Finite Elements Method in Implant Prosthetics

This chapter is devoted to the study of behavior of functional loadings for implant prosthetics rehabilitation by finite elements method (FEM). It presents a numerical calculation of stress, displacement, and strain in implant and surrounding bone, which is used to assess risk factors from a biomechanical point. The masticatory forces are simulated by axial and/or non-axial loads, and they are responsible for the biomechanical response of the bone-tissue-implant-crown system. This chapter represents an analysis of this response in view of highlighting the factors involved in implant stability and success. The safety factor for different loading cases is calculated as well. A good agreement with other study results and clinical studies is obtained

Three-Dimensional Finite Element Analysis of Mandibular Overdentures Supported by Mini-Implants

Title from PDF of title page viewed January 3, 2018Thesis advisors: Cynthia S. Petrie and Mary P. WalkerVitaIncludes bibliographical references (pages 55-65)Thesis (M.S.)--School of Dentistry. University of Missouri--Kansas City, 2017This study examined the effect of using two anterior denture-supporting mini implants (mIMP2) compared to four (two anterior and two posterior) denture-supporting mini-implants (mIMP4) on the stress experienced by the mini-implants and the strain experienced by the peri-implant and analogous posterior bone. The stress and strain values were also compared to known values of strength for the mini-implants and physiologic strain values. Finite element modeling was used to study the effects. Two models were created identically, with the exception of the number of denture-supporting mini-implants used, and contained modeled mucosa, cortical bone, cancellous bone, and the mini-implants. The models were loaded over one second with three 70N loads bilaterally and results with collected using a PostView program. The anterior mini-implants in both models showed stresses that would not put them at risk for fracture. The posterior mini-implants in mIMP4 experienced stresses above their yield point, indicating that they could be at risk for fracture. Strain in the peri-implant bone anteriorly and the posterior bone in mIMP2 was in the physiologic range. The posterior peri implant bone in mIMP4 showed strains that were above physiologic, which indicates this region could be at risk for bone resorption. Based on the limitations of this study, posterior mini-implants and posterior peri implant bone could be at risk for fracture and pathologic resorption. Dentists must weigh the risks and benefits of using mini-implants to support overdentures in each clinical case to determine if the treatment could be successful in light of the potential negative consequences.Introduction -- Materials and methods -- Results -- Discussion -- Conclusions

Within-subject comparison of two- versus three-implant-assisted mandibular overdenture : patient-based outcomes

