A proposta deste estudo foi avaliar o comportamento mecânico de dois designs de conexão implante/abutment; hexágono externo e triângulo interno, utilizando parafusos convencionais e parafusos experimentais cone morse. O estudo foi dividido em duas fases: na primeira, foi avaliado o efeito do carregamento mecânico na perda de torque dos parafusos. 40 implantes foram utilizados. Os implantes e abutments foram divididos em 4 grupos: Grupo 1: hexágono externo/parafuso convencional (HE); Grupo 2: triângulo interno/parafuso convencional (TI); Grupo 3: hexágono externo/parafuso cone morse (HECM); Grupo 4: triângulo interno/parafuso cone morse (TICM). Os abutments foram instalados em seus respectivos implantes com torque de aperto de 32Ncm; após intervalo de 10 minutos, foram medidos os valores dos torques de desaperto. Os abutments foram instalados novamente com torque de 32Ncm, e após 10 minutos foram carregados mecanicamente, simulando 1 ano de função oral normal; após o carregamento, os torques de desaperto dos parafusos foram medidos novamente. Os dados foram analisados com o teste one-way ANOVA, com nível de significância de p≤0,05%. Análises por microscopia óptica foram realizadas antes e após os ensaios. Na segunda fase, foi avaliada a resistência à flexão dos conjuntos implante/abutment. Os mesmos 40 conjuntos foram utilizados. Os testes foram realizados em máquina universal de ensaios, com célula de carga de 500 kgf, deslocamento de 1mm/min, e inclinação de 45°. A força máxima de flexão (FMF) e a força de ruptura (FR) foram determinadas. As informações coletadas foram analisadas com o teste one-way ANOVA, para p≤0,05. Análises por microscopia óptica foram realizadas para estudo dos componentes após os ensaios de resistência flexural. Os resultados sugeriram que houve diferença significante (p=0,000) na pré-carga residual antes e após carregamento mecânico entre os dois tipos de parafuso: os parafusos cone morse apresentaram torques de desaperto significativamente superiores aos apresentados pelos parafusos planos convencionais. Houve diferença significante nos resultados da FMF obtidos pelos parafusos planos convencionais e pelos parafusos cone morse (p=0,011), sendo que os conjuntos implante/abutment com parafusos cone morse apresentaram maior resistência à flexão. Para os resultados da FR houve influência significante do tipo de conexão (p=0,019), com melhores resultados para a conexão triângulo interno. Considerando as limitações deste estudo, concluiu-se que os parafusos cone morse apresentaram maiores torques de desaperto em comparação aos parafusos planos convencionais; que o design da conexão protética não teve influência significante sobre o torque de desaperto dos parafusos; que os parafusos cone morse obtiveram maiores valores de resistência à flexão, e que a conexão em triângulo interno obteve maiores valores para a força de ruptura. / The purpose of this study was to evaluate the mechanical behavior of two implant/abutment connection designs; external hex and internal tri-channel, using conventional screws and experimental conical screws. The study was divided in two parts; the first evaluated the effect of mechanical loading in the torque loss of the screws. 40 implants were used. The implants and abutments were divided in 4 groups: Group 1: external hex/conventional screw (HE); Group 2: tri-channel/conventional screw (TI); Group 3: external hex/conical screw (HECM); Group 4: tri-channel/conical screw (TICM). The abutments were installed in their respective implants with a tightening torque of 32Ncm, after a 10 minute interval, loosening torque were measured. The abutments were installed again with a 32Ncm torque, and after 10 minutes, they were mechanically loaded, simulating 1 year of normal oral function; after loading, loosening torques of the screws were measured again. Data were analyzed with one-way ANOVA test, with significance level of p≤0,05. Optical microscopy analysis were performed before and after the tests. The second part evaluated the flexural resistance of the implant/abutment assemblies. The same 40 assemblies were used. The tests were performed in an universal testing machine, with a 500kgf load cell, 1mm/min displacement, and 45° angulation. Maximum bending moment (FMF) and rupture force (FR) were determined. Collected information were analyzed with one-way ANOVA test, for p≤0,05. Optical microscopy analysis were performed for study of the components after the flexural resistance tests. The results suggested that there were significant differences (p=0,000) in the residual preload before and after mechanical loading between the two types of screws: conical screws showed significantly higher loosening torques than conventional flat screws. There were significant differences in the FMF obtained by the conventional flat screws and by the conical screws (p=0,000); the implant/abutment assemblies with conical screws presented higher flexural resistance. For the FR results, there was significant influence of the type of connection (p=0,019); the tri-channel connection presented better results. Considering the limitations of this study, it was concluded that the conical screws presented higher loosening torques compared to conventional flat screws; the design of the implant/abutment connection presented no significant influence on the loosening torques of the screws; conical screws showed higher bending moment values; and the tri-channel connection obtained higher rupture force values.

