A finite element thermal analysis of various dowel and core materials.

Aim: Thermal analysis of the temperature and stress distribution of parallel sided, threaded and non-threaded dowels and core materials under thermal loading within a maxillary central incisor using a three dimensional finite element study. Materials and Methods: 3D models of endodontically treated maxillary central incisor with parallel sided, threaded and non- threaded post and core materials were simulated using the ANSYS software. Materials simulated were parallel sided cast gold post and core, parallel sided fibre reinforced composite (FRC) post and core, and parallel sided, threaded, prefabricated stainless steel post and amalgam core. Thermal loads simulating hot (60 degree C/ 333K) and cold (15 degree C/288K) liquid were applied for 15 seconds at the incisal edge. The temperature changes at the selected nodes were obtained on the various post and core materials, interface between post and dentin, interface between core and dentin, within the dentin and within the cement layer. Results: Temperature and stress distribution pattern were represented in numerical and color coding and results interpreted. Thermal stresses arises as a result of temperature changes. A decreased temperature gradient of the metallic dowels and core (T1 hot - 0.002K, T3 hot - 1.071K, T1 cold -0.99K, T3 cold - 0K) were obtained than that of the FRC dowel and core of 1.982K(hot) and1.55K(cold) respectively due to the higher thermal conductivity of the metals. Higher thermal stress values of 3.567 Mpa(hot) and 3.092 Mpa(cold) respectively were obtained for the FRC dowels and higher stress values of 39.679 Mpa(hot) and 57.855 Mpa(cold) respectively were also obtained for the FRC cores. These values indicated that thermal stresses of the FRC dowel and core were greater than that of cast gold dowel and core and prefabricated stainless steel dowel and amalgam core due to its high coefficient of thermal expansion. Maximum stress values of the FRC dowel and core of 1.87 Mpa(hot) and 2.57 Mpa(cold) respectively were also generated in the cement layer, core and metal ceramic crown. The junction of the metal ceramic crown and dentin demonstrated the maximum stress. Higher thermal stress values of 59.162 ± 10 Mpa were obtained in the restoration and the coronal portion of the dentin than the stress levels of .0039 ± 10Mpa in the supporting bone due to an increased thermal expansion. Conclusion: Non-metallic dowel and core materials such as fibre reinforced composite dowels (FRC) generate greater stress than metallic dowel and core materials. This emphasized the preferable use of the metallic dowel and core materials in the oral environment.

The effect of urea on the corrosion behavior of different dental alloys.

Objective: Intraoral corrosion of dental alloys has biological, functional, and esthetic consequences. Since it is well known that the salivary urea concentrations undergo changes with various diseases, the present study was undertaken to determine the effect of salivary urea concentrations on the corrosion behavior of commonly used dental casting alloys. Materials and Methods: Three casting alloys were subjected to polarization scans in synthetic saliva with three different urea concentrations. Results: Cyclic polarization clearly showed that urea levels above 20 mg/100 ml decreased corrosion current densities, increased the corrosion potentials and, at much higher urea levels, the breakdown potentials. Conclusion: The data indicate that elevated urea levels reduced the corrosion susceptibility of all alloys, possibly through adsorption of organics onto the metal surface. This study indicates that corrosion testing performed in sterile saline or synthetic saliva without organic components could be misleading.

Effect of retorque on loosening torque of prosthetic screws under two levels of fit of implant-supported dentures

This study evaluated the influence of retorque on loosening torque (Lt) of prosthetic screws in implant-supported dentures with different fit levels. Ten mandibular implant-supported dentures were fabricated and then 20 cast models were then prepared using prosthetic structures to create 2 fit levels: passive fit (Pf) and misfit (Mf). Two tightening techniques were also evaluated: initial torque only (T1); and initial torque and retorque after 10 min (T2). Gold or titanium screws were used, resulting in 4 groups to each one: Pf/T1, Pf/T2, Mf/T1, Mf/T2. The Lt was measured 24 h after the tightening torque using digital torque meter. Data were analyzed statistically by two-way ANOVA and Tukey's test (α=0.05), separately for each screw material. For titanium screws, no significant difference (p>0.05) was found between Pf/T1 and Pf/T2, or between Pf/T2 and Mf/T2. However, statistically significant difference (p<0.05) was found between Pf/T1 and Mf/T1, and between Mf/T1 and Mf/T2. Mf reduced the Lt using T1, while and T2 increased the Lt for Mf. Retorque and fit were shown to have no significant influence on the Lt of the gold screws. Retorque application made insignificant the misfit effect on the Lt of the titanium screws, suggesting that this procedure should be performed routinely during the screw tightening in multi-unit dentures.

