Effect of Sprue Design in Nickel-Chromium Cast Crown Margin

ABSTRACT Objective: To determine the effect of sprue design on the marginal accuracy of the casting. Material and Methods: It was an experimental in-vitro study. There are forty-four crowns of single sprue group with a forty-four double sprue group that was compared in 6 different locations of the margin. The sections were inspected under a microscope at 50X magnification and took a micrograph. The radius from an actual casting edge to a possibly excellent margin was then documented as marginal discrepancy (d), in µm. The marginal discrepancy was documented for each of the six sections per casting. Thus 264 sections were measured for each group. Data were analysed using (ANOVA) for analysis of variance. For bivariate analyses, Chi-square and Student t test were used. The significance level was set at < 0.05. Results: The marginal discrepancy was greater in the single sprue group of cast crown (43.1 ± 4.74 µm) and in double sprue group of cast crown was less (25.7 ± 4.25 µm). This difference is statistically significant (p<0.05). The correlation between single sprue group of casting with a double sprue group of casting by student's t-test where determination height was 95%. Conclusion: Double sprue design produces a higher accurate margin than single sprue design in the nickel-chromium alloy cast crown.

Efeito das técnicas de inclusão convencional e rápida sobre a resistência ao impacto de revestimentos odontológicos / Effect of the conventional and fast inclusion techniques on the impact strength of dental investments

Objetivo: Comparar a resistência ao impacto de revestimentos submetidos a duas diferentes técnicas de inclusão. Métodos: Foram utilizados quatro revestimentos (All Therm - R1; Flash - R2, Heat Shock - R3 e Micro Fine - R4) em duas diferentes técnicas de inclusão (Convencional - T1 ou Rápida - T2). Os corpos-de-prova de cada grupo (n=15) foram obtidos por meio de uma matriz de silicone (70mmx12mmx12mm), vazando-se os revestimentos proporcionados e manipulados conforme as recomendações dos fabricantes. Após aquecimento em forno, foram submetidos ao teste de resistência ao impacto, com potência de trabalho de 40Kpcm, correspondente a 3,94J. Resultados: Em ordem decrescente de valores de resistência ao impacto (kJ/m2), os grupos se distribuíram da seguinte forma: R3T1 (1,34±0,11); R3T2 (1,22±0,07); R4T2 (1,21±0,09); R2T1 (1,16±0,10); R4T1 (1,16±0,07); R1T2 (1,12±0,07); R2T2 (1,12±0,08) e R1T1 (1,09±0,10). Nenhum grupo apresentou valor significantemente diferente (p>0,05) quanto ao fator técnica. Entre os grupos T1 só R3 diferiu dos demais revestimentos e entre os grupos T2, R3 e R4 apresentaram maiores valores. Conclusão: As diferentes técnicas de inclusão não exerceram influência sobre a resistência ao impacto dos revestimentos testados.

Objective: Compare the impact strength of investments submitted to two different investing techniques. Methods: Four investments were used (All Therm - R1; Flash - R2, Heat Shock - R3 and Micro Fine - R4) in two different investing techniques (Conventional - T1 or Accelerated - T2). Each group sample (n=15) was obtained by means of a silicone die (70mmx12mmx12mm), and the investments were poured according to the manufacturer´s instructions. After heating in an oven, the samples were submitted to the impact test with an impact load of 40Kpcm, corresponding to 3.94J. Results: The following impact strength values were obtained (kJ/m2) in decreasing order: R3T1 (1.348±0.116); R3T2 (1.221±0.075); R4T2 (1.217±0.096); R2T1 (1.162±0.101); R4T1 (1.162±0.075); R1T2 (1.126±0.077); R2T2 (1.126±0.085) and R1T1 (1.099±0.106). No group presented a significantly different value (p>.05) with regard to technique. Among the T1 groups, only R3 differed from the other investments and among the T2 groups, R3 and R4 presented higher values. Conclusion: Different investing techniques did not influence the impact strength of the tested investments.

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.