A proposta deste estudo foi avaliar o comportamento mecânico de dois designs de conexão implante/abutment; hexágono externo e triângulo interno, utilizando parafusos convencionais e parafusos experimentais cone morse. O estudo foi dividido em duas fases: na primeira, foi avaliado o efeito do carregamento mecânico na perda de torque dos parafusos. 40 implantes foram utilizados. Os implantes e abutments foram divididos em 4 grupos: Grupo 1: hexágono externo/parafuso convencional (HE); Grupo 2: triângulo interno/parafuso convencional (TI); Grupo 3: hexágono externo/parafuso cone morse (HECM); Grupo 4: triângulo interno/parafuso cone morse (TICM). Os abutments foram instalados em seus respectivos implantes com torque de aperto de 32Ncm; após intervalo de 10 minutos, foram medidos os valores dos torques de desaperto. Os abutments foram instalados novamente com torque de 32Ncm, e após 10 minutos foram carregados mecanicamente, simulando 1 ano de função oral normal; após o carregamento, os torques de desaperto dos parafusos foram medidos novamente. Os dados foram analisados com o teste one-way ANOVA, com nível de significância de p≤0,05%. Análises por microscopia óptica foram realizadas antes e após os ensaios. Na segunda fase, foi avaliada a resistência à flexão dos conjuntos implante/abutment. Os mesmos 40 conjuntos foram utilizados. Os testes foram realizados em máquina universal de ensaios, com célula de carga de 500 kgf, deslocamento de 1mm/min, e inclinação de 45°. A força máxima de flexão (FMF) e a força de ruptura (FR) foram determinadas. As informações coletadas foram analisadas com o teste one-way ANOVA, para p≤0,05. Análises por microscopia óptica foram realizadas para estudo dos componentes após os ensaios de resistência flexural. Os resultados sugeriram que houve diferença significante (p=0,000) na pré-carga residual antes e após carregamento mecânico entre os dois tipos de parafuso: os parafusos cone morse apresentaram torques de desaperto significativamente superiores aos apresentados pelos parafusos planos convencionais. Houve diferença significante nos resultados da FMF obtidos pelos parafusos planos convencionais e pelos parafusos cone morse (p=0,011), sendo que os conjuntos implante/abutment com parafusos cone morse apresentaram maior resistência à flexão. Para os resultados da FR houve influência significante do tipo de conexão (p=0,019), com melhores resultados para a conexão triângulo interno. Considerando as limitações deste estudo, concluiu-se que os parafusos cone morse apresentaram maiores torques de desaperto em comparação aos parafusos planos convencionais; que o design da conexão protética não teve influência significante sobre o torque de desaperto dos parafusos; que os parafusos cone morse obtiveram maiores valores de resistência à flexão, e que a conexão em triângulo interno obteve maiores valores para a força de ruptura. / The purpose of this study was to evaluate the mechanical behavior of two implant/abutment connection designs; external hex and internal tri-channel, using conventional screws and experimental conical screws. The study was divided in two parts; the first evaluated the effect of mechanical loading in the torque loss of the screws. 40 implants were used. The implants and abutments were divided in 4 groups: Group 1: external hex/conventional screw (HE); Group 2: tri-channel/conventional screw (TI); Group 3: external hex/conical screw (HECM); Group 4: tri-channel/conical screw (TICM). The abutments were installed in their respective implants with a tightening torque of 32Ncm, after a 10 minute interval, loosening torque were measured. The abutments were installed again with a 32Ncm torque, and after 10 minutes, they were mechanically loaded, simulating 1 year of normal oral function; after loading, loosening torques of the screws were measured again. Data were analyzed with one-way ANOVA test, with significance level of p≤0,05. Optical microscopy analysis were performed before and after the tests. The second part evaluated the flexural resistance of the implant/abutment assemblies. The same 40 assemblies were used. The tests were performed in an universal testing machine, with a 500kgf load cell, 1mm/min displacement, and 45° angulation. Maximum bending moment (FMF) and rupture force (FR) were determined. Collected information were analyzed with one-way ANOVA test, for p≤0,05. Optical microscopy analysis were performed for study of the components after the flexural resistance tests. The results suggested that there were significant differences (p=0,000) in the residual preload before and after mechanical loading between the two types of screws: conical screws showed significantly higher loosening torques than conventional flat screws. There were significant differences in the FMF obtained by the conventional flat screws and by the conical screws (p=0,000); the implant/abutment assemblies with conical screws presented higher flexural resistance. For the FR results, there was significant influence of the type of connection (p=0,019); the tri-channel connection presented better results. Considering the limitations of this study, it was concluded that the conical screws presented higher loosening torques compared to conventional flat screws; the design of the implant/abutment connection presented no significant influence on the loosening torques of the screws; conical screws showed higher bending moment values; and the tri-channel connection obtained higher rupture force values.

