Finite element analysis of four thread-form configurations in a stepped screw implant

The purpose of this study was to determine the optimal thread form configuration for an experimental stepped screw implant. Two-dimensional finite element analysis was applied to model the experimental stepped screw implant in a standard cross-section of the posterior human mandible digitized from a CT-generated patient data set. Four different thread form configurations: v-thread (V), thin-thread (T), and two square-thread forms of 0.24 mm (S1) and 0.36 mm (S2) thread width were compared under oblique load in normal cortical bone condition. The support-type constraint position changed from middle to the base of the bone segment. In middle support-type constraint position only the thin-thread (T) model demonstrated significantly different stress distribution from the other three models, however, in base support-type constraint position T and S1 models demonstrated significantly different stress distribution from the other two models. The results implies that v-thread (V) or large square-thread (S2) are optimal thread form for the experimental stepped screw implant. While, minimal support constraints allow clearer differentiation of the stress picture between the different stepped screw types at the trabecular bone-implant interface.     

氧化锆陶瓷颈圈牙种植体有限元分析

目的 :探讨氧化锆陶瓷 (ZrO2)颈圈牙种植体在生理加载条件下的生物力学安全性能 ,为该类种植体的结构设计和研究提供数据。方法 :依据螺旋CT针对中切牙位上颌骨扫描数据 ,建立上颌骨及种植体装配的三维有限元模型 ,分别就种植体穿心连接螺钉在不同预紧力 (100N/120N/150N/200N)、不同载荷 (100N/200N/300N)、不同加载角度(50、100、150、200、250、300)条件下进行有限元分析计算。结果 :本文研究条件下 ,连接螺钉的预紧力在120 -150N较合适 ;300N轴线加载条件下氧化锆陶瓷颈圈处于安全范围 ;斜向加载对于陶瓷颈圈中的应力影响较大。加载角度150可满足300N颌力加载 ;加载角度300 时颌力在250N以下才能保证安全性。结论 :在颌力加载不高于250N的情况下,氧化锆陶瓷颈圈牙种植体结构的力学性能可满足要求     

A mimic osseointegrated implant model for three-dimensional finite element analysis

The purpose of this study was to develop a new three-dimensional (3D) mimic model of an osseointegrated implant for finite element analysis (FEA) and to evaluate stress distributions in comparison with a model commonly used in most studies as a control. Based on the 3D computer graphic data obtained by serial in vivo bucco-lingual peri-implant bone structure at 75 microm interval in monkey, a mimic FEA model with trabecular structure and a control model with uniform cancellous bone were constructed. A vertical load of 143 N was applied at the top of the implant and induced stress was evaluated at the peri-implant bone. In the mimic model, stress was distributed at both cortical and cancellous bones (1-5 MPa) in bucco-lingual central planes, but concentrated at the cortical crest (3-7 MPa) in the mesio-distal central plane. In contrast, the control model presented stress concentration at the cortical crest around the implant (5-14 MPa), with less stress (0-1 MPa) at the peri-implant cancellous bone in both planes. The findings, that stress distribution at the peri-implant bone were quite different between the mimic and control models, suggest the need to carefully interpret stress distribution in previous studies with models of uniform cancellous peri-implant bone.     

两种摩擦系数对种植体基台的固位螺钉松动影响的有限元分析

目的:通过三维有限元法,研究种植义齿在扭矩一定的情况下,摩擦系数改变对固位螺钉松动的影响.方法:本研究应用Ansysis 9.0软件,计算结果由三维数字化图像和图表两种形式来说明:三维数字化图像反映每种模型在各种工况下的应力分布总特征和趋势;图表说明摩擦系数为0.26和0.12种植体基台所受三种外力不同的情况(螺杆等效应力最大值应力、最大值部位、位移最大值).结果:在垂直加载35N力情况下,摩擦系数为0.26,螺钉上的最大等效应力为19.076MPa,摩擦系数为0.12,螺钉上的最大等效应力为21.404MPa;在水平加载10N力的情况下,摩擦系数为0.26,螺钉上的最大等效应力为19.118MPa,摩擦系数为0.12,螺钉上的最大等效应力为21.474MPa;在倾斜45°加载70N的情况下,摩擦系数为0.26,螺钉上的最大等效应力为44.336MPa,摩擦系数为0.12,螺钉上的最大等效应力为45.214MPa,螺钉上的应力分布规律大致相同,均在螺钉的第一个螺纹附近.结论:种植体基台施加的垂直35N、水平10N、倾斜45°70N不同外力,对固位螺钉应力及剩余位移的影响也不同,它们之间呈线形相关.固位螺钉柄与螺丝头交界变化的部位,为螺丝的危险界面.     

