不同直径种植体与天然牙联合支持固定桥的应力分析

目的:通过三维有限元方法研究种植体直径对天然牙种植体联合固定桥周围骨组织应力的影响。方法:CT扫描获得志愿者DICOM数据,通过Mimics软件、Imageware逆向工程软件及ANSYS软件处理,先建立左侧下颌第二前磨牙和第二磨牙支持的天然牙固定桥三维有限元模型,用不同直径种植体替换下颌第二磨牙得到一系列种植体-天然牙联合支持式固定桥的三维有限元模型。分别在垂直向和斜向45°集中加载下,对比分析天然牙及种植体周围的应力分布情况。结果:相同加载条件下,不同模型的第二前磨牙(天然牙)颈部应力无明显区别。对联合支持式固定桥,当种植体直径由3.5 mm增加为4.3 mm时,种植体颈部和基台的应力明显降低(近1/2);随种植体直径增加,2处应力也继续降低,但降低的幅度明显放缓。结论:随着种植体直径的增大,种植体颈缘处骨组织及基台的von Mises应力逐渐减小,但对天然牙周围的应力影响较小。斜向载荷时,天然牙、种植体周围骨组织及基台受到的von Mises应力显著增大,更易导致固定桥修复的失败。     

天然牙与种植体联合支持套简冠固定桥的骨组织应力分析

目的：研究天然牙与种植体联合支持式套筒冠固定桥牙周组织的应力分布情况。方法：选择1例左侧下颌第一磨牙缺失病例,分别设计以左侧下颌第二前磨牙与种植体（位于下颌第二磨牙）联合支持固定桥模型（模型Ⅰ）和套筒冠固定桥模型（模型Ⅱ）。在分散垂直和分散斜向2种载荷情况下,采用三维有限元法分析基牙及种植体周围骨组织的应力分布情况。结果：分散垂直载荷下,模型Ⅰ中的天然牙和种植体周围骨组织最大等效应力值分别为2．58MPa和43．92MPa;模型Ⅱ中,相应的最大等效应力值分别为2．17MPa和20．23MPa。分散斜向载荷下,模型Ⅰ中的天然牙和种植体周围骨组织最大等效应力值分别为2．23MPa和46．37MPa;模型Ⅱ中．相应的最大等效应力值分别为1．91MPa和21.19MPa。结论：套筒冠固位体能缓冲种植体周围骨组织的部分应力,但对垂直应力和侧向应力的缓冲能力差别不大。进行天然牙与种植体联合支持固定桥修复时,可在种植体端设计套筒冠固位体．以缓冲种植体周围骨组织的应力水平,防止或减轻种植体支持组织的损伤。     

固定义齿倾斜基牙牙周应力分布的三维有限元研究

目的 :用三维有限元方法对近中倾斜的下颌第二磨牙单独受力及作为固定桥基牙后受力时牙周支持组织中的应力分布进行比较分析。方法 :采用薄层CT扫描技术和Ansys有限元分析软件建立下颌第一磨牙缺失、下颌第二磨牙近中倾斜 3 0°、行双端三单位固定桥修复前后的三维有限元模型 ,施加载荷计算并分析牙周支持组织中的应力分布状况。结果 :修复前 ,第二磨牙近中牙槽嵴顶、根尖处应力值较大 ,修复后 ,第二磨牙根周应力值减小 ,第二前磨牙颈部及根尖应力值增大 ,应力分布得到改善。结论 :在一定的倾斜角度内 ,从生物力学角度来评价固定修复有利于倾斜基牙的牙周健康。     

