磨牙的三维有限元分析

目的探讨动态载荷作用条件下,双种植体单冠修复下颌磨牙的最佳聚合角度。方法分别建立聚合角度为0°、5°、10°、15°双种植体单冠修复下颌磨牙的三维有限元模型,对修复体施加一个周期为0.875 s的动态载荷,分析种植体周围骨组织的应力分布和种植体-基台复合体位移值情况。结果①种植体周围皮质骨最大Von-Mises应力值:5°聚合角度模型>10°聚合角度模型>15°聚合角度模型>0°聚合角度模型;种植体周围松质骨最大Von-Mises应力值:15°聚合角度模型>10°聚合角度模型>5°聚合角度模型>0°聚合角度模型;②种植体-基台复合体最大位移峰值:15°聚合角度模型>5°聚合角度模型>10°聚合角度模型>0°聚合角度模型。结论动态载荷下,双种植体单冠修复下颌磨牙的最佳聚合角度为0°。     

上颌前牙种植修复最佳美学位置的三维有限元分析

目的:观察上颌前牙种植体位于不同位置时周围骨的应力应变分布,验证上颌前牙种植危险带或者安全带的范围。方法:通过建立三维模型,利用有限元软件计算种植体位于不同位置时,周围骨质及牙周膜的应力分布。结果:在唇舌向模型组中,种植体越靠近唇侧,种植体的最大应力值均逐渐减小,骨组织的最大应力无明显趋势;在近远中向模型组中,种植体越靠近邻牙,种植体及周围骨组织的最大应力值逐渐增大;在冠根向移动模型组中,种植体越往根方向移位,种植体的最大应力值逐渐减小,而骨组织的最大应力值则逐渐增大。结论:上颌前牙美学区种植体理想位置在近远中位置上至少保持牙齿表面与种植体肩台保持1.5mm距离或者种植体体部表面与邻牙牙根表面相距2mm;在唇舌向位置上如果唇侧骨量不足则至少保留唇侧骨壁1mm,如果骨量充足则应使种植体肩台位于邻牙外形高点线的腭侧2mm之内;在冠根向位置上种植体肩台应位于邻牙釉牙骨质界根方1mm处。     

氧化锆瓷基台与钛种植体联合应用中不同连接体设计的有限元分析

目的：分析不同氧化锆基台对基台自身及钛种植体周围骨组织应力的影响,为氧化锆基台设计提供理论依据。方法：采用计算机辅助设计建立5种不同设计的氧化锆基台模型,并根据不同的基台模型设计了与之对应的种植体、牙槽骨及全瓷冠模型。用三维有限元方法对每个模型进行100N的斜向加载,分析不同氧化锆基台的设计对基台自身及牙槽骨应力分布及应力峰值的影响。结果：5种设计的等效应力的分布基本一致,基台的应力主集中在基台颈部连接体上方,皮质骨及松质骨的应力主集中于骨与种植体连接的最上方。5种设计等效应力的峰值不同,圆形连接体设计时氧化锆基台,皮质骨及松质骨的等效应力峰值均小于其他各设计组。结论：圆形连接体设计是本研究5种设计中氧化锆基台与钛种植体相连的最佳设计形式。     

氧化锆角度基台及种植体周骨壁应力分布的有限元分析

目的研究氧化锆角度基台及种植体周骨壁应力的分布情况,为临床应用提供参考。方法采用三维有限元分析方法,对氧化锆直基台、15°、20°基台修复时的种植体基台、固定螺丝及种植体周骨壁应力的分布进行分析,并与常规钛基台进行比较。结果角度基台模型的基台、螺丝、种植体周骨壁的等效应力大于直基台;20°基台模型的基台、螺丝、种植体周骨壁等效应力远远大于15°基台模型;氧化锆基台模型与钛基台模型相比,2组无显著差异。结论基台角度对应力分布有影响,并随角度的增大而增大,提示临床上应注意种植体植入方向,尽量使用直基台或小角度基台,以减少种植体颈部骨吸收及修复并发症的发生;基台材料改变对基台、螺丝、种植体周骨壁的应力分布无显著影响,从生物力学考虑,临床上可以放心选用氧化锆角度基台。     

