Ricardo Alexandre Zavanelli

Reliability of Metalloceramic and Zirconia-based Ceramic Crowns

Despite the increasing utilization of all-ceramic crown systems, their mechanical performance relative to that of metal ceramic restorations (MCR) has yet to be determined. This investigation tested the hypothesis that MCR present higher reliability over two Y-TZP all-ceramic crown systems under mouth-motion fatigue conditions. A CAD-based tooth preparation with the average dimensions of a mandibular first molar was used as a master die to fabricate all restorations. One 0.5-mm Pd-Ag and two Y-TZP system cores were veneered with 1.5 mm porcelain. Crowns were cemented onto aged (60 days in water) composite (Z100, 3M/ESPE) reproductions of the die. Mouth-motion fatigue was performed, and use level probability Weibull curves were determined. Failure modes of all systems included chipping or fracture of the porcelain veneer initiating at the indentation site. Fatigue was an acceleration factor for all-ceramic systems, but not for the MCR system. The latter presented significantly higher reliability under mouth-motion cyclic mechanical testing.

Thermal/mechanical simulation and laboratory fatigue testing of an alternative yttria tetragonal zirconia polycrystal core-veneer all-ceramic layered crown design

This study evaluated the stress levels at the core layer and the veneer layer of zirconia crowns (comprising an alternative core design vs. a standard core design) under mechanical/thermal simulation, and subjected simulated models to laboratory mouth-motion fatigue. The dimensions of a mandibular first molar were imported into computer-aided design (CAD) software and a tooth preparation was modeled. A crown was designed using the space between the original tooth and the prepared tooth. The alternative core presented an additional lingual shoulder that lowered the veneer bulk of the cusps. Finite element analyses evaluated the residual maximum principal stresses fields at the core and veneer of both designs under loading and when cooled from 900 degrees C to 25 degrees C. Crowns were fabricated and mouth-motion fatigued, generating master Weibull curves and reliability data. Thermal modeling showed low residual stress fields throughout the bulk of the cusps for both groups. Mechanical simulation depicted a shift in stress levels to the core of the alternative design compared with the standard design. Significantly higher reliability was found for the alternative core. Regardless of the alternative configuration, thermal and mechanical computer simulations showed stress in the alternative core design comparable and higher to that of the standard configuration, respectively. Such a mechanical scenario probably led to the higher reliability of the alternative design under fatigue.

Conventional and modified veneered zirconia vs. metalloceramic: fatigue and finite element analysis.

PURPOSE The purpose of this study was to test the hypothesis that all-ceramic crown core-veneer system reliability is improved by modifying the core design and as a result is comparable in reliability to metal-ceramic retainers (MCR). Finite element analysis (FEA) was performed to verify maximum principal stress distribution in the systems. MATERIALS AND METHODS A first lower molar full crown preparation was modeled by reducing the height of proximal walls by 1.5 mm and occlusal surface by 2.0 mm. The CAD-based preparation was replicated and positioned in a dental articulator for specimen fabrication. Conventional (0.5 mm uniform thickness) and modified (2.5 mm height, 1 mm thickness at the lingual extending to proximals) zirconia (Y-TZP) core designs were produced with 1.5 mm veneer porcelain. MCR controls were fabricated following conventional design. All crowns were resin cemented to 30-day aged composite dies, aged 14 days in water and either single-loaded to failure or step-stress fatigue tested. The loads were positioned either on the mesiobuccal or mesiolingual cusp (n = 21 for each ceramic system and cusp). Probability Weibull and use level probability curves were calculated. Crack evolution was followed, and postmortem specimens were analyzed and compared to clinical failures. RESULTS Compared to conventional and MCRs, increased levels of stress were observed in the core region for the modified Y-TZP core design. The reliability was higher in the Y-TZP-lingual-modified group at 100,000 cycles and 200 N, but not significantly different from the MCR-mesiolingual group. The MCR-distobuccal group showed the highest reliability. Fracture modes for Y-TZP groups were veneer chipping not exposing the core for the conventional design groups, and exposing the veneer-core interface for the modified group. MCR fractures were mostly chipping combined with metal coping exposure. CONCLUSIONS FEA showed higher levels of stress for both Y-TZP core designs and veneer layers compared to MCR. Core design modification resulted in fatigue reliability response of Y-TZP comparable to MCR at 100,000 cycles and 200 N. Fracture modes observed matched with clinical scenarios.

Conventional and modified veneered zirconia vs. metalloceramic

PURPOSE The purpose of this study was to test the hypothesis that all-ceramic crown core-veneer system reliability is improved by modifying the core design and as a result is comparable in reliability to metal-ceramic retainers (MCR). Finite element analysis (FEA) was performed to verify maximum principal stress distribution in the systems. MATERIALS AND METHODS A first lower molar full crown preparation was modeled by reducing the height of proximal walls by 1.5 mm and occlusal surface by 2.0 mm. The CAD-based preparation was replicated and positioned in a dental articulator for specimen fabrication. Conventional (0.5 mm uniform thickness) and modified (2.5 mm height, 1 mm thickness at the lingual extending to proximals) zirconia (Y-TZP) core designs were produced with 1.5 mm veneer porcelain. MCR controls were fabricated following conventional design. All crowns were resin cemented to 30-day aged composite dies, aged 14 days in water and either single-loaded to failure or step-stress fatigue tested. The loads were positioned either on the mesiobuccal or mesiolingual cusp (n = 21 for each ceramic system and cusp). Probability Weibull and use level probability curves were calculated. Crack evolution was followed, and postmortem specimens were analyzed and compared to clinical failures. RESULTS Compared to conventional and MCRs, increased levels of stress were observed in the core region for the modified Y-TZP core design. The reliability was higher in the Y-TZP-lingual-modified group at 100,000 cycles and 200 N, but not significantly different from the MCR-mesiolingual group. The MCR-distobuccal group showed the highest reliability. Fracture modes for Y-TZP groups were veneer chipping not exposing the core for the conventional design groups, and exposing the veneer-core interface for the modified group. MCR fractures were mostly chipping combined with metal coping exposure. CONCLUSIONS FEA showed higher levels of stress for both Y-TZP core designs and veneer layers compared to MCR. Core design modification resulted in fatigue reliability response of Y-TZP comparable to MCR at 100,000 cycles and 200 N. Fracture modes observed matched with clinical scenarios.

