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.     

Photoelastic stress analysis of load transfer to implants and natural teeth comparing rigid and semirigid connectors

STATEMENT OF PROBLEM: Controversy exists regarding the connection of implants to natural teeth. PURPOSE: This simulation study measured photoelastically the biologic behavior of implants. Stress transfer patterns with variable implant support and simulated natural teeth through rigid and nonrigid connection were examined under simulated functional loads. MATERIAL AND METHODS: A photoelastic model of a human left mandible edentulous distal to first premolar was fabricated having 2 screw type implants (3.75x13 mm) embedded within the edentulous area. Two fixed prosthetic restorations were fabricated with either a nonsplinted proximal contact or a soldered proximal contact, and cast precision dowel attachment between implant areas and simulated tooth. Simulated vertical occlusal loads were applied at fixed locations on the restorations. Stresses, which developed in the supporting structure, were monitored photoelastically and recorded photographically. RESULTS: The rigid connector in the 1 implant situation caused only slightly higher stresses in the supporting structure than the nonrigid connector. The distally loaded 1 and 2 implant-supported restoration produced the highest apical stresses, which occurred at the distal implant. The rigid connector demonstrated the greatest stress transfer in the 2 implant-supported restoration. CONCLUSIONS: Lower stresses apical to the tooth or implant occurred with forces applied further from the supporting abutment. Although the least stress was observed when using a nonrigid connector, the rigid connector in particular situations caused only slightly higher stresses in the supporting structure. The rigid connector demonstrated more widespread stress transfer in the 2 implant-supported restoration. Recommendations for selection of connector design should be based on sound clinical periodontal health of a tooth and the support provided by implants.     

Strains recorded in a combined tooth-implant restoration: an in vivo study

Implant-supported fixed prosthesis is a treatment option to restore missing teeth. Occasionally, it is necessary to connect teeth and implants as abutments for these restorations. Whether such restorations can be recommended is a matter of debate. This in vivo study measured strains involved in connecting implants to a natural tooth and compared rigid and nonrigid tooth/implant connections. A patient was treated with mandibular unilateral fixed prosthesis supported by two implants and one proximal tooth. Strain gauges were cemented to the experimental framework restoration. Recordings were obtained from the restorations while the patient bit on a wooden stick on the day of placement and after 2 weeks in function, using both rigid and nonrigid attachment connections. A significant difference was found in horizontal deformation of the tooth/crown between day 1 and 2 weeks later. Vertical deformations were smaller than horizontal ones. After applying biting forces, horizontal and vertical deformations were maintained. Strain recorded in a clinical setting revealed mostly horizontal strains generated in a combined tooth/implant device. These strains were maintained after a 2-week recording. Within the limitation of this study, combined tooth/implant restorations could be a potential complication and could cause an intrusion of a natural abutment regardless of the type of connection (rigid or nonrigid).     

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.     

Influence of the Connector and Implant Design on the Implant–Tooth‐Connected Prostheses

Purpose: The purpose of this study was to evaluate stress transfer patterns between implant–tooth‐connected prostheses comparing rigid and semirigid connectors and internal and external hexagon implants. Materials and Methods: Two models were made of photoelastic resin PL‐2, with an internal hexagon implant of 4.00 × 13 mm and another with an external hexagon implant of 4.00 × 13 mm. Three denture designs were fabricated for each implant model, incorporating one type of connection in each one to connect implants and teeth: 1) welded rigid connection; 2) semirigid connection; and 3) rigid connection with occlusal screw. The models were placed in the polariscope, and 100‐N axial forces were applied on fixed points on the occlusal surface of the dentures. Results: There was a trend toward less intensity in the stresses on the semirigid connection and solid rigid connection in the model with the external hexagon; among the three types of connections in the model with the internal hexagon implant, the semirigid connection was the most unfavorable one; in the tooth–implant association, it is preferable to use the external hexagon implant. Conclusions: The internal hexagon implant establishes a greater depth of hexagon retention and an increase in the level of denture stability in comparison with the implant with the external hexagon. However, this greater stability of the internal hexagon generated greater stresses in the abutment structures. Therefore, when this association is necessary, it is preferable to use the external hexagon implant.     

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.     

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).     

