Limitations of reuse for silver-palladium alloys -Evaluating post-recasting heat treatment impact on corrosion resistance.

The aim of this study was to investigate the effect of repeated casting and heat treatment on the corrosion resistance of a commercial Ag-Pd-Cu-Au alloy as evaluated by electrochemical techniques. After repeated casting, the fifth cast of the Ag-Pd-Cu-Au alloy exhibited dramatic degradation of properties, although upon heat treatment, this corrosion resistance did improve. Despite the improvement by heat treatment, after five castings, this alloy may not have satisfactory hardness for clinical use. These results of this study demonstrate that, up to the fourth cast and heat treatment, the Ag-Pd-Cu-Au alloy has acceptable corrosion resistance and hardness.

Malignant mesothelioma due to asbestos exposure in dental tape.

Although most cases of malignant mesothelioma of the pleura are caused by one or more readily recognized sources of exposure to asbestos, cases of the disease with more occult exposure occur, especially since asbestos has been used in over 3,000 products. Dental lining tape contained asbestos from the 1930s until at least the 1970s and was used in the lost wax method of casting crowns, bridges, and other metal dental prosthetic devices. We report six cases of pathology-verified malignant mesothelioma, mostly among dentists, following exposure to airborne dust from asbestos dental tape, which resulted in asbestos tort litigation. According to evidence available at present, chrysotile asbestos was the type of asbestos used in dental tape in the past in the United States, and the described cases followed relatively brief and intermittent exposure to this type of asbestos. These cases underscore the need for comprehensive exposure histories to determine exposure scenarios. Am. J. Ind. Med. 60:437-442, 2017. © 2017 Wiley Periodicals, Inc.

Evaluación visual y radiográfica de discontinuidades en estructuras metálicas de prótesis parciales removibles / Visual and radiographic evaluation of discontinuities of metal structures in removable partial dentures

El presente trabajo tiene como objetivo diseñar una metodología que permita a la Cátedra de Dentaduras Parciales Removibles obtener registros permanentes para el estudio y evaluación de posibles discontinuidades y/o defectos (forma, ubicación, tamaño, orientación y tipo) que puedan estar presentes en las estructuras metálicas de las prótesis parciales removibles (PPR). Se realizó una inspección visual y radiográfica para identificar la presencia de discontinuidades en las estructuras de PPR. Se evaluaron 108 estructuras seleccionadas aleatoriamente de la población de casos realizados por los estudiantes de pregrado de la Facultad de Odontología de la UCV en el período octubre 1998 - abril 1999. La inspección radiográfica permitió detectar una cantidad significativa de fallas en las estructuras evaluadas que no lograban determinarse con la inspección visual. Con relación a los elementos que constituyen una PPR, la mayor frecuencia de fallas se encontraron ubicadas en el conector mayor. Es de notar que sólo el 25,93 por ciento de las estructuras evaluadas no presentaron fallas. Entre las discontinuidades se detectaron; porosidades, inclusiones y fisuras en un porcentaje bastante importante (74,07 por ciento). Cuando contrastamos con la inspección visual, se demuestra la potencialidad de la inspección propuesta pues visualmente, sólo pudo detectarse un 7,41 por ciento de discontinuidades

Casting alloys: side-effects.

Side-effects from dental materials are a minor problem, but should be recognized. In recent questionnaire surveys about side-effects, the incidence was estimated to be 1:300 in periodontics and 1:2600 in pedodontics. None of these reactions was related to dental casting alloys. In prosthodontics, the incidence was calculated to be about 1:400, and about 27% were related to base-metal alloys for removable partial dentures (cobalt, chromium, nickel) and to noble/gold-based alloys for porcelain-fused-to-metal restorations. The complaints consisted of intra-oral reactions (such as redness, swelling, and pain of the oral mucosa and lips), oral/gingival lichenoid reactions, and a few instances of systemic reactions. In orthodontics, the incidence was 1:100, and most reactions (85%) were related to metal parts of the extra-oral anchorage devices. Even though the extensive use of base-metal alloys has been of major concern to the dental profession, relatively few case reports substantiate this concern. Allergy to gold-based dental restorations has been more commonly reported. Palladium-based alloys have been associated with several cases of stomatitis and oral lichenoid reactions. Palladium allergy seems to occur mainly in patients who are very sensitive to nickel. All casting alloys, except titanium, seem to have a potential for eliciting adverse reactions in individual hypersensitive patients. Tolerance induction may be a possible benefit of the use of intra-orally placed alloys. In non-sensitized individuals, oral antigenic contacts to nickel and chromium may induce tolerance rather than sensitization. A variety of systemic diseases and reactions has been claimed to be caused by dental materials. The claims are generally poorly documented.

