Zirconia in Dental and Other Biomedical Applications: An Overview

An extensive range of biocompatible materials has been used in patients. Diverse biomedical applications demand different properties of materials, implicating mechanical, physical, chemical, and biochemical properties. Amongst biocompatible ceramics, zirconia-based biomaterials are considered as a biomaterial for retexture of hard tissues related to their excellent mechanical properties and good biological and chemical compatibilities. Zirconia is used in dentistry and in orthopedics, specifically in the area of femoral heads for total hip replacements.

Simulated occlusal adjustments and their effects on zirconia and antagonist artificial enamel

PURPOSE: The aim of this study was to evaluate the effect of occlusal adjustments on the surface roughness of yttria-tetragonal zirconia polycrystal (Y-TZP) and wear of opposing artificial enamel.

Effect of Grinding and Multi-Stimuli Aging on the Fatigue Strength of a Y-TZP Ceramic

Abstract This study aimed to investigate the effect of grinding and multi-stimuli aging on the fatigue strength, surface topography and the phase transformation of Y-TZP ceramic. Discs were manufactured according to ISO-6872:2008 for biaxial flexure testing (diameter: 15 mm; thickness: 1.2 mm) and randomly assigned considering two factors "grinding" and "aging": C- control (as-sintered); CA- control + aging; G- ground; GA- ground + aging. Grinding was carried out with coarse diamond burs under water-cooling. Aging protocols consisted of: autoclave (134°C, 2 bars pressure, 20 hours), followed by storage for 365 days (samples were kept untouched at room temperature), and by mechanical cycling (106 cycles by 20 Hz under a load of 50% from the biaxial flexure monotonic tests). Flexural fatigue strengths (20,000 cycles; 6 Hz) were determined under sinusoidal cyclic loading using staircase approach. Additionally, surface topography analysis by FE-SEM and phase transformation analysis by X-ray Diffractometry were performed. Dixon and Mood methodology was used to analyze the fatigue strength data. Grinding promotes alterations of topographical pattern, while aging apparently did not alter it. Grinding triggered t-m phase transformation without impacting the fatigue strength of the Y-TZP ceramic; and aging promoted an intense t-m transformation that resulted in a toughening mechanism leading to higher fatigue strength for as-sintered condition, and a tendency of increase for ground condition (C < CA; G = GA). It concludes that grinding and aging procedures did not affect deleteriously the fatigue strength of the evaluated Y-TZP ceramic, although, it promotes surface topography alterations, except to aging, and t-m phase transformation.

Resumo Este estudo objetivou investigar o efeito do desgaste e envelhecimento (estímulos combinados) na resistência à fadiga, topografia superficial e transformação de fase de uma cerâmica Y-TZP. Discos para teste de flexão biaxial foram confeccionados segundo as normas da ISO-6872:2008 (15 mm Ø; 1,2 mm espessura) e randomicamente distribuídos de acordo com os fatores "desgaste" e "envelhecimento": C- controle (sinterizado); CA- controle envelhecido; G- desgaste; GA- desgaste envelhecido. O desgaste foi feito com pontas diamantadas de granulação grossa sob irrigação com água. Os protocolos de envelhecimento consistiram em: autoclave (134°C, 2 bar de pressão, 20 horas), 365 dias armazenados em temperatura ambiente, e ciclagem mecânica (106 ciclos a 20 Hz em um intervalo de carga de até 50% da carga monotônica observada em testes estáticos). A resistência à fadiga foi determinada para 20.000 ciclos à 6 Hz sob carregamento sinusoidal através do método de escada. Adicionalmente, análises de topografia superficial em microscopia eletrônica de varredura e de transformação de fase por difração de raios-X foram executadas. A metodologia de Dixon e Mood foi usada para analisar os dados de resistência à fadiga. Foi observado que o desgaste promove uma alteração de padrão topográfico superficial; enquanto o envelhecimento aparentemente não demonstra influência. Em relação à transformação de fase e resistência à fadiga, o desgaste desencadeou um aumento de fase m sem impactar na resistência à fadiga da cerâmica Y-TZP; já o envelhecimento promoveu uma intensa transformação de fase, resultando no mecanismo de tenacificação, que gerou um aumento na resistência à fadiga para a condição sinterizada e uma tendência a aumento na condição desgaste (C < CA; G = GA). Os dados elucidam que o desgaste e o envelhecimento não impactaram negativamente na resistência à fadiga da cerâmica Y-TZP, apesar de promoverem alterações de topografia superficial e intensa transformação de fase de t-m respectivamente.

