RESUMO
STATEMENT OF PROBLEM: Whether adhesive zirconia ceramic removable partial denture attachments are feasible with current technology is unclear. PURPOSE: The purpose of this finite element analysis and in vitro study was to evaluate the effect of the lever arm, tooth preparation, and aging on the loading of the tooth-zirconia attachment interface. MATERIAL AND METHODS: Three different finite element analysis (FEA) models allowing for the loading of an adhesive attachment either directly or through a removable partial denture were used. Two models represented a human tooth with 2 different types of attachments, while the third model also included a removable partial denture. For the evaluation of bond strength, a combination of shear and hydrostatic stress was used. In addition, composite resin teeth were fabricated, and zirconia bars were bonded to them with varying tooth preparations and lever arm lengths. In 1 group the influence of aging was analyzed. Fracture load was determined by using a universal testing machine. Statistical analysis was based on the Shapiro-Wilk normality test, ANOVA, and Games-Howell test (α=.05). RESULTS: The maximum stress of 65 MPa occurring in the bonding area was reduced to 37 MPa by adding a retainer to the attachment. Loading of the denture resulted in a maximum stress of 9 MPa. Mean fracture loads ranged from 33.6 N to 209.1 N. Preparing a flat bonding surface showed a nonsignificant increase (P=.197), whereas aging led to a nonsignificant decrease in fracture load (P=.075). A lever arm extended by 2 mm significantly reduced fracture load (P=.002). The addition of an occlusal-distal (OD) cavity led to a nonsignificant increase (P=.186), which became significant when a mesial-occlusal-distal (MOD) preparation was applied (P=.001). CONCLUSIONS: Adhesive zirconia attachments should use a MOD cavity and have a cross section of at least 2.5×2.5 mm. The attachment should not extend more than 3 mm.
Assuntos
Prótese Parcial Removível , Cerâmica , Cimentos Dentários , Análise do Estresse Dentário/métodos , Análise de Elementos Finitos , Humanos , Teste de Materiais , ZircônioRESUMO
Acetabular cup endoprostheses are frequently placed in pelvic bone, employing the mechanical principle of press fit. While a sufficiently stable bone-implant connection is desirable, deformation of the cup and fracture of the pelvis should be avoided. The goal of this work is to demonstrate the importance of the elastic properties of bone on the amount of press fit achievable in a specific situation. On the basis of previous work describing the relation between relative bone mineral density and relative elastic modulus for cortical and trabecular bone, mechanical equations were used for analyzing the press-fit loading situation of an acetabular cup. Additionally, a two-dimensional finite element model was used for visualizing the stress and strain situation in the host bone occurring as a consequence of implant insertion, as well as the effect of moment loads acting on the acetabular cup. Given the fact that oversizing the implant for a specific recipient site is the only clinical means of optimizing press fit, knowledge of the elastic properties of the host bone before implant selection would be beneficial. Such information could, for instance, be derived from intraoperative compressive testing of the host bone.
Assuntos
Acetábulo/fisiologia , Acetábulo/cirurgia , Artroplastia de Quadril/métodos , Densidade Óssea/fisiologia , Prótese de Quadril , Modelos Biológicos , Ajuste de Prótese/métodos , Força Compressiva , Simulação por Computador , Desenho Assistido por Computador , Módulo de Elasticidade/fisiologia , Análise de Falha de Equipamento , Fricção , Humanos , Pressão , Desenho de Prótese , Estresse Mecânico , Propriedades de Superfície , Temperatura , Resistência à Tração/fisiologiaRESUMO
OBJECTIVES: It was the purpose of this finite element analysis to compare the implant-restoration connection created by Procera Implant Bridge (PIB) and conventional screw-retained prostheses with respect to screw loading and gap formation. METHOD AND MATERIALS: Finite element models representing a conventional screw-retained restoration and a PIB were set up. A horizontal load of 200N was applied on the restorations while resulting gap formation and screw loading was recorded. RESULTS: Increasing the preload of the retaining screws led to a decrease in gap formation. Smaller gaps were observed in the conventional restorations. Loading of the screws was of comparable magnitudes in both cases. CONCLUSION: The use of screw-retained implant-supported restorations representing butt-joint connections at the restorative interface may result in increased gap formation.
