Finite element analysis of deflections in major connectors for maxillary RPDs

PURPOSE: The effect of major connector design on deflection in maxillary removable partial denture (RPD) frameworks under simulated occlusal loading was analyzed by means of three-dimensional finite element models. MATERIALS AND METHODS: Thirteen maxillary major connectors were produced for a Kennedy Class II case. Eleven frameworks consisted of posterior palatal straps with different anteroposterior widths at the midline. Anteroposterior and horseshoe bars were also constructed for comparison. In each framework, the occlusal rest on the abutment adjacent to the edentulous ridge was fixed in a vertical direction, and the rest on the contralateral side was fixed in all directions. A biting force of 20 N was vertically distributed simultaneously on each of the three missing posterior teeth locations. RESULTS: For the posterior palatal straps, the maximum vertical displacement at the saddle and the buccal displacement at both the saddle and the rest adjacent to the saddle decreased as their connector width increased from 6 to 29 mm, whereas maximum distal displacements were insensitive to the connector width. The posterior straps with anteroposterior widths of more than 18 mm revealed comparable rigidity to the anteroposterior bar. The horseshoe bar and the posterior straps with smaller widths demonstrated greater displacements than the other frameworks. CONCLUSION: The rigid connectors proved to be the most effective in transmitting applied occlusal forces to the contralateral side of the framework.     

数字化可摘局部义齿支架模型的建立与结构强度的有限元分析

目的:建立数字化可摘局部义齿支架模型,对其进行结构强度分析和形态优化。方法:通过3Shape Dental System软件设计上颌肯氏II类牙列缺损可摘局部义齿支架,使用Abaqus/CAE有限元软件分析支架受力及其对基牙、黏膜以及牙槽嵴的影响。结果:数字化模型精度高,支架结构完整、适合性较好。基于数字化支架建立的有限元模型相似性高。支架小连接体应力集中,远端下沉,缺隙侧基牙应力大于对侧基牙,缺牙区远端出现高应力区。有限元分析结果能够反应支架在口内的受力和运动情况。结论:运用有限元法对数字化支架进行分析和优化,能够完善数字化支架设计和制作过程。     

不同临床设计的ERA附着体义齿修复下颌牙列游离端缺损的三维有限元分析

目的:研究3种不同临床设计ERA附着体义齿修复下颌远中游离端缺损的应力及位移分布.方法:建立ERA附着体义齿修复下颌远中游离端缺损的三维有限元模型,根据临床设计分为基本组、支托组和跨弓组.应用有限元法研究在垂直及45°斜向2种载荷方向100 N的作用下,基牙及基托下黏膜的应力和位移以及基托的位移情况.结果:2种载荷下3组模型均在远中基牙远中邻面肩台出现应力集中,远中基牙预备体咬合面位移最大,支托组基牙位移最大,分别为14.91 μm和63.09μm,其次为基本组(9.38 μm和50.56μm),跨弓组最小(8.85 μm和47.31μnn).结论:在本研究条件下,为远中游离端牙列缺损设计基本的ERA附着体义齿更趋于合理.     

Nonlinear finite element analysis of a splinted implant with various connectors and occlusal forces

PURPOSE: The aim of this study was to analyze the biomechanics in an implant/tooth-supported system under different occlusal forces with rigid and nonrigid connectors by adopting a nonlinear finite element (FE) approach. MATERIALS AND METHODS: A model containing 1 Frialit-2 implant (placed in the second molar position) splinted to the mandibular second premolar was constructed. Nonlinear contact elements were used to simulate a realistic interface fixation between the implant body and abutment screw and the sliding keyway stress-breaker function. Stress distributions in the splinting system with rigid and nonrigid connectors were observed when vertical forces were applied to the tooth, pontic, implant abutment, or complete prosthesis in 10 simulated models. RESULTS: The displacement obtained from the natural tooth increased 11 times than that of the implant, and the peak stress values within the implant system (sigmaI, max) increased significantly when vertical forces acted only on the premolar of a fixed prosthesis with a rigid connector. The sigmaI, max values seen in the splinting prosthesis were not significantly different when vertical forces (50 N) were applied to the pontic, molar (implant) only, or the entire prosthesis, respectively, regardless of whether rigid or nonrigid connectors were used. Moreover, the peak stress values in the implant system and prosthesis were significantly reduced in single- or multiple-contact situations once vertical forces on the pontic were decreased. DISCUSSION: The compensatory mechanism between the implant components and keyway sliding function of the implant/tooth-supported prosthesis could be realistically simulated using nonlinear contact FE analysis. The nonrigid connector (keyway device) significantly exploited its function only when the splinting system received light occlusal forces. CONCLUSION: Minimization of the occlusal loading force on the pontic area through occlusal adjustment procedures to redistribute stress within the implant system in the maximum intercuspation position for an implant/tooth-supported prosthesis is recommended.     

