O objetivo deste estudo foi analisar, por meio do método dos elementos finitos, como ocorreram as distribuições de tensões nos dentes, osso e aparelho ortodôntico, durante a fase de retração por deslizamento (150g), em um caso com extrações. Simularam-se duas posições do gancho (mesial e distal de canino), duas alturas do gancho (4 e 9mm) e duas alturas posteriores (gancho do tubo do molar e no miniimplante, a 9mm do arco). A amostra consistiu do corte axial da TCFC, de uma mulher de 17 anos de idade, com dentes bem nivelados. Foi desenvolvido um modelo 3D, da geometria da hemi-maxila direita e um modelo numérico, para obter os regimes de tensões e deformações gerados em um sistema de movimentação ortodôntica, por meio do software ANSYS® versão 12.0. Os sólidos dos braquetes e do fio ortodôntico foram incluídos a partir das dimensões fornecidas pelo fabricante. A montagem de todos os componentes foi feita por meio do SolidWorks 2009 SP4.1. A partir do cálculo das respostas do modelo, às cargas a que foi submetido, verificou-se que, os dentes que sofreram maiores concentrações de tensões foram os justapostos aos ganchos, sendo mais intensas as do gancho mesial, particularmente nos incisivos laterais. Embora, a solicitação de tensões no arco tenha sido semelhante em todos os modelos, na posição distal do gancho, houve maior concentração de tensões na extensão imediatamente distal. Os modelos com ganchos de 4mm, diferente aos de 9mm, apresentaram distribuições de tensões mais uniformes, causando menos estresse aos dentes e osso e semelhante ao arco. O modelo com vetor de força direcionado do gancho da mesial do canino ao miniimplante foi o único que mostrou variações, mostrando distribuições de forças mais elevadas na região anterior e posterior ao ser comparado com o vetor de força direcionado ao tubo do primeiro molar. / The aim of this study was to evaluate, by means of finite element analysis, the tensions distrubutions on the teeth, bone and orthodontic appliance, during en-masse retraction sliding mechanics (150g), in an extraction case. It was taken into account two hook positions (mesial and distal to the canine), two hook heights (4mm and 9mm) and two posterior heights ( the first molar tube and the mini-implant, located 9mm from the archwire). The sample of this study consisted of an axial cut realized in a cone beam computed tomography of a 17 years old woman with leveling teeh. It was developed a 3D computed model of a right hemi-maxilla and a computednumerical model capable of getting the systems tensions and deformations generated from an orthodontic moviment system, through a finite element software, ANSYS® 12.0. Observing manufactores specifications, brakets and archwire solids were included in this solid geometric model. The assembly of all componentes were made though the SolidWorks 2009 SP4.1 software. The loads model responses were calculated. The bigger concentration of tension were on the teeth located between the hook. The model with the mesial hook, suffered more intense tensions, mainly on lateral incisors. Although, the tensions request on the archwire were similars in all models, when the hook was located distaly, there were more intense tensions in its immediately distal extension. The 4mm hook models, compared with the 9mm, presented more uniform tensions distribution causing less stress to the teeth and bone and similar to the archwire. The only model that demonstrated variations, was the model with the vector force from the mesial hook and to the mini-implant. This model, demostrated higher tensions distributions on the anterior and posterior region if compared to the first molar tube vector force.