A estabilidade da prótese na junção parafusada está diretamente relacionada ao seu grau de adaptação e assentamento bem como à pré-carga que é gerada para unir os componentes. O afrouxamento e/ ou fratura do parafuso do pilar e também a desadaptação rotacional na interface implante/ pilar têm sido relatados como os maiores problemas encontrados em reabilitações unitárias parafusadas, em especial áreas de pré-molares e molares. Desta forma, o objetivo deste estudo foi avaliar a liberdade rotacional (LR) de 20 pilares protéticos tipo UCLA calcináveis (10 totalmente plásticos e 10 com a base usinada em Tilite - Neodent Implante Osteointegrável), fundidos em liga de NiCr e Tilite, respectivamente, sobre 10 implantes de hexágono externo (Hexágono Externo, HE Neodent Implante Osteointegrável) para próteses unitárias e, também o torque de afrouxamento do parafuso do pilar, submetidos à ciclagem mecânica. Um dispositivo foi fabricado para medir os ângulos de liberdade rotacional entre os hexágonos de implante e pilar em três diferentes tempos: antes e após o processo de fundição e depois da ciclagem mecânica. Os grupos foram classificados de acordo com as leituras de LR: (1) pilares novos + implantes novos; (2) pilares fundidos + implantes novos; (3) pilares fundidos + implantes, ambos ciclados; (4) outros pilares novos + implantes ciclados e (5) os mesmos pilares após fundição + implantes ciclados. Foram medidas as distâncias entre os lados e vértices do hexágono externo dos implantes e interno dos pilares. Para a realização da ciclagem mecânica, foi utilizada uma máquina de ensaio cuja carga média aplicada foi de 120 N em sentido axial, com componente oblíquo, a uma freqüência de 101 ciclos por minuto (1,8 Hz), durante 500.000 ciclos. O torque de aperto dos parafusos de fixação foi de 32 N.cm e o de afrouxamento mensurado após fadiga. Atestada a normalidade da amostra aplicou-se o teste t de Student para comparações em par (p<0,05). Os resultados encontrados foram: para LR (em graus): Grupo Tilite (1) 2,930 ± 0,273; (2) 4,506 ± 2,448; (3) 5,126 ± 2,885; (4) 3,229 ± 0,235; (5) 2,813 ± 0,406; Grupo NiCr: (1) 4,684 ± 0,788; (2) 3,21 ± 1,370; (3) 3,818 ± 1,904; (4) 6,029 ± 0,503; (5) 4,421 ± 2,499. A análise estatística revelou que não houve significância entre nenhuma das diferentes leituras de LR tanto para os pilares do grupo NiCr quanto para os do Tilite; todavia, quando a comparação foi feita entre os pilares, houve diferença estatística significativa para as leituras (1) e (4), com maiores valores para os pilares plásticos calcináveis. O destorque para o grupo NiCr foi de 13,26 ± 4,32 N.cm com perda de torque de 41,44% e, para o grupo Tilite de 13,72 ± 7,36 N.cm e perda de torque de 42,88%. Houve expressiva perda de torque para ambos os grupos, porém não houve diferença estatística na comparação entre as ligas. A quantidade de ciclos aplicada não foi suficiente para alterar de forma significativa a LR nos conjuntos implante/ pilar quando avaliados para cada tipo de liga. A aplicação de cargas cíclicas alterou de forma significativa as dimensões dos implantes. / Prosthesis stability is related to misfit and screw joint preload. The screw loosening or fracture and rotational misfit have been related as the major problems in screwed single implant restorations, especially in molar or premolar areas. The aim of this study was to evaluate the rotational freedom and detorque of 20 UCLA type abutment (10 plastic and 10 machined abutments) cast in NiCr and NiCrTi alloys respectively, over 10 external hexagon implants submitted to mechanical cycling. A device was made to measure the rotational freedom between the implant hexagon and abutment in three different times: before and after the cast procedure and after the mechanical cycling. Groups were classified according the rotational misfit register: (1) new abutments + new implants; (2) cast abutments + new implants; (3) cycled cast abutments + cycled implants; (4) new abutments + cycled implants, and, (5) cast abutments + cycled implants. Measurements were made in the sides and vertices of external hexagon of the implants and internal hexagon of the abutments. Specimens were positioned with 30° of inclination in relation to the vertical axis in an eletromechanical machine for mechanical cycling (5.0x105 cycles) using 120N axial load and 1.8 Hz of frequence. The abutment screws were tightened to a torque of 32N.cm and the detorque measurement was registered after mechanical cycling. The