Assuntos
Projeto do Implante Dentário-Pivô/instrumentação , Prótese Dentária Fixada por Implante , Análise do Estresse Dentário , Retenção de Dentadura/instrumentação , Prótese Parcial Fixa , Prótese Dentária Fixada por Implante/efeitos adversos , Análise de Elementos Finitos , HumanosRESUMO
Micromotion between dental implant and bony socket may occur in immediate-loading scenarios. Excessive micromotion surpassing an estimated threshold of approximately 150 µm may result in fibrous encapsulation instead of osseointegration of the implant. As finite element analysis (FEA) has been applied in this field, it was the aim of this study to evaluate the effect of implant-related variables and modeling parameters on simulating micromotion phenomena. Three-dimensional FEA models representing a dental implant within a bony socket were constructed and used for evaluating micromotion (global displacement) and stress transfer (von Mises equivalent stress) at the implant-bone interface when static loads were applied. A parametric study was conducted altering implant geometry (cylinder, screw), direction of loading (axial, horizontal), healing status (immediate implant, osseointegrated implant), and contact type between implant and bone (friction free, friction, rigid). Adding threads to a cylindrically shaped implant as well as changing the contact type between implant and bone from friction free to rigid led to a reduction of implant displacement. On the other hand, reducing the elastic modulus of bone for simulating an immediate implant caused a substantial increase in displacement of the implant. Altering the direction of loading from axial to horizontal caused a change in loading patterns from uniform loading surrounding the whole implant to localized loading in the cervical area. Implant-related and bone-related factors determine the degree of micromotion of a dental implant during the healing phase, which should be considered when choosing a loading protocol.
Assuntos
Implantes Dentários , Análise do Estresse Dentário , Carga Imediata em Implante Dentário , Osseointegração , Dente Suporte , Implantação Dentária Endóssea , Análise do Estresse Dentário/métodos , Módulo de Elasticidade , Análise de Elementos Finitos , Fricção , Humanos , Modelos Lineares , Modelos Biológicos , MovimentoRESUMO
Micromotion of dental implants may interfere with the process of osseointegration. Using three different types of virtual biomechanical models, varying contact types between implant and bone were simulated, and implant deformation, bone deformation, and stress at the implant-bone interface were recorded under an axial load of 200 N, which reflects a common biting force. Without friction between implant and bone, a symmetric loading situation of the bone with maximum loading and displacement at the apex of the implant was recorded. The addition of threads led to a decrease in loading and displacement at the apical part, but loading and displacement were also observed at the vertical walls of the implants. Introducing friction between implant and bone decreased global displacement. In a force fit situation, load transfer predominantly occurred in the cervical area of the implant. For freshly inserted implants, micromotion was constant along the vertical walls of the implant, whereas, for osseointegrated implants, the distribution of micromotion depended on the location. In the cervical aspect some minor micromotion in the range of 0.75 µm could be found, while at the most apical part almost no relative displacement between implant and bone occurred.
RESUMO
Vertical root fractures (VRF) of endodontically treated teeth constitute a severe clinical condition frequently requiring removal of the affected tooth. Numerous attempts have been made to find the cause for VRF without reaching definitive conclusions. As changes in moisture content have been reported to appear as a consequence of root canal therapy, it is the goal of this paper to evaluate associated volume changes as a possible cause for VRF. Considering disk shaped horizontal cross sections of endodontically treated teeth with a moisture content of dentin decreasing from the root surface towards the root canal, both relative circumferential and relative radial stresses resulting from volume changes of dentin were calculated. It could be shown that the presence of a root canal itself increases radial and circumferential stresses acting on root dentin by a factor of two. Reduction in moisture content of dentin at the wall of the root canal results in shrinkage of the tooth structure and tensile stress. On the outer surface of the root, compressive stresses occur. Thus, VRF would start at the canal wall and propagate to the root surface. The theory presented appears to be consistent with previous reports on stress development as a consequence of dehydration of dentin and finite element analysis on root fractures. It may be concluded that dehydration of dentin induces cracks at the walls of a root canal which subsequently grow as a result of cyclic loading or traumatic overload.