Fatigue Reliability of 3 Single-Unit Implant-Abutment Designs

Objectives: Because the mechanical behavior of the implant-abutment system is critical for the longevity of implant-supported reconstructions, this study evaluated the fatigue reliability of different implant-abutment systems used as single-unit crowns and their failure modes. Methods and Materials: Sixty-three Ti-6Al-4V implants were divided in 3 groups: Replace Select (RS); IC-IMP Osseotite; and Unitite were restored with their respective abutments. Anatomically correct central incisor metal crowns were cemented and subjected to separate single load to failure tests and step-stress accelerated life testing (n = 18). A master Weibull curve and reliability for a mission of 50,000 cycles at 200 N were calculated. Polarized-light and scanning electron microscopes were used for failure analyses. Results: The load at failure mean values during step-stress accelerated life testing were 348.14 N for RS, 324.07 N for Osseotite, and 321.29 N for the Unitite systems. No differences in reliability levels were detected between systems, and only the RS system mechanical failures were shown to be accelerated by damage accumulation. Failure modes differed between systems. Conclusions: The 3 evaluated systems did not present significantly different reliability; however, failure modes were different.

Perception and expectation. What do patients really want from the dental treatment

Universidade Estadual Paulista Faculdade de Odontologia Departamento de Materiais Odontologicos e Protese

Impacto da reabilitação com próteses fixas metal free na qualidade de vida

Nos tratamentos reabilitadores que envolvem a estetica, e fundamental considerar a expectativa e a satisfacao do paciente com o tratamento realizado. Nao preencher as necessidades esteticas solicitadas pelo paciente pode acarretar de prejuizos emocionais a nao adesao ao tratamento. Esta pesquisa teve como objetivo avaliar a qualidade de vida de pacientes reabilitados com proteses metal free . Foram avaliados todos os pacientes que aceitaram participar da pesquisa e que receberam tratamento reabilitador estetico. Os pacientes foram avaliados imediatamente antes do inicio do tratamento e 30 dias apos a conclusao do caso por meio do questionario de qualidade de vida OHIP-14. Os dados obtidos foram submetidos a analise estatistica. Os resultados obtidos mostram que houve uma reducao significativa em todos os dominios do OHIP-14. Logo, as reabilitacoes esteticas quando levam em consideracao os anseios do paciente e seguem um protocolo de tratamento adequado, alcancam o sucesso tanto para a saude oral e geral, quanto para o conforto e expectativas do paciente. Descritores: Reabilitacao Bucal; Estetica Dentaria; Qualidade de Vida.

Coroas Endoncrown: uma revisão de literatura e relato de caso

Dentes tratados endodonticamente possuem reducao da rigidez e resistencia devido a perda da integridade estrutural. Este fato pode acarretar em longo prazo falhas biomecânicas, falta de elasticidade e de resistencia a tracao frente as forcas mastigatorias, nao sendo incomum que problemas mais graves como fraturas ocorram. Logo, a escolha da reabilitacao funcional e estetica desse paciente deve ser selecionada com muita cautela, ja que a longevidade do tratamento endodontico pode ser influenciada pela selecao do material restaurador, assim como do preparo protetico do remanescente que conserve o maximo de estrutura dentaria sadia. Este trabalho teve como objetivo apresentar uma revisao da literatura sobre o tema endocrown e ilustrar sua execucao com caso clinico. O caso clinico evidenciou que a tecnica endocrown esta indicada para dentes posteriores, principalmente molares, que apresentem coroa clinica curta e espaco interoclusal insuficiente e estar associada as cerâmicas adesivas. Trata-se de um procedimento que visa a preservacao da estrutura dental e resultados esteticos harmoniosos, alem de executado em menos sessoes clinicas. A literatura apoia que em comparacao as tradicionais coroas totais, a resistencia a fratura apresenta-se superior. E importante salientar que o sucesso clinico traduzido por longevidade e conforto e dependente do correto preparo e do uso das cerâmicas adesivas. Descritores : Protese Dentaria; Protese Parcial Fixa; Dente Molar; Dente nao Vital.

Preparos minimamente invasivos para solução cosmética de manchamento por tetraciclina: relato de caso

Currently aesthetics has been the main reason why many patients seek dental office for prosthetic rehabilitation treatment. In this context, laminates or ceramic veneers are restorative form of minimally invasive approach, which has aesthetic and long-lived results. The objective of this article was to report a case with the use of ceramic laminates made of IPS e.max (IvoclarVivadent) for the restoration of teeth stained by tetracycline. The staining caused by tetracycline exhibits varying degrees of severity (grade I, II, III and IV) requiring specific approach for each occurrence. The clinical case in question addressed the planning and execution of clinical protocol for aesthetic resolution staining tetracycline grade III. With the running account of minimally invasive and restores this case, it can be concluded that the determination of the staining degree is compromised will dictate the necessary amount of wear and the type of minimally invasive indirect restoration. One can also conclude that all stages of clinical and laboratory executions are essential to the success of the cosmetic result, highlighting the indirect ceramic system to be selected and the color of the cement agent. Descriptors: Ceramics; Mouth Rehabilitation; Esthetics, Dental.