下颌固定桥基牙牙槽骨单侧吸收对基牙应力分布的影响

目的:研究双端固定桥基牙牙槽骨单侧吸收对基牙应力分布的影响。方法:采用螺旋CT扫描获取健康人下颌骨、牙齿、牙周支持组织的二维图像,通过图像合成软件建立三维数字模型,并应用三维有限元分析软件生成下颌后牙三单位固定桥的三维有限元分析模型。在相同垂直和水平载荷情况下,分析基牙牙槽骨单侧吸收时固定桥各基牙的应力分布。结果:当前磨牙端基牙牙槽骨单侧吸收达25%、磨牙端基牙牙槽骨无吸收时,前磨牙端基牙开始出现应力集中;当磨牙端基牙牙槽骨单侧吸收达35%、前磨牙端基牙牙槽骨无吸收时,磨牙端基牙开始出现应力集中。结论:下颌后牙双端固定桥基牙应力分布与基牙牙槽骨吸收形式密切相关,但二者之间不是线性关系而是存在临界区,基牙牙槽骨单侧吸收的程度对基牙应力分布的影响弱于多侧吸收。     

Photoelastic stress analysis of implant-tooth connected prostheses with segmented and nonsegmented abutments

STATEMENT OF PROBLEM: There is some question about whether implant abutment selection affects the transfer of load between connected implants and natural teeth. PURPOSE: The purpose of this study was to compare stress transfer patterns with either 1 or 2 posterior implants connected to a single anteriorly located simulated natural tooth with either 1 or 2 segmented and nonsegmented implant abutments under relevant functional loads by use of the photoelastic stress analysis technique. MATERIAL AND METHODS: A model of a human left mandible, edentulous posterior to the first premolar, with two 3.75-mm x 13-mm screw-type implants embedded within the edentulous area, was fabricated from photoelastic materials. The implants were in the first and second molar positions. Two fixed partial denture prosthetic restorations were fabricated with either segmented conical abutments or nonsegmented UCLA abutments. Vertical occlusal loads were applied at fixed locations on the restorations. The photoelastic stress fringes that developed in the supporting mandible were monitored visually and recorded photographically. The stress intensity (number of fringes), stress concentrations (closeness of fringes), and their locations were subjectively compared. RESULTS: Loading on the restoration over the simulated tooth generated apical stresses of similar intensity (fringe order) at the tooth and the first molar implant for both abutment types. Low-level stress was transferred to the second molar implant. Loading directed on the implant-supported region of the restoration demonstrated low transfer of stress to the simulated tooth. Nonvertical stress transfer with slightly higher intensity was observed for the nonsegmented abutment. CONCLUSION: Within the limitations of this simulation study, stress distribution and intensity for the 2 implant conditions was similar for segmented and nonsegmented abutment designs. Magnitude of stresses observed for both abutment designs was similar for the single implant condition. Vertical loading produced more nonaxial stresses away from the force applied for the 1 implant condition with the nonsegmented abutment. Direct loading results were similar for both abutment designs. Specific recommendations for selection of implant abutment and application should be based on clinical criteria.     

The effect of retainer thickness on posterior resin-banded prostheses: a finite element study

According to its design concept, a resin-bonded prosthesis, compared with the conventional fixed partial denture, is a weak and unstable structure. Therefore, a resin-bonded prosthesis induces a higher failure rate, especially in the posterior region. Recently, adhesion agents have been profoundly improved. However, the design guidelines of posterior resin-bonded prostheses (RBP) have seldom been evaluated from a biomechanical perspective. The objective of this study was to investigate the biomechanical effects of the retainer thickness on posterior RBP using the finite element method. A solid model of a posterior mandibular resin-bonded prosthesis, which employed the second molar and second premolar as the abutment teeth, was constructed and meshed with various retainer thickness (ranging from 0.2 to 1.0 mm). Horizontal and vertical loadings of 200 N were applied respectively at the central fossa of the pontic to examine the stress level at the interface between the retainer and abutment teeth. All exterior nodes in the root, below the cementoenamel junction were fixed as the boundary condition. The results showed that horizontal loading would induce higher interfacial stresses than the vertical loading which indicated that the horizontal component of the occlusal force plays a more important role in evaluating the debonding phenomenon. Further, the peak interfacial stresses increased as the retainer thickness decreased and, based on the fitted relation between retainer thickness and interfacial stresses, a 0.4 mm retainer thickness was suggested as the minimum required to prevent severe interfacial stresses increasing.     