Orientador: Altair Antoninha Del Bel Cury / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-21T17:30:39Z (GMT). No. of bitstreams: 1 Andrade_CamilaLimade_M.pdf: 1540257 bytes, checksum: bda7c72558234d710525932300d299a1 (MD5) Previous issue date: 2012 / Resumo: Este estudo avaliou a influência da ancoragem apical de implantes sub-cristais com plataforma switching em região posterior de maxila quanto a estabilidade primária e comportamento biomecânico. Quatro modelos de ancoragem óssea foram utilizados nas avaliações: implante de 4,0 x 13 mm de comprimento fixado bicorticalmente (A), implante de 4,0 × 11 mm de comprimento ancorado apenas na cortical da crista (B) ou 2 milímetros posicionados sub-cristal com (C) ou sem (D) o ápice ancorado no osso cortical do assoalho do seio maxilar. A estabilidade primária foi verificada pelo torque de inserção e medida de frequência de ressonância (ISQ) de implantes inseridos em blocos de poliuretano (n=5). O comportamento biomecânico foi obtido através de análise por elementos finitos (AEF), em que os modelos virtuais foram construídos para representar as diferentes ancoragens ósseas. O tecido ósseo foi considerado anisotrópico e um coeficiente de fricção de 0,3 foi utilizado na interface osso-implante para simular carregamento imediato. Todos os modelos foram carregados com 200 N de força distribuída em três pontos oclusais na coroa cerâmica do pré-molar para simular contato cêntrico ou um contato na cúspide vestibular para simular contato excêntrico. A ancoragem do ápice na cortical óssea aumentou a estabilidade primária dos implantes sub-cristais (torque de inserção 43.2±4.1; ISQ 77.2±2.4), entretanto, também aumentou os valores de tensão / deformação quando comparado com o implante sub-cristal ancorado apenas em osso trabecular. O osso trabecular é capaz de dissipar as tensões pelo aumento da micromovimentação, especialmente sob carga excêntrica. A ancoragem do ápice dos implantes sub-cristais na cortical do seio maxilar é benéfica do ponto de vista biomecânico, por direcionar as forças tanto cêntricas quanto excêntricas para a região cortical e contribuir para diminuir a micromovimentação do implante / Abstract: This study evaluated the influence of apical anchorage of implants with platform switching at posterior maxilla on primary stability and biomechanical behavior of subcristal implants. Four anchorage designs were used in evaluations: one 4.0×13 mm length implant was fixed bicortically (A), and one 4.0×11 mm length implant was anchored only in crystal cortical (B) or positioned 2 mm subcrestally with (C) or without (D) its apex anchored in cortical bone. Primary stability was accessed by insertion torque and resonance frequency measurements (ISQ) of implants inserted in polyurethane blocks (n=5). The biomechanical behavior was accessed by finite element analysis (FEA), in which virtual models were constructed to representing one of the anchorage designs. The bone tissue was considered anisotropic and a 0.3 frictional coefficient was used at the implant-bone interface to simulate immediate placement. All models were loaded with 200 N force distributed over three occlusal points on the premolar ceramic crown to simulate centric contacting or over one contact at buccal cusp to simulate eccentric contacting. The anchorage of apex into cortical bone testing material improved the primary stability of subcrestal implants (insertion torque 43.2 ± 4.1; ISQ 77.2 ± 2.4); however, the stress/strain values also increased when compared to the subcristal implant anchored only into trabecular bone. The trabecular bone is able to dissipate the stresses by increasing micromotion, especially at eccentric loading. The anchorage of subcristal implant apex into sinus floor cortical bone is biomechanically beneficial, for directing the centric and eccentric forces to cortical region and reduces the micromotion implant / Mestrado / Protese Dental / Mestra em Clínica Odontológica

Qu’est-ce qu’un paysage patrimonial ? C’est un nouveau regard porté par des acteurs sur un paysage qui, selon la définition de Lévy et Lussault (2003) « est censé mériter d’être transmis du passé, pour trouver une valeur dans le présent ». C’est « un ensemble d’attributs, de représentations et de pratiques fixés sur un objet non contemporain […] dont est décrété collectivement l’importance présente, intrinsèque (ce en quoi cet objet est représentatif d’une histoire des objets de société) et extrinsèque (ce en quoi cet objet recèle des valeurs supports d’une mémoire collective), qui exige qu’on le conserve et le transmette ». Afin de définir les propriétés patrimoniales du paysage, ces personnes s’organisent en groupes et tentent de communiquer entre eux. Chacun construit une représentation du paysage autour d’attributs spécifiques qui présentent un intérêt pour le groupe. Toutes ces représentations sont différentes et pourtant elles concernent bien un seul et unique paysage. Lorsqu’il s’agit de réaliser une action qui aura un effet sur cet espace commun, les acteurs se mettent à interagir au sein d’un « réseau collectif ». L’action peut