Retrieval of the resilient element in an osseointegrated implant system.

A fractured apical fragment of the resilient intramobile element within the IMZ dental implant cylinder is difficult to remove. The continued usefulness of the implant will be compromised if the fractured intramobile element is not removed. Two methods of retrieving the apical fragment without causing damage to the internal threads of the implant cylinder are described.     

Trauma to an osseointegrated anterior dental implant: a case report

Abstract –  Single tooth implant systems have been shown to offer a safe and highly predictable option for the replacement of anterior teeth. There is however, a paucity of evidence on the result of trauma to single tooth implant systems, particularly in the vulnerable anterior maxillary area. This article presents a report on the outcome of a traumatic incident to an osseointegrated single tooth implant.     

Finite element analysis of fixed prostheses attached to osseointegrated implants

The effect of defined stresses on cantilevered prostheses attached to osseointegrated implants was assessed by finite element analysis. The effect of stress on a cantilever, consisting of a ductile alloy in contact with a brittle polymer, was demonstrated to be complex. The distribution of applied stresses also influenced the results. Possible fracture and distortion of both materials were demonstrated. Finite element analysis is a particularly useful system for predicting stress behavior and can be employed to produce an optimal prosthetic design that reduces the potential for clinical failure.     

Finite element analysis to determine implant preload

STATEMENT OF PROBLEM: The nature of the forces used to clamp implant components together, and how they are generated and sustained, is lacking in the literature. PURPOSE: This study examined the dynamic nature of developing the preload in an implant complex using finite element analysis. METHODS: The implant complex was modeled in accordance with the geometric designs for the Nobel Biocare implant systems. A thread helix design for the abutment screw and implant screw bore was modeled to create the geometric design for these units of the implant systems. Using the software programs HyperWorks and LS3D-Dyna, 2 3-dimensional finite element models of (1) a Branemark System 3.75 x 10-mm titanium Mark III implant, a CeraOne titanium abutment, a Unigrip gold alloy abutment screw, and (2) a Replace Select System 4.30 x 10-mm titanium implant, a Straight Esthetic titanium abutment, and a TorqTite titanium abutment screw were created. Modeling the threads to the machining specifications permitted simulation of screw tightening. The abutment screws were subjected to a tightening torque in increments of 1 Ncm from 0 to 64 Ncm using ABAQUS software. Using these models, the effect of the coefficient of friction on the development of preload amount in the implant complex during and after abutment screw tightening was determined. In the first experiment, the coefficient of friction was set to 0.20 between the titanium bearing surface of the abutments and the implant bearing surfaces, and 0.26 between the gold abutment screw and the titanium implant screw bore. In the second experiment, the coefficient of friction was varied; the titanium implant and titanium abutment bearing surfaces were set to a coefficient of friction of 0.20, whereas the Mark III gold and the Replace Select titanium abutment screws and their respective titanium screw bores in the implants were set to 0.12. The preload amount (N) was determined from the finite element analysis. RESULTS: The stress distribution pattern clearly demonstrated a transfer of preload force from the screw to the implant during tightening. A preload of 75% of the yield strength of the abutment screw was not established using the recommended tightening torques. CONCLUSION: Using finite element analysis, a torque of 32 Ncm applied to the abutment screws in the implant assemblies studied in the presence of a coefficient of friction of 0.26 resulted in a lower than optimum preload for the abutment screws. To reach the desired preload of 75% of the yield strength, using a torque of 32 Ncm applied to the abutment screws in the implant assemblies studied, the coefficient of friction between the implant components should be 0.12.     