Considerations for the Survival of Complete Arch Implant-Supported Zirconia Restorations; Status of Antagonistic Arches and Stress Distribution on Frameworks: A Case Report

This report describes two cases of complete arch implant-supported restorations. The first patient had seven dental implants in each arch with monolithic zirconia frameworks. At four weeks' follow-up, the one-piece maxillary framework was fractured, which was re-designed and re-fabricated using laser-sintered cobalt-chrome alloy. The second patient had four implants in the mandible only. A mandibular monolithic zirconia framework and a maxillary conventional complete denture were fabricated and delivered. At five years' follow-up, the patient reported no significant discomfort. Careful consideration and monitoring of the status of antagonistic arches and stress distribution on zirconia frameworks were suggested for complete arch implant-supported fixed restorations

Effects of Light-Curing on the Immediate and Delayed Micro-Shear Bond Strength between Yttria-Tetragonal Zirconia Polycrystal Ceramics and Universal Adhesive

PURPOSE: To evaluate the effect of light-curing on the immediate and delayed micro-shear bond strength (microSBS) between yttria-tetragonal zirconia polycrystal (Y-TZP) ceramics and RelyX Ultimate when using Single Bond Universal (SBU). MATERIALS AND METHODS: Y-TZP ceramic specimens were ground with #600-grit SiC paper. SBU was applied and RelyX Ultimate was mixed and placed on the Y-TZP surface. The specimens were divided into three groups depending on whether light curing was done after adhesive (SBU) and resin cement application: uncured after adhesive and uncured after resin cement application (UU); uncured after adhesive, but light cured after resin cement (UC); and light cured after adhesive and light cured resin cement (CC). The three groups were further divided depending on the timing of microSBS testing: immediate at 24 hours (UUI, UCI, CCI) and delayed at 4 weeks (UUD, UCD, CCD). microSBS was statistically analyzed using one-way ANOVA and Student-Newman-Keuls multiple comparison test (P0.05). At 4 weeks, microSBS of UUD group (24.43+/-2.88 MPa) had significantly increased over time compared to UUI group (P<0.05). The SEM results showed mixed failure in UCI and CCI group, while UUI group showed adhesive failure. CONCLUSION: Light-curing of universal adhesive before or after application of RelyX Ultimate resin cement significantly improved the immediate microSBS of resin cement to air-abrasion treated Y-TZP surface. After 4 weeks, the delayed microSBS of the non-light curing group significantly improved to the level of light-cured groups.

Stress analysis of cantilever-fixed partial denture connector design using the finite element method / Análise de tensões de desenhos de conectores de pontes cantilever pelo método dos elementos finitos

Purpose: To analyze the stress distribution on a cantilever-fixed partial denture after simulation of maximum mastication loads in order to optimize its design. Methods: A cantilever-fixed partial denture framework was designed in the CAD-CAM system Everest®Kavo v2.0 using two materials, titanium and zirconium, with connectors of 5.28 mm² and 9.05 mm², respectively. A finite element model was built for stress analysis using simulations of mastication load. Results: For zirconia, only the molar cantilever with the smaller connector area and a 0.5-mm fillet exceeded the considered threshold resistance value of 575 MPa. All the other designs yielded resistances below this value. For titanium, only cantilevers with 9.05 mm² connector area and fillets of 1 or 1.4 mm presented stress values inferior to titanium yield strengh. Conclusion: Within the limitations of this study, it can be concluded that titanium cantilever-fixed partial denture frameworks with a 5.28 mm² connector area cannot support maximum mastication loads; frameworks of this material require larger connectors with fillets introduced in the gingival embrasure. Zirconia, however, supports maximum bite forces in most situations with both molar and premolar design cantilevers. Precaution should be taken when dealing with smaller connectors of 5.28 mm².