alors faire l’objet de négociations, de tensions, de conflits, d’un accord ou d’un abandon en fonction de la position de chacun. Toutefois, que l’action ait été portée jusqu’à son aboutissement ou bien qu’elle ait été abandonnée, les acteurs ont échangé leurs regards au sujet du paysage pendant toute la phase d’interaction. Donc, au fur et à mesure des actions réalisées sur l’espace, les acteurs construisent un regard commun du paysage que l’on qualifie de « représentation collective ».Contrairement à un objet matériel, le paysage est difficilement quantifiable. L’acquisition pour ce dernier d’une valeur patrimoniale demande donc un processus complexe qualifié de « processus de patrimonialisation ». Ce processus n’a rien d’anodin pour les acteurs présents, il perturbe la représentation collective qui avait été créé au fur et à mesure de leurs échanges. Dans ce désordre social, les acteurs vont lutter pour faire valoir leur représentation du paysage, créant ainsi une nouvelle représentation collective. Dans ce contexte, notre thèse pose la problématique suivante : En se situant à l’échelle d’un territoire qui subit une transformation du regard vers un contexte patrimonial, dans quelle mesure les acteurs agricoles et non-agricoles se coordonnent et construisent une nouvelle représentation collective axée sur le maintien de l’élevage, l’utilisation de l’espace et la gestion du paysage ?Pour répondre à cette problématique, nous avons mobilisé les réseaux d’acteurs agricoles et non agricoles existant sur deux sites dans le Massif central (les Causses et les Cévennes et la Chaîne des Puys – faille de Limagne) qui sont inscrits ou en recherche d’inscription au patrimoine mondial de l’UNESCO. Après une rapide description des deux sites, nous avons expliqué notre positionnement en ce qui concerne l’aspect collectif plutôt qu’individuel dans la construction d’une représentation du paysage et autour de l’organisation et de la gestion de ce dernier. Nous avons ensuite construit une méthodologie qui s’inspire de cet apport théorique. Grâce à elle, nous avons su mener une centaine d’enquêtes qui nous ont permis d’identifier et d’analyser sur les sites les deux réseaux dans lesquels les acteurs collectifs s’organisent pour intégrer ce nouvel enjeu patrimonial dans leur représentation du paysage. Cette organisation en réseau se concrétise autour d’une série d’actions destinées en outre à la gestion du patrimoine, mais aussi au soutien de l’élevage et à la valorisation de la production agricole. Ainsi, nous constatons que le processus de patrimonialisation contribue indirectement, en influençant la représentation collective de l’espace agricole, à l’évolution des pratiques agricoles qui sont elles-mêmes responsables de la construction de l’espace. / What is a landscape heritage? It is a new look by actors on a landscape wichi, according to Levy & Lussault (2003) “is supposed to deserve a transfer from past to find a value in present”. It is “a collection of attributes, representations, practices fixed on a non-contemporary object […] whose present importance is declared collectively, intrinsic (how this objet is representative of history of society’s objects) and extrinsic (how this object contains the values of a collective memory), which requires its conservation and its transmission.In order to define the heritage properties of landscape, people organize themselves into groups and try to communicate with each other’s. Each constructs a representation of the landscape around specific attributes that are of interest to the group. All these representations are different and yet they concern a single landscape. When it comes to carrying out an action that will have an effect on this common space, the groups interact with each other within a “collective network”. The action may be the subject of negotiations, tensions, conflicts, agreement or abandonment depending on the position of each person. However, whether the action was carried out or abandoned, the actors have exchanged their views on the landscape throughout the collective network. Therefore, as actions are progressively carried out on patrimonial landscape, groups of people construct a common view of this landscape: it is the “collective representation of the landscape”.Unlike a material object, the landscape is difficult to quantify. The acquisition for the latter of a heritage value therefore requires a complex process called “patrimonialization process”. For the groups of people present in the landscape, this process is not insignificant. It disrupts the collective representation of the landscape that has been built in the collective network. In the resulting social disorder, the groups will struggle to assert their representation of the landscape in a new collective representation. In this context, our thesis poses the following problem: Considering a territory undergoing a transformation of the look towards a heritage context, to what extent do agricultural and non-agricultural stakeholders build a new collective representation focused on keeping livestock, use of space and landscape management?To