Assuntos
Dentina/metabolismo , Análise de Elementos Finitos , Fenômenos Mecânicos , Fraturas dos Dentes/metabolismo , Raiz Dentária/metabolismo , Estresse Mecânico , Fraturas dos Dentes/etiologia , Raiz Dentária/lesõesRESUMO
PURPOSE: Current methods for the evaluation of alveolar bone quality and dental implant stability have been shown to provide inconsistent results. The aim of this investigation was to validate a novel diagnostic device (BoneProbe) for the objective classification of alveolar bone during dental implant surgery. MATERIALS AND METHODS: A metal cylinder (diameter, 3.5 mm) split into six segments was used as a sensor that could be positioned in implant sockets and expanded while the force needed to expand the site was recorded. Simulating all surgical steps, implants were placed into polyurethane foam materials (n = 100 implants) and human cadaver bone (n = 110 implants). Bone quality (cortical bone thickness, trabecular bone density, drilling resistance, implant insertion torque, compressive testing) and primary implant stability (Osstell, Periotest) were evaluated as reference data. RESULTS: In polyurethane foam, significant correlations between all parameters (Pearson correlation coefficients) and a significant influence of the different polyurethane foam materials on all measurement results (multiple analysis of variance with Pillai trace) were found. In general, in human cadaver bone, weaker correlations between the different measurement techniques were seen (Pearson product-moment correlation). With the exception of compressive testing and radiographic assessment of trabecular bone density, all methods were able to differentiate between mandibular and maxillary bone. CONCLUSIONS: Based on these in vitro results, it appears that intraoperative testing of alveolar bone allows for a reproducible classification of bone quality. Because the proposed system is independent of any specific implant design, this device could be used for establishing a universally valid bone classification system.
Assuntos
Processo Alveolar/anatomia & histologia , Densidade Óssea/fisiologia , Implantação Dentária Endóssea/instrumentação , Cuidados Intraoperatórios/instrumentação , Cadáver , Módulo de Elasticidade , Desenho de Equipamento , Humanos , Mandíbula/anatomia & histologia , Maxila/anatomia & histologia , Modelos Anatômicos , Osteotomia/instrumentação , Poliuretanos/química , Estresse Mecânico , Torque , VibraçãoRESUMO
Alveolar bone quality is considered to be an important prognostic factor in dental implant stability. Although numerous methods have been described, no technique allows for reliable diagnostics. The purpose of this study was to determine if strain measurements on the shaft of a contra angle handpiece during implant bed preparation could be used for the determination of bone quality. Experiments in polyurethane foam and human cadaver bone were conducted to investigate whether strain measurements could be correlated with other diagnostic parameters, such as the surgeon's tactile sensation during drilling, implant insertion torque, implant stability, elastic modulus of bone and bone quality as assessed radiographically. Tests were also performed to determine if strain measurements could be used to distinguish various types of bone. As axial feed and contact pressure during the drilling process could not be standardized under simulated clinical conditions, substantial deviations in the time needed to complete the drilling occurred. Under controlled circumstances using polyurethane foam, this problem could be addressed by a normalization procedure, but great variations occurred in human cadaver bone. As bone quality could not be reliably determined, especially when a cortical layer was present, strain measurements on a contra angle handpiece appears to be inappropriate for this purpose.