Development of an RPD CAD system with finite element stress analysis

Summary  The structural design of removable partial dentures (RPDs) is critical for preventing distortion of the prosthesis, protecting abutment teeth and residual ridges as well as for high masticatory performance. The aim of this study was to clarify the feasibility and utility of a computer-aided designing (CAD) system with finite element analysis (FEA) for molar teeth arrangement in unilateral distal extension base RPDs. The shapes of artificial teeth and residual ridge were measured and converted into point group data. Solid models were created from surface-modelled point group data in a 3D surface CAD format. An occlusal rim was created on the residual ridge mucosa and the occlusal rim - residual ridge mucosa model with FEA function was created. Stress distribution on the residual ridge mucosa was compared by changing the loading point. The artificial teeth were then arranged in locations with the lowest amount of stress. After building an artificial teeth – saddle – residual ridge mucosa model, stress distribution in the residual ridge mucosa was re-evaluated by simulating occlusal force. On the occlusal rim - residual ridge mucosa model, stress was reduced when the loading point was located around the buccal shelf where functional cusps of artificial teeth were charted. It was confirmed that stress distribution in the residual ridge mucosa was equalized on the artificial teeth – saddle – residual ridge mucosa model. This system might be clinically useful tool for designing RPDs if FEA-guided designing of retainers and connectors can be added.     

SD附着体固位远中游离端可摘局部义齿三维有限元应力分析

目的：对比分析刚性及弹性附着体义齿的应力分布，为临床选用附着体提供理论参考。方法：建立下颌第二磨牙游离缺失的附着体义齿三维模型。采用有限元应力分析方法，分析2种附着体义齿基牙应力分布情况。结果：（1）在垂直载荷下，2种附着体基牙在牙槽嵴顶处均有应力集中。弹性附着体基牙牙根主应力下降26％-58％；剩余牙槽嵴应力峰值减小50％。（2）斜向载荷时，应力集中更明显，弹性附着体应力峰值仍有一定减小。结论：弹性附着体固位的可摘局部义齿，更有利于保护基牙及支持组织，保护剩余牙槽嵴。     

Finite element contact stress analysis of the RPD abutment tooth and periodontal ligament

OBJECTIVES: The purpose of this study was to determine the influence of the occlusal rest position in removable partial dentures on the displacement of the abutment tooth and the stress distribution in the periodontal ligament (PL). METHODS: We constructed three-dimensional finite element models of the mandibular first and second premolars. A layer of the PL and a mesial or distal occlusal rest were produced on the second premolar as an abutment. A zero displacement was prescribed on the outer surface of the PL and the first premolar. In each simulation, the rest was moved 0.05 mm vertically to the apical direction, with or without restriction of horizontal movements. We simulated the contact phenomena on the abutment surfaces, and calculated the movements of the abutment and stress distributions in the PL. RESULTS: We observed a maximum distal displacement of 42 microm at the buccal cusp of the abutment and a principal compressive stress of 0.35 MPa in the PL when the abutment was vertically loaded by a distal rest that was allowed to move horizontally. However, the displacements and stresses were relatively small, and were all within the physiological limitations of the tissues. The restriction of the horizontal movement of the rests was effective in reducing the horizontal displacements of the abutment, regardless of the rest position. CONCLUSIONS: The single vertical load exerted from either the mesial or distal rest on the abutment was unlikely to cause any mechanical damage to its supporting tissues.     

固定桥双基牙侧牙槽骨吸收对基牙应力分布的影响

目的:探讨固定桥双基牙侧牙槽骨有不同程度水平吸收时,基牙牙周膜的等效应力值和分布的变化,以指导临床固定桥的合理设计。方法:采用螺旋CT扫描技术与Mimics、Ansys软件相结合建立双基牙侧牙槽骨有不同程度水平吸收后的三基牙双端固定桥的三维有限元模型,施加垂直和斜向45°载荷,分析双基牙侧牙周膜的应力分布状况。结果:①斜向载荷下各模型应力值均大于垂直向载荷时的应力,应力集中现象也较垂直向载荷时明显;②在垂直或倾斜载荷下,有牙槽骨吸收的第二前磨牙侧增加牙周组织健康的第一前磨牙时,应力均变大以分担牙合力;若增加的第一前磨牙有不同程度的牙槽骨吸收,垂直载荷时应力值变化不大,斜向载荷时应力值减小,但应力集中现象较无吸收时明显。结论:增加牙槽骨有不同程度吸收的基牙不能有效地发挥分散牙合力的作用,不适合做固定桥基牙。加载方向是影响应力分布的重要因素,应注意防止产生过大的侧向力。     