Biomechanical Evaluation of Tooth‐ and Implant‐Supported Fixed Dental Prostheses with Various Nonrigid Connector Positions: A Finite Element Analysis

Purpose: In the tooth‐ and implant‐supported fixed dental prosthesis (FDP), rigid and nonrigid connector (NRC) designs have been preferred by clinicians for many years. The aim of this study was to analyze the stress distribution on the connecting areas of the superstructure and supporting structure of the tooth‐ and implant‐supported FDP designs under both static vertical and oblique occlusal loads. Materials and Methods: Four 2D finite element analysis (FEA) models were prepared presuming that the first and second molars were missing, and that the implant (3.80‐mm diameter × 13‐mm length) was placed in the second molar NRC design and patrix‐matrix position supported by teeth/implants. Nonlinear contact elements were used to simulate a realistic interface fixation within the implant system and the sliding function of the NRC. Supporting periodontal ligament and alveolar bone (cortical and trabecular) were also modeled. Linear static analysis was performed on the prepared 2D solid models with a total masticatory force of 250 N (50 N for premolar, 100 N for first molar, 100 N for second molar), 0° (at a right angle) and 30° to the long axis of the supports. The maximum equivalent Von Mises (VM_Max) was analyzed around the supporting teeth/implant and connector areas on tooth‐ and implant‐supported FDP. Results: The simulated results indicated that the highest level of VM_Max (400.377 MPa) was observed on the NRC with the matrix positioned on the implant site of tooth‐ and implant‐supported FDP under vertical occlusal load. The highest level of VM_Max (392.8 MPa) under oblique occlusal load was also observed on the same model; however, the lowest VM_Max value around implants was observed with the NRC when the patrix was positioned on the implant site of the FDP. Under vertical occlusal loads, in designs where the NRC was placed on the implant site, the stress formed around the implant decreased when compared to the designs where the NRCs were positioned on the tooth site. Conclusions: The efficiency of the NRC exhibited varying behavior depending on the direction of the load applied. The use of the patrix part of the NRC on the implant site may be more efficient in reducing the stress formation around the implant.     

Nonrigid connection of tooth with implants in the esthetic zone with a ceramic restoration: a clinical report

Restoring edentulous areas with fixed prostheses can be challenging, especially when key abutment teeth are missing and implant placement is not an option. Sometimes, clinicians are faced with situations where teeth have to be connected with implants even though long-term prognosis of those connections may be questionable. This clinical report presents a connection of 2 implants with 1 tooth in the esthetic zone with a nonrigid connection. Two zirconia custom abutments and 1 zirconia coping definitively cemented on the tooth were used. A zirconia superstructure, veneered with porcelain, was cemented with provisional cement on the abutments and the coping.     

Freestanding and tooth-implant connected prostheses in the treatment of partially edentulous patients Part II: An up to 15-years radiographic evaluation

Abstract: A total of 123 patients were followed between January 1983 and July 1998 with 140 tooth‐implant connected prostheses. The age of the patients at prosthesis installation ranged from 20 to 79 years (mean 51.8). 339 (Brånemark^® system) implants were connected to 313 teeth. The loading time ranged from 1.5 to 15 years (mean: 6.5). 123 patients were randomly selected as a control group with freestanding implant‐supported prostheses only. The age of the patients at prosthesis installation ranged from 22 to 78 years (mean 52.3). The loading time for the 329 freestanding (Brånemark^® system) implants ranged from 1.3 to 14.5 years (mean: 6.2). Evolution of the marginal bone stability around the implant in the tooth‐implant connected as well as the freestanding group was studied with respect to the prognosis of the implants. Over the period from 0 to 15 years, there was significantly more marginal bone loss (0.7 mm) in tooth‐implant connected versus freestanding prostheses. No significant difference in marginal bone loss was found between the non‐rigid tooth‐implant connected prostheses versus freestanding prostheses. However, there was a significant difference in marginal bone loss for rigid and multi‐connected tooth‐implant connected prostheses versus freestanding ones. The results of this study indicate that more bone is lost around implants which are rigidly connected to teeth. This suggests that bending load, which is increased in tooth‐implant connected prostheses, might be responsible for this phenomenon. These observations favor the use of freestanding prostheses whenever possible. However, the clinical significance of greater bone loss in rigid versus non‐rigid connections might outweigh the annoying phenomenon of tooth intrusion in the case of non‐rigid tooth connection, when connection is considered.     

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.     

Mechanical aspects of a Br?nemark implant connected to a natural tooth: an in vitro study.

Mechanical in vitro tests of the Br?nemark implant disclose that the screw joint which attaches the prosthetic gold cylinder and the transmucosal abutment to the fixture forms a flexible system. This inherent flexibility seems to match well the vertical mobility of a supporting tooth connected to the implant. Calculations of vertical load distribution based on measured flexibility data demonstrate that the forces are shared almost equally between tooth and implant even without taking the flexibility of the surrounding bone or the prosthesis into account. The therapy of a single Br?nemark implant connected to a natural tooth should be considered without any additional element of a flexible nature. Mechanical tests and theoretical considerations, however, indicate that the transverse mobility of the connected tooth should be limited and that the attachment of the prosthesis to the tooth should be of a rigid design to avoid gold-screw loosening.     

