Influence of the recast and different marginal configurations in the cervical and interior adaptation of Ni-Cr alloy total metallic crowns / Influencia da refusão de uma liga de niquel-cromo na adaptação cervical e interna de coroas totais com diferentes configurações marginais

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

The aim of the present study was to verify the influence of the heat source on the castability and hardness of a Ni-Cr-based commercial alloy ? VERA BONO II - in three different conditions: new (first use), recast, and new mixed with scraps. In order to evaluate castability, 10 specimens were made for each alloy condition, using a polyester sieve with 11x11 filaments, 0.22mm thick, resulting in a screen with 100 square spaces. This screen was fixed to 0.25mm threads along the extension of two sides, and a post was fixed to its vertex. In order to perform hardness analysis, circular specimens made of regular blue wax measuring 8.0 mm in diameter and 2.0 mm thick were connected to the post, forming the sprue. The patterns were then fixed to the casting chamber, so that the distance from the base to the reservoir was 0.5 cm. A surface tension-reducing solution was abundantly applied to the patterns and after drying, the patterns were embedded into a phosphate-bonded investment - Termocast (Polidental, São Paulo, Brazil) manipulated under vacuum pressure, following manufacturer s instructions regarding proportions and manipulation times. Casting rings were placed in an electric oven (Bravac) until the temperature of 900°C was reached, and were then filled with approximately 15 grams of alloy, molten either by an oxigen/acethylen gas torch or by induction as heat sources. Following this procedure, castability evaluate hardness Rockwell 30T, specimens were embedded in chemically activated acrylic resin and then placed on a Testor HTI Super-Panambra hardness teste r. Hardness values for each specimen were obtained, and the average hardness was calculated. Results were submitted to analysis of variance and averages were compared by Tukey s test at 5% probability. There were statistically significant differences between the heat sources applied to the different types of alloy, with induction presenting the best castability results. There were no statistically significant differences in the average hardness values between torch or induction as the heating source for new and mixed alloys, although induction showed the best results, leading to statistically significant differences in hardness, when recast alloy was used

ASSUNTO(S)

dental materials materiais dentarios

ACESSO AO ARTIGO

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