Failing factors associated with osseointegrated dental implant loss

PURPOSE: Dental implants are currently the aesthetic and functional alternative for tooth replacement. Despite the high success rate shown by longitudinal studies, failures do occur, even in patients who present appropriate clinical conditions. The aim of the present study was to identify factors related to, or determinant of, dental implant loss in patients of the Latin-American Dental Research Institute, Curitiba, PR, Brazil. MATERIALS AND METHODS: Retrospective analysis of 3578 records of patients who had implants placed in this institute during the period of 1996 to 2006 was performed. Beyond records, panoramic and periapical radiographs were analyzed. RESULTS: Of the 3578 individuals implant treated, failures occurred in 126 (3.5%) patients (mean age 52.2 +/- 10.6 years). Men lost more implants (4.5%) than did women (3.1%) (P = 0.05). Most failure occurred before loading (88.2%). Failure was more frequent when the implant was installed in the posterior jaw (58.5%). The main detectable causes of implant loss were evaluated. Most implant losses (75%) did not have an apparent clinical cause. Identified causes were 17.5% iatrogenic conditions (surgical technique, contamination, and/or occlusal trauma), poor bone quality and quantity (3%), peri-implantitis (1%), and 3.5% missing data. CONCLUSIONS: The results obtained in this study suggest that host factors can be contributing to the failure of implants.     

Finite element analysis of narrow dental implants

Narrow-diameter implants (NDIs) traditionally have been associated to higher rates of failure in comparison with regular-diameter implants (RDIs) and wide-diameter implants (WDIs), since they generate a more unfavorable stress distribution in peri-implant bone. However, it is well known that the load sharing effect associated with prostheses supported by multiple implants (also called splinted prostheses) affords mechanical benefits. The present study involves finite element analysis (FEA) to determine whether the risks linked to NDIs could be mitigated by the mechanical advantages afforded by the splinting concept. For this purpose, a three-dimensional (3D) model of a real maxilla was reconstructed from computed tomography (CT) images, and different implants (NDIs, RDIs and WDIs) and prostheses were created using computer-aided design (CAD) tools. Biting forces were simulated on the prostheses corresponding to three different rehabilitation solutions: single-implant restoration, three-unit bridge and all-on-four treatment. Stress distribution around the implants was calculated, and overloading in bone was quantified within peri-implant volumes enclosed by cylinders with a diameter 0.1 mm greater than that of each implant. The mechanical benefits of the splinting concept were confirmed: the peri-implant overloaded volume around NDIs splinted by means of the three-unit bridge was significantly reduced in comparison with the nonsplinted condition and, most importantly, proved even smaller than that around nonsplinted implants with a larger diameter (RDIs). However, splinted NDIs supporting the all-on-four prosthesis led to the highest risk of overloading found in the study, due to the increase in compressive stress generated around the tilted implant when loading the cantilevered molar.     

Evaluation of design parameters of osseointegrated dental implants using finite element analysis

Finite element analyses were performed for various shapes of dental implant to study effects on stress distribution generated in the surrounding jaw bone and to determine an optimal thread shape for even stress distribution. It was found that the square thread shape filleted with a small radius was more effective on stress distribution than other dental implants used in the analyses. Additional analyses were performed on the implant with the thread shape obtained from previous analyses for varying other design parameters, such as the width of thread end and height of thread for various load directions, to determine the optimal dimensions of the implant. Stress distribution was more effective in the case when the width of thread end and the height of thread were 0.5p and 0.46p, respectively, where p is the screw pitch. Then, using the optimal implant thread dimensions determined previously, stress analyses were performed with various screw pitches and implant lengths, to investigate effects on stress distribution and to find the way to reduce the maximum effective stress generated in the jaw bone. Results show that the maximum effective stress decreased not only as screw pitch decreased gradually but also as implant length increased.     

螺旋形种植体骨界面初始应力的三维有限元分析

目的：分析螺旋形种植体植入下颌骨后骨界面初始应力的分布。方法：用三维有限元的方法对不同弹性模量和不同直径种植体植入后骨界面的初始应力进行分析。结果：螺旋形种植体植入下颌骨后，骨界面的初始应力大小为23．2MPa。主要分布在种植体和骨密质接触的颈部。结论：初始应力的大小与种植体弹性模量无关；随着种植体直径的增加，初始应力逐渐增大。     

Finite element analysis of interface geometry effects on the crestal bone surrounding a dental implant.