Stress analysis of effects of nonrigid connectors on fixed partial dentures with pier abutments

STATEMENT OF PROBLEM: In some patients, the pattern of missing teeth may require the use of a fixed partial denture (FPD) with an intermediate pier abutment. Information is needed regarding the biomechanical behavior and the position of a nonrigid connector for this treatment option. PURPOSE: The purpose of this study was to evaluate, by means of finite element method (FEM), the effects of rigid and nonrigid design types on stress distribution for 5-unit FPDs with pier abutments. MATERIAL AND METHODS: A 3-dimensional cross-section FEM model (SAP 2000) simulating a 5-unit metal ceramic FPD with a pier abutment with rigid or nonrigid designs (connector location at the mesial region of the second molar, at the distal region of the second premolar, at the mesial region of the second premolar, and at the distal region of the canine) was developed. In the model, the canine, second premolar, and second molar served as abutments. A supporting periodontal ligament and alveolar bone (cortical and trabecular) were modeled. A 50-N static vertical occlusal load was applied on the cusp of each abutment to calculate the stress distributions. Three different types of load were evaluated: loading of all cusps to simulate maximum centric occlusion contacts, loading of the canine to simulate a single anterior contact, and loading of the second molar to simulate a posterior contact. RESULTS: The analysis of the von Mises stress values revealed that maximum stress concentrations were located at the load areas for all models. Also, for all models, the highest stress values were located at connectors and cervical regions of abutment teeth, especially at the pier abutment. CONCLUSIONS: The area of maximum stress concentration at the pier abutment was decreased by the use of a nonrigid connector at the distal region of the second premolar.     

下颌全口覆盖义齿的加强结构对基托下黏膜应力分布影响的三维有限元分析

目的 分析下颌全口覆盖义齿加强前后及不同的加强设计对基托下黏膜应力分布的影响.方法 采用三维有限元法,设定只有两侧尖牙残根残留的下颌牙槽嵴为实验对象,残根上形成根帽,并分别建立无加强,钢丝加强和铸造结构加强的覆盖义齿3个有限元模型,在单侧第一双尖牙区及第二磨牙区垂直加载49 N的力,对覆盖义齿基托下黏膜应力分布的情况进行分析.结果 第一双尖牙区加载时,基托下黏膜应力总和表示为按无加强、钢丝加强和铸造结构加强的顺序依次减小,与加载位置无关.与无加强和钢丝加强比较,铸造结构加强的最大应力显示为最小,且基托下应力分布更均匀和广泛.结论 使用了覆盖根帽顶点和牙槽嵴顶的加强结构加强的覆盖义齿能够有效的分散负载,使下颌覆盖义齿基托下应力分布更均匀和广泛,有利于基托下黏膜的保护.     

An evaluation of the stress effect of different occlusion concepts on hybrid abutment and implant supported monolithic zirconia fixed prosthesis: A finite element analysis

PURPOSEThe aim of this study is to evaluate the effects of canine guidance occlusion and group function occlusion on the degree of stress to the bone, implants, abutments, and crowns using finite element analysis (FEA).MATERIALS AND METHODSThis study included the implant-prosthesis system of a three-unit bridge made of monolithic zirconia and hybrid abutments. Three-dimensional (3D) models of a bone-level implant system and a titanium base abutment were created using the original implant components. Two titanium implants, measuring 4 × 11 mm each, were selected. The loads were applied in two oblique directions of 15° and 30° under two occlusal movement conditions. In the canine guidance condition, loads (100 N) were applied to the canine crown only. In the group function condition, loads were applied to all three teeth. In this loading, a force of 100 N was applied to the canine, and 200-N forces were applied to each premolar. The stress distribution among all the components of the implant-bridge system was assessed using ANSYS SpaceClaim 2020 R2 software and finite element analysis.RESULTSMaximum stress was found in the group function occlusion. The maximum stress increased with an increase in the angle of occlusal force.CONCLUSIONThe canine guidance occlusion with monolithic zirconia crown materials is promising for implant-supported prostheses in the canine and premolar areas.     