Este estudo avaliou a influência do retorque no Ta dos parafusos protéticos em próteses implantossuportadas com diferentes níveis de adaptação. Foram confeccionadas 10 próteses mandibulares implantossuportadas. Vinte modelos de gesso foram fabricados utilizando as estruturas protéticas para criar os 2 níveis de adaptação: adaptação passiva (AP) e desajuste (D). Foram avaliadas 2 técnicas de aperto do parafuso: inicial torque (T1); e inicial torque e retorque após 10 min (T2). Foram usados parafusos de ouro e titânio, resultando em 4 grupos para cada material do parafuso: AP/T1, AP/T2, D/T1, D/T2. O Ta foi mensurado 24 h após o torque de aperto utilizando torquímetro digital. Os resultados foram analisados pela ANOVA (2 fatores) e teste de Tukey (α=0,05), separadamente para cada material dos parafusos. Para os parafusos de titânio, não foi encontrada diferença estatística significante entre AP/T1 e AP/T2, ou AP/T2 e D/T2; porém, diferença significante foi encontrada entre AP/T1 e D/T1, ou D/T1 e D/T2. Onde, D reduziu a Ta utilizando T1; e T2 aumentou o Ta para D. Retorque e adaptação não apresentaram influência significante no Ta dos parafusos de ouro. A aplicação do retorque tornou insignificante o efeito do desajuste no Ta dos parafusos de titânio, sugerindo que este procedimento deveria ser usado rotineiramente durante os parafusos protéticos de titânio em próteses múltiplas.

The electrochemical properties of four dental casting suprastructure alloys coupled with titanium implants

OBJECTIVES: As the choice of suprastructure alloy to be combined with titanium for the oral cavity is still a much debated issue, the aim of this study was to investigate the electrochemical interaction of the suprastructure/implant couples under the determined experiment conditions. MATERIAL AND METHODS: The potentiodynamic polarization curves and open-circuit potentials (OCP) of four UCLA type suprastructures coupled with straight Swiss Plus implant fixtures were taken in Afnor type artificial saliva solution at 37°C. The concentration of ions leached into artificial saliva solutions was estimated with ICP-MS. SEM images of the margins of suprastructure/implant couples were obtained before and after the electrochemical tests. RESULTS: The OCP value of titanium became passive at the most negative potential. The lowest difference between the initial and constant OCP value was exhibited by the Au based suprastructure. Suprastructures made greater contributions to the potentiodynamic polarization curves of the implant/suprastructure couples. According to the ICP-MS results, Pd based and Au based couples dissolved less than Co-Ni based and Co-Cr based couples. CONCLUSIONS: Within the conditions this study, it may be concluded that the titanium implant forms a stable passive oxide layer in artificial saliva exposed to open air and does not affect the corrosion properties of the suprastructures. Pd based and Au based couples have been found to be more corrosion-resistant than base alloy couples.

Preload and torque removal evaluation of three different abutment screws for single standing implant restorations

Several authors still consider the mechanical problems of fracture and component loosening as the main causes of failure of implant-supported restorations. The purpose of this in vitro study was to compare the preload of three types of screw for transmucosal abutment attachment used in single implant-supported prosthesis through strain gauge and removal torque measurements. Three external hex fixtures were used, and each received a transmucosal abutment (Cera One®), which was fixed to the implant with its respective screw: Group A- gold screw, Group B- titanium screw and Group C- surface-treated titanium screw (Ti-Tite®). Ten screws of each type were attached applying a 30.07±0.28 Ncm torque force and maintained in position for 5 minutes. After this, the preload values were measured using strain gauges and a measurement cell. Gold screws presented higher preload values (131.72±8.98 N), followed by surface-treated titanium screws (97.78±4.68 N) and titanium screws (37.03±5.69 N). ANOVA (p<0.05) and Tukey's test (p<0.05) were applied. Statistically significant differences were found among the groups for both preload and removal torque values. In conclusion, gold screws may be indicated to achieve superior longevity of the abutment-implant connection and, consequently, prosthetic restoration due to greater preload values yielded.

