A incompatibilidade entre o módulo de elasticidade (E) do endentador e dos materiais cerâmicos durante os testes de fadiga tem gerado controvérsias. Foram testadas as hipóteses que coroas totalmente cerâmicas apresentarão confiabilidade à fadiga acelerada progressiva do tipo step-stress (hipótese 1) e modos de falha (hipótese 2) similares, quando dois endentadores, um à base de carboneto de tungstênio (WC, E = 600 GPa) e outro de cerâmica esteatite [SB, E = 90 GPa] forem utilizados para transferir a carga. Para avaliar o efeito dos endentadores, um preparo para coroa total em um molar inferior foi realizado. A partir deste modelo mestre, 42 coroas à base de Y-TZP e 42 réplicas em resina composta foram produzidas. As réplicas em resina foram envelhecidas por 30 dias. Todas as coroas foram cimentadas sobre estas réplicas com cimento autoadesivo (Rely X Unicem - 3M/ESPE, St. Paul, EUA) e divididas em dois grupos de acordo com o endentador (WC ou SB). As coroas foram submetidas tanto ao teste de resistência à fratura (n = 3 por grupo), empregado para determinar os perfis de carga (leve, moderado e agressivo) quanto à fadiga (n = 18 por grupo), utilizando um endentador novo para cada coroa. Impressões de todas as coroas e endentadores submetidos ao perfil leve foram obtidas, em pontos específicos do perfil (0, 40k, e, 80k 120k, 160k), vazadas com resina epóxi e avaliadas sob MEV, com a finalidade de inspecionar a morfologia e medir a área endentada. O Use level Probability mostrou sobreposição entre os intervalos de confiança, indicando que não houve diferença significante entre os grupos, independente do critério de falha. O módulo de Weibull Beta (&#x3B2;) calculado para IA (análise inicial) foi de 1,99 e 1,67 para SB e WC, respectivamente, apontando que a fadiga acelerou o fracasso em ambos os grupos. Este não foi o caso para os valores de &#x3B2; para a análise de FA (análise final) (SB = 1,1 e WC = 0,72), revelando que a carga pode ter influenciado sozinha o mecanismo de falha. Ambos os endentadores produziram padrões semelhantes de desgaste/danos nas coroas. A análise fractográfica revelou modos de falhas concorrentes, mas as trincas tipo cone parciais foram as mais dominantes em ambos os grupos. As medições das áreas endentadas mostraram diferença estatística entre os grupos (SB vs. WC) (p <0,05). No geral, o endentador WC exibiu área maior do que a produzida pelo SB. O endentador mais compatível (SB) com a superfície cerâmica produziu confiabilidade e modos de falhas semelhantes ao ser comparada com o WC; assim, as hipóteses 1 e 2 foram aceitas. / Concerns about elastic modulus (E) mismatch between indenter and ceramic materials during fatigue testing have generated controversy. We hypothesized that all-ceramic crowns will exhibit similar step-stress sliding contact fatigue reliability (hypothesis 1) and failure characteristics (hypothesis 2) when using high stiffness tungsten carbide (WC, E = 600 GPa) vs enamel like steatite (SB, E = 90 GPa) indenters. To evaluate the effect of indenters, a preparation for a full crown was made on a first lower molar. From this master die 42 Y-TZPveneered all-ceramic crowns and 42 tooth-resin réplicas were made. Crowns were cemented onto the aged (30 days) tooth-resin réplicas with self-adhesive resin-based cement (Rely X UniCem - 3M/ESPE, St. Paul, USA). After, crowns were divided into two groups according to indenter (WC or SB). Specimens were subject to single-load to fracture (n = 3 per indenter type) to determine the step-stress profiles (mild, moderate, and aggressive) and to mouthmotion step-stress fatigue-tested (n = 18 per indenter type). Two failure modes were determined (inital analysis [IA] and final analysis [FA]). For each crown, a new indenter was used and labelled accordingly for surface damage evaluation. Impressions from all crowns subjected to mild profile were taken following a pre-arranged number of cycles (0, 40k, 80k, 120k e, 160k), poured with epoxy resin and SEM evaluated to inspect the morphology and to measure the indented area. The use level probability plots of the fatigue data showed overlap between the 2-sided 90% confidence bounds. The calculated Weibull Beta (&#x3B2;) for IA was 1.99 and 1.67 for SB and WC, respectively, pointing out that fatigue accelerated the failure in both groups. This was not the case for the &#x3B2; values for the FA analysis (SB = 1.1 and WC = 0.72), revealing tha the load alone dicted the failure mechanism. Both indenters produced similar pattern of wear on crown surfaces. Fractographic landmarks showed competing failure modes, but partial cone cracks were the most dominant for both groups. The indented area measurements showed statistical difference between groups (SB vs WC) (p < .05). Overall, the WC indenter displayed the largest area than SB, except when 120k was taken into account. The more compliant SB indenter led to similar reliability and failure modes to WC (hypotheses 1 and 2 accepted).

CAD/CAM technology had evolved extensively from the time when it was first used clinically in the 1980s. Today, CAD/CAM technology can be used to fabricate crowns, design and mill fixed partial denture frameworks, set teeth and fabricate complete dentures as well as to mill interim restorations. An extensive literature review found many research studies on the evaluation of the accuracy of the CAD/CAM ceramic crowns as compared to other ceramic crowns but little research had been done to evaluate the accuracy of interim restorations. This article describes the method in which CAD/CAM as well as conventional interim crowns were fabricated, cemented onto their dies, dye stained, thermocycled as well as sectioned with their marginal discrepancies investigated.