Efeito de um revestimento com processamento rápido para fundição de titânio na camada de reação, porosidade interna, fluidez, rugosidade superficial e adaptação marginal de copings / Effect of short-cycle investment for titanium castings on the reaction layer, internal porosity, castability, surface roughness and coping marginal misfit

A aplicação do titânio e ligas de titânio para implantes dentários e próteses têm crescido nos últimos anos devido às suas excelentes propriedades físicas e mecânicas. No entanto, o titânio tem alto ponto de fusão (1668ºC) e sob elevadas temperaturas, reage com elementos do ar atmosférico (oxigênio, nitrogênio, hidrogênio) e com componentes de diversos revestimentos. As reações entre o metal fundido e alguns elementos de revestimentos, principalmente fosfatados ou à base de sílica, resultam na formação de uma zona de contaminação superficial denominada "α-case". Para minimizar este problema, revestimentos contendo óxidos menos reativos, tais como Al2O3, MgO, ZrO2 e CaO, têm sido desenvolvidos. Os revestimentos especiais para fundição de titânio à base de sílica, de MgO, alumina e espinélio apresentam um tempo de processamento bastante longo (8 a 10 horas). Recentemente, foi desenvolvido um revestimento à base espinélio com processamento acelerado (Trinell - Dentaurum, Ispringen, Germany) que permite a utilização de uma técnica de secagem em forno de microondas e temperatura de aquecimento inicial do forno de 400 ºC, diminuindo o tempo de processamento para cerca de 5 horas. No entanto, não existem estudos que comprovem a eficiência deste novo revestimento. O propósito deste estudo foi avaliar o efeito do novo material Trinell (TR) na camada de reação, porosidade interna, fluidez, rugosidade superficial e adaptação marginal de estruturas fundidas em titânio, quando comparado a dois revestimentos convencionais para fundição de titânio: um revestimento fosfatado, Rematitan Plus (RP) - controle negativo e outro à base de espinélio Rematitan Ultra (RU) - controle positivo. A camada de reação foi avaliada por meio de ensaio dureza Vickers; a medida da porosidade interna foi determinada por exame radiográfico; a rugosidade superficial foi medida em rugosímetro; a fluidez foi determinada pela porcentagem de filamentos fundidos em relação à extensão total de filamentos do padrão de nylon em forma de malha e a adaptação marginal de estruturas fundidas em Ti cp. sobre um pilar cônico 5.0, montado sobre implante HE, foi medida por análise de imagens. Para os valores de dureza Vickers, aplicou-se a análise de variância a dois critérios e teste de Tukey para comparação de médias (α = 0,05). Nas duas primeiras profundidades (25 µm e 50 µm) foram encontrados os maiores valores de dureza, enquanto a partir de 100 µm até 350 µm, os valores foram menores e estatisticamente iguais entre si. Nos espécimes fundidos com RP, foi encontrada maior dureza (199,71 VHN) do que para aqueles fundidos com RU (174,87 VHN) e TR (175,52 VHN), não havendo diferença significante entre os revestimentos à base de espinélio. A interação material X profundidade mostrou igualdade entre os espécimes fundidos com os três materiais a partir de 100 µm. Para os testes de preenchimento do molde, rugosidade superficial e adaptação marginal de componentes protéticos, diante do não atendimento aos critérios de aplicação de teste paramétrico, adotou-se o teste não-paramétrico Kruskal-Wallis. Foi observada pequena incidência de poros nas peças fundidas com RP, enquanto os piores resultados foram obtidos com RU, seguido de TR. No teste de rugosidade superficial, os espécimes fundidos com RP apresentaram-se significativamente mais rugosos do que os fundidos com RU e TR, iguais entre si. O preenchimento do molde em fundições com RP foi significativamente menor do que aquelas feitas com RU e TR. Os maiores valores de desadaptação marginal foram observados nas amostras fundidas com o RP (20,82 µm) e não houve diferença significante entre RU (8,35 µm) e TR (7,67 µm). Concluiu-se que o novo revestimento à base de espinélio (TR), com secagem em forno de microondas e processamento térmico acelerado, é capaz de produzir estruturas fundidas com características de camada de reação, preenchimento do molde, rugosidade superficial e adaptação marginal semelhante àquelas obtidas em fundições feitas com o material RU e superiores à RP, com exceção da porosidade, onde RP apresentou o melhor comportamento

