Thesis (M.S.D.)--Indiana University School of Dentistry, 2009. / Title from PDF t.p. (viewed Feb. 5, 2010) Advisor(s): Michael A. Cochran, Chair of the Research Committee, Armando E. Soto Rojas, Margherita R. Fontana, Timothy Carlson, Tien-Min Gabriel Chu. Curriculum vitae. Includes abstract. Includes bibliographical references (leaves 56-61).

Thesis (M.S.)--School of Dentistry. University of Missouri--Kansas City, 2008. / "A thesis in oral biology." Advisor: Mary P. Walker. Typescript. Vita. Title from "catalog record" of the print edition Description based on contents viewed Aug. 07, 2009. Includes bibliographical references (leaves 39-45). Online version of the print edition.

Made available in DSpace on 2014-06-11T19:33:01Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-09-06Bitstream added on 2014-06-13T20:24:31Z : No. of bitstreams: 1 vieira_aem_dr_araca.pdf: 862313 bytes, checksum: 73131cab7febe9ed9ca73177596b76b0 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Bisco Inc., Il, Usa / Bosworth Company, Il, Usa / O presente trabalho avaliou a capacidade da microtomografia de raios-X (XMT) laboratorial e síncrotron para mensurar coeficientes de absorção linear em escala micrométrica em estudos in vitro utilizando dentes bovinos e ciclagem de pH. Sendo assim, este estudo foi desenvolvido em cinco manuscritos, com os seguintes objetivos: traçar parâmetros e determinar um protocolo para a quantificação do conteúdo mineral de esmalte bovino utilizando XMT laboratorial e síncrotron; analisar a estrutura da junção amelo-dentinária em incisivos bovinos utilizando XMT síncrotron; determinar o potencial anti-cárie do fosfato de cálcio amorfo (ACP) presente em selantes de fóssulas e fissuras, utilizando dentes bovinos, ciclagem de pH, microdureza de superfície e XMT síncrotron; e avaliar, através de análise de microdureza de superfície e XMT síncrotron, a capacidade de uma pasta contendo CPP-ACP para ativar a remineralização do esmalte dental. Os resultados obtidos mostram que: a XMT propiciou a determinação da quantidade mineral com uma precisão mais adequada, sendo a melhor resolução espacial obtida através da luz síncrotron; a junção amelo-dentinária apresentou-se menos mineralizada que a dentina ou esmalte; o fosfato de cálcio amorfo presente nos materiais testados não foi capaz de inibir a desmineralização ou ativar a remineralização do esmalte bovino, em ciclagem de pH, tanto quanto os íons flúor. Conclui-se que a XMT é capaz de determinar pequenas alterações na mineralização do dente bovino após ciclagem de pH. / This study evaluated the ability of laboratory and synchrotron X-ray microtomography (XMT) for measuring linear attenuation coefficient at micrometer scale of in vitro studies using bovine teeth and pH-cycling. For that, this study included five papers, with the following aims: to define parameters and a protocol for quantification of mineral content of bovine enamel using laboratory and synchrotron XMT; to analyze the dentinoenamel junction (DEJ) structure in bovine incisors using synchrotron XMT; to determine the anti-caries potential of amorphous calcium phosphate (ACP) in pit and fissure sealants, using bovine teeth, pH-cycling, surface hardness and synchrotron XMT; and to evaluate, through surface hardness analysis and synchrotron XMT, the ability of a CPP-ACP paste to enhance enamel remineralization. The results showed that: XMT provided mineral quantification with an adequate precision; synchrotron microtomography provided the best spatial resolution; DEJ was less mineralized on the average than dentin or enamel; addition of ACP to the materials did not inhibit demineralization or enhance remineralization of bovine enamel in a pH-cycling as fluoride ions. It was possible to conclude that XMT can determine small alterations in the mineralization of bovine tooth after pH-cycling.

