Development of polimeric composite material for use in the confection of dies

Na Odontologia, ao se confeccionar peças restauradoras dentárias, pela técnica indireta, o processo mais rotineiramente empregado utiliza um modelo de gesso, obtido a partir de um molde de elastômero, tomado de um dente preparado. Vários fatores podem influenciar na boa precisão de ajustes destas peças como o escoamento do material de vazamento dentro da moldagem, a compatibilidade do material de vazamento com o da moldagem, o tempo de presa, a estabilidade dimensional, a resistência mecânica do material quando da separação moldagem/modelo, a resistência a abrasão e a fidelidade de reprodução de detalhes. Materiais foram introduzidos na odontologia para utilização na confecção de troquéis no intuito de minimizar as desvantagens do gesso, como baixa resistência a abrasão e ligeira expansão de presa. Dentre eles os troquéis metalizados e as resinas epóxicas, que tem vantagens em relação às propriedades mecânicas, porém o primeiro exige técnica demorada e de alto custo e o segundo apresenta contração. O presente trabalho se propõe a testar uma nova composição de poliéster insaturado com estireno adicionado ao carbonato de cálcio em diferentes proporções (10, 20, 30, 40, 50, 60 e 70%) e compará-la ao gesso tipo IV e a resina epoxídica com óxido de alumínio, através de ensaios mecânicos, de abrasão e de alteração dimensional, para avaliar a possibilidade de sua utilização como material de confecção de troquéis para a construção de restaurações indiretas. Para caracterização dos materiais foram feitas análises de espectrometria no infravermelho, Calorimetria de varredura diferencial, termogravimétrica e Microscopia eletrônica de varredura. O compósito a base de poliéster insaturado com 50% de carbonato de cálcio se mostrou viável para utilização como material para troquel. Quando comparado aos materiais de controle mostrou propriedades mecânicas próximas as da resina epoxídica e bem superiores ao gesso, resistência a abrasão superior ao gesso e inferior a resina epoxídica e alteração dimensional próxima a resina epoxídica e maior ao gesso. Sendo a formulação do poliéster/carbonato de cálcio apenas constituída de polímero, catalisador e carga, é possível melhorar a formulação modificando a carga e/ou acrescentando aditivos visando minimizar a contração de polimerização.In dentistry, the most commonly used procedure to manufacture indirect dental restorations uses a cast of type IV stone. This cast is made from an elastomeric impression of a prepared tooth. Many factors may influence the accuracy of adaptation of these restorations, such as the flow of the pouring material into the mold, the compatibility between the pouring and the impression materials, the setting time, the dimensional stability, the mechanical strength of the material during the mold / cast separation, the abrasion resistance and fidelity to reproduce details. Materials were introduced for preparing dies in order to minimize the disadvantages of the stone, such as its low resistance to abrasion and slight expansion of setting. These materials include metal-plated dies and epoxy resins, which have advantages concerning mechanical properties. However, the first one has a time-consuming technique and requires high costs while the second material shows shrinkage. This study tested a new composition of unsaturated polyester with styrene added to calcium carbonate in different proportions (10, 20, 30, 40, 50, 60 and 70%) and compared it to the type IV stone and to the epoxy resin with aluminum oxide. This comparison was made by mechanical, abrasion and dimensional changes tests in order to evaluate the possibility of using it as material for dies in the process of construction of indirect restorations. The materials were characterized using the analysis of the infrared spectrometry, differential scanning calorimetry, thermogravimetric and scanning electron microscopy. The composite based on unsaturated polyester with 50% calcium carbonate (P5) was considered viable as material for dies. When it was compared to the control materials the following results were found: a) the mechanical properties of P5 are similar to those ones of the epoxy resin and well above the stone ones; b) the abrasion resistance of this new material is lower in relation to the epoxy resin, but higher than the stone one; c) the values for dimensional changes were similar to the epoxy resin ones and superior to those ones found in stone. As the formulation of polyester / calcium carbonate only consists of a polymer, a catalyst and filler particles, it is possible to improve its composition by modifying the filler particles and / or adding additives to minimize the shrinkage of polymerization

Influence of the casting material on the dimensional accuracy of dental dies

The purpose of this study was to evaluate the dimensional accuracy of different materials used in the confection of dies. Two stainless steel standard models were confected. One of the models, which was 2 mm larger than the other model, was used to provide a uniform relief for the two-step putty-wash impression technique. Thirty impressions were obtained using a polyvinyl siloxane impression material and randomly divided into three groups (n = 10) according to the type of casting material: type IV dental stone, commercially available epoxy resin (Tri-Epoxy), and industrial epoxy resin (Sikadur). After the setting/polymerization of the casting material, the dimensional stability was measured in terms of the height, diameter of the base and diameter of the top from the obtained dies and from the standard metal model using a profile projector. Results were analyzed by ANOVA and Dunnet test (α = 0.05). In the height values, no significant difference was observed between the groups, except for Sikadur casts, which showed lower mean values. The Tri-Epoxi group showed statistically lower mean base diameter values, compared with the other groups, and both epoxy resin groups showed statistically lower mean top diameter values, compared with that for the type IV dental stone group. We concluded that type IV gypsum and the commercially available epoxy resin showed similar behavior in most areas. The industrial epoxy resin did not show the same characteristics, although the diameter of the base obtained with it was similar to that obtained with type IV dental stone

Técnica de silhueta aplicada em preparação odontológica - relato de caso

Objective: the present study aims to show, through a case report, a wear technique capable to provide a correct full crown preparation. Case Report: as the patient’s need, tooth 21 was prepared for total crown by means of the silhouette technique, in which the volume of dental wear is guided by the thickness of the drills, as well as by the observation of the half dental profile formed after initial wear. A photographic sequence was performed to allow the understanding of preparation stages and its importance. Results: the final preparation presented ideal dimensions, within the proposed treatment. Conclusion: this approach allowed the correct orientation of the desired preparation.Objetivo: o presente estudo tem como objetivo mostrar, por meio de relato de caso, uma técnica de desgaste capaz de proporcionar uma correta preparação total da coroa. Relato de Caso: como o paciente necessidade, o dente 21 foi preparado para coroa total por meio da técnica de silhueta, na qual o volume de desgaste dentário é guiado pela espessura das brocas, bem como pela observação do perfil do meio dente formado após o desgaste inicial. Uma seqüência fotográfica foi realizada para permitir a compreensão dos estágios de preparação e importância. Resultados: a preparação final apresentou dimensões ideais, dentro do tratamento proposto. Conclusão: esta abordagem permitiu a correta orientação do a preparação desejada