address this problem, we have mobilized the networks of agricultural and non-agricultural actors existing at two sites in the Massif Central that are registered or in search of inscription on the UNESCO World Heritage (“Les Causses et les Cévennes” and “La Chaîne des Puys - faille de Limagne”). After a brief description of the two sites, we have explained our positioning as regards the collective rather than the individual aspect in the construction of a representation of the landscape and around the organization and management of the landscape. We have then constructed a methodology that is inspired by this theoretical contribution. Thanks to it, we managed to conduct a hundred interviews which enabled us to identify and analyze on the sites the two networks in which the collective actors are organizing to integrate this new heritage stake in their representation of the landscape. This network organization materializes around a series of actions aimed to the management of the heritage, as well as support for livestock rising and the enhancement of agricultural production. Thus, we note that the process of patrimonialization contributes indirectly, by influencing the collective representation of agricultural space, to the evolution of agricultural practices which are themselves responsible for the construction of space

Individuals often have difficulty identifying the heuristics that affect their decision-making (NOFSINGER and BAKER, 2002). However, Menkhoff, Brozynki and Schmidt (2006) show that individuals knowledgeable about the influence of heuristics in decision making may have fewer episodes of bounded rationality compared to individuals unrelated to this knowledge. According to Mussweiler et al. (2000), the Anchorage is one of the most striking influences on judgment and decision making. In this context, the main objective of this research was to verify the existence of heuristics in the anchoring of the numerical estimates of experts and non-specialists in real estate, when subjected to experimental tasks related to the field of domain expert and outside their field of knowledge, in order Thorsteinson et al. (2008), who argue that the effects of Anchorage makers are reduced when subjects have more knowledge about the problems in question. Thus, we performed a experiment with 324 subjects makers were divided into groups for Calibration and Experimental Groups, through the application of two decision-making tasks (T1 and T2), using the model Jacowitz and Kahneman (1995). It is noteworthy that many studies have been conducted in Anchorage to verify the presence of the anchoring heuristic in the process of judgment and decision making. However, this study, besides the proposal to study the effects of Anchorage during the decision making process related to quantitative, as the main contribution presented additional verification of the manifestation of Anchorage as a control variable (knowledge) is removed from the decisionmaking task. This procedure is called by Cozby (2006) a test handling, consisting in an attempt to directly measure whether the manipulation of a variable has the intended effect on the respondents. The results obtained through statistical t test for independent samples showed that there is evidence of the anchoring heuristic in decision making of individual members of the experimental group of non-experts (anchor and anchor low-high) in both T1 and T2. With respect to experts, it was revealed that T1 is no evidence of the anchoring heuristic, which corroborates the results found by Jacowitz and Kahneman (1995) and Luppe (2006). However, in relation to the second decision-making task (T2), it was observed that the mean differences were not statistically significant, implying that, at T2, are not found evidence of Anchorage in the decision process of experts, contradicting the results by Norfhcraft and Neale (1987) and Dorow (2009), who found evidence of Anchorage in the decision process when they were real estate brokers who underwent estimates for the real estate market. / Os indivíduos normalmente têm dificuldade em identificar as heurísticas que afetam suas tomadas de decisões (BAKER e NOFSINGER, 2002). No entanto, Menkhoff, Schmidt e Brozynki (2006) revelam que indivíduos conhecedores da influência das heurísticas no processo decisório podem apresentar menos episódios de racionalidade limitada se comparados aos indivíduos alheios a esse conhecimento. Segundo Mussweiler et al (2000), a Ancoragem consiste em uma das influências mais notáveis em julgamento e tomada de decisão. Neste contexto, o objetivo principal desta pesquisa consistiu em verificar a existência da heurística da Ancoragem nas estimativas numéricas de especialistas e não-especialistas em mercado imobiliário, quando submetidos a tarefas experimentais relacionadas ao campo de domínio do especialista e fora do seu campo de conhecimento, tendo em vista Thorsteinson et al. (2008), os quais argumentam que os efeitos da Ancoragem são reduzidos quando sujeitos decisores têm mais conhecimento acerca dos problemas em questão. Assim, foi realizado um quase-experimento