Design Equations for Mixed-Mode Fracture of Dental Ceramic-Cement Interfaces Using the Brazil-Nut-Sandwich Test.

Dental interfaces are subject to mixed-mode loading. This study provides practical guidance for determining interfacial fracture toughness of dental ceramic systems. We address interfacial fracture of a composite resin cement sandwiched between two dental ceramic materials. Emphasis is placed on sandwich disc specimens with cracks originating from elliptical-shaped flaws near the center, for which analytical fracture mechanics methods fail to predict. The interaction integral method is used to provide accurate finite element solutions for cracks with elliptical-shaped flaws in a Brazil-nut-sandwich specimen. The developed model was first validated with existing experimental data and then used to evaluate the three most widely used dental ceramic systems: polycrystalline ceramics (zirconia), glass-ceramics (lithium disilicate), and feldspathic ceramics (porcelain). Contrary to disc specimens with ideal cracks, those with cracks emanating from elliptical-shaped flaws do not exhibit a monotonic increase in interfacial toughness. Also, interfacial fracture toughness is seen to have a direct relationship with the aspect ratio of elliptical-shaped flaws and an inverse relationship with the modulus ratio of the constituents. The presence of an elliptical-shaped flaw significantly changes the interfacial fracture behavior of sandwich structures. Semi-empirical design equations are provided for fracture toughness and stress intensity factors for interfacial cracks. The developed design equations provide practical guidance for determining interfacial fracture toughness of selected dental ceramic material systems. Those equations take into account four critical factors: size of the elliptical flaw, modulus ratio of constituent materials, loading angle, and applied load.

Cerámicas: una actualización / Ceramics: an update / Cerâmica: uma atualização

Las cerámicas dentales utilizadas para restaurar y reemplazar tejido dental perdido de los dientes o las piezas dentales mismas, han sufrido una enorme transformación desde que aparecieron las primeras porcelanas hace ya varias décadas. Con las feldespáticas se podían hacer dientes, coronas y puentes pero, necesitaban un soporte de metal para que no sufran fracturas con los esfuerzos masticatorios, y por ello no tenían una apa-riencia vital. Hoy en día, han aparecido muchas otras cerámicas con diferentes y mejoradas características mecánicas y ópticas, lo que ha permitido que los odontólogos puedan por primera vez ofrecer a sus pacientes dientes artificiales con sorprendente naturalidad. Objetivo: Describir la clasificación actual, las características mecánicas y ópticas, así como la microestructura y los usos clínicos de las diferentes cerámicas dentales utilizadas hoy en día. Materiales y métodos: Revisión de la literatura acerca del tema, en tres de los más importantes buscadores de internet (Pubmed,Cochrane,Web of Science). Limitando su busca a artículos en inglés y publicados en los journals de investigación de materiales dentales con calificación Q1 y Q2. Resul-tados: Se revisaron 69 artículos publicados entre 1975 y 2019 los cuales aportaron una fuente interesante de información que permitió desarrollar el conocimiento acerca de la clasificación, microestructura, propiedades mecánicas y ópticas, usos clínicos y forma de procesamiento de las cerámicas. Conclusiones: Actualmente los odontólogos tienen a disposición una amplia variedad de materiales cerámicos con diferentes composicio-nes y características únicas que son necesarias conocer al momento de escoger la cerámica específica para cada necesidad de los pacientes.