种植体-基台连接形式对种植体周围骨组织应力分布的影响

目的分析种植体-基台连接形式对种植体周围骨组织应力分布的影响，从生物力学角度探讨平台转换连接形式防止或减少种植体周围骨吸收的可能机制。方法利用COSMOSM2．85软件包建立种植体支持的下颌第一磨牙三维有限元模型，种植体-基台的连接形式分别采用平齐对接（模型A）和平台转换（模型B）。采用垂直和斜向两种形式加载，载荷均为200N，比较两种模型种植体周围骨组织的应力分布情况以及种植体-骨界面颊舌侧相同位置的von Mises应力大小。结果不同加载条件下两种模型种植体周围骨组织应力集中在种植体颈部颊舌侧骨皮质内，斜向加载时最大von Mises应力值高于垂直加载时。模型A和模型B骨组织内最大von Mises应力值在垂直加载时，分别为11．61MPa和7．15MPa，斜向加载时分别为22．07MPa和11．87MPa。距离种植体-基台连接处越远，von Mises应力值越小，骨皮质到骨松质交界处的应力变化最明显。与模型A相比，模型B种植体-骨界面相同节点的最大von Mises应力值较小。结论与平齐对接形式相比，平台转换设计可改善种植体周围骨组织的应力分布，降低种植体颈部骨组织所受的应力。     

Three Dimensional Finite Element Analysis of Stress Distribution Around Implant with Straight and Angled Abutments in Different Bone Qualities

The aim of the study was to compare the stress distribution around implant in different bone qualities of D1, D2, D3, and D4 with straight and angled abutments using three dimensional finite element analysis. A three dimensional finite element model of the premaxilla region, and two solid 4.3 × 10 mm implant, one with a straight abutment and the other with an angled abutment was done. Four distinctly different bone qualities of D1, D2, D3, and D4 were made. A static load of 178 N was applied at the centre of incisal edge along the long axis of each abutment. The maximum equivalent von Misses stress values around the implants were recorded. The distribution of stresses changed considerably with abutment angulation. As angulation increased from 0° to 15° the concentration of Von Misses stresses shifted to the cortical layer of bone on the facial side of the fixture. Although Von Misses stress increased in straight abutment as the bone quality changed from D1 to D4, it was more noticeable under the loading side of the angulated abutments. The high stresses induced through angled abutments at the cervical zone of the implant due to forces and moments could be a dominant factor that may aggravate the peri-implant bone loss or changes the existing peri-implantitis direction.     

The influence of abutment angulation on micromotion level for immediately loaded dental implants: a 3-D finite element analysis

PURPOSE: To investigate the micromotion between the implant and surrounding bone caused by the implementation of an angled abutment for an immediately loaded single dental implant located in the anterior maxilla. MATERIALS AND METHODS: A simplified half premaxillary bone model was fabricated. The dimension of the alveolar ridge was adopted from a dry human skull. Based on Br?nemark protocol for Mk IV implants in type-3 bone, an immediate loading model was developed by press-fitting a 4-mm-diameter cylinder implant into a 3.15-mm osteotomy site in a numeric model. Material properties were assigned to the simulated model, and the model was meshed. A bite force of 89 N was applied to the tops of the 0-degree, 15-degree, and 25-degree angled abutments at a 120-degree angle to the abutment long axis. The micromotion between the bone-implant interfaces was calculated using ANSYS 9.0 software featuring a nonlinear contact algorithm. RESULTS: The micromotion values for 15-degree and 25-degree angled abutments were 119% and 134%, respectively, compared to the corresponding values for straight abutments. Compared to straight abutments, the 25-degree abutments resulted in increased maximum von Mises stresses to a level of 18%. Most of the stresses were concentrated within the cortical bone around the neck of the implants. CONCLUSION: Within the limits of the present finite element analysis study, abutment angulation up to 25 degrees can increase the stress in the peri-implant bone by 18% and the micromotion level by 30%.     