RÉSUMÉ Objectifs: Cette étude cherche à évaluer l’influence de l’ajout d’un implant additionnel dans la région médiane mandibulaire sur la perception des patients porteurs d’une prothèse préexistante assistée par deux implants. Méthodes: Cette étude fait partie d’un essai clinique qui a été mené à l'Université de Montréal. Dix-sept personnes édentées (âge moyen de 61,9 ± 6,6 ans) ont reçu trois implants dans la région mandibulaire interforaminale. Deux implants ont été place près des trous mentonniers et le troisième au niveau de la ligne médiane. Au début de l’essai, les sujets ont été appareillés d’une prothèse de recouvrement mandibulaire assistée par les deux implants distaux. Ces implants étaient coiffés par des attaches individuelles Locator®. Le troisième implant n’a pas été mis en charge initialement et il est resté sans attache pour deux ans. Après cette période, une attache Locator a été installée sur le troisième implant et la prothèse de recouvrement a été modifiée pour accommoder ce mécanisme de rétention additionnel. Les mouvements antéropostérieurs de la prothèse tel que perçus par les patients ainsi que ceux évalués en cliniques ont été mesurés avant et après cette modification. La satisfaction des patients, leurs perceptions et leurs attentes vis-à-vis les prothèses mandibulaires ainsi que la volonté de payer ont été évaluées. La collecte de données a été effectuée à l'aide de questionnaires auto administré validés, à la suite de la modification et après six semaines d’utilisation. Des données sociodémographiques ont également été recueillies. Des statistiques descriptives et les essais non paramétriques ont été employés pour l'analyse statistique. Résultats: Les résultats ont indiqué une diminution statistiquement significative dans le mouvement antéropostérieur de la prothèse mandibulaire (p = 0,005) tel qu’évalué en clinique. Les patients ont rapporté une amélioration au niveau de la stabilité de la prothèse mandibulaire (p = 0,005), de même qu’au niveau de leur capacité à parler (p = 0,011) et à mastiquer les aliments durs (p = 0,012). L'ajout d'un troisième implant a répondu aux attentes des patients en ce qui concerne la stabilité (pour 94 % des patients), la rétention (100 %) et le confort (82,4%) de la prothèse mandibulaire. Sur une période de six semaines, la prothèse de recouvrement mandibulaire assistée par trois implants a contribué à l'augmentation de la satisfaction générale des patients, mais cette amélioration n'était pas statistiquement significative. Environ 80 % des patients recommanderaient ce type de prothèse à leurs pairs, mais seulement 47 % d'entre eux accepteraient de payer l’augmentation du coût de traitement associée à la pose d’un troisième implant. Conclusions: L'ajout d'un troisième implant dans la région médiane d’une prothèse préexistante assistée par deux implants a permis d'obtenir de meilleurs résultats au niveau de l’expérience du patient. Cependant, le coût supplémentaire du traitement peut influencer les choix du patient.ABSTRACT Objectives: This study aims to assess the impact of an additional midline implant to support an existing mandibular two-implant overdenture, on patient-based outcomes (patients’ satisfaction and expectations). Methods: This study was nested within a previous clinical trial conducted at the Université de Montréal. Seventeen edentulous individuals (mean age: 61.9 ± 6.6 years) received three threaded implants in the interforaminal mandibular area and a mandibular overdenture using two Locator® attachments. The midline implant was left unloaded over a two-year period. At the two-year follow-up, using a standard protocol, the third implant received a Locator® attachment and the overdenture was converted to a three-implant-assisted overdenture. The clinical and perceived anterior–posterior movements of mandibular prostheses were measured before and after the conversion. Patients’ expectation and satisfaction in regard to mandibular prosthesis as well as their willingness to pay the cost for the conversion were evaluated by using validated self-administered questionnaires. Data collection was conducted at baseline and after six weeks of wearing the converted mandibular prosthesis. Socio-demographic data were also collected. Descriptive statistics and non-paramteric tests were used for statistical analysis. Results: Data analysis revealed a statistically significant decrease in the anterior–posterior movement (p = 0.005) of overdenture as evaluated by clinicians. Study participants reported an increase in perceived stability of the overdenture (p = 0.005), and in their ability to speak (p = 0.011) and to chew hard food (p = 0.012). The addition of a third implant met the expectations of 94% of patients in regard to lower denture stability, 100% for retention, and 82.4% for comfort. The 3-implant-assisted mandibular overdenture increased patients’ general satisfaction over a short period of time, but this improvement was not statistically significant. About 80% of patients would recommend this type of prosthesis to their peers but only 47% of them would agree to pay a large increase in the cost of treatment compared to 2-implant overdenture. Conclusions: The addition of a midline third implant to an existing 2-mandibular-implant overdenture will lead to better patient-based outcomes. However, the additional cost of the treatment may influence patient preferences

Explore the Dynamic Characteristics of Dental Structures: Modelling, Remodelling, Implantology and Optimisation