Prótesis parcial fija por la técnica de electrodeposición con oro: relato de caso clínico / Fixed partial denture by the technique of gold electrodeposition: report of a case

Electrodeposición es la deposición galvánica de la aleación de oro con 99% de pureza (24K) para el uso odontológico, teniendo como principio la electrólisis. Este sistema de electrodeposición permite la confeción de una cofia de oro con una excelente adaptación marginal. Puede ser fabricado con un espesor mínimo de 0,2mm haciendo posible realizar un desgaste menor en la preparación de pilares, y sobre esa fina infraestructura se puede aplicar una capa mayor de cerámica optimizando la estética cuando se compara con la fundición de estructuras convencionales. Hace posible la confección de coronas y prótesis parciales fijas. Las coronas metal-cerámicas confeccionadas por la técnica de electrodeposición otorgan una estética satisfactoria, debido a una apariencia mas natural y mejor calidad del color. Adicionalmente presenta características ventajosas como ausencia de corrosión y una excelente biocompatibilidad con los tejidos periodontales. Este trabajo muestra la confección de coronas metalocerámicas totales hechas con cofias por electrodeposición, teniendo como objetivo presentar una alternativa en prótesis parcial fija para los profesionales.

Electrodeposition is the galvanic deposition of the gold alloy with 99% of purity (24K) for the dentistry use, having like principle electrolysis. This electrodeposition system allows the preparation of pure gold coping with an excellent marginal fit. It can be made with a minimum thickness of 0,2mm doing possible to make a less teeth reduction, and on that fine infrastructure can be applied to a greater layer of ceramics optimizing the aesthetic when it is compared with the cast conventional copings. It is possible the preparation of unitary and fixed partial prostheses. The metal-ceramics crowns made by the electrodeposition technique present an aesthetic satisfactory, due to a natural appearance and better quality of the color. Additionally, it presents advantageous characteristics as corrosion absence and an excellent biocompatibility with periodontal tissues. This work shows the preparation of complete metal-ceramics crowns made with copings by electrodeposition, having as objective present an alternative in fixed partial prosthetics for the professionals.

Pasado, presente y futuro de los arcos / Past, present and future of archwires

El objetivo de este trabajo es poder brindar al profesional una guía acerca de los diferentes metales, tanto tradicionales como exóticos, y sus propiedades, para permitir la elección de los arcos según las necesidades de cada tratamiento, no teniendo que seguir siempre una prescripción determinada.

Estudio in vitro de la adaptación marginal de dos aleaciones de plata-paladio / An in vitro study of the marginal accuracy of two silver-palladium alloys

En este estudio descriptivo comparativo se analizó la adaptación marginal de dos diferentes aleaciones de plata-paladio (J-7 y Jorcast), colocadas en 28 segundos premolares superiores. Se utilizaron restauraciones de coronas completas e incrustaciones inlay MOD, teniendo en cuenta si había alguna variación en los resultados, antes y después del pulido y manejando como grupo control oro tipo II (casting gold). Las muestras fueron cementadas en los dientes y acriladas para ser observadas al microscopio electrónico de barrido (SEM). Los resultados indican que las aleaciones de plata-paladio, antes y después del pulido, tanto en restauraciones de coronas completas como en incrustaciones MOD, presentan una adaptación marginal muy similar a las aleaciones de oro tipo III, convirtiéndose así en una alternativa confiable para su utilización en la práctica odontológica

Ligas alternativas em Odontologia: comparação com liga nobre em testes laboratoriais / Alternative alloys in Dentistry: comparison with noble alloys in laboratorial tests

The authors have developed a research about three differents kinds of alloys and the gold alloy behind laboratorial and fusion texts. The comportment of each one was analysed and compared with the gold alloy