Peri-implant bone loss as a function of tooth-implant distance

PURPOSE: In a retrospective study, the radiographs of 39 patients with Applegate-Kennedy Class I or II in the posterior mandible who had been treated with screw-anchored fixed partial dentures supported by IMZ implants and natural teeth were examined for the presence of radiologically detectable peri-implant bone loss. Furthermore, the results were correlated with a mathematical model. MATERIALS AND METHODS: The radiographs of the implants were digitized, and the areas of bone atrophy mesial and distal to the implants were determined semi-automatically. The data obtained were correlated with the distance between the implant and the abutment tooth. The connection between the tooth-supported crown and the implant-supported denture was made with a vertical screw-lock precision attachment. In a mathematical analysis it was assumed that the fixed partial prosthesis was a rigid beam with 3 elastically embedded supports. RESULTS: The mean distance between the tooth and the first implant was 11.02 mm (SD: 4.24), and between the tooth and the second implant was 20.25 mm (SD: 5.16). Peri-implant bone loss significantly followed a rational function (mesial implant: P = .03, distal implant: P = .02), meaning that, as the tooth-implant distance increased, the area of atrophy became rapidly larger and then diminished gradually. Distances of 8 to 14 mm between the tooth and the first implant and of 17 to 21 mm between the tooth and the second implant were associated with a more pronounced bone loss. These results were also confirmed mathematically. CONCLUSION: A tooth-implant distance of 8 to 14 mm for the first implant and 17 to 21 mm for the second implant should be avoided for implant placement if prosthetic rehabilitation is planned using a fixed partial denture supported by a premolar and 2 IMZ implants in the mandible. Although this investigation was done on IMZ implants only, the results were confirmed by a mathematical model, which indicated that the observed bone loss may be the same in other types of implants placed in the same positions.     

The effect of connector design on cement retention in an implant and natural tooth-supported fixed partial denture

This study investigated the effect of connector design, rigid or nonrigid, on cement retention in a combined implant and natural tooth-supported fixed partial denture. A prepared natural tooth was placed in a Plexiglas block in a manner that it could move approximately the same as a healthy premolar. An endosseous implant was placed in the block so that it was immobile. Joining the prepared tooth and implant was a fixed partial denture that could be made rigid or nonrigid. The natural tooth retainer was cemented to the prepared tooth, and the implant retainer was affixed to the implant fixture with a gold screw. One year of stress was applied to the fixed partial denture by a force simulation machine. Twenty randomly ordered tests were completed, 10 of each connector design. Retentive values for the cemented retainers were recorded and statistically compared by use of Student's independent t test. No significant difference in cement retentive strength between designs was found (p less than 0.05).     

The three-dimensional finite element analysis of fixed bridge restoration supported by the combination of teeth and osseointegrated implants

This study investigated the designs of osseointegrated prostheses in cases of free-end partial edentulism using comparative stress interpreted with the three-dimensional finite element method. Three free-end fixed osseointegrated prostheses models with various connection designs (i.e., rigidly connected to an abutment tooth and an implant, rigidly connected to an implant and two abutment teeth, and rigidly connected to an implant and three abutment teeth) were studied. The stress values of the three models loaded with vertical, buccolingual, and linguobuccal directions at 30 degrees angled to vertical axis forces were analyzed. When the fixed partial denture was connected to the three natural abutment teeth and an implant, the lowest levels of stress in the bone were noted.     