The dental ceramics used to restore and replace lost tooth tissue or the teeth have undergone a huge trans-formation since the first porcelains appeared several decades ago. With the feldspathic teeth, crowns and bridges could be made but, they needed a metal support so that they did not suffer fractures with the mastica-tory efforts, and therefore they did not have a vital appearance. Today, many other ceramics with different and improved mechanical and optical characteristics have appeared, which has allowed dentists to offer artificial teeth to their patients for the first time with surprising naturalness. Objective: Describe the current classifica-tion, mechanical and optical characteristics, as well as the microstructure and clinical uses of the different dental ceramics used today. Materials and methods: Review about the literature on the subject, in three of the most important internet search engines (Pubmed, Cochrane, Web of Science). Limiting your search to articles in English and published in the journals of research of dental materials with qualification Q1 and Q2. Results:69 articles published between 1975 and 2019 were reviewed, which provided an interesting source of informa-tion that allowed the development of knowledge about classification, microstructure, mechanical and optical properties, clinical uses and method of processing ceramics. Conclusions: Currently, dentists have available a wide variety of ceramic materials with different compositions and unique characteristics that are necessary to know when choosing the specific ceramic for each patient need.

A cerâmica dentária usada para restaurar e substituir o tecido dentário perdido ou as próprias peças dentárias sofreram uma enorme transformação desde que as primeiras porcelanas surgiram várias décadas atrás. Com os materiais feldespáticos, podiam ser feitas coroas e pontes, mas eles precisavam de um suporte de metal para não sofrer fraturas com os esforços mastigatórios e, portanto, não tinham uma aparência de vitalidade. Hoje, outras cerâmicas com características mecânicas e ópticas diferentes e aprimoradas surgiram, o que permitiu aos dentistas oferecer dentes artificiais a seus pacientes pela primeira vez com uma naturalidade surpreendente. Objetivo: Descrever a classificação atual, características mecânicas e ópticas, bem como a microestrutura e os usos clínicos das diferentes cerâmicas odontológicas utilizadas atualmente. Materiais e métodos: Revisão da literatura sobre o assunto, em três dos mais importantes mecanismos de busca na In-ternet (Pubmed, Cochrane, Web of Science). Limitando a sua pesquisa a artigos em inglês e publicados nas revistas científicas de materiais dentários com qualificação Q1 e Q2. Resultados: Foram revisados 69 artigos publicados entre 1975 e 2019, que forneceram uma fonte interessante de informações que permitiram desen-volver conhecimento sobre a classificação, microestrutura, propriedades mecânicas e ópticas, usos clínicos e forma de processamento da cerâmica. Conclusões: Atualmente, os dentistas têm disponível uma ampla variedade de materiais cerâmicos com composição diferente e características únicas que são necessárias conhecer ao escolher a cerâmica específica para cada necessidade do paciente.

Influence of specimens' geometry and materials on the thermal stresses in dental restorative materials during thermal cycling.

OBJECTIVES: Thermal cycling is widely used to simulate the aging of restorative materials corresponding to the changes of temperature in the oral cavity. However, test parameters present in literature vary considerably, which prevents comparison between different reports. The aim of this work is to assess the influence of the specimens' geometry and materials on the thermal stresses developed during thermal cycling tests. MATERIALS AND METHODS: Finite elements method was used to simulate the conditions of thermal cycling tests for three different sample geometries: a three-points bending test sample, a cylinder rod and more complex shape of a restoration crown. Two different restorative systems were considered: all-ceramic (zirconia coupled with porcelain) and metal-ceramic (CoCrMo alloy coupled with porcelain). The stress state of each sample was evaluated throughout the test cycle. RESULTS: The results show that the sample geometry has great influence on the stress state, with difference of up to 230% in the maximum stress between samples of the same composition. The location of maximum stress also changed from the interface between materials to the external wall. CONCLUSIONS: Maximum absolute stress values were found to vary between 2 and 4MPa, which might not be critical even for ceramics. During multi-cycle testing these stresses would cause different fatigue in various locations. The zirconia-based specimens and zirconia-based restoration (crown) exhibited the most similar stress states. Thus it might be recommended to use these geometries for fast screening of the materials for this type of restorations. CLINICAL SIGNIFICANCE: The selection of specimens' geometry and materials should be carefully considered when aging conditions close to clinical ones want to be simulated.