Avaliaçäo objetiva (espectrofotometria) e subjetiva (visual) das alteraçöes no brilho de quatro ligas metálicas odontológicas (ouro, níquel-cromo, cobre-alumínio e amálgama), mantidas no meio bucal por 6 meses / Objective evaluation (spectrophotometry) and subjective (visual) of luster alterations of four dental metalic alloys (gold, nickel-chromium, cooper aluminum and amalgam), maintened in the mouth for 6 months

Neste estudo foram utilizadas quatro ligas metálicas, sendo uma liga de ouro tipo IV que serviu como controle, uma liga de cobre-alumínio, uma liga de níquel-cromo e uma liga para amálgama. Padröes em forma de discos com 6 mm de diâmetro e 2 mm de espessura foram fundidas e sofreram acabamento pelos métodos convencionais após inclusäo em blocos de resina acrílica. O aspecto das peças foi avaliado clinicamente em uma escala de 0 a 3, quanto a ocorrência de manchas, brilho e descoloraçäo, sendo posteriormente avaliadas em um espectrofotômetro utilizando-se mudanças cromáticas na luz a fim de quantificar a refletância superficial. As peças foram fixadas na regiäo posterior da face vestibular de dentaduras superiores de pacientes, tendo suas características superficiais novamente analisadas depois de um, três e seis meses, com o propósito de observar o comportamento clínico das ligas. As peças foram combinadas entre si da seguinte maneira: 5 peças de ouro com 5 de cobre-alumínio, 5 de ouro com 5 de níquel-cromo, 5 de Sybraloy com 5 de cobre-alumínio, 5 de Sybraloy com 5 de níquel-cromo, 5 de cobre-alumínio com 5 de cobre-alumínio, 5 de cobre-alumínio com 5 de níquel-cromo, 5 de níquel-cromo com 5 de níquel-cromo. Em cada dentadura foram colocadas no máximo quatro peças, sendo duas de cada lado, respeitando a combinaçäo acima. Os resultados e conclusöes foram: A - Avaliaçäo objetiva: 1 - as ligas metálicas, quando testadas com outras ligas mo meio oral, em funçäo do tempo, apresentaram alteraçäo de cor; 2 - em funçäo do tempo, a liga que teve menor alteraçäo de cor foi a de Ni-Cr, as outras três näo mostraram diferenças significantes entre si. B - Avaliaçäo subjetiva: 1 - resistência à oxidaçäo: liga de ouro apresentou melhores resultados enquanto o amálgama e a liga de cobre-alumínio apresentaram os piores resultados; 2 - resistência à descoloraçäo: ao longo do tempo e em ordem decrescente as ligas que apresentaram os melhores resultados foram ouro, níquel-cromo, cobre-alumínio e amálgama; 3 - perda de brilho: em funçäo do tempo todas as ligas perderam brilho de forma semelhante, embora o amálgama tenha mostrado os piores resultados

Estudo comparativo das propriedades de resistência à traçäo e ao dobramento e análise metalográfica de uniöes soldadas, pré e pós-cerâmica, de liga de metal nobre / Comparative study of the properties of tensile strenght and bending and metallographic analysis of soldered joints, pre and post-ceramic, of precious metal alloy

Utilizou-se 66 hemi-corpos de prova, de metal nobre (Degudent Universal), para trabalhos metalo-cerâmicos, que proporcionaram 33 juntas soldadas (corpos de prova) unidos com solda de alta temperatura de fusäo (solda pré-cerâmica) e solda de baixa temperatura de fusäo (solda pós-cerâmica). Estes corpos de prova foram submetidos a testes que permitiram avaliar, comparativamente, suas propriedades de resistência à traçäo e resistência ao dobramento, assim como o comportamento estrutural, destas uniöes soldadas, através do microscópio metalográfico. A "máquina de ensaios universal" foi empregada para verificar a força de traçäo necessária para romper 18 dessas juntas soldadas; 12 dessas juntas foram unidas com solda de alta temperatura de fusäo sendo a metade submetida a recozimentos sucessivos, simulando a aplicaçäo das diversas camadas de porcelana...