A comparison of the accuracy of patterns processed from an inlay casting wax, an auto-polymerized resin and a light-cured resin pattern material.

Background: Traditionally, inlay casting waxes have been used to fabricate patterns for castings. Newer resin pattern materials offer greater rigidity and strength, allowing easier laboratory and intraoral adjustment without the fear of pattern damage. They also claim to possess a greater dimensional stability when compared to inlay wax. Aims: This study attempted to determine and compare the marginal accuracy of patterns fabricated from an inlay casting wax, an autopolymerized pattern resin and a light polymerized pattern resin on storage off the die for varying time intervals. Materials and Methods: Ten patterns each were fabricated from an inlay casting wax (GC Corp., Tokyo, Japan), an autopolymerized resin pattern material (Pattern resin, GC Corp, Tokyo, Japan) and a light-cured resin pattern material (Palavit GLC, Hereaus Kulzer GmbH, Germany). The completed patterns were stored off the die at room temperature. Marginal gaps were evaluated by reseating the patterns on their respective dies and observing it under a stereomicroscope at 1, 12, and 24 h intervals after pattern fabrication. Results: The results revealed that the inlay wax showed a significantly greater marginal discrepancy at the 12 and 24 h intervals. The autopolymerized resin showed an initial (at 1 h) marginal discrepancy slightly greater than inlay wax, but showed a significantly less marginal gap (as compared to inlay wax) at the other two time intervals. The light-cured resin proved to be significantly more dimensionally stable, and showed minimal change during the storage period. Conclusion: The resin pattern materials studied, undergo a significantly less dimensional change than the inlay waxes on prolonged storage. They would possibly be a better alternative to inlay wax in situations requiring high precision or when delayed investment (more than 1 h) of patterns can be expected.

Evaluation and comparison of castability between an indigenous and imported Ni-Cr alloy.

Context: Since 1907 casting restorations have been in use in dentistry. Numerous companies have been manufacturing and marketing base metal alloys. Gold was a major component of casting alloys. But alloys with less than 65% gold tarnished easily and the increase in cost of gold post-1970s lead to the revival of base metal alloys such as nickel-chromium and cobalt-chromium alloys which were in use since 1930s. Aim: This study was conducted to evaluate and compare the castability between an indigenous alloy and an imported alloy, as imported base metal alloys are considered to be expensive for fabrication of crowns and bridges. Materials and Methods: This study was conducted to evaluate and compare the castability (for the accurate fabrication of crowns and bridges) between an indigenous base metal alloy-Non-ferrous Materials Technology Development Centre (NFTDC), Hyderabad (Alloy A) -and an imported base metal alloys (Alloy B). Castability measurement was obtained by counting the number of completely formed line segments surrounding the 81 squares in the pattern and later calculating the percentage values. The percentage obtained was taken as the castability value for a particular base metal alloy. The percentage of castability was determined by counting only the number of completely cast segments in a perfect casting (81 × 2 = 162), and then multiplying the resulting fraction by 100 to give the percentage completeness. Statistical Analysis Used: The Student t-test was used. Results: When the castability of alloys A and B was compared, the calculated value was less than the tabular value (1.171 < 2.048) leading to the conclusion that castability between alloys A and B is insignificant. Therefore we conclude that both the alloys have the same castability. Conclusions: Using the above-mentioned materials and following the method to test castability, we were able to derive favorable results. As the results were satisfactory, we can conclude that the castability of the indigenous alloy is on par with the imported alloy.

Shear bond strength of porcelain veneer with fresh and recasting Ni-Cr alloy: a comparative in vitro study / Resistência de união ao cisalhamento entre porcelana de recobrimento e liga de Ni-Cr nova e refundida: estudo in vitro comparativo