Doctor of Philosophy / The commercial introduction of glass infiltrated slip cast ceramic technology as a core dental ceramic for crowns and bridges began in 1990. The system known as Inceram® provided a metal free ceramic core with a flexural strength that was reported to be between 400 and 600 MPa. The first aim of this study was to investigate in vitro fractures for this type of crown that occurred from high localized occlusal loading. The second aim was to propose suitable guidelines for the construction of crowns that are more crack resistant when loaded by a spherical object such as an opposinc cusp. The review of the literature identified Young’s modulus (E) as an important aspect for the behaviour of a brittle solid when it is exposed to load. Young’s modulus is involved in the total energy of the solid, its free surface energy, its toughness, parameters involved in contact areas, stresses from indenters on those contact areas and at the interface between two materials with different moduli. This mismatch was to become more important when Finite Element Analysis was applied to the test results. A second physical property that has importance in bilaminar minerals is Poisson’s ratio. Less important than Young’s modulus, Poisson’s ratio still provides some of the answers to crack propagation at an interface, highlighted by the description of Dundurs parameters (Mencik 1996). The use of Weibull statistics provided information concerning reliability for different core to veneer thickness ratios in the experimental models and crown designs. The first experimental part was to establish a crown model suitable for investigation. The porcelain jacked crown restoration for an upper incisor was chosen because it provided the best opportunity to vary the construction parameters of the crown without sacrificing the aesthetics. The results from this initial in vitro study established thickness ranges for the standard design of these crowns, the loads that could be expected and the two types of fracture patterns that might occur when the bilaminar system is loaded via a hard steel ball indenter in the middle of the palatal surface. The data from chapter three were then compared with two basic bilaminar and monolithic disc designs to establish the relevance of the dimensions of the ISO standard test specimen design for flexural strength. The results of this chapter confirmed that the loads were in the same range for the bilaminate discs, and that the flexural strengths for the two component parts were in agreement with other known results. The use of Finite Element Analysis (FEA) was employed to provide an additional method for testing the model to establish areas when principal stresses might lie and how they were distributed. It was found that the ISO flexural strength test was not ideal for testing bilaminates because it did not account for the large mismatch in Young’s modulus between the two component materials. The FEA revealed an unexpected increase in tensile stress on the bottom surface of the In-Ceram when it was the bottom layer in the bilaminate. The FEA did confirm the difference between a flat punch and a ball indenter for stress intensities around the contact area with the ball indenter producing higher stresses for a given load…

Doctor of Philosophy / The commercial introduction of glass infiltrated slip cast ceramic technology as a core dental ceramic for crowns and bridges began in 1990. The system known as Inceram® provided a metal free ceramic core with a flexural strength that was reported to be between 400 and 600 MPa. The first aim of this study was to investigate in vitro fractures for this type of crown that occurred from high localized occlusal loading. The second aim was to propose suitable guidelines for the construction of crowns that are more crack resistant when loaded by a spherical object such as an opposinc cusp. The review of the literature identified Young’s modulus (E) as an important aspect for the behaviour of a brittle solid when it is exposed to load. Young’s modulus is involved in the total energy of the solid, its free surface energy, its toughness, parameters involved in contact areas, stresses from indenters on those contact areas and at the interface between two materials with different moduli. This mismatch was to become more important when Finite Element Analysis was applied to the test results. A second physical property that has importance in bilaminar minerals is Poisson’s ratio. Less important than Young’s modulus, Poisson’s ratio still provides some of the answers to crack propagation at an interface, highlighted by the description of Dundurs parameters (Mencik 1996). The use of Weibull statistics provided information concerning reliability for different core to veneer thickness ratios in the experimental models and crown designs. The first experimental part was to establish a crown model suitable for investigation. The porcelain jacked crown restoration for an upper incisor was chosen because it provided the best opportunity to vary the construction parameters of the crown without sacrificing the aesthetics. The results from this initial in vitro study established thickness ranges for the standard design of these crowns, the loads that could be expected and the two types of fracture patterns that might occur when the bilaminar system is loaded via a hard steel ball indenter in the middle of the palatal surface. The data from chapter three were then compared with two basic bilaminar and monolithic disc designs to establish the relevance of the dimensions of the ISO standard test specimen design for flexural strength. The results of this chapter confirmed that the loads were in the same range for the bilaminate discs, and that the flexural strengths for the two component parts were in agreement with other known results. The use of Finite Element Analysis (FEA) was employed to provide an additional method for testing the model to establish areas when principal stresses might lie and how they were distributed. It was found that the ISO flexural strength test was not ideal for testing bilaminates because it did not account for the large mismatch in Young’s modulus between the two component materials. The FEA revealed an unexpected increase in tensile stress on the bottom surface of the In-Ceram when it was the bottom layer in the bilaminate. The FEA did confirm the difference between a flat punch and a ball indenter for stress intensities around the contact area with the ball indenter producing higher stresses for a given load…

Thesis (M.S.)--University of Michigan, 1987.

Thesis (doctoral)--Friedrich-Wilhelms-Universität zu Berlin, 1915. / Vita. Includes bibliographical references and index.

Thesis (M.S. )--University of Tennessee Health Science Center, 2008 / Title from title page screen (viewed on July 30, 2008). Research advisor: Edward F. Harris, Ph.D. Document formatted into pages (xvi, 154 p. : ill.). Vita. Abstract. Includes bibliographical references (p. 148-154).

Thesis (M.S.)--University of Michigan, 1987.

Thesis (M.S.)--University of Michigan, 1987.

Thesis (M.S.)--University of Michigan, 1976.