The effect of variation of residual ridge angle on partial denture abutment tooth movement

Using a laboratory model simulating a free-end saddle partial denture situation, the effect of variation of the angulation of the crest of the residual alveolar ridge to the horizontal on movement of the abutment tooth and saddle was observed. It was found that the inclination of the residual ridge affected the direction and magnitude of abutment tooth movement. The direction of abutment tooth movement was not related to the position of the occlusal rest. However, the magnitude of saddle and abutment tooth movement is affected by the design of the clasp used.     

上颌游离端可摘局部义齿修复基牙的三维有限元应力分析

目的：本研究采用三维有限元动态分析法，对上颌游离端可摘局部义齿修复双尖牙基牙进行应力分析。方法：利用工程扫描系统、计算机辅助设计软件和有限元程序，模拟天然牙齿建立三维有限元模型。根据基牙的受力情况制作7种实验模型，并结合He支托的不同设计，常规载荷下，对基牙在近远中、颊舌向和咬合方向进行应力分析。结果：1)游离末端基牙远中牙颈部为最大应力区。2)远中He支托对基牙的损伤较近中殆支托大，He支托设计位置越向近中移动，其对基牙的损伤越小。3)颊舌向外力和近远中方向外力对基牙造成的损害比来自咬合方向明显大。结论：上颌游离可摘局部义齿，使用近中He支托，远中固位臂加远中邻面板的类似设计更有效地减少不良应力对基牙带来的伤害。     

上颌全口义齿的加强结构对基托下黏膜应力分布的影响

目的：分析上颌全口义齿加强前后及不同的加强设计，对基托下黏膜应力分布的影响。方法：采用三维有限元法，建立无加强（BS），铸造结构加强BA，BD和BDr等4种上颌全口义齿三维有限元模型。设定P1，M1，PMc和PMe等4种垂直加载条件，加载力合计98N。对全口义齿基托下黏膜的应力分布进行分析。结果：在相同加载条件下，黏膜应力峰值表示为按BS，BA，BD，BDr的顺序依次减小。BDr基托下黏膜应力峰值最小，应力分布更均匀和广泛。结论：使用覆盖牙槽嵴顶及后堤区的铸造加强结构的上颌全口义齿能够使基托下黏膜应力分布更均匀和广泛，有利于保护基托下黏膜组织。     

Influence of occlusal forces on stress distribution in preloaded dental implant screws

STATEMENT OF PROBLEM: Abutment and prosthetic loosening of single and multiple screw-retained, implant-supported fixed partial dentures is a concern. PURPOSE: The purpose of this study was to investigate stress distribution of preloaded dental implant screws in 3 implant-to-abutment joint systems under simulated occlusal forces. MATERIAL AND METHODS: Three abutment-to-implant joint systems were simulated by using the 3-dimensional finite element analysis method: (1) Branemark external hexagonal screw-retained abutment, (2) ITI 8-degree Morse tapered cemented abutment, and (3) ITI 8-degree Morse tapered plus internal octagonal screw-retained abutment. A thermal load and contact analysis method were used to simulate the preload resulting from the manufacturers' recommended torques in implant screw joint assemblies. The simulated preloaded implants were then loaded with 3 simulated static occlusal loads (10 N; horizontal, 35 N; vertical, 70 N; oblique) on the crown position onto the implant complex. RESULTS: Numeric and graphical results demonstrated that the stresses increased in both the abutment and prosthetic screws in the finite element models after simulated horizontal loading. However, when vertical and oblique static loads were applied, stresses decreased in the external hexagonal and internal octagonal plus 8-degree Morse tapered abutment and prosthetic screws with the exception of the prosthetic screw of ITI abutment after 70-N oblique loading. Stresses increased in the ITI 8-degree Morse tapered cemented abutment after both vertical and oblique loads. CONCLUSION: Although an increase or decrease was demonstrated for the maximum calculated stress values in preloaded screws after occlusal loads, these maximum stress values were well below the yield stress of both abutment and prosthetic screws of 2 implant systems tested. The results imply that the 3 implant-to-abutment joint systems tested may not fail under the simulated occlusal forces.     

Influence of abutment height on strain in a mandibular overdenture

The purpose of this study was to investigate the influence of coping heights on the strain around the abutment teeth and at the middle part of mandibular overdentures, using strain gauges. A mandibular edentulous model with a silicone artificial mucosa of thickness 2 mm was made. Two artificial roots were embedded on both sides in the canine position. The coping had a dome-shaped upper surface at a height of 0, 2, 4 and 6 mm. On the lingual polished surface of the overdenture, three strain gauges were attached in the left canine position at the vertical level corresponding to the top of the 6, 4 and 2 mm copings and two strain gauges were attached in the middle section (upper and lower). A vertical loading of 49 N was applied on the occlusal surface of first premolar, first molar and second molar. When loading on the first premolar adjacent to an abutment, the largest tensile strain was observed on the overdenture surface close to the top of each coping, independent of coping heights. When loading on the first premolar on the opposite side, the tensile strains around the coping were remarkably smaller. In the middle part of the overdenture, the compressive strains became larger by reducing the coping height or loading on distal point. The largest tensile strain was observed on the overdenture surface close to the top of copings, independent of coping heights.     