Using a two-dimensional axisymmetric finite element analysis technique, different geometrical configurations of implants, abutments, and interfaces have been investigated to alter the stress distribution in the crestal bone region. The crestal bone region is of particular interest due to observations of progressive bone resorption (saucerization). The ability of a prosthetic restoration-implant construct to transfer an appropriate stress at this region will, by definition of Wolff's law (bone's response to strain) and principles of bone remodeling, help to maintain the integrity of the surrounding bone via force transfer. The two geometries investigated involved a traditional flat mating surface and a slanted (oblique) mating surface. In both models a vertical load of 400 N (63 N/rad across 2 pi radians) was applied to the abutment apex. In the crestal bone region the oblique mating surface increased the transfer of horizontal stress 67 percent over the traditional flat mating surface design. The magnitude of stress transferred and the area which it was transferred across was increased in this region. Results indicate potentially more favorable mechanical conditions for bone maintenance surrounding an endosseous dental implant may be achieved if force is transferred preferentially via circumferential grooves and an oblique (dished) implant-abutment mating surface. These theoretical results are consistent with basic principles of stress transfer, stress shielding, and remodeling as well as clinical observations of bone maintenance and resorption.     

Stress distribution in the single-unit osseointegrated dental implant: finite element analyses of axial and off-axial loading

Occlusal overload may contribute to the extensive crestal bone loss often noted around late-failure dental implants. A particularly high risk of traumatic overload occurs with the posterior single-unit implant restoration because the restoration itself is usually wider than the implant, creating the potential for a cantilever effect with high bending moments. The objective of this study was to evaluate the simulated effects of axial and off-axial vertical loads on stress gradients at the implant/bone interface of a single-unit osseointegrated root-form endosseous dental implant. A two-dimensional finite element model was generated. A 490-N load was applied at 0, 2, 4, and 6 mm from the vertical axis of the implant. Off-axis loading resulted in greatly increased compressive stresses within the crestal cortical bone on the side to which the load was applied and similarly increased tensile stresses on the side opposite the load. These stresses increased considerably with each mm increase off axis of the applied load. These data suggest that off-axis loading of single-unit implant restorations provides a significant contribution to increased stresses at the implant/cortical bone interface. The distance off axis at which the load is applied is also significant.     

Surgical repositioning of osseointegrated malposed dental implant with segmental osteotomy

ABSTRACT: After extensive research, the practice with dental implants has been used on a large scale. With the increase in its indications in various local conditions, more complications have been observed. Among these, one of the most frequent is the installation of the implants in a three-dimensional altered position, making the prosthesis and aesthetics more difficult to achieve. For this reason, techniques such as segmental osteotomy have been developed and adapted to implantology to reestablish the adequate position of these implants with correct aesthetic outcome and function. The present clinical report shows the segmental osteotomy technique in a malposed osseointegrated dental position of the upper central incisor with 1-year follow-up.     

First molar replacement with an osseointegrated implant

The effective use of two osseointegrated Br?nemark implants for the replacement of a single first molar is described. A first molar lost to endodontic failure was replaced using two 10-mm titanium fixtures in the area previously occupied by the mesial and distal roots of the molar. The use of multiple fixtures in the molar area provided a better distribution of forces to the alveolar bone. At 1-year recall, the patient exhibited excellent oral hygiene and normal function. Adequate bone dimensions are a prerequisite to this treatment.     

有限元分析在牙体充填中的应用

牙体缺损是口腔科中常见病、多发病,多数情况下能够用充填的方法进行修复,然而充填修复后,会引起剩余牙体组织的应力变化,从而影响疾病治疗的效果。有限元分析法是口腔生物力学研究的有效方法,利用该方法可以为口腔疾病治疗方法的评价、优化洞型设计以及合理应用充填材料提供了力学基础。本文从洞型设计、充填材料以及改良后的隧道洞型这三个方面对牙体应力分布的影响,对有限元分析法在牙体充填修复中的应用情况作一综述。