天然牙-种植体联合支持式义齿的应力分析

目的:比较以常规固定桥、固定式套筒冠和CEKA冠外精密附着体为上部结构的天然牙-种植体联合支持义齿的应力分布情况,寻求联合支持义齿上部结构的优化设计方案。方法:利用ANSYS三维有限元法,建立下颌右侧第一磨牙缺失、以下颌第二前磨牙和种植体(位于下颌第二磨牙)联合支持局部固定义齿的三维有限元模型,采用分散垂直和分散斜向(45°)两种加载方式(总加载力200N)。结果:2种加载条件下,固定式套筒冠和CEKA附着体都明显降低了种植体和天然牙周围骨组织的应力,垂直加载时,前者应力值低于后者;斜向加载时,后者低于前者,但后者会使天然牙局部应力有所增加。斜向加载时,种植体及其周围骨组织和天然牙及其周围骨组织的应力值均大于垂直加载条件下的应力值。结论:固定式套筒冠和CEKA附着体均能改善联合支持义齿的应力分布,CEKA附着体对侧向力的缓冲作用较优。     

Effects of a removable partial denture and its rest location on the forces exerted on an abutment tooth in vivo

The 3-dimensional forces exerted on an abutment tooth of a removable partial denture (RPD) were measured in vivo during clenching using a force-measuring device with a piezoelectric transducer. The device was mounted on the mandibular right second premolar of a subject with an edentulous maxilla. The magnitude of the forces was higher and the direction was more posterior without the RPD in place. The direction was most posterior with an RPD with a distal rest only and most anterior with an RPD with a mesial rest only. The 3-dimensional forces exerted on an abutment tooth thus depend on both the presence of a denture and the rest location.     

A natural tooth's stress distribution in occlusion with a dental implant

The loss of one or more teeth is normally treated with conventional fixed or removable partial dentures or with implant supported fixed or removable dentures. This study investigated stresses formed around the implant and the antagonist natural tooth under occlusal force in the substitution of a missing lower first molar with a rigid or resilient IMZ (Intra Mobil Zylinder) implant, using the finite element stress analysis method. The results indicate that a bite force of 143 N resulted in high compressive stresses around the roots of a natural tooth opposing a restoration supported by an IMZ implant with rigid type abutment. It is speculated that these high compressive stresses may contribute to intrusion of the tooth.     

Abutment load transfer by removable partial denture obturator frameworks in different acquired maxillary defects

STATEMENT OF PROBLEM: Excessive stress on abutment teeth adjacent to a maxillary resection defect during loading of partial denture obturator frameworks may shorten the life of the teeth. PURPOSE: The aim of this study was to photoelastically compare the forces exerted on the supporting structures of abutment teeth in 3 differently sized surgical resections with removable partial denture designs used to restore such maxillectomy defects. MATERIAL AND METHODS: Composite photoelastic models were constructed of a human maxilla that had undergone each of 3 maxillectomies: partial, radical, and radical involving the contralateral premaxilla. The abutment teeth included all remaining anterior teeth, the first premolar, and second molar, except the radical maxillectomy, which included the contralateral premaxilla where all remaining teeth were used as abutment teeth. All abutment teeth were restored with complete metal crowns, and removable partial denture frameworks were fabricated. Loading zones were selected according to the resection, and a 10-lb load was applied at each load point. The resulting stresses were observed and recorded photographically in a circular polariscope. The 2 teeth adjacent to the resection were then splinted, and the loading regimens were repeated. RESULTS: Without splinting, loads closer to the defect produced lingual tipping of the teeth adjacent to the resection and a mesial tipping tendency of the second molar. The tipping effects were greatest in the model with the largest resection. Splinting reduced tipping of the teeth adjacent to the resection and produced more uniform stress around these 2 abutment tooth roots for all of the models. CONCLUSION: The results of this in vitro study suggest that splinting the 2 teeth adjacent to a resection defect improves stress distribution around the roots during loading. This could increase the clinical life of the abutment teeth.     