The influence of prosthesis designs and loading conditions on the stress distribution of tooth-implant supported prostheses

The aim of this study was to observe the influence of prosthesis design and loading condition on the stress distributions of tooth-implant supported prostheses. Six 2D finite element models, two reference models, and four experimental models were computed to simulate different prosthesis designs. Six different loading conditions were applied to investigate the stress distributions of tooth and implant, respectively. The stresses of reference models were considered as 100%; the stresses of experimental models at the same locations were compared with those of reference models. The stresses around implants were higher than those around teeth. When vertical loading was applied only on the implant, the stresses to both the implant and teeth were at their lowest. The highest stress to the tooth was in the model TTPF and the lowest in the model TPFF. The highest stress to the implant was in the model TPPF and the lowest in the model TPFF. These data indicated that the loading on the tooth-implant supported prosthesis was mainly supported by the implant. Minimizing the loading on the tooth decreased the stress to both the tooth and the implant. Adding fixtures as abutment was more effective in decreasing the stress than adding tooth as abutment in tooth-implant supported prosthesis.     

Biomechanical interactions in tooth-implant-supported fixed partial dentures with variations in the number of splinted teeth and connector type: a finite element analysis.

OBJECTIVE: The aim of this study was to investigate the biomechanical interactions in tooth-implant-supported fixed partial dentures (FPDs) under several loading conditions with different numbers of splinted teeth and connector types (rigid and non-rigid) by adopting the three-dimensional (3D) non-linear finite element (FE) approach. MATERIAL AND METHODS: A 3D FE FPD model was constructed containing one Frialit-2 implant in the mandibular second-molar region splinted to the first and second premolars. Frictional contact elements were used to simulate realistic interface conditions within the implant system and the non-rigid connector function. The main effects for each level of the three investigated factors (loading condition, number of splinted teeth and connector type) in terms of the stress values and dissimilar mobility of the natural teeth and implant were computed for all models. RESULTS: The results indicated that load condition was the main factor affecting the stress developed in the implant, bone and prosthesis when comparing the type of connector and the number of splinted teeth. The stress values were significantly reduced in centric or lateral contact situations once the occlusal forces on the pontic were decreased. However, the prosthesis stress for the non-rigid connections was increased more than 3.4-fold relative to the rigid connections. Moreover, the average tooth-to-implant displacement ratios (R(TID)) with a non-rigid connection were obviously larger than those for rigid connections under axial loading forces. Adding an extra tooth to support a three-unit tooth-implant FPD only exploited its function when the prosthesis withstood lateral occlusal forces. CONCLUSIONS: The load condition is the main factor affecting stress distribution in different components (bone, prosthesis and implant) of tooth-implant-supported FPDs. Minimizing the occlusal loading force on the pontic area through selective grinding procedures could reduce the stress values obviously. A non-rigid connector may more efficiently compensate for the dissimilar mobility between the implant and natural teeth under axial loading forces but with the risk of increasing unfavorable stresses in the prosthesis.     

Three-dimensional stress analysis of tooth/lmplant-retained long-span fixed dentures

PURPOSE: The aim was to assess the influence of connection of the canine teeth to implant-retained long-span fixed dentures on stress in mandibular bone using finite element analysis. MATERIALS AND METHODS: Each 3-dimensional model included bone, 6 implants, both natural canines, and superstructures. Each model simulated 1 of 4 prosthetic designs: a tooth/implant-retained 1-piece superstructure (One-piece), 3-piece superstructures with an anterior and 2 posterior segments with unconnected teeth (UnConnect), 3-piece superstructures with the teeth connected to the posterior segments (PostConnect), and 3-piece superstructures with the teeth connected to the anterior segment (AntConnect). A nonlinear elastic modulus was applied to the periodontal ligament (PDL). Maximum intercuspal (IP), canine-protected (CP), and group-function (GF) occlusions were simulated. RESULTS: The maximum stresses in the peri-implant regions of the bone were lower for the One-piece than for the other superstructures. In PostConnect and AntConnect, the maximum stress in the PDL was lower than that in UnConnect, but the stress in the peri-implant bone was comparable in those 3 models. The stresses were lower in the GF model than in the CP model. The stress created in the peri-implant bone was insensitive to the modes of the teeth/implant connection in long-span fixed dentures. CONCLUSION: Within the limitation of the mechanical analysis, it is suggested that the connection of the canine tooth to the implant-retained long-span superstructures is an acceptable option in partially edentulous patients.     