Bicortically stabilized implant load transfer

PURPOSE: Questions exist as to the potential advantages of bicortical stabilization of implants in the mandible through engagement of the lingual cortical plate. The purpose of this investigation was to determine photoelastically the effect of lingual cortical plate engagement on implant load transfer. MATERIALS AND METHODS: Composite photoelastic models of an edentulous posterior segment of a mandible were fabricated using plastics of different modulus to simulate cortical and trabecular bone. One model included a 3.75 x 15-mm threaded implant that engaged the simulated lingual cortical plate, while in the other model the implant was centrally located within the simulated trabecular bone. A metal superstructure was cast using an abutment cylinder. Simulated vertical occlusal loads were applied to the superstructure over the implant and at fixed buccal cantilever lengths. Stresses that developed within the model were monitored photoelastically and recorded photographically. Peri-implant defects were then formed in the models and the loading and recording procedures were repeated. RESULTS: Lingual cortical plate engagement generated the highest stresses at the lingual cortical plate and the buccal crestal cortical layer at the implant neck. Stress intensity within the buccal plate at the implant neck was lower than that in the centrally placed implant. In the presence of a peri-implant defect, for all load conditions, more load was borne by the trabecular bone. Increasing cantilever lengths caused asymmetric load transfer with higher maximum stresses. DISCUSSION: For both implant placements, a large portion of the applied load was taken by the crestal cortical bone simulant. Engagement of the lingual cortical plate reduced maximum stress in the crestal cortical bone by approximately 25%. With peri-implant defects, the simulated trabecular bone provided the main support of the applied load. Longer buccal cantilever lengths increased maximum stresses for all placement and crestal bone conditions. CONCLUSIONS: The results of this investigation do not indicate a clear load transfer advantage to apical engagement of the lingual cortical plate in this model.     

The effect of the design of a mandibular implant-supported zirconia prosthesis on stress distribution

Statement of problemProsthetic complications have been frequently reported in implant-supported complete-arch prosthesis. Prosthetic restorations designed with an all-on-four treatment concept and fabricated from zirconia ceramic may be used to overcome these problems.PurposeThe purpose of this biomechanical study was to evaluate the effects of cantilever length and inclination of implant on the stress distribution in bone tissue, implant, and a monolithic zirconia ceramic-lithium disilicate glass-ceramic superstructure for all-on-four prosthesis.Material and methodsAll-on-four mandibular prosthesis fabricated from a zirconia and lithium disilicate glass-ceramic (LDGC) superstructure was designed with cantilever lengths of either 5 mm or 9 mm and posterior implants with a distal tilt of either 15 or 30 degrees. Stresses were evaluated with a simulated application of a static load of 600 N.ResultsIncreasing implant inclination from 15 to 30 degrees led to a decrease in maximum principal stress (MaxPS) values of approximately 4 to 7 MPa in cortical bone around all implants except the right anterior implant in the designs with short cantilevers and an increase in MaxPS values (approximately 3 to 19 MPa) in the same places in the designs with the long cantilevers. Increasing cantilever length from 5 to 9 mm resulted in an increase in minimum principal stress (MinPS) values of approximately 3 to 13 MPa in the cortical bone surrounding all posterior implants. In the designs with the long cantilever, MaxPS values increased approximately 3 to 4 MPa in spongy bone adjacent to the right posterior implant. An increase in cantilever length also led to higher vMS values at the first and second implant grooves in the right posterior implant in the design with the 15-degree implant tilt. An increase in implant inclination in the design with the short cantilever resulted in lower vMS values at the apex and all grooves of the left posterior implant, whereas in the design with the long cantilever, an increase in implant inclination resulted in lower stress values in the first and second grooves of the same implant. An increase in implant inclination led to in an increase in vMS values in the core structure.ConclusionsIn zirconia ceramic restorations by using an all-on-four design with an LDGC superstructure, short cantilevers may be preferable because they result in a more favorable distribution of stress than long cantilevers. An increase in implant angulation from 15 to 30 degrees decreased MaxPS values in cortical bone.     

Impact Fracture Resistance of Two Titanium‐Abutment Systems Versus a Single‐Piece Ceramic Implant