Orientador: Alberto Carlos Botazzo Delbem / Banca: Robson Frederico Cunha / Banca: Cássia Cilene Dezan Garbelini / Banca: Cínthia Pereira Machado Tabchoury / Banca: Célio Percinoto / Resumo: O presente trabalho avaliou a capacidade da microtomografia de raios-X (XMT) laboratorial e síncrotron para mensurar coeficientes de absorção linear em escala micrométrica em estudos in vitro utilizando dentes bovinos e ciclagem de pH. Sendo assim, este estudo foi desenvolvido em cinco manuscritos, com os seguintes objetivos: traçar parâmetros e determinar um protocolo para a quantificação do conteúdo mineral de esmalte bovino utilizando XMT laboratorial e síncrotron; analisar a estrutura da junção amelo-dentinária em incisivos bovinos utilizando XMT síncrotron; determinar o potencial anti-cárie do fosfato de cálcio amorfo (ACP) presente em selantes de fóssulas e fissuras, utilizando dentes bovinos, ciclagem de pH, microdureza de superfície e XMT síncrotron; e avaliar, através de análise de microdureza de superfície e XMT síncrotron, a capacidade de uma pasta contendo CPP-ACP para ativar a remineralização do esmalte dental. Os resultados obtidos mostram que: a XMT propiciou a determinação da quantidade mineral com uma precisão mais adequada, sendo a melhor resolução espacial obtida através da luz síncrotron; a junção amelo-dentinária apresentou-se menos mineralizada que a dentina ou esmalte; o fosfato de cálcio amorfo presente nos materiais testados não foi capaz de inibir a desmineralização ou ativar a remineralização do esmalte bovino, em ciclagem de pH, tanto quanto os íons flúor. Conclui-se que a XMT é capaz de determinar pequenas alterações na mineralização do dente bovino após ciclagem de pH. / Abstract: This study evaluated the ability of laboratory and synchrotron X-ray microtomography (XMT) for measuring linear attenuation coefficient at micrometer scale of in vitro studies using bovine teeth and pH-cycling. For that, this study included five papers, with the following aims: to define parameters and a protocol for quantification of mineral content of bovine enamel using laboratory and synchrotron XMT; to analyze the dentinoenamel junction (DEJ) structure in bovine incisors using synchrotron XMT; to determine the anti-caries potential of amorphous calcium phosphate (ACP) in pit and fissure sealants, using bovine teeth, pH-cycling, surface hardness and synchrotron XMT; and to evaluate, through surface hardness analysis and synchrotron XMT, the ability of a CPP-ACP paste to enhance enamel remineralization. The results showed that: XMT provided mineral quantification with an adequate precision; synchrotron microtomography provided the best spatial resolution; DEJ was less mineralized on the average than dentin or enamel; addition of ACP to the materials did not inhibit demineralization or enhance remineralization of bovine enamel in a pH-cycling as fluoride ions. It was possible to conclude that XMT can determine small alterations in the mineralization of bovine tooth after pH-cycling. / Doutor

EDF souhaite conforter la justification de l’intégrité des cuves de réacteurs nucléaires à eau pressurisée, basées sur l’amorçage de fissure, par le concept d’arrêt de fissure. L'objectif de la thèse est de consolider les travaux de prévision de l’arrêt des fissures fragiles dans l’acier de cuve. Des essais d'arrêt de fissure isothermes réalisés entre -150°C et -50°C sur des éprouvettes CT et sur des anneaux en compression ont été analysés. Les analyses fractographiques montrent que la propagation et l’arrêt de fissure se produisent en clivage même si de la déchirure ductile précède la propagation instable de fissure. Un critère local d’arrêt de fissure fragile est appliqué lors de calculs par éléments finis en élastoviscoplasticité et en dynamique : la rupture se produit si la contrainte principale maximale est égale à une contrainte critique. Ce critère permet de bien prédire les vitesses de propagation ainsi que les longueurs de fissure à l’arrêt. La contrainte critique augmente avec la température en relation avec les signes de dissipation observés sur les surfaces de rupture. Une dépendance du critère à la géométrie est observée. Elle peut être liée aux hypothèses de calculs réalisés en bidimensionnel. L’étude de la dynamique de la structure montre que le phénomène d’arrêt de fissure est fortement lié à la dynamique globale de la structure : l’arrêt et la fermeture de la fissure interviennent simultanément. / EDF wants to complete the assessment of reactor pressure vessels usually based on crack initiation concept by crack arrest concept. The work aims at improving the knowledge of cleavage crack arrest in reactor pressure vessel steel. For that purpose, isothermal crack arrest experiments were performed for temperatures ranging from –150°C up to –50°C on compact tensile specimens and on pre-cracked rings submitted to compressive loading. Fractographic observations revealed that the whole crack propagation and arrest occurs by cleavage even if ductile tearing occurs before initiation of the unstable crack propagation. A local cleavage crack arrest criterion is applied in finite element computations carried out in elastoviscoplasticity and in full dynamics: the crack propagates since the largest principal stress reaches a critical stress. The application of this criterion on the experiments leads to a good prediction of the crack speed and of the crack length and shows that the critical stress increases with the temperature in relation with dissipation features observed on the fracture surfaces. Dependence to the geometry is observed; it can be due to the assumption used for the 2D computations. The study of the structural dynamic shows that the crack arrest phenomenon is very linked to the global dynamics of the structure: crack arrest and crack closure occur approximately at the same time.