冠外弹性附着体义齿修复游离端缺牙的有限元分析

目的:观察冠外弹性附着体(extracoronal resilient attachment,ERA)运动的力学特点及其对游离端义齿支持组织的影响。方法:建立ERA附着体义齿修复牙列游离端缺损的有限元建模,观察在相同的附着体结构下,阴阳极之间的连接方式和载荷因素对义齿支持组织EQV应力(equivalent stress)的影响。结果:附着体刚性与弹性连接方式下的应力分布规律相同,但颊舌向载荷下,弹性组的基牙牙周组织应力较刚性组小,而缺牙区牙槽嵴远中区域的应力较大(P<0.05)。弹性组中的附着体在颊舌向载荷下的转动达到最大值。结论:ERA附着体通过义齿基托部分的旋转和下沉运动,使部分力转移至缺牙区牙槽嵴的远中区域;其在侧运动中的缓冲作用优势明显。     

Splinting osseointegrated implants and natural teeth in rehabilitation of partially edentulous patients. Part I: Laboratory and clinical studies

summary A significant clinical consideration in the restoration of partial edentulism with implant and tooth-supported prostheses is whether implants and natural teeth abutments should be splinted, and if so, in what manner. This article presents a review of laboratory and clinical studies related to splinting. Stress analysis studies reveal high stress concentration around the implant neck when rigidly connected to teeth. This was not borne out in in vivo studies in short-span bridges. While stress absorbing elements have been advocated to redistribute and reduce stress concentration away from the implant neck where bone resorption is often seen, finite element analysis and photo-elastic studies demonstrate that such stress absorbing elements may be effective only when their resiliency is in the same order of magnitude as the periodontal ligament. Clinical studies reporting life table statistics in combined implant and tooth restorations do not show adverse effects of splinting teeth to implants. These studies, however, are mostly short-term reports oh survival with results that are as yet inconclusive. The issue of connecting with rigid or non-rigid connectors remains unresolved with a growing body of information favouring retrievable short-span rigid connection to non-mobile teeth. Root intrusion is a potential clinical hazard of non-rigid connection.     

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.     

Mechanical interactions of an implant/tooth-supported system under different periodontal supports and number of splinted teeth with rigid and non-rigid connections

OBJECTIVES: This study investigated the mechanical interactions of implant-teeth splinting systems under different periodontal supports and number of splinted teeth with rigid and non-rigid connectors using non-linear finite element (FE) approach. METHODS: Two FE models with normal and compromised periodontal supports containing a Frialit-2 implant splinted to the first and second premolars were constructed. Non-linear contact elements were used to simulate a realistic interface fixation within the implant system and the sliding function of the non-rigid connector. ANOVA was used to test for relative importance of the investigated factors and main effects for each level of the three investigated factors (periodontal supports, teeth splinting and connector designs) in terms of the stress values were performed. RESULTS: The simulated results indicated that the cross-interaction of the periodontal support and the splinting situation was a major factor affecting the stress value in alveolar bone. An additional splinting decreased the stress values of bone significantly for a compromised periodontal support. The individual factor of periodontal support also influenced the stress found in the alveolar bone (28%) and implant (72%), and the stress values increased when the periodontal support was reduced. Using different connectors affected the stresses found in bone (15%), implant (21%) and prosthesis (99%). The stress values of the implant and prosthesis increased, but were decreased in bone when the splinting system used non-rigid connectors. The mobility of natural teeth and the implant system between non-rigid and rigid connections showed only small differences. CONCLUSIONS: A non-rigid connector should be used with caution since it breaks the stress transfer and increases the unfavorable stress values in the implant system and prosthesis. The tooth/implant-supported system with an additional splinting is more efficient in compromised periodontal supports.     

A comparison of the stress transfer characteristics of a dental implant with a rigid or a resilient internal element

It has been suggested that there is a unique set of problems associated with joining an implant and a natural tooth with a fixed partial denture. The manufacturer of the IMZ implant system claims that this procedure can be accomplished successfully because of the planned stress-distributing characteristics of their resin internal (intramobile) element. This study compared the difference in the stress patterns generated in photoelastic plastic by an IMZ implant with a resilient or a rigid internal element. Under a standardized cantilever load, the stress patterns were photographed in the field of a circular polariscope. The total stress areas were calculated and a statistical comparison performed. The static load conditions of the model demonstrated no statistical difference between the area of stress pattern generated by an IMZ implant with or without a resilient internal element. Moreover, a single load produced the same deflection of the cantilever beam regardless of which element was interposed.