com 324 sujeitos decisores, divididos em Grupos de Calibragem e Grupos Experimentais, por meio da aplicação de duas tarefas decisórias (T1 e T2), utilizando-se o Modelo de Jacowitz e Kahneman (1995). Ressalta-se que muitos estudos sobre Ancoragem têm sido realizados no sentido de verificar a presença da heurística da Ancoragem no processo de julgamento e tomada de decisão. No entanto, este estudo, além da proposta de estudar os efeitos da Ancoragem durante o processo decisório relacionado a decisões quantitativas, apresentou como principal contribuição adicional a verificação da manifestação da Ancoragem quando uma variável de controle (conhecimento) é retirada da tarefa decisória. Tal procedimento é denominado por Cozby (2006) como um Teste de Manipulação, consistindo em uma tentativa para medir diretamente se a manipulação de uma variável tem o efeito pretendido sobre os respondentes. Os resultados obtidos, por meio do teste estatístico t para amostras independentes, demonstraram que há evidências da heurística da Ancoragem no processo decisório dos indivíduos integrantes do Grupo Experimental de não-especialistas (âncora baixa e âncora alta), tanto em T1 quanto em T2. No que tange aos especialistas, foi possível perceber que em T1 há evidências da heurística da Ancoragem, corroborando com os resultados encontrados por Jacowitz e Kahneman (1995) e Luppe (2006). No entanto, em relação à segunda tarefa decisória (T2), observou-se que as diferenças de médias não foram estatisticamente significantes, inferindo-se que, em T2, não são encontradas evidências da Ancoragem no processo decisório dos especialistas, contrariando os resultados encontrados por Norfhcraft e Neale (1987) e Dorow (2009), os quais encontraram evidências da Ancoragem no processo decisório de corretores imobiliários quando foram submetidos à realização de estimativas referentes ao mercado de imóveis.

Coral reefs provide economic and environmental services to millions of people as areas for recreation, sources of food, jobs, and shoreline protection; and are now under threat from multiple stresses (NOAA 2002). Anthropogenic impact from acute physical events such as commercial vessel grounding and anchor drags have been well documented throughout the world and southeast Florida. However little data exist on the chronic effects of large commercial vessels anchoring on reef resources. The Port Miami commercial anchorage was designated circa 1927 and was delineated over approximately 700 acres of reef resources. Anchorage use, benthic resources, and substrate composition were surveyed to understand the impact commercial vessel anchoring activities have had. Survey sites included both random sites within the anchorage to understand the cumulative chronic effect of anchoring activity, as well as targeted surveys at recently anchored sites to understand the immediate impacts of those anchoring events. Survey data were also compared to anchorage use data to understand how vessel traffic patterns influenced impact. Results indicated that there was both significant differences at acute recent impact sites and chronic impact sites. Generally, Outer Reef chronic impact sites had more evidence of chronic impacts both in the benthic community and substrate composition than Inner Reef sites. Significant differences on Outer Reef included an increase in the percent cover of small rubble, a decrease in octocoral percent cover, and a decrease in the density of larger octocoral size classes. Significant differences on Inner Reef included a decrease in the number of scleractinian species present compared to control sites.

M.Ing.(Electrical and Electronic Engineering) / The study investigated whether non-destructive impact testing, aided by supervised machine learning methods, could be used to identify improper roof bolt installations, related to insufficient grout coverage. The testing method involved the installation of four roof bolts, with varying installation properties, into a 1511 × 940 × 1350mm rock test block. Three fully grouted bolts served as examples of proper installations, with the fourth bolt grouted only up to half the length of the borehole serving as an improper roof bolt installation. The testing procedure involved placing sensors directly onto the bolts and mechanically impacting a chosen bolt while measuring the response on all the bolts. The focus was on gaining understanding of the working principle of the testing technique and how the measured response was influenced by the presence of signal-modifying factors of the physical test block geometry, such as changes in material properties, boundary changes, cracks or empty boreholes. It was shown that the roof bolt integrity testing method aided by supervised machine learning methods could identify and classify both properly and improperly grouted roof bolts on the small sample of test bolts, in a series of tests conducted at the CSIR Centre for Mining Innovation premises. The method was also shown to be robust enough to do so even in the presence of the signal-modifying factors of the physical test block geometry.