Introduction: Dental alloys are routinely subjected to multiple casting procedures. Repeated casting of the same alloys may cause loss of trace elements (such as Sn, Si, Mn, etc.) that are essential for the metal ceramic bond. A common practice is to include a proportion of new metal with the previously cast metal that is thought to replenish the lost elements. Objective: The study was done to evaluate the effect of variation in percentage of recasted Ni-Cr alloy used and to compare the effects with the shear bond strength of porcelain to the fresh ingot Ni-Cr alloy. Materials and methods: Uniform patterns were fabricated, invested and casting was done in five different combinations of fresh and recast alloy. A hundred percent fresh alloy; 25% recast with 75% fresh alloy; 50% recast and 50% fresh alloy; 75% recast and 25% fresh alloy; 100% recast alloys. After uniform porcelain application and firing, the specimens were subjected to shear bond test using a universal testing machine. Data were statistically analyzed using Duncans’s multiple comparison test. Results: The results showed that the mean shear bond strength of the 100% fresh alloy was maximum and 100% recast alloy was least among the groups tested. The mean shear bond strength of castings obtained from 100% fresh, 25% recast, and 50% recast alloy were similar to each other and showed statistically significant difference when compared to the 100% recast group. Seventy five percent recast group did not show statistically significant difference with 100% recast alloy. Arch Oral Res. 2011 May/Aug.;7(2)177-82 Rajalbandi SK, Kumar V, Sajjan S. 178 Introduction The Development of “Taggarts” technique of casting by lost wax process into the Dentistry gave an impetus to use alloyed metals as a restoration (1). Most of the dental laboratories commonly use the sprue and button from a previous casting as a part of the melt for the new casting (2, 3). This practice is especially detrimental with ceramometal...

Introdução: Ligas dentárias são rotineiramente submetidas a procedimentos de fundição múltipla. Fundiçõesrepetidas da mesma liga podem causar perda de elementos-traço, tais como Sn, Si e Mn, os quais são essenciaispara a união entre metal e cerâmica. Uma prática comum é a de incluir uma proporção de liga nova com ometal anteriormente fundido visando repor esses elementos perdidos. Objetivo: O presente estudo avaliou oefeito da variação da porcentagem de liga de Ni-Cr refundida na resistência de união ao cisalhamento comporcelana, comparado a liga de Ni-Cr nova. Materials e métodos: Padrões uniformes foram confeccionados,incluídos e fundidos sob cinco diferentes combinações de liga nova e refundida: 100% liga nova; 25% ligarefundida + 75% liga nova; 50% liga refundida + 50% liga nova; 75% liga refundida + 25% liga nova; 100%liga refundida. Após a aplicação uniforme da porcelana e sua posterior cocção, as amostras foram submetidasao teste de cisalhamento utilizando uma máquina universal de ensaios. Os dados foram analisados estatisticamenteatravés do teste de comparações múltiplas de Duncan. Resultados: Os resultados mostraram que amaior resistência de união ao cisalhamento para a liga 100% nova, e a menor resistência para a liga 100%refundida. A resistência de união ao cisalhamento das fundições com 100% de liga nova, 25% e 50% de ligarefundida foi similar e estatisticamente diferente do grupo com 100% de liga refundida. O grupo com 75%de liga refundida não mostrou diferença estatisticamente significante com o grupo de liga 100% refundida.Conclusão: Pode-se concluir que o mínimo de 50% de liga nova para a fundição é uma margem de segurançapara a refundição de ligas de Ni-Cr.

Effect of phosphate-bonded investments on titanium reaction layer and crown fit

This study analyzed the reaction layer and measured the marginal crown fit of cast titanium applied to different phosphate-bonded investments, prepared under the following conditions (liquid concentration/casting temperature): Rema Exakt (RE) - 100 percent/237°C, 75 percent/287°C, Castorit Super C (CS)-100 percent/70°C, 75 percent/141°C and Rematitan Plus (RP)- 100 percent/430°C (special to titanium cast, as the control group). The reaction layer was studied using the Vickers hardness test, and analyzed by two way ANOVA and Tukey's HSD tests (á = 0.05). Digital photographs were taken of the crowns seated on the die, the misfit was measured using an image analysis system and One-way ANOVA, and Tukey's test was applied (á = 0.05). The hardness decreased from the surface (601.17 VHN) to 150 ìm (204.03 VHN). The group CS 75 percent/141°C presented higher hardness than the other groups, revealing higher surface contamination, but there were no differences among the groups at measurements deeper than 150 ìm. The castings made with CS - 100 percent/70°C presented the lowest levels of marginal misfit, followed by RE -100 percent/237°C. The conventional investments CS (100 percent) and RE (100 percent) showed better marginal fit than RP, but the CS (75 percent) had higher surface contamination.