The properties of a structure can be both narrowly and broadly described. The mechanical properties, as a narrow sense of property, are those that are quantitative and can be directly measured through experiments. They can be used as a metric to compare the benefits of one material versus another. Examples include Young’s modulus, tensile strength, natural frequency, viscosity, etc. Those with a broader definition, can be hardly measured directly. This thesis aims to study the dynamic properties of dental complex through experiments, clinical trials and computational simulations, thereby bridging some gaps between the numerical study and clinical application. The natural frequency and mode shapes, of human maxilla model with different levels of integrities and properties of the periodontal ligament (PDL), are obtained through the complex modal analysis. It is shown that the comprehensiveness of a computational model significantly affects the characterisation of dynamic behaviours, with decreasing natural frequencies and changed mode shapes as a result of the models with higher extents of integrity and preciseness. It is also found that the PDL plays a very important role in quantifying natural frequencies. Meanwhile, damping properties and the heterogeneity of materials also have an influence on the dynamic properties of dental structures. The understanding of dynamic properties enables to further investigate how it can influence the response when applying an external stimulus. In a parallel preliminary clinical trial, 13 patients requiring bilateral maxillary premolar extractions were recruited and applied with mechanical vibrations of approximately 20 g and 50 Hz, using a split mouth design. It is found that both the space closure and canine distalisation of the vibration group are significantly faster and higher than those of the control group (p<0.05). The pressure within the PDL is computationally calculated to be higher with the vibration group for maxillary teeth for both linguo-buccal and mesial-distal directions. A further increased PDL response can be observed if increasing the frequency until reaching a local natural frequency. The vibration of 50 Hz or higher is thus approved to be a potential stimulus accelerating orthodontic treatment. The pivotal role of soft tissue the PDL is further studied by quantitatively establishing pressure thresholds regulating orthodontic tooth movement (OTM). The centre of resistance and moment to force ratio are also examined via simulation. Distally-directed tipping and translational forces, ranging from 7.5 g to 300 g, are exerted onto maxillary teeth. The hydrostatic stress is quantified from nonlinear finite element analysis (FEA) and compared with normal capillary and systolic blood pressure for driving the tissue remodelling. Localised and volume-averaged hydrostatic stress are introduced to describe OTM. By comparing with clinical results in past literature, the volume average of hydrostatic stress in PDL was proved to describe the process of OTM more indicatively. Global measurement of hydrostatic pressure in the PDL better characterised OTM, implying that OTM occurs only when the majority of PDL volume is critically stressed. The FEA results provide new insights into relevant orthodontic biomechanics and help establish optimal orthodontic force for a specific patient. Implant-supported fixed partial denture (FPD) with cantilever extension can transfer excessive load to the bone surrounding implants and stress/strain concentration which potentially leads to bone resorption. The immediate biomechanical response and long-term bone remodelling outcomes are examined. It is indicated that during the chewing cycles, the regions near implant necks and apexes experience high von Mises stress (VMS) and equivalent strain (EQS) than the middle regions in all configurations, with or without the cantilever. The patient-specific dynamic loading data and CT based mandibular model allow us to model the biomechanical responses more realistically. The results provide the data for clinical assessment of implant configuration to improve longevity and reliability of the implant-supported FPD restoration. On the other hand, the results show that the three-implant supported and distally cantilevered FPDs see noticeable and continuous bone apposition, mainly adjacent to the cervical and apical regions. The bridged and mesially cantilevered FPDs show bone resorption or no visible bone formation in some areas. Caution should be taken when selecting the FPD with cantilever due to the risk of overloading bone resorption. The position of FPD pontics plays a critical role in mechanobiological functionality and bone remodelling. As an important loading condition of dental biomechanics, the accurate assignment of masticatory loads has long been demanded. Methods involving different principles have been applied to acquire or assess the muscular co-activation during normal or unhealthy stomatognathic functioning. Their accuracy and capability of direct quantification, especially when using alone, are however questioned. We establish a clinically validated Sequential Kriging Optimisation (SKO) model, coupled with the FEM and in vivo occlusal records, to further the understanding of muscular functionality following a fibula free flap (FFF) surgery. The results, within the limitations of the current study, indicates the statistical advantage of agreeing occlusal measurements and hence the reliability of using the SKO model over the traditionally adopted optimality criteria. It is therefore speculated that mastication is not optimally controlled to a definite degree. It is also found that the maximum muscular capacity slightly decreases whereas the actual muscle forces fluctuate over the 28-month period