Zirconia para rehabilitación completa maxilar sobre implantes: Caso clínico / Use of zirconia in full maxillary rehabilitation on implants: Clinical case report

La zirconia (ZrO2) es un material cerámico con propiedades mecánicas adecuadas para uso en estructuras sobre implantes. Los núcleos de zirconia para prótesis parcial fija en dientes e implantes anteriores y posteriores ahora están disponibles. Actualmente, la exactitud y precisión en la elaboración de estructuras son un prerrequisito para el éxito a largo plazo en restauraciones implanto soportadas. La elaboración de estructuras de zirconia requiere de un amplio conocimiento por parte del clínico y el técnico para lograr un adecuado ajuste y pasividad. En este artículo se describe la elaboración de una estructura de ZrO2, y coronas individuales para rehabilitar el segmento maxilar con seis implantes.

Zirconia (ZrO2) is a ceramic material possessing suitable mechanic properties for usage in frameworks over implants. Presently, there is availability of zirconia cores for fixed partial prostheses in anterior and posterior teeth and implants. Accuracy and precision in framework manufacturing are a pre-requisite for long-term success in restorations supported by implants. Manufacturing of zirconia framework requires wide knowledge and skill in clinical operators as well as technicians in order to achieve suitable adjustment and passiveness. The present article describes the manufacture of a ZrO2 structure and individual crowns to rehabilitate the maxillary segment with six implants.

Técnica Indirecta Para Reparación De Prótesis Parcial Fija Metal-Porcelana Relato Del Caso

Debido a la excelente estética y biocompatibilidad, las restauraciones con cerámicas son frecuentemente utilizadas en la práctica clínica diaria. A pesar de la evolución de las propiedades mecánicas de las cerámicas, existen casos extensos en que la indicación principal es el uso de coronas metalo-cerâmicas. Frente a la posibilidad de la fractura de esas prótesis, que ocurren del 5 y al 10% en 10 años de uso, existe la opción de reparar dichas prótesis, disminuyendo el costo y el tiempo operacional. Cuando la falla expone la porción metálica de la pieza, se indica una reparación indirecta, que consiste en la confección de una sobre estructura, cementada en la región previamente preparada, a partir de un modelo de trabajo. El objetivo de este trabajo fue demostrar una técnica de reparación indirecta de prótesis parciales fijas utilizando una sobre estructura metalo-cerámica.

Due the excellent esthetic and biocompatibility, metal ceramic restrations are frequently used at clinical daily practice. In sipte of the ceramic mechanical properties evolution, there are extensive cases that the primary indication are metalceramic crowns. Ahead of the possible fractures of these prosthesis, that happen from the 5 to 10% in 10 years of use, there are option to repair it, diminishing cost and chair time. When the failure expose the metal portion it indicates a indirect repair wich consist in manufacturing of a overlay, cemented on region that was previosly prepared, from a work cast. The aim of this study was demonstrate a indirect repair technique of fixed partial dentures using a metalceramic overlay.

Factores que influencian la selección del color en prótesis fija: Revisión de literatura

El valor estético de una restauración cerámica es parcialmente influenciado por múltiples factores. Muchos de estos factores son conocidos por el odontólogo, sin embargo, existen otros , tales como: grosor de la cerámica, color del agente cementante, color de la estructura dental subyacente, limitaciones de las guías de colores disponibles, composición de los materiales cerámicos, etc. que pueden interferir en la correcta selección del color, siendo un problema clínico muy común. El propósito de este trabajo fue hacer una revisión bibliográfica sobre la influencia de los factores físicos y sensoriales y como estos pueden afectar en la selección del color de las restauraciones protésicas con el fin de evitarlos o disminuirlos.

The esthetic value of dental ceramic restorations is influenced by several factors. Many factors is know by the dentist , however, others factors like: ceramic thickness, luting agent, shade guides, color of dental substrate, the limited range of available ceramic shades, varying compositions of ceramic materials, is a common clinical problem. The aim of this study was made a literature review of the influence of physical and sensorial factors on the shade selection in ceramics restorations for avoid or minimize these factors.