Effect of temperature variation on the cytotoxicity of cast dental alloys and commercially pure titanium

Cell culture system has been used to evaluate alloy cytotoxicity under different environments, testing the extracts, but the effect of temperature variation on the cytotoxicity of dental alloys has not been analyzed. OBJECTIVE: The aim of the present study was to investigate if temperature variation could affect dental alloy cytotoxicity, testing alloy extracts in an epithelial cell culture system. MATERIAL AND METHODS: Discs of Ni-Cr, Co-Cr-Mo, Ni-Cr-Ti, Ti-6Al-4V and commercially pure titanium (cp Ti) were cast by arc melting, under argon atmosphere, injected by vacuum-pressure. Discs were immersed in artificial saliva and subjected to different temperatures: 37ºC and thermocycling (37ºC/5ºC/37ºC/55ºC/37ºC). After thermocycling, extracts were put in a subconfluent culture during 6 h, and the number of cells and their viability were used to evaluate cytotoxicity in these temperatures. For each alloy, data from temperature conditions were compared by Student's t-test (α=0.05). RESULTS: The cytotoxicity tests with alloy/metal extracts showed that Ni-Cr, Co-Cr-Mo, Ti-6Al-4V and cp Ti extracts (p>0.05) did not affect cell number or cell viability, while Ni-Cr-Ti (p<0.05) extract decreased cell number and viability when the alloy was subjected to thermocycling. CONCLUSION: Within the limitations of the present study, the Ni-Cr-Ti alloy had cell number and viability decreased when subjected to temperature variation, while the other alloys/metal extracts did not show these results.

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.

Effect of commercial dental investments at low temperature on the marginal adaptation of cast cp Ti inlays

Aim: The purpose of this study was to evaluate the adaptation of inlay restorations cast in commercially pure titanium (cp Ti) after inclusion of the wax patterns in either a phosphate-bonded investment (Rematitan Plus®) or a silicon oxide-based investment (Termocast®). Methods: The wax patterns were prepared over an inlay-type mold. After waxing, 5 measurements of the marginal adaptation were made on the mesial and distal faces. Five wax patterns were included in each type of investment under vacuum. The cast specimens were repositioned in the mold and other 5 measurements of the adaptation were made based on the same initial testing conditions. Data were analyzed statistically by two-way ANOVA and Duncan’s post-hoc (P<0.01) using the SPSS statistical software package version 12.0 (SPSS, Chicago, IL, USA). Results: The mean marginal discrepancies of the MOD inlays were higher in the Termocast® Group. Termocast® presented significantly greater marginal discrepancy than Rematitan Plus®. Due to the great permeability of the investment refractory material, internal porosity was extremely rare in Rematitan Plus® and more common in Termocast®. Conclusion: It may be concluded that Termocast® investment should not be indicated for cp Ti casting due to poor adaptation and porosity on the casting surface.

Microhardness of Ni-Cr alloys under different casting conditions

Este estudo avaliou a microdureza de ligas de Ni-Cr usadas em prótese fixa fundidas sob diferentes condições. As condições de fundição foram: (1-maçarico) chama composta por uma mistura de gás/oxigênio e centrífuga sem o controle do ambiente de fundição; (2-indução/argônio) indução eletromagnética com o ambiente controlado com argônio; (3-indução/vácuo) indução eletromagnética com o ambiente sob vácuo; (4-indução/ar) indução eletromagnética sem o controle da atmosfera. Foram utilizadas três ligas: Ni-Cr-Mo-Ti, Ni-Cr-Mo-Be e Ni-Cr-Mo-Nb. Foram realizadas 4 fundições com 5 espécimes cilíndricos de 15 mm de comprimento (diâmetro de 1,6 mm). Depois das fundições os espécimes foram embutidos e polidos para as mensurações de microdureza Vickers (VH) em um Shimadzu HMV-2 (1.000 g por 10 s). Um total de 5 indentações foram feitas por anel, uma em cada espécime. Os dados de VH foram avaliados pelos testes de ANOVA e Tukey (a = 0,05) para contraste de média. A microdureza das ligas apresentou a seguinte ordem: Ni-Cr-Mo-Ti (422 ± 7,8) > Ni-Cr-Mo-Nb (415 ± 7,6) > Ni-Cr-Mo-Be (359 ± 10,7), sendo diferentes entre si. Os valores obtidos nas condições indução/argônio e indução/vácuo foram semelhantes entre si (p > 0,05) e menores que os obtidos nas condições indução/ar e maçarico, estes últimos semelhantes entre si (p > 0,05). A microdureza das ligas é dependente da composição da liga e do método de fundição. A dureza das ligas de Ni-Cr foi maior quando fundidas nas condições indução/ar e maçarico.