rotational freedom results were: NiCrTi groups - (1) 2.930 ± 0.273; (2) 4.506 ± 2.448; (3) 5.126 ± 2.885; (4) 3.229 ± 0.235; (5) 2.813 ± 0.406; and NiCr groups - (1) 4.684 ± 0.788; (2) 3.21 ± 1.370; (3) 3.818 ± 1.904; (4) 6.029 ± 0.503; (5) 4.421 ± 2.499. Statistical analysis (p<0.05) showed that there is not significance among the different rotational freedom of NiCrTi or NiCr abutments; but there is statistically significant difference between (1) and (4) with higher values to the plastic abutments. Detorque of NiCr group was 13.26±4.32N.cm (-41.44%) and to the NiCrTi group was 13.72±7.36N.cm (-42.88%) but there is not statistically significant difference between the alloys. The mechanical cycling did not statistically influence the rotational freedom in the abutment/implant system when evaluated to each alloy but influenced the implant dimension.

Trabecular bone is a porous composite material which consists of a mineral phase (mainly hydroxyapatite), organic phase (mostly type I collagen) and water assembled into a complex, hierarchical structure. In biomechanical modelling, its mechanical response to loads is generally assumed to be instantaneous, i.e. it is treated as a time-independent material. It is, however, recognised that the response of trabecular bone to loads is time-dependent. Study of this time-dependent behaviour is important in several contexts such as: to understand energy dissipation ability of bone; to understand the age-related non-traumatic fractures; to predict implant loosening due to cyclic loading; to understand progressive vertebral deformity; and for pre-clinical evaluation of total joint replacement. To investigate time-dependent behaviour, bovine trabecular bone samples were subjected to compressive loading, creep, unloading and recovery at multiple load levels (corresponding to apparent strain of 2,000-25,000 με). The results show that: the time-dependent behaviour of trabecular bone comprises of both recoverable and irrecoverable strains; the strain response is nonlinearly related to applied load levels; and the response is associated with bone volume fraction. It was found that bone with low porosity demonstrates elastic stiffening followed by elastic softening, while elastic softening is demonstrated by porous bone at relatively low loads. Linear, nonlinear viscoelastic and nonlinear viscoelastic-viscoplastic constitutive models were developed to predict trabecular bone's time-dependent behaviour. Nonlinear viscoelastic constitutive model was found to predict the recovery behaviour well, while nonlinear viscoelastic-viscoplastic model predicts the full creep-recovery behaviour reasonably well. Depending on the requirements all these models can be used to incorporate time-dependent behaviour in finite element models. To evaluate the contribution of the key constituents of trabecular bone and its microstructure, tests were conducted on demineralised and deproteinised samples. Reversed cyclic loading experiments (tension to compression) were conducted on demineralised trabecular bone samples. It was found that demineralised bone exhibits asymmetric mechanical response - elastic stiffening in tension and softening in compression. This tension to compression transition was found to be smooth. Tensile multiple-load-creep-unload-recovery experiments on demineralised trabecular samples show irrecoverable strain (or residual strain) even at the low stress levels. Demineralised trabecular bone samples demonstrate elastic stiffening with increasing load levels in tension, and their time-dependent behaviour is nonlinear with respect to applied loads . Nonlinear viscoelastic constitutive model was developed which can predict its recovery behaviour well. Experiments on deproteinised samples showed that their modulus and strength are reasonably well related to bone volume fraction. The study considers an application of time-dependent behaviour of trabecular bone. Time-dependent properties are assigned to trabecular bone in a bone-screw system, in which the screw is subjected to cyclic loading. It is found that separation between bone and the screw at the interface can increase with increasing number of cycles which can accentuate loosening. The relative larger deformation occurs when this system to be loaded at the higher loading frequency. The deformation at the bone-screw interface is related to trabecular bone's bone volume fraction; screws in a more porous bone are at a higher risk of loosening.