Precast prestressed concrete piles are widely used in deep foundation construction. Due to unexpected site soil conditions and difficulties associated with transportation and handling long precast piles, splicing is sometimes necessary at the construction site. Available splicing methods utilize steel type connections that are more suitable for reinforced concrete construction and result in limited tensile capacity at the splice. This dissertation describes studies associated with the development of a new post-tensioned splicing system using staggered, embedded anchorages. The new system has the potential to provide the same tensile capacity as a one piece prestressed pile. To develop the post-tensioned splicing system it was necessary to conduct varied numerical analyses to solve immediate technical problems associated with the design, fabrication and testing of a prototype. This included the design of a self-stressing prestressing bed, optimization of the shape of the embedded anchorages and their layout within the piles being spliced. The focus of the dissertation is on non-linear finite element studies conducted to model the flexure behavior of prototype laboratory and full-sized spliced piles in comparison to their identical non-spliced counterpart. Though finite element analysis of prestressed elements is not new, issues relating to modeling post-tensioned, spliced elements with embedded, staggered anchorages have not been the subject of any previous investigation and constitute the principal contribution of this study. Nonlinear finite element analysis was conducted using ANSYS. The William-Warnke failure criterion used to establish concrete failure. A three-dimensional analysis was conducted in which SOLID65 element was used for modeling concrete and LINK8 for the prestressing strands. The post-tensioning ducts were modeled using PIPE20 elements. Perfect bond was assumed between the concrete and the ducts. Embedded anchorages were modeled as fixed locations within the concrete. Epoxy used to join the two splicing surfaces was modeled using contact elements. Since the layout of the post-tensioning ducts was staggered, a full model was required. In contrast, advantage was taken of symmetry for the analysis of the one piece controls. The finite element model was able to accurately capture the flexural behavior of both the control and the spliced piles. The results suggested that tensile separation at the splice interface acted as a pivot about which the section rotated. As a result, the compression failure zone in the spliced pile was confined to a smaller region compared to the control. The stress distribution in the spliced pile indicated that the concrete in the cover above the splice was crushed at the ultimate stage before the steel had yielded. As a result, the ultimate capacity of the spliced pile was controlled by concrete failure. The results also indicated that, among the multiple layers of post-tensioning strands, only one approached yield while others remained in the elastic range. As a result, when the applied load was released, the spliced pile rebounded back to a large degree, which resulted in a much smaller residual permanent deformation. This behavior of a spliced pile can be beneficial for structures in a seismic zone because it will induce smaller secondary moments. This study helped to refine and improve the new post-tensioned splicing system. Its availability makes it possible to extend and further improve the concept without the need for costly prototype fabrication and testing.

Corrosion of steel tendons is a major problem for post-tensioned concrete, especially because corrosion of the steel strands is often hard to detect inside grouted ducts. Non-metallic tendons can serve as an alternative material to steel for post-tensioning applications. Carbon fiber reinforced polymer (CFRP), given its higher strength and elastic modulus, as well as excellent durability and fatigue strength, is the most practical option for post-tensioning applications. The primary objective of this research project was to assess the feasibility of the use of innovative carbon fiber reinforced polymer (CFRP) tendons and to develop guidelines for CFRP in post-tensioned bridge applications, including segmental bridges and pier caps. An experimental investigation and a numerical simulation were conducted to compare the performance of a scaled segmental bridge model, post-tensioned with two types of carbon fiber strands and steel strands. The model was tested at different prestress levels and at different loading configurations. While the study confirms feasibility of both types of carbon fiber strands for segmental bridge applications, and their similar serviceability behavior, strands with higher elastic modulus could improve structural performance and minimize displacements beyond service loads. As the second component of the project, a side-by-side comparison of two types of carbon fiber strands against steel strands was conducted in a scaled pier cap model. Two different strand arrangements were used for post-tensioning, with eight and six strands, respectively representing an over-design and a slight under-design relative to the factored demand. The model was tested under service and factored loads. The investigation confirmed the feasibility of using carbon fiber strands in unbonded post-tensioning of pier caps. Considering both serviceability and overload conditions, the general performance of the pier cap model was deemed acceptable using either type of carbon fiber strands and quite comparable to that of steel strands. In another component of this research, creep stress tests were conducted with carbon fiber composite cable (CFCC). The anchorages for all the specimens were prepared using a commercially available expansive grout. Specimens withstood 95% of the guaranteed capacity provided by the manufacturer for a period of five months, without any sign of rupture.