The use of titanium and titanium alloys in dental implant and prosthesis has increased in the past few years because of their excellent physical and mechanical properties. However, titanium has a high melting point (1668 ºC) and inherent reactivity with elements of atmospheric air (oxygen, nitrogen, hydrogen) and with components of several investment materials under high temperatures. The reactions between molten metal and some of the elements of phosphate-bonded and other silica-based investment materials result in the development of a surface contamination zone called "α-case". To minimize this problem, new investment materials containing less reactive oxides, such as Al2O3, MgO, ZrO2 and CaO have been developed. The commercial silica-, MgO-, Al2O3 - and spinel-based investments especially formulated to titanium casting demand a processing time in a range of 8 to 10 hours. Recently, a new short-cycle spinel-based investment (Trinell - Dentaurum, Ispringen, Germany) was developed. It has a reduced processing time - 5 hours in the furnace- because of an investment drying technique into microwaves oven followed by an initial heating in furnace at 400 °C. However, there are not studies which verify the efficiency of this new investment. The aim of this study was to evaluate the reaction layer, the internal porosity, the surface roughness, the castability and the marginal misfit of titanium castings performed with the new material, Trinell (TR), in comparison to two conventional investments for titanium castings: phosphate-bonded Rematitan Plus (RP) - negative control, and the spinel-based Rematitan Ultra (RU) - positive control. The reaction layer was evaluated by Vickers hardness; the measure of the internal porosity was determined by radiographic test; the surface roughness was measured with a surface-test analyzer, the castability was determined by the percentage of completely cast filaments (percentage of the total extension of mesh pattern filaments); and the marginal misfit of the coping/abutment interface was measured by image analysis. The averages of Vickers hardness were compared by variance analysis (two-way) and Tukey test (α = 0.05). The highest values of hardness were found in the two first depths (25 µm and 50 µm), while from 100 µm to 350 µm the values were lower and statistical equal. The specimens cast with RP had higher hardness (199.71 VHN) than that cast with RU (174.87 VHN) and TR (175.52 VHN), which were significant equal. Regarding the material X depth interaction, no statistical difference was found among the specimens cast with the three materials from 100 µm to 350 µm. A non-parametric test (Kruskal-Wallis) was used for castability, surface roughness and coping misfit tests. Low incidence of pores was observed in the RP castings. The worse results were obtained in RU castings, followed by TR castings. In the surface roughness test, the specimens cast with RP presented significantly higher values of roughness than that cast with RU and TR. No significant difference was observed between RU and TR. The castability of RP castings was significant lower than the castability of RU and TR castings. The highest misfit values were observed in RP castings (20.82 µm) and no significant difference were found between RU (8.35 µm) and TR (7.67 µm). It was concluded that the new spinel-based investment (TR) with microwave oven drying and reduced speed operation is able to produce casting structures with reaction layer, castability, surface roughness and marginal misfit similar to the castings made with RU material and better than RP. However, RP presented lower internal porosity than RU and TR

Internal adaptation of cast titanium crowns

As the adaptation of titanium crowns obtained by Rematitan Plus investment, specific for titanium, is not recognized to be suitable, this study evaluated the effect of the concentration of the specific liquid and the temperature of the mold of investments on the internal misfit of crowns cast on commercially pure titanium. Individual dies of epoxy resin were obtained, representing teeth prepared for full-crown restoration with a 6-degree axial surface convergence angle and shoulder (1.0 mm). For the waxing of each crown, a ring-shaped stainless steel matrix (8.0mm internal diameter; 7.5 mm height) was adapted above the individual dies of epoxy resin. The Rematian Plus investment was mixed according to the manufacturer's instructions using two different concentrations of the specific liquid: 100 percent, 75 percent. Casting was performed in a Discovery Plasma Ar-arc vacuum-pressure casting machine with molds at temperatures of 430°C, 515°C and 600°C. The crowns were cleaned individually in a solution (1 percent HF + 13 percent HNO3) for 10 min using a ultrasonic cleaner, with no internal adaptations, and luted with zinc phosphate cement under a 5 kg static load. The crown and die assemblies were embedded in resin and sectioned longitudinally. The area occupied by cement was observed using stereoscopic lens (10X) and measured by the Leica Qwin image analysis system (mm²). The data for each experimental condition (n=8) were analyzed by Kruskal-Wallis non-parametric test (á=0.05). The results showed that liquid dilution and the increase in mold temperature did not significantly influence the levels of internal fit of the cast titanium crowns. The lowest means (±SD) of internal misfit were obtained for the 430°C/100 percent: (7.25 mm² ±1.59) and 600°C/100 percent (8.8 mm² ±2.25) groups, which presented statistically similar levels of internal misfit.