The influence of the alveolar ridge shape on the stress distribution in a free-end saddle removable partial denture supported by implant

The alveolar ridge shape plays an important role in predicting the demand on the support tooth and alveolar bone in the removable partial denture (RPD) treatment. However, these data are unclear when the RPD is associated with implants. This study evaluated the influence of the alveolar ridge shape on the stress distribution of a free-end saddle RPD partially supported by implant using 2-dimensioanl finite element analysis (FEA). Four mathematical models (M) of a mandibular hemiarch simulating various alveolar ridge shapes (1-distal desceding, 2-concave, 3-horizontal and 4-distal ascending) were built. Tooth 33 was placed as the abutment. Two RPDs, one supported by tooth and fibromucosa (MB) and other one supported by tooth and implant (MC) were simulated. MA was the control (no RPD). The load (50N) were applied simultaneously on each cusp. Appropriate boundary conditions were assigned on the border of alveolar bone. Ansys 10.0 software was used to calculate the stress fields and the von Mises equivalent stress criteria (sigmavM) was applied to analyze the results. The distal ascending shape showed the highest sigmavM for cortical and medullar bone. The alveolar ridge shape had little effect on changing the sigmavM based on the same prosthesis, mainly around the abutment tooth.     

固定桥不同桥体龈端形态修复下颌第一磨牙的三维有限元分析

目的 应用三维有限元分析法探讨不同桥体龈端形态对固定桥基牙及牙周膜应力分布的影响.方法 利用健康成人牙列的锥形束CT(CBCT)原始数据,通过三维建模软件建立下颌第一磨牙缺失,第二前磨牙与第二磨牙为基牙的双端固定桥,并模拟三种不同桥体龈端形态,即改良鞍式、改良盖嵴式、船底式.利用Ansys 17.0对已建立的三种不同龈...     

冠外固位体义齿基牙牙周组织应力分布的三维有限元分析

目的研究下颌第一磨牙缺失、第二磨牙近中倾斜30°或45°时,用栓道附着体义齿或套筒冠义齿2种冠外固位体(extra-coronal retainer,ECR)义齿修复的基牙牙周组织应力分布。方法采用CT扫描技术和Mimics、Freeform、ANSYS软件,建立下颌第一磨牙缺失、第二磨牙近中倾斜30°或45°及ECR义齿修复后的三维有限元模型,模拟加载并计算分析基牙牙周组织应力的分布情况。结果下颌第二磨牙近中倾斜30°、45°模型,修复前第二前磨牙Von Mises应力分别是2.80 MPa、3.47 MPa,栓道附着体义齿修复后分别是19.26 MPa、25.18 MPa,套筒冠义齿修复后分别是19.47 MPa、24.48 MPa,ECR义齿修复后下颌第二前磨牙牙周组织应力明显增大;修复前第二磨牙Von Mises应力分别是20.45 MPa、20.50 MPa,栓道附着体义齿修复后分别是15.02 MPa、11.84 MPa,套筒冠义齿修复后分别是18.04 MPa、12.18 MPa,ECR义齿修复后下颌第二磨牙牙周组织应力明显减小。结论栓道附着体义齿和套筒冠义齿均能改善倾斜基牙牙周组织的应力分布,当下颌第二磨牙近中倾斜角度过大或下颌第二前磨牙牙周状况欠佳时,应该考虑增加近中端基牙数目。     

三种活动义齿基牙及其支持组织表面的应力分析

目的 :比较在局部可摘义齿修复中锻造卡环、铸造卡环和隐形义齿对基牙牙周组织表面应力的差异。方法 :分别用三种不同卡环的固位方式制作双侧游离端局部义齿 ,施加垂直压力 ,测试不同位点牙周组织表面应力。结果 :三种卡环义齿对基牙根尖部牙周组织的作用力无显著差别 ,而对牙颈部牙周组织及支承牙槽嵴的应力差异显著 (P <0 .0 5 ) ,具有统计学意义。结论 :在相同加载条件下 ,铸造卡环对牙颈部牙周组织产生的应力最大 ,隐形义齿对支承牙槽嵴产生的应力最大。