京都大学 / 新制・課程博士 / 博士(医科学) / 甲第23425号 / 医科博第130号 / 新制||医科||9(附属図書館) / 京都大学大学院医学研究科医科学専攻 / (主査)教授 萩原 正敏, 教授 戸井 雅和, 教授 武藤 学 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

December 2011. A thesis submitted to the College of Dental Medicine of Nova Southeastern University of the degree of Master of Science in Dentistry. Background: Temporary anchorage devices (TADs) provide a versatile means by which orthodontic anchorage can be established without the need for patient compliance and complex force systems. Their use is predicated on their ability to remain stable throughout the course of treatment in which they are needed. This has been shown to be the result of "primary stability" which is achieved through mechanical interlocking of the screw threads with the surrounding bone immediately upon placement. Therefore, evaluating the factors that can either enhance or detract from the primary stability of TADs can serve to improve the predictability of their success. Objectives: The objectives of this study were to describe how variations in synthetic cortical bone thickness and the angle of force applied in relation to the long axis of TADs affects their stability in terms of pull-out strength, and to ascertain the perspectives of practicing orthodontists in the state of Florida on their experiences with temporary anchorage devices with regards to success and failure. Methods: For the bench top study, 90 1.5x8mm long neck Orthotechnology Spider Screws were randomly allocated to 9 groups of 10 TADs each. The 9 groups were established based on both the thickness of synthetic cortical bone (1.0, 1.5, and 2.0mm) and the angle of force vector applied relative to the long axis of the TADs (45, 90, and 1800). Pull-out testing was carried out by applying a force to the TADs via a universal testing machine (Instron, Canton, MA) at a rate of 2.0mm/minute. Real-time graphical and digital readings were recorded, with the forces being recorded in Newtons (N). Each miniscrew was subjected to the pull force until peak force values were obtained. For the 450 and 1800 tests, the force registered at the time-point of pull-out, or screw head movement of 1.5mm within the synthetic bone blocks. The determination of 1.5mm of movement was made due the dramatically erratic deflection observed by the digital and graphical readouts at precisely this point. For the survey portion of this study, A customized survey was developed for this study. The survey was composed of 12 questions, some of which were obtained from a questionnaire that was created by Buschang et al.54 The additional questions were devised by the members of this research project, with the aim of answering questions regarding the clinical experiences that practicing orthodontists experienced with TADs. Results: For the bench top study: Implants placed in 2.0mm of synthetic cortical bone and pulled at an angle of 1800 had the highest pull-out strength among all groups (258.38N), while those placed in 1.0mm of synthetic cortical bone and pulled at an angle of 900 exhibited the lowest (67.11N). When evaluated separately, a cortical bone thickness of 2.0 mm displayed the highest pull-out forces for the three angles of force application, and 1800 angle of force displayed the highest-pull-out forces for the three cortical bone thicknesses. Conversely, 1.0mm of cortical bone thickness displayed the lowest pull-out forces for the three angles of force application, and 900 angle of force displayed the highest-pull-out forces for the three cortical bone thicknesses. For the survey: The most important factor associated with TAD failure was cited as placement location by 45.7% (n=16) of respondents, while root proximity was cited as the least important factor by 35.3% (n=12) of respondents. For the site from which practitioners indicated that they experience the greatest success, 81.8% cited the palate, while 51.9% responded that they experience the highest failure rates for the posterior maxilla (distal to the cuspids). Conclusions: A synthetic cortical bone thickness of 2mm and pull forces applied parallel to the long axis of TADs resulted in the greatest resistance to pull-out.