L’objectif de cette thèse est de comprendre les micro-mécanismes physiques de propagation et d’arrêt de fissure de clivage dans l’acier de cuve 16MND5 et de proposer un modèle de prédiction robuste et physiquement fondé, en s’appuyant sur une campagne d’essais de rupture fragile sur éprouvettes de laboratoire finement instrumentées, associée à la modélisation numérique de ces essais. Dans un premier temps, des expériences ont été menées sur des éprouvettes CT25 de différentes épaisseurs à cinq températures (-150°C, -125°C, -100°C, -75°C, -50°C). Des trajets de fissures rectilignes et branchées (deux fissures se développant de manière quasi-symétrique) ont été observés. Pour estimer la vitesse de propagation, une caméra ultra-rapide a été utilisée, associée à la mise au point d’un protocole expérimental permettant d’observer la face de l’éprouvette dans l’enceinte thermique, sans givrage. Des observations à 500 000 images.s-1 ont permis de caractériser finement la vitesse instantanée de la fissure sur le ligament complet de la CT (~25 mm). En parallèle, pour pouvoir analyser les essais et l’impact de la viscosité sur la réponse mécanique autour de la fissure, le comportement élasto-viscoplastique du matériau a été étudié jusqu’à une vitesse de déformation de 104 s-1 pour les températures étudiées. La méthode des éléments finis étendus (X-FEM) a été utilisée dans le code de calcul CAST3M pour modéliser la propagation de fissure. Les simulations numériques associent l’approche locale de la rupture en dynamique non linéaire et un critère de propagation en contrainte critique de type RKR à une distance caractéristique. Les travaux réalisés ont permis de confirmer la forme du critère proposé par Prabel à -125°C, et d’identifier les dépendances de ce critère à la température et à la vitesse de déformation. A partir d’analyses numériques en 2D et 3D, un critère multi-température fonction croissante de la vitesse de déformation est proposé. Des modélisations prédictives ont permis de valider le critère sur deux géométries d’éprouvettes (CT et anneau) en mode I à différentes températures. Des observations MEB et des analyses 3D au microscope optique montrent que le mécanisme de rupture est le clivage associé à des zones de cisaillement ductile entre les différents plans de fissuration. L’étude de la fraction surfacique des marches de cisaillement et des contraintes de fermeture associées tend à justifier le critère mis en place. Un modèle analytique est proposé permettant de justifier le critère déduit des modélisations numériques. Ce modèle considère que les ligaments retiennent la lèvre de la fissure et induisent donc des contraintes de fermeture au niveau de la pointe de fissure qu’il faut compenser pour atteindre la contrainte de clivage effective en pointe de fissure. Cette résistance des ligaments est directement reliée à la loi de comportement du matériau et justifie la dépendance du critère de rupture identifié à la vitesse de déformation. Enfin, les branchements de fissure ont été analysés via le dépouillement des vidéos obtenues avec la caméra rapide qui mettent en évidence un amorçage initial rectiligne, puis un amorçage de fissures multiples de part et d’autre du plan de fissure qui conduisent à l’arrêt de la fissure initiale, l’une de ces fissures ‘secondaires’ conduisant ensuite à la rupture de l’éprouvette. Les rôles essentiels de l’épaisseur et du chargement dans ce mécanisme de branchement sont soulignés. L’augmentation de l’épaisseur réduit la fréquence d’apparition de ce mécanisme et finit même par l’annuler. Logiquement l’intensité du chargement doit être suffisamment importante pour créer cette zone