Cette thèse porte sur l’étude du dévissage spontané d’assemblages vissés, sous sollicitations dynamiques transversales. Un travail expérimental et numérique a été réalisé pour caractériser ce phénomène, dans des conditions proches de celles des assemblages réels. Une expérimentation a permis de provoquer le dévissage d’un boulon, en soumettant l’assemblage à des vibrations transversales par rapport à l’axe de la vis. Les effets de la précharge, du traitement de surface et de la disposition des vis ont été explorés. Ces résultats ont été confrontés avec ceux obtenus par un modèle numérique détaillé utilisant la méthode des éléments finis. Cependant, en raison de la complexité de la géométrie et des difficultés de modélisation à l’échelle locale, le temps de calcul est très important et peut être prohibitif pour une étude industrielle. Afin de remédier à cette difficulté, des modèles simplifiés ont été développés, l’un avec une approche par éléments finis associés à un connecteur cinématique, et l’autre par modélisation unidimensionnelle. Ces modèles simplifiés reproduisent correctement le phénomène du dévissage spontané et confirment leur efficacité en gain de temps de calcul. / This thesis focuses on the study of the self-loosening of bolted joints under transverse dynamic loads. Experimental and numerical work was carried out in order to reveal this phenomenon under conditions close to those of actual assemblies. An experiment allowed the loosening of a bolt to be caused by subjecting the assembly to transverse vibration with respect to the axis of the screw. Effects of preload, surface treatment and disposal of the screws were explored. These results were compared with those obtained by a detailed numerical model using the finite element method. However, due to the complexity of the geometry and modeling challenges at the local level, the computation time was very long and may be prohibitive for an industrial study. To remedy this problem, two simplified models were developed, one with a finite element approach associated with a kinematic connector, and one by unidimensional modeling. These simplified models correctly reproduce the self-loosening phenomenon and confirm their efficiency in terms of computation time.

Aseptic loosening due to polyethylene wear presents one of the most frequently occurring joint replacement complications requiring a revision surgery. Numerous scientific works and publications deal with the issue of morphology, determination and distribution of wear particles. Few studies, however, determine reliably amounts of particles in individual periprosthetic zones. The objective of this work was to evaluate the correlation between amounts of wear particles and periprosthetic osteolysis findings. Description of distribution of these particles in the surroundings of joint replacement presented further objectives of the work. Wear particles were isolated from granuloma obtained during revisions of total hip replacements. Amounts of wear particles were determined using IRc. These findings were correlated with X-ray examinations and intraoperative findings. Method of progressive enzymatic degradation of tissue was used in order to describe wear particles distribution in polyethylene granuloma and surrounding periprosthetic tissues. Results showed uneven incidence of wear particles in the surroundings of the total joint replacement. The incidence correlated with X-ray examinations and intraoperative findings. Distribution of particles was described as well as new determination methods and further...