The tilted posterior tooth. Part III: Abutment for a fixed partial denture

The problem of achieving a common path of insertion for a fixed partial denture when a tilted posterior abutment is involved can usually be solved by well planned tooth preparation in conjunction at times with intentional endodontic therapy. When tooth preparation alone cannot solve the problem, the mechanical solutions of the locked attachment and the telescopic retainer are available and must be considered. Other problems involved with the tilted abutment, adjacent tilted teeth, space reduction, supraversion of the antagonist, and the problem of a long-span fixed partial denture were discussed.     

Load transfer characteristics of unilateral distal extension removable partial dentures with polyacetal resin supporting components

Background:  To photoelastically examine load transfer by unilateral distal extension removable partial dentures with supporting and retentive components made of the lower stiffness polyacetal resins.
Methods:  A mandibular photoelastic model, with edentulous space distal to the right second premolar and missing the left first molar, was constructed to determine the load transmission characteristics of a unilateral distal extension base removable partial denture. Individual simulants were used for tooth structure, periodontal ligament, and alveolar bone. Three designs were fabricated: a major connector and clasps made from polyacetal resin, a metal framework as the major connector with polyacetal resin clasp and denture base, and a traditional metal framework I-bar removable partial denture. Simulated posterior bilateral and unilateral occlusal loads were applied to the removable partial dentures.
Results:  Under bilateral and left side unilateral loading, the highest stress was observed adjacent to the left side posterior teeth with the polyacetal removable partial denture. The lowest stress was seen with the traditional metal framework. Unilateral loads on the right edentulous region produced similar distributed stress under the denture base with all three designs but a somewhat higher intensity with the polyacetal framework.
Conclusions:  The polyacetal resin removable partial denture concentrated the highest stresses to the abutment and the bone. The traditional metal framework I-bar removable partial denture most equitably distributed force. The hybrid design that combined a metal framework and polyacetal clasp and denture base may be a viable alternative when aesthetics are of primary concern.     

用三维有限元方法对单端固定桥进行应力分析

目的分析磨牙游离缺失单端固定桥修复的受力情况。方法运用三维有限元应力分析法,对一侧磨牙游离缺失通过改变牙槽骨支持高度,采用不同基牙数目,不同桥体长度建立不同的单端固定桥有限元模型进行应力和位移的计算和分析。结果较高的应力集中在游离端近中的基牙上,牙槽骨高度降低会增加基牙的移位及应力集中;单纯增加基牙的数目不会导致牙周组织中应力明显相应减少;基牙数目增加会减少修复体移位及应力集中;增加桥体长度会引起义齿应力明显增加和向远中移位。结论游离缺失端行单端固定桥修复最好选择桥体为一个磨牙长度,且基牙数至少两个,以提高单端固定桥修复的成功率。     

The influence of medial implant location in three-unit posterior cantilever fixed partial dentures on stress distribution in surrounding mandibular bone

This study examined the influence of medial implant location in three-unit posterior cantilever fixed partial dentures (FPDs) on stress distribution in mandibular bone surrounding two implants. A three-dimensional finite element model that included three-unit FPD and two cylindrical-type implants (4 mm in diameter and 10 mm in length) osseointegrated in the posterior mandible, was digitized. Five different models were created according to the medial implant location between the missing second premolar and the first molar location. The distal implant was fixed at the missing second molar location. Oblique bite force of 100 N at 30 degrees buccal to the vertical direction was directed on each of three artificial teeth, respectively and simultaneously, while the lower surface of the mandible was fixed. The maximum equivalent stress in the cortical and the trabecular bone generally increased as the medial implant shifted to a distal position. Under the simultaneous bite force, relatively low maximum stresses within the cortical bone: between 55 MPa and 57 MPa, were shown in the models with the medial implant placed within the range of one implant diameter from the most medial position, while higher maximum stresses: between 64 MPa and 73 MPa, were demonstrated with more distally placed medial implants. The results suggest that reasonably low mechanical stress in the surrounding bone may be assured when the medial implant is placed in the range between the missing second premolar position and one implant diameter distal from that location.     