Assuntos
Processo Alveolar/fisiologia , Densidade Óssea/fisiologia , Implantação Dentária Endóssea/métodos , Instrumentos Odontológicos , Processo Alveolar/diagnóstico por imagem , Fenômenos Biomecânicos , Substitutos Ósseos/química , Cadáver , Implantação Dentária Endóssea/instrumentação , Implantes Dentários , Retenção em Prótese Dentária , Módulo de Elasticidade , Desenho de Equipamento , Humanos , Mandíbula/cirurgia , Maxila/cirurgia , Osteotomia/instrumentação , Poliuretanos/química , Pressão , Radiografia , Reprodutibilidade dos Testes , Estresse Mecânico , Alvéolo Dental/cirurgia , Torque , Tato/fisiologia , VibraçãoRESUMO
PURPOSE: Stress caused by a non-passively fitting implant superstructure may induce bone adaptation, thereby changing the magnitude of static implant loading. MATERIALS AND METHODS: In a previous investigation, repeated in vivo strain measurements were conducted on an implant-supported bar to evaluate changes in the magnitude of misfit resulting from bone remodeling processes. Both maximum (445 µm/m) and minimum (383 µm/m) strain values were simulated using a three-dimensional finite element model. The horizontal misfit needed to simulate experimentally determined strain values and the resulting stresses occurring in the restoration and the bone were quantified as von Mises equivalent stress. Additionally, different stages of osseointegration were modeled by altering the elastic modulus of bone immediately surrounding the implants. RESULTS: To simulate the maximum strain value, a horizontal misfit of 83.3 µm had to be introduced, whereas the minimum strain value could be simulated via a horizontal misfit of 71.5 µm. Maximum misfit caused stress magnitudes of 105 MPa in cortical bone and 5.3 MPa in trabecular bone. Minimum misfit caused stress magnitudes of 90 MPa in cortical bone and 4.6 MPa in trabecular bone. The difference between maximum and minimum horizontal misfit was 12 µm and led to a reduction in maximum stress levels of 15 MPa in cortical bone and 0.7 MPa in trabecular bone. Progressing osseointegration affected the stress situation of the supporting implants. CONCLUSIONS: Within the limitations of this investigation, it can be concluded that bone adaptation may lead to implant site displacement in the range of several micrometers. Early fixation of non-passively fitting superstructures on implants may lead to greater passivity of fit.
Assuntos
Processo Alveolar/fisiologia , Remodelação Óssea/fisiologia , Implantes Dentários , Prótese Dentária Fixada por Implante , Planejamento de Dentadura , Estresse Mecânico , Adaptação Fisiológica , Fenômenos Biomecânicos , Simulação por Computador , Projeto do Implante Dentário-Pivô , Análise do Estresse Dentário/instrumentação , Análise do Estresse Dentário/métodos , Análise de Elementos Finitos , Humanos , Arcada Edêntula/reabilitação , Osseointegração/fisiologiaRESUMO
OBJECTIVE: Finite element analysis (FEA) has been frequently used to study the loading situation of dental implants and bone resulting from the fixation of nonpassively fitting restorations. The goal of the present investigation was to demonstrate the effect of geometric model parameters and mesh size on FEA results. METHOD AND MATERIALS: Five three-dimensional FEA models representing a three-unit fixed dental prosthesis (FDP) supported by two terminal implants were constructed. The models differed in terms of mesh size, bone geometry, implants, and restoration and were created either by joining virtual free-form objects or utilizing optical scans of existing components. By applying thermal changes in volume of specific elements in the area of the FDP pontic, a horizontal misfit of 10 Μm between implants and the restoration was introduced. The resulting loading situation of the bone around the implants was recorded as von Mises equivalent stress. RESULTS: Maximum stress magnitudes ranging from 13.1 to 24.9 MPa occurred in the cortical part of the implant site where the neck of the implant penetrates bone. In trabecular bone, loading magnitudes were lower by a factor of 20. Modeling implant threads did have a remarkable effect on the stress situation as well as different span lengths of the restorations modeled. All other parameters led only to small variations in maximum loading magnitudes. CONCLUSION: Simplistic FEA models based on virtual free-form objects with limited level of mesh refinement seem to allow for a basic evaluation of peri-implant bone loading resulting from the fixation of misfitting superstructures.