plastique étendue : les essais qui présentent une propagation rectiligne sont les essais pour lesquels les chargements à l’amorçage sont les plus faibles. / The purpose of this PhD thesis is to understand physical mechanisms of cleavage crack propagation and arrest in the 16MND5 PWR vessel steel and to propose a robust predicting model based on a brittle fracture experimental campaign of finely instrumented laboratory specimens associated with numerical computations. First, experiments were carried out on thin CT25 specimens at five temperatures (-150°C, -125°C, - 100°C, -75°C, -50°C). Two kinds of crack path, straight or branching path, have been observed. To characterize crack propagation and to measure crack speed, a high-speed framing camera system was used, combined with the development of an experimental protocol which allowed to observe CT surface without icing inside the thermal chamber and on the specimen. The framing camera (520 000 fps) has allowed to have a very accurate estimation of crack speed on the complete ligament of CT (~ 25 mm). Besides, to analyse experiments and to study the impact of viscosity on the mechanical response around the crack tip, the elastic-viscoplastic behavior of the ferritic steel has been studied up to a strain rate of 104 s-1 for the tested temperatures.The eXtended Finite Element Method (X-FEM) was used in CAST3M FE software to model crack propagation. Numerical computations combine a local non linear dynamic approach with a RKR type fracture stress criterion to a characteristic distance. The work carried out has confirmed the form of the criterion proposed by Prabel at -125°C, and has identified the dependencies of the criterion on temperature and strain rate. From numerical analyzes in 2D and 3D, a multi-temperature fracture stress criterion, increasing function of the strain rate, was proposed. Predictive modeling were used to confirm the identified criterion on two specimen geometries (CT and compressive ring) in mode I at different temperatures. SEM observations and 3D analyzes made with optical microscope showed that the fracture mechanism was the cleavage associated with ductile shear zones between the different planes of cracking. The study of the surface fraction of ductile shear zones and associated closing stress tends to justify the established criterion. An analytical model is proposed to justify the criterion deduced from numerical modeling. This model assumes that the ligaments hold the crack lips and therefore induce closing stress at the crack tip which has to be compensated to achieve the effective cleavage stress at the crack tip. This resistance of ligaments is directly related to the mechanical behavior of the material and justifies the dependence of fracture stress criterion with strain rate. Lastly, the crack branching was analyzed thanks to movies obtained with the high-speed camera. The cleavage crack propagates in a straight way over few millimeters. Then, new cracks appear on both sides of the initial crack lips which leads to the arrest of the initial crack. One of the new cracks leads to the failure of the CT specimen. The essential role of the thickness and loading on this branching mechanism is emphasized. The increased thickness reduces the frequency of occurrence of this mechanism and eventually even cancel. Low thicknesses lead to more extensive plasticity at the crack tip and generates the germs for the triggering of secondary cracks that appear. Logically, the intensity of loading must be large enough to create this extended plastic zone : the experiments with a straight path are the tests for which the initial loadings are the lowest.