Objetivo: Analisar a distribuição de tensões em próteses parciais fixas em cantilever após aplicação de cargas simuladoras da mastigação, de forma a otimizar o seu desenho. Metodologia: Obteve-se a infra-estrutura de uma prótese parcial fixa em cantilever no sistema CAD-CAM Everest®Kavo v2.0, considerando dois materiais: titânio e zircônia, com conectores de 5,28 mm² e 9,05 mm², respectivamente. Gerou-se um modelo de elementos finitos, onde foram efetuadas análises de tensões com cargas simuladoras da mastigação. Resultados: Para zircônia, apenas o cantilever molar com área de conector mais reduzida, e concordância de 0,5 mm, excedeu o valor de resistência 575 MPa. Para o titânio, apenas o cantilever de 9,05 mm², com concordâncias de 1 e 1,4 mm, apresentou valores inferiores à tensão do titânio. Conclusão: Dentro das limitações deste estudo pode-se concluir que as infra-estruturas de titânio em cantilever não suportam cargas mastigatórias máximas com uma área de conector de 5,28 mm² e requerem conectores de áreas superiores, com concordâncias introduzidas na embrasura gengival. A zircônia geralmente suporta forças mastigatórias máximas com cantilever molar ou pré-molar. Deve-se ter precaução quando a área dos conectores é reduzida para 5,28 mm².

CAD-CAM all-ceramic fully sintered zirconia crowns for the oral rehabilitation of an amelogenesis imperfecta case / Coroas CAD-CAM de zircônia totalmente sinterizada para reabilitação oral de um caso de amelogenesis imperfecta

Purpose: To present a case report of a patient with amelogenesis imperfecta rehabilitated with 26 CAD-CAM all-ceramic fully sintered zirconia crowns.Case description: A male subject, 28 year-old, sought dental treatment presenting a clinical condition compatible with amelogenesis imperfecta. All teeth had yellow, brown, and white areas of weak enamel. Composite restorations were present on teeth 14, 16, 24, 25, 26, 27, and 46; dental caries were shown on teeth 36, 37, and 47. Hipersensitivity was reported. The treatment included fully sintered zirconia crowns for all teeth, using a CAD-CAM system. No problems of marginal adaptation of the crowns were detected, and the final results were satisfactory for both the patient and the clinician. Conclusion: The clinical rehabilitation of an amelogenesis imperfecta case is a challenge, and a multidisciplinary approach is required. Zirconia all-ceramics crowns are an excellent option to restore dental aesthetics as the opaque zirconia coping can mask dischromic abutments, and the crowns have biocompatibility and improved physical properties.

Objetivo: Apresentar o caso clínico de um paciente com amelogenesis imperfecta, que foi reabilitado com 26 coroas CAD-CAM de zircônia totalmente sinterizada. Descrição do caso: Um sujeito do sexo masculino, 28 anos, procurou tratamento odontológico apresentando uma condição clínica compatível com amelogenesis imperfecta. Todos os dentes tinham áreas amarelas, marrons e brancas de esmalte enfraquecido. Havia restaurações de resina composta nos dentes 14, 16, 24, 25, 26, 27 e 46; cárie dentária estava presente nos dentes 36, 37 e 47. Relatou-se hipersensibilidade dentária. O tratamento incluiu coroas de zircônia totalmente sinterizada para todos os dentes, usando um sistema CAD-CAM. Nenhum problema de adaptação marginal das coroas foi detectado e os resultados finais foram satisfatórios para ambos o paciente e o clínico. Conclusão: A reabilitação clínica de amelogenesis imperfecta é um desafio e a abordagem multidisciplinar deve ser mandatória. As coroas de zircônia são uma excelente opção para a reabilitação de pacientes com esta anomalia, pois o opaco dos copings de zircônia pode mascarar as diferentes cores dos pilares e o resultado final é esteticamente aceitável, com biocompatibilidade e propriedades físicas superiores.