Assuntos
Processo Alveolar/fisiologia , Implantes Dentários , Adaptação Marginal Dentária , Prótese Dentária Fixada por Implante , Planejamento de Dentadura , Análise de Elementos Finitos , Fenômenos Biomecânicos , Simulação por Computador , Dente Suporte , Cimentos Dentários/química , Retenção de Dentadura , Prótese Parcial Fixa , Módulo de Elasticidade , Humanos , Imageamento Tridimensional , Modelos Biológicos , Estresse Mecânico , Propriedades de SuperfícieRESUMO
PURPOSE: To show, by comparison of horizontal, vertical, and angular misfit in a three-dimensional finite element model, that clinical methods for the evaluation of implant framework fit cannot provide objective results. MATERIALS AND METHODS: Two three-dimensional finite element models were designed for the simulation of experimentally determined strain values of three-unit fixed dental prostheses supported by two implants. Horizontal, vertical, and angular misfits between implants and restorations were used to create predetermined strain levels. The magnitudes of misfit and resulting bone loading were recorded as von Mises equivalent stresses for the different types of misfit. RESULTS: A horizontal misfit of 36 µm and a vertical misfit of 79 µm had to be modeled to simulate the experimentally determined strain values. An angular misfit of 0.083 degree (equivalent to a gap of 3 µm on one aspect of the implant) resulted in comparable strain levels. Bone loading in the cortical area around both implants ranged from 50 to 90 MPa for horizontal and vertical misfit. In trabecular bone, loading of 2 to 5 MPa was found. For the angular misfit, bone loading up to 20 MPa in the cortical layer and 1 MPa in the cervical part of the trabecular bone occurred at the implant where the misfit had been introduced. Horizontal and vertical misfits led to comparable loading patterns around both supporting implants. Under angular misfit, bone loading mainly occurred around the implant where the misfit had been introduced. Almost no loading was observed in the circumference of the contralateral implant. CONCLUSIONS: Minimal angular misfits between implant abutments and restorations, which cannot be detected clinically, may lead to substantial bone loading.
Assuntos
Processo Alveolar/fisiologia , Dente Suporte/efeitos adversos , Implantes Dentários/efeitos adversos , Prótese Dentária Fixada por Implante/efeitos adversos , Análise do Estresse Dentário , Fenômenos Biomecânicos , Simulação por Computador , Análise do Estresse Dentário/métodos , Análise de Elementos Finitos , Humanos , Imageamento Tridimensional , Modelos Biológicos , Ajuste de PróteseRESUMO
PURPOSE: Contradictory results have been reported on the comparability of implant stability measurements performed with the Periotest and the Osstell Mentor devices. The purpose of the present finite element analysis was to simulate the influence of the parameters implant length, bone quality (cortical thickness and damping factor), bone loss, and quality of transducer fixation on resonance frequency analysis (RFA) and damping capacity measurements. MATERIALS AND METHODS: Three-dimensional finite element models of implants placed in human mandibular bone were designed for the simulation of Periotest (Periotest value; PTV) and RFA (implant stability quotient) measurements. Three values for each of the parameters implant length, damping capacity of cortical and trabecular bone, thickness of cortical bone, bone loss, and quality of transducer fixation were obtained. Measurements were simulated at four stages of osseointegration. RESULTS: For all parameters, an increase in implant stability was found with increasing levels of osseointegration. Implant stability was positively correlated with implant length and thickness of cortical bone, with slightly converging values at increased levels of osseointegration. Varying the damping factor of bone had no significant effect. Implant stability was negatively correlated with bone loss, with slightly converging values at increased levels of osseointegration. Linear changes in implant length and bone loss caused nonlinear effects in implant stability values. Stiffness of transducer fixation had an impact on RFA measurements when values below 10 GPa were applied. CONCLUSION: Although both measuring devices reacted similarly when different parameters of implant stability were changed, good correlation between Periotest values and implant stability quotients was observed only when measurement values of implants without bone loss were considered.
Assuntos
Simulação por Computador , Implantes Dentários , Retenção em Prótese Dentária , Análise do Estresse Dentário/métodos , Modelos Biológicos , Perda do Osso Alveolar , Densidade Óssea , Planejamento de Prótese Dentária , Módulo de Elasticidade , Análise de Elementos Finitos , Humanos , Mandíbula , Osseointegração , Transdutores , VibraçãoRESUMO
Osteoporosis is characterized by decreasing of bone mass and bone strength with advanced age. For characterization of material properties of dense and cellular bone the volumetric bone mineral density (vBMD) is one of the most important contributing factors to bone strength. Often bending tests of whole bone are used to get information about the state of osteoporosis. In a first step, different types of cellular structures are considered to characterize vBMD and its influence to elastic and plastic material properties. Afterwards, the classical theory of plastic bending is used to describe the non-linear moment-curvature relation of a whole bone. For bending of whole bone with sandwich structure an effective second moment of area can be defined. The shape factor as a pure geometrical value is considered to define bone strength. This factor is discussed for a bone with circular cross section and different thickness of cortical bone. The deduced relations and the decrease of material properties are used to demonstrate the influence of osteoporosis to bone bending strength. It can be shown that the elastic and plastic material properties of bone are related to a relative bone mineral density. Starting from an elastic-plastic bone behavior with an constant yield stress the non-linear moment-curvature relation in bending is related to yielding of the fibres in the cross section. The ultimate moment is characterized by a shape factor depending on the geometry of the cross section and on the change of cortical thickness.