La compacité des matériaux granulaires est une grandeur qui intéresse un grand nombre de secteurs, notamment les bétons hydrauliques. Lorsque les fractions granulaires ne possèdent pas des rapports de tailles infinis, deux interactions géométriques se développent : l’effet de paroi et l’effet de desserrement. La première peut se décrire ainsi : une grosse particule isolée constitue un « intrus » contre lequel viennent se ranger les petites particules, créant un supplément de vides à l’interface. La seconde se produit lorsque les petits grains sont insuffisamment fins pour se glisser entre les gros. Nous analysons comment elles sont prises en compte dans un certain nombre de modèles d’empilement en nous fixant finalement sur celui de de Larrard et al. : le modèle d’empilement compressible (MEC), l’un des plus efficaces. Dans celui-ci, les effets de paroi et de desserrement sont quantifiés par l’intermédiaire de deux coefficients dont les expressions sont obtenues par lissage de données expérimentales en fonction du rapport des diamètres fins/gros. Cependant, il n’existe aucune théorie pleinement satisfaisante permettant de les obtenir. Cette thèse vise à combler ce chaînon manquant. Nous avons conduit notre étude dans le cadre des empilements ordonnés et compacts de particules afin d’être en adéquation avec les hypothèses de constitution du MEC qui propose, comme préalable à l’obtention de la compacité réelle, la détermination d’une compacité virtuelle définie comme la compacité maximale susceptible d’être atteinte si l’on pouvait déposer, un à un, chaque grain à son emplacement idéal. Cette façon de procéder permet la création de cellules élémentaires juxtaposées. Dans ce cadre, l’interaction exercée par une espèce granulaire sur une autre de taille différente est menée à partir d’une étude localisée autour d’une particule « intruse » de la classe dominée, entourée de particules de la classe dominante. La simulation numérique apporte une confirmation de la validité du modèle. En plus de fournir des coefficients d’effets de paroi et de desserrement très proches de ceux prédits théoriquement, elle a permis l’étude d’empilements désordonnés de compacité maximale pour des billes bidispersées sans frottement dont les rapports de tailles valent 0,2 et 0,4. Le concept de « pressions partielles », qui tient compte à la fois des aspects géométrique et mécanique, a permis d’affiner la notion de classe dominante et de mieux appréhender la constitution du squelette porteur de l’édifice granulaire. En plus des zones constituées par les « fins dominants » et par les « gros dominants », il existe une zone mixte que nous avons dénommée « zone de synergie du squelette porteur » où les « pressions partielles » fines-grosses sont les plus importantes. En tenant compte de la nouvelle théorie développée pour les interactions géométriques, le modèle d’empilement compressible (MEC) subit une évolution et devient le MEC 4-paramètres, qui sont : les coefficients d’effet de paroi et d’effet de desserrement, le rapport de tailles de caverne critique et l’indice de compaction du mélange. Ce dernier ayant subi un nouvel étalonnage, le MEC 4-paramètres montre son efficacité quant à la prédiction de compacités sur mélanges binaires à partir de l’analyse de 780 résultats obtenus sur différents types de matériaux. Enfin, un modèle visant à prédire la viscosité d’une suspension concentrée de particules sphériques multidimensionnelles suspendues dans un fluide visqueux est présenté. Compatible avec la relation d’Einstein, il fait appel au concept de changement d’échelle de Farris et à une loi de viscosité de type Krieger-Dougherty. Lorsque la fraction volumique de solide atteint sa valeur critique, la suspension devient empilement et le mélange atteint la compacité du squelette solide déterminée par le MEC 4-paramètres / Packing density of granular materials is a quantity which interests many sectors, in particular hydraulic concrete. When two monodimensional grain classes have no very different sizes, two geometrical interactions develop : the wall effect and the loosening effect. The first one express the perturbation of the packing of the small grains at the interface between large and small grains. The second one occurs when small grains are not enough fine to insert into small cavities created by the touching larger grains. We analyze how they are taken into account in existing packing models. We select finally the compressible packing model (CPM) of de Larrard et al., one of the most effective. In this one, wall effect and loosening effect are quantified by two coefficients. They can, of course, be calculated from experimental results on binary mixtures, as a function of fine/coarse diameter ratios. However, there is no satisfactory theory allowing to calculate them. This doctoral thesis is done to fill this missing link. Ordered and very packed piles of particles are used as a reference frame to be in adequation with the CPM assumptions which require, before the calculation of the real packing density, the determination of a virtual packing density. The latter is defined as the maximum packing density attainable if each particle could be positioned in its ideal location. This approach allows the creation of elementary juxtaposed cells. In that context, the effect