Stress variations in recast Ni-Cr alloy--a finite element analysis.

A finite element analysis was carried out to analyse the stress variations in a mandibular posterior fixed partial denture (FPD), made of recast nickel-chromium alloy. A two dimensional finite element model was developed and then analysed with STAAD III/ISDS program with an occlusal load of 1 kg applied to the casting surface. The analysis revealed that the connectors experienced maximum stresses and the generated stress values decreased within the fixed partial denture made of recast Ni-Cr alloy. It seemed unlikely that FPD inspite of being made of recast alloy might fail before the other tissue components show signs of degeneration thus establishing the potential for recycling the Ni-Cr alloy in actual dental practice.

An investigation into the effect of solidification shrinkage on distortion of casting and flexure strength of various solders for base metal alloys. A laboratory study.

This study was undertaken to determine the distortion due to solidification shrinkage and to evaluate the flexure strength properties of soldered joints between combination of three commercially available base metal alloys and solders. Ninety rectangular bars were cast using three commercially available alloys for soldering (30 bars of each alloys). Ten bars of each alloy were soldered using electrical soldering unit and solder recommended by respective manufacturers, twenty bars (ten pairs each) were soldered using other solders. Length between the references markings on the specimen were measured using a vernier caliper and travelling microscope to check the possible solidification shrinkage. The specimens were then subjected to flexure strength evaluation using a universal testing machine. Statistical comparison of dimensional changes due to solidification shrinkage and flexure strength evaluation of soldered joints was done using analysis of variance test. Recommended Ni-Cr solders showed less shrinkage compared to that of the Co-Cr solders from the tested specimens and superior flexure strength was found in Co-Cr alloy specimen (P value P > .001) soldered with Co-Cr alloy solders.

Influência do tipo de reconstruçäo na retençäo de coroas totais fundidas / Influence of reconstruction type in the casting full crowns

A finalidade deste estudo foi verificar a resistência à remoçäo por traçäo de coroas totais fundidas cimentadas em dentes reconstruídos com núcleo fundido, amálgama e resina composta, associados a pinos retidos em dentina ou no conduto radicular, comparando sua retentividade com a de coroas metálicas fundidas cimentadas em dentes com preparos feitos totalmente em estrutura dentária sadia. Foram selecionados 60 molares superiores recém-extraídos, 10 dentes para cada condiçäo experimental, os quais foram incluídos por suas raízes até 1 mm da junçäo cemento-esmalte em bases plásticas, com resina acrílica ativada quimicamente, para receber preparo tipo coroa total. Com exceçäo da condiçäo controle (dente sem reconstruçäo), as demais tiveram, após preparo cavitário, o corte da porçäo coronária a 1,5 mm do ângulo cavosuperficial, bem como a remoçäo do teto da câmara pulpar...

Avaliaçäo da adaptaçäo gengival de coroas totais e restauraçöes M.O.D. fundidas a partir de padröes de cera e mistos (resina + cera) / Evaluation of the gingival misfiting of fulls crowns and M.O.D. casting restorations from wax and mixed patterns (wax and resin)

O propósito da presente pesquisa foi verificar a adaptaçäo gengival de coroas totais e incrustaçöes do tipo M.O.D. e mistos (resina + cera) obtidos por 3 operadores. As leituras de adaptaçäo eram feitas diretamente nos troquéis metálicos-padräo, com microscópio comparador, em quatro pontos diametralmente opostos na regiäo gengival nas duas caixas proximais, no caso das incrustaçöes tipo M.O.D., e computadas as médias respectivas. Foram necessárias 10 réplicas para cada condiçäo experimental, num total de 360 fundaçöes. Após a análise estatística dos resultados, concluiu-se que: - as incrustaçöes tipo M.O.D. tendem à apresentar melhor adaptaçäo gengival que as coroas totais, independentemente do tipo de padräo...