Assuntos
Densidade Óssea/fisiologia , Osso e Ossos/fisiologia , Desenvolvimento Ósseo/fisiologia , Elasticidade , Fêmur/fisiologia , Humanos , Rádio (Anatomia)/fisiologia , Estresse Mecânico , Resistência à Tração/fisiologiaRESUMO
PURPOSE: Implant-borne fixed partial dentures (FPDs) should fit passively in order to avoid complications ranging from screw loosening to loss of osseointegration. The aim of this study was to measure the strain development of three-unit and five-unit screw- and cement-retained implant-supported FPDs. Additionally, the influence of the parameters retention mechanism and FPD span were evaluated. MATERIALS AND METHODS: Three Straumann implants were anchored in a measurement model based on a real-life patient situation and strain gauges (SGs) were fixed mesially and distally adjacent to the implants and on the pontics of the superstructures. During cement setting and screw fixation of 40 implant FPDs (10 samples from each group: three-unit cementable; five-unit cementable; three-unit screw-retained; five-unit screw-retained), strain development was recorded. For statistical analysis, multivariate two-sample tests were performed with the level of significance set at p= 0.1. RESULTS: The mean strain values for the four FPD groups at the different SG sites ranged from 26.0 to 637.6 microm/m. When comparing the four groups, no significant differences in strain magnitude could be detected. Similarly, a comparison of the two FPD spans revealed no significant difference (p= 0.18 for cementable FPDs; p= 0.22 for screw-retained FPDs). A comparison of the two fixation modes also revealed no significant difference (p= 0.67 for three-unit FPDs; p= 0.25 for five-unit FPDs). CONCLUSION: FPD span and retention mechanism appear to have only a minor influence on strain development in implant FPDs. As implant-supported restorations have proven to be successful over time, the question arises as to whether an "absolute" passive fit is a prerequisite for successful implant restorations.
Assuntos
Implantes Dentários , Prótese Dentária Fixada por Implante , Análise do Estresse Dentário/métodos , Planejamento de Dentadura , Retenção de Dentadura/métodos , Prótese Parcial Fixa , Cimentação/métodos , Cimentos Dentários , Implantação Dentária Endóssea , Retenção de Dentadura/instrumentação , Humanos , Ajuste de PróteseRESUMO
PURPOSE: It is believed that implant-supported fixed partial dentures (FPDs) should display passive fit. The objective of this in vivo-based finite element analysis (FEA) was to quantify the magnitude of bone loading occurring on account of the fixation of cemented or screw-retained 5-unit superstructures. MATERIALS AND METHODS: Based on a patient situation with 3 implants, 4 different groups of restorations with 10 samples each were fabricated. Strain gauges on the pontics of the restorations were used for in vivo measurements. Using the values obtained, bone loading in 3-dimensional FE models was simulated as von Mises equivalent stress. RESULTS: The in vivo measured mean strain values ranged from 32 microm/m to 458 microm/m at the different sites. FEA revealed stresses between 5 and 30 MPa in the cortical area, while in trabecular bone values ranging from 2 MPa to 5 MPa were observed. Stress of a similar magnitude was found for axial implant loading with 200 N. DISCUSSION: Assuming that the axial loading of a single implant with 200 N is within the realm of the bone's adaptation ability, it would appear that the amount of stress resulting from the fixation of superstructures alone does not constitute a risk. CONCLUSIONS: The level of precision of fit which can be obtained in superstructure fabrication would appear to suffice to produce restorations that do not cause bone damage.