Este trabalho trata de fissura, uma das principais patologias que podem ocorrer em edifícios residenciais em alvenaria estrutural, visando identificar os locais onde elas aparecem com mais frequência, para assim procurar formas de evitá-las. Inicialmente foram realizadas visitas a vários edifícios em alvenaria estrutural de forma a levantar as principais fissuras encontradas nesse tipo de estrutura. Identificou-se que as fissuras são mais frequentes nos contornos de aberturas, diante disse foi realizado um estudo teórico, com a utilização de um programa computacional, para se determinar algumas das principais causas prováveis dessas patologias através de modelos numéricos adequados. Finalmente, foram analisadas algumas das soluções para as patologias encontradas, tentando sugerir as melhores soluções para cada caso. / This paper deals with fissure, one of major diseases that can occur in a structural masonry residential buildings, in order to identify the locals they usually occur, to seek ways to avoid them. Initially were realized visits a several structural masonry buildings to analise the principals fissures in this type of structure. Was identified that the fissures are more frequently in the contours of openings, given this, was realized a theoretical study using a finite element computer program to identify some of the main possible causes of these pathologies through adequate numerical models. Finally, some possible solutions for the conditions found were analyzed, trying to suggest the best solutions for each case.

Indiana University-Purdue University Indianapolis (IUPUI) / This clinical study investigated the efficacy of the new LED LCU technology when compared to that of the QTH LCU by evaluating retention and wear of Clinpro (3M ESPE) sealant material over six months of function. This study was designed as a split mouth, randomized clinical study. Sealants were placed and polymerized on contralateral teeth of 35 patients, 33 of which successfully completed the study. The sealants were evaluated for clinical retention at baseline, three months, and six months by two evaluators. For the wear analysis, the area of the sealant wear at six months is reported. Nine pairs of molars and 22 pairs of premolar teeth were used. This sample size is smaller than the original sample used for clinical evaluation, because a number of the baseline impressions had to be discarded due to poor impression quality. Subsequent impressions were taken at three months, and six months. Epoxy replicas were made from the impressions and the occlusal surface of each replica was digitized using SigmaScan software. A cummulative legit model was applied to the clinical data, and a linear model was applied to the wear analysis. The results for clinical retention over the six months of function were as follows. At Baseline, for the QTH, 97.3 percent of the teeth received an Alpha score; 2.7 percent received a score of B. For the LED, 87.7 percent received a score of A; 12.3 percent received a score of B. At three months follow-up, for the QTH, 93.1 percent received a score of A; 6.9 percent received a score of B. For the LED, 86.1 percent received a score of A; 12.5 percent received a score of B, and 1.14 percent received a score of C. At six months follow-up, for QTH; 91.7 percent received a score of A; 8.3 percent received a score of B. For the LED, 83.3 percent received a score of A; 15.3 percent received a score of B, and 1.14 percent received a score of C. The hypothesis was that there would be no significant difference in clinical retention and wear of Clinpro's sealant polymerized with the QTH or the LED light sources over six months of function. Based on the results of this clinical study, the following conclusions can be made: 1) At baseline, Clinpro's sealant polymerized with QTH light source showed marginally significant better retention than LED light source (p-value 0.05001). 2) There was no significant difference between light sources for sealant clinical retention at three-month and six-month follow up visits. 3) Wear analysis resulted in marginally significant more wear for molar sealants polymerized with LED LCU (p-value 0.0755). 4) Wear analysis showed no significant difference for premolar sealants polymerized with either light source.

Questions as to the tempo and mode of changes in faunal composition at the Triassic/Jurassic boundary remain unanswered. Inquiries are hampered by a general paucity of sections containing correlatable Late Triassic/Early Jurassic strata. Vertebrate fossil material from Cromhall Quarry, recovered as part of an extended project centered on Late Triassic fissure infillings in southwestern Britain, was organized into a biostratigraphic scheme in 1993. This scheme could prove important in correlating Late Triassic continental strata. The Cromhall data consists of taxonomic counts from individual Stratigraphic levels within a series of fissures. Level counts were sorted into a series of sequential sedimentary and faunal associations that rest on the assumption that significant differences in faunal composition occur between individual fissures, but do not exist between individual sedimentary strata within any one fissure. Before the biostratigraphic framework could be utilized, the actual degree of similarity between the fissure faunas had to be quantified and tested. The original database, and counts from newly processed material, were subjected to Principle Components and Cluster Analyses. The analyses suggest that the majority of stratigraphic levels within any one fissure contain faunas with very similar composition. Levels from fissures that are temporally sequential contain faunas that are somewhat similar in composition. Overlap, in faunas found in strata at the top and bottom of sequential fissures, can be detected. In addition, there is a trend toward increased presence of certain taxa in the younger levels. These results indicate that the biostratigraphic framework may be used to enhance Triassic-Jurassic boundary research. / Master of Science

Lors de cette étude, un banc de fatigue thermique a été mis au point pour conduire des essais sur une éprouvette cylindrique en acier X38CrMoV5 de dureté 42-47 HRC. Diverses conditions d'essai ont été investiguées, la température maxi du cycle thermique (500 à 685°C), et la vitesse de chauffage (0.7 à 6.5 s). L'effet de ces paramètres sur le dommage a été étudié. La densité et la morphologie des réseaux de faïençage ont été quantifiées par analyse d'images. Des champs de T,