Background: The number of patients with oral implants has increased significantly. However, the literature addressing the effect of impact force on titanium and/or ceramic implants is inconclusive. This study sought to determine the fracture resistance to impact load of titanium and ceramic endosseous oral implants. Materials and Methods: Endosseous oral implants were vertically positioned in two different mounting media: brass and a bone‐simulation material. The implant configurations tested included an experimental one‐piece Y‐TZP implant and a commercially available titanium implant (external hex) with both titanium and zirconia abutments. The specimens were subjected to an impact load using a pendulum impact tester with tup weights varying from 0.9 to 4.5 kg delivered at a radius of 40.64 mm. Loads were delivered to the abutment at a point 4.27 mm above the implant fixture and block junction. Statistical differences (p < .05) were established using the F‐test for variances and, when different, t‐test assuming unequal variances. Results: For implants clamped in brass, the titanium implant with titanium abutment required the greatest energy to fracture the implant‐abutment system (only the abutment screw failed). The ceramic implant and ceramic abutment on titanium implant presented the lowest fracture energy (p < .01). No significant differences were observed when different systems were inserted into the foam blocks of the bone substitute (p > .25). Conclusion: This investigation showed that the fracture energy of two titanium‐abutment systems versus a single‐piece Y‐TZP implant in foam blocks simulating bone elastic modulus was not different, and that differences occurred when the embedding material elastic modulus was increased an order of magnitude.     

Hard tissue reaction to dual acid-etched titanium implants: influence of plaque accumulation. A histological study in humans

OBJECTIVES: The aim of this investigation was to evaluate histologically, histometrically, and histomorphometrically the influence of plaque accumulation on the peri-implant hard tissues. MATERIAL AND METHODS: Twelve fully edentulous subjects were selected for this investigation. Four to five standard titanium screw implants were placed interforaminally. Two small custom-made screw implants were incorporated in the region of the former first molar, one in each lower quadrant. One month after abutment connection, plaque control was terminated randomly at one of the custom-made implants and continued at the other implant. The custom-made implants and the surrounding tissue were harvested after different time points of plaque accumulation (7, 21, or 90 days). Thus, according to the plaque control program and implant removal time, there were six groups each with four implants for investigation. After histologic processing of the biopsies, histologic, histometric, and histomorphometric analyses were performed. RESULTS: Four of the 24 implants were unavailable for analysis. One implant was mobile at abutment connection and another implant was mobile 2 weeks after abutment connection; both implants had to be removed. The bone around two implants was destroyed during the removal with the trephine bur; therefore, these two implants could not be evaluated histologically either. No differences in the histologic appearance of the peri-implant bone between the different groups could be observed. Histomorphometrically, the implant surface in contact with mineralized bone as a fraction of the implant surface (measured from the buccal to the lingual implant shoulder) varied between 59% and 73%. The implant surface in contact with mineralized bone from the first bone-to-implant contact buccally to the first bone-to-implant contact lingually varied between 80.6% and 91.5%. The values for the distance from the implant shoulder to the first bone-to-implant contact, i.e. peri-implant bone loss, varied from 1.1 to 2.2 mm. No statistically significant differences could be found between any of the evaluated variables. CONCLUSIONS: This clinical investigation is the first to evaluate the hard tissue reactions to different plaque accumulation periods. Within the limits of this experiment, it can be concluded that the bone reaction toward the different plaque accumulation periods and in the different plaque control/accumulation groups were similar. It can be further concluded that the observed bone loss is rather attributed to the establishment of the biologic width than to plaque accumulation.     

Stress Distribution after Installation of Fixed Frameworks with Marginal Gaps over Angled and Parallel Implants: A Photoelastic Analysis

PURPOSE: The objective of this work was to compare by photoelastic analysis the stress distribution along a fixed framework placed over angled or parallel implants with different gap values between the framework and one of the implants. MATERIALS AND METHODS: Two photoelastic models were created: (i) with parallel implants; (ii) with a 30 degrees angled central implant. In both cases, three implants were used, and CP titanium frameworks were constructed with commercial components. A plane polariscope was used to observe the photoelastic fringes generated after initial framework assembly, and also when an axial load of 100 N was applied over the central implant. For both models, stress analysis was conducted on well-fitting frameworks and on another with a 150 microm vertical gap between the framework and the central implant. RESULTS: The photoelastic analysis indicated that in the model with parallel implants, stress distribution followed the implant axis, and in the model with an angled implant, a higher and nonhomogeneous stress concentration was observed around the apical region of the lateral implants. The placement of an ill-fitting framework resulted in increased preload stress patterns. CONCLUSION: Stresses were generated after screw tightening of the frameworks, increasing when a load was applied and when a vertical gap was present. Angled implants resulted in oblique stress patterns, which were not transferred with homogeneity to the polymeric model.