An Investigation of Tooth/Implant-Supported Fixed Prosthesis Designs with Two Different Stress Analysis Methods: An in vitro Study

PURPOSE: Tooth/implant-supported fixed prostheses (TIFPs) present biomechanical design problems, because the implant is rigidly anchored within the alveolus, and the tooth is attached by the periodontal ligament that allows movement. While TIFP designs with rigid connectors (RCs) are preferred by many clinicians, the designs containing non-rigid connectors (NRCs) are suggested as a method to compensate for these mobility differences. However, studies have failed to show the advantage of one design over the other. This study examined stresses formed around the implant and natural tooth abutments under occlusal forces, using two dimensional finite element (2D-FEM) and photoelastic stress analysis methods (PSAM). MATERIALS AND METHODS: Connection of TIFP designs were investigated in distal extension situations using stress analysis interpreted with the 2D-FEM and PSAM. Three TIFP (screw type implant, 3.75 mm x 13 mm) models with various connection designs (i.e., rigidly connected to an abutment tooth, connected to an abutment tooth with an NRC, connected to an abutment implant with an NRC) were studied. The stress values of the three models loaded with vertical forces (250 N) were analyzed. RESULTS: The highest level of stresses around the implant abutment was noted on the TIFPs with the RC. On the other hand, NRCs incorporated into prostheses at the site of the implant abutment reduced the level of stresses in bone. CONCLUSION: It could be suggested that if tooth and implant abutments are to be used together as fixed prostheses supports, NRCs should be placed on the implant abutment-supported site.     

Intrusion Of Teeth In The Combination Implant-to-Natural-Tooth Fixed Partial Denture: A Review of the Theories

This article reviews the literature dealing with the combination implant-to-natural-tooth-supported fixed partial denture. The restoration of masticatory function with a combination implant-to-natural-tooth fixed partial denture is associated with a variety of undesirable clinical sequelae, including the breakage of implant components, damage to the abutment teeth, or intrusion of the abutment teeth. Theories regarding intrusion of abutment teeth combined with implants for fixed partial dentures are only speculative. Several theories are presented to explain the intrusion of natural teeth in association with implant-to-natural-tooth fixed partial dentures. One of the first theories was based on the idea that a lack of normal stimulation of the periodontal ligament produces atrophy of the periodontal ligament and intrusion of the tooth. The remaining theories relate to excessive forces being placed on the natural tooth, resulting in movement of the tooth to a less stressful position. These forces are placed on the tooth by differential energy dissipation, mandibular flexion and torsion, flexion of the fixed partial denture framework, impaired rebound memory, debris impaction or microjamming, or ratchet effect related to the use of precision attachments. Based a review of the literature, a philosophy for treating combination implant-to-natural-tooth restorations is presented.     

Mechanical analysis of the effects of implant position and abutment height on implant-assisted removable partial dentures

PurposeAn increasing number of clinical reports describe the use of dental implants as abutments in implant-assisted removable partial dentures (IARPD). We used three-dimensional finite element analysis to evaluate IARPD as a unilateral mandibular distal extension denture. Specifically, the mechanical effects of implant position and abutment height on the abutment tooth, denture, and denture-supporting tissue were assessed.MethodsThe models analyzed were defects of the left mandibular second premolar and first and second molars prosthetically treated with an IARPD using one implant for each tooth position. There were two abutment heights: one equal to that of the mucosa and another that was elevated 2 mm above the mucosa. Six models were constructed.ResultsFor mucosal-level abutments, movement of the abutment tooth was lower for implants positioned distal to the abutment tooth than for those positioned medial to the abutment tooth. For elevated abutments, movement of the abutment tooth was lower for implants positioned medial to the abutment tooth than for those positioned distal to the abutment tooth.ConclusionsThe mechanical effects on abutment teeth at the same implant position differed in relation to implant abutment height.