[Clinical post-treatment evaluation of powder metallurgically produced tooth replacements]. / Klinische Nachuntersuchungen von pulvermetallurgisch hergestelltem Zahnersatz.

258 units of fixed crowns and inlays, produced with the powder metallurgic Degusint-System (Degussa), were clinically evaluated 6 and 12 months after insertion. Periodontal examinations, especially of the crevicular fluid flow, failed to show higher amounts of marginal inflammation due to the subgingival localization of the margins of fixed sintermetallic restorations compared with reference teeth of the same individual. Plaque accumulations during the wearing period were quite the same as those observed with crowns.

Avaliaçäo do desajuste cervical de coroas metalocerâmicas, obtidas a partir da fundiçäo com cinco ligas de Ni-Cr e duas porcelanas odontológicas / Evaluation of the cervical disadjustment of metal ceramic crowns, by casting with five Ni-Cr alloys and two dental porcelains

O presente trabalho teve como objetivo avaliar o desajuste cervical de infra-estruturas para coroas metalocerâmicas, antes e após a aplicaçäo de porcelana. Cinco marcas comerciais de liga de Ni-Cr foram usadas (Biobond II, Durabond II, Kromalit, Nicrodent e Resistal P). Cem troquéis de gesso foram obtidos a partir de um outro metálico com características de um preparo para coroa metalocerâmica. Cinco conjuntos troquel/matriz de gesso foram confeccionados para padronizar a forma e espessura dos padröes de cera que, a seguir, foram fundidos e divididos aleatoriamente em dois grupos de cinquenta casquetes, sendo dez para cada liga estudada. O desajuste cervical foi entäo avaliado em microscópio comparador. Após esse procedimento, a porcelana foi aplicada e uma matriz de silicona (Provil P) foi usada para padronizar a forma e espessura da porcela...

Análise da influência do reaquecimento das moldagens de siliconas de adiçäo e mercaptanas sobre a adaptaçäo de fundiçöes em ligas para metalocerâmica / Influence analysis of reheating impressions of adition silicone and mercaptans on the fit adaptation in metal ceramic alloys

Este estudo foi desenvolvido para verificar a influência do reaquecimento das moldagens de silicona de adiçäo e mercaptanas sobre as fundiçöes em ligas de níquel-cromo. Foram realizadas 20 moldagens em cada material, utilizando-se um dispositivo especialmente construído para isso. Os vazamentos foram efetuados com gesso tipo IV sendo 10 moldagens de cada material vazados após atingirem a temperatura ambiente e 10 após reaquecimento até a temperatura em que ocorreu a polimerizaçäo, ou seja 37ºC. Os troquéis obtidos foram medidos através de uma coroa frezada de dimensöes conhecidas previamente. Em seguida foram esculpidos em cera sobre os troquéis 40 casquetes de cera, os quais foram processados segundo a técnica em uso atual para fundiçäo metalocerâmica. As fundiçöes obtidas foram medidas sobre os troquéis de gesso, em seguida sobre o troquel original de aço, que serviu para as moldagens. Algumas verificaçöes puderam ser realizadas, tais como: - As siliconas mostraram resultados superiores aos da mercaptana. - O reaquecimento mostrou-se eficiente no sentido de incrementar a precisäo das moldagens, para ambos os materiais. - O processo de fundiçäo näo revelou diferenças estatisticamente significantes entre nenhuma das condiçöes, o que demonstra que sua variabilidade é maior que a melhoria que se obtém na precisäo das moldagens usando-se materiais mais precisos e a técnica de reaquecimento

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...

Apparent cytotoxicity of base metal casting alloys.

The cytotoxic potentials of three Ni-Cr based alloys and an Fe-Cr based alloy were assessed. In tissue culture, casting of all four test materials and powders of the Fe-Cr based material did not elicit adverse cellular changes. However, cultures containing Ni-Cr powders showed prominent zones of lysis and cell alteration. The cytotoxic potential of products obtained from the surfaces of casting alloys may offer an expedient means for estimation of long-term clinical toxicity.