of a smaller grain (loosening effect) or a larger grain (wall effect) on the packed class is based on the study of a foreign sphere surrounded by dominant class neighbours. The numerical simulation confirms the validity of the model. In addition to predict wall effect and loosening effect coefficients close to those determined theoretically, numerical simulation was used to predict the solid fraction of maximally dense disordered packings of bidisperse spherical frictionless particles with 0,2 and 0,4 size ratios. The « partial pressures » concept, that includes both geometrical and mechanical aspects, allows to complete and improve the notion of dominant class and to better understand the build-up of the granular skeleton. In addition with « small grains packed » and « large grains packed » zones, the numerical simulation has highlighted a joint zone, called « synergism zone of the granular skeleton » where « partial pressures » fine-large particles are the most important. With this new theory developed for geometrical interactions, the compressible packing model (CPM) is evolving to the new 4-parameter CPM which are : the wall effect coefficient, the loosening effect coefficient, the critical cavity size ratio and the compaction index of the mixing, which requires a new recalibration. The 4-parameter CPM demonstrates its efficiency to predict the packing density of binary mixtures from the analysis of 780 results obtained on different types of materials. Finally, a model intended to predict the viscosity of a multimodal concentrated suspension with spherical particles suspended in a viscous fluid is presented. We resort to the iterative approach advocated by Farris and to a power-law relation (Krieger-Dougherty type) for the relative viscosity, compatible with the Einstein relation appropriate for a dilute suspension. When the solid volume fraction reaches its critical value, the suspension is jammed and the mixture reaches the packing density of the solid skeleton calculated with the 4-parameter CPM

Background: In a retrospective study, risk factors for complications after the bridging of mandibular defects using reconstruction plates were reviewed. Especially the loosening of the plate-screw-mandible complex should be analyzed with a finite element model in order to reduce plate complications in future. Patients and Methods: We examined 60 patients who underwent a treatment with reconstruction plates after tumor resection during a period of 10 years. The problem of screw loosening was additionally reviewed by means of a finite element study, and a model for the loosening process was developed. Results: Our postoperative examination showed that 26 patients suffered from complications that required an early removal of the plate. These complications were oral or extraoral plate exposures, the looseness of screws with or without plate displacement, and plate fractures. Thereby, we noticed that maxillary and mandibular areas of opposing teeth, the size of the mandible defect, and the crossing of the orofacial midline are all risk factors for plate complications. On the basis of the finite element model, a modified arrangement of the screws was derived. Hence, a new type of resection plate was established. Conclusions: By repositioning the screw holes along the long axis of the plate, the transition from tensile force to torque force of the screws in the screw-plate-bone complex can be minimized. Thereby, the complication of screw loosening will be considerably reduced. / Hintergrund: In einer retrospektiven Studie wurden Risikofaktoren für Komplikationen nach Überbrückung von Unterkieferdefekten mit Rekonstruktionsplatten geprüft. Insbesondere die Lockerungsvorgänge des Schrauben- Platten-Unterkiefer-Verbundes sollten mit einer Finite- Elemente-Modellierung analysiert werden, um in Zukunft eine Reduzierung der Plattenkomplikationen erreichen zu können. Patienten und Methoden: Es wurden 60 Patienten untersucht, welche im Zeitraum von 10 Jahren im Rahmen von Tumoroperationen mit Rekonstruktionsplatten versorgt wurden. Das Problem der Lockerung der Plattenschrauben wurde zusätzlich mittels einer Finite-Elemente-Studie überprüft und ein Modell für den Lockerungsvorgang erarbeitet. Ergebnisse: Die Nachuntersuchungen ergaben, dass bei 26 Patienten die Platte wegen Komplikationen vorzeitig entfernt werden musste. Die Komplikationen traten als orale und extraorale Plattenfreilage, als Schraubenlockerung ohne oder mit Plattendislokationen und als Plattenbrüche auf. Dabei konnte festgestellt werden, dass bestehende Stützzonen des körpereigenen Restgebisses, die Größe des Unterkieferdefektes und dessen Mittellinienüberschreitung Risikofaktoren für Plattenkomplikationen darstellen. Anhand der Finite-Elemente-Modellierung wurde eine veränderte Schraubenanordnung abgeleitet. Daraus resultiert eine neue Form der Resektionsplatte. Schlussfolgerungen: Durch die Verschiebung der Schraubenlöcher aus der Längsachse der Platte kann der Übergang von der Zugbelastung zur Drehmomentbelastung der Schrauben im Schrauben-Platten-Knochen-Verbund der Platte minimiert werden. Dadurch werden Schraubenlockerungen als Komplikationen wesentlich seltener auftreten. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

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