Mechanical and thermal properties of hydroxyaptite filled poly (methyl methacrylate) heat processed denture base material

The aim of this study was to evaluate the effect of powder-to-liquid ratio on the glass transition temperature (Tg) and the tensile properties of denture base material prepared from poly (methyl methacrylate) (PMMA) and hydroxyapatite (HA) previously treated with 3-trimethoxysilylpropyl methacrylate (gamma-MPS). Specimens for mechanical testing were prepared by adding composites powder (PMMA, BPO and HA) to the monomer (MMA and EGDMA) followed by hand mixing as in dental laboratory description usage. The glass transition temperature was studied by using differential scanning calorimetry (DSC). It was observed that the tensile properties and the Tg were affected by the powder-to-liquid ratio. The mechanical characterization of the materials were performed by using single edge notch-tension (SEN-T) specimens; the fracture toughness was slightly higher in formulation which contained HA filler compared to commercial denture base material.

Uso de la energía de microondas en el procesamiento de prótesis odontológicas / Uso da energia de microondas no processamento de próteses odontológicas

Se han propuesto métodos alternativos de procesamiento de resina para prótesis odontológicas, en el sentido de perfeccionar las técnicas y los resultados de prótesis removibles, sean parciales o totales. En este trabajo, los autores hacen una revisión crítica de la técnica del procesamiento por energía de microondas, en la cual se explican las investigaciones desarrolladas para evaluar los pros y los contras de su uso como método alternativo de polimerización de las resinas para base de prótesis. En este contexto, los autores concluyen que este método, a pesar de ser relativamente reciente, es plausible de ser utilizado en la elaboracíon de trabajos protéticos, por tratarse de una técnica sencilla, limpia y rápida, admitiendo trabajos con calidad equivalente a la de los métodos convencionales

Accuracy and porosity of denture bases submitted to two polymerization cycles.

In this study was verified accuracy and porosity of denture bases submitted to double cycles of polymerization. Thirty-Six master casts were made in dental stone from the impression of the metal die. They were divided in three groups. Denture bases of conventional acrylic resin were made on the casts of the groups I (GI-control) and II (GII), polymerized in water bath during 9 hours at 73 degrees C, and specific resin for microwave polymerization were made on the casts of the group III (GIII) and cured at 500 W during 3 minutes. Accuracy was verified by the weight of a impression material put between the denture base and cast die under load of 2 Kg. Afterwards, all the denture bases were relined by addition method and those of the group I and II were relined with the same material and polymerization technic. The denture bases of the group II were filled with the same resin, however cured in microwave oven with 500 W during 3 minutes. Accuracy was reevaluated. The porosity was verified by the immersion of the specimens in a solution of permanent black ink and the pores were counted through a stereo light microscope under magnification of 6.3 x. The average and standard deviation obtained for accuracy before and after the relining were respectively: GI: 0.63 +/- 0.02 - 0.66 +/- 0.03; GII: 0.63 +/- 0.03 - 0.68 +/- 0.03: GIII: 0.58 +/- 0.02 - 0.80 +/- 0.05. There was a significant difference (p < 0.05 as tested by Tukey) only for the group III. The average and standard deviation for porosity before and after the relining were respectively: GI: 8.33 +/- 0.63 - 9.25 +/- 0.85; GII: 8.17 +/- 0.98 - 10.08 +/- 1.63: GIII: 5.41 +/- 0.78 - 6.58 +/- 1.02. There was a significant difference (p < 0.05) for the group III before relining. The conclusion is that after relining, the conventional resin cured by water bath or microwaves energy showed a better adaptation, and the highest number of pores.

Alteraçäo dimensional e porosidade da resina acrílica para bases de dentaduras, em funçäo de variáveis de processamento / Dimensional change and porosities of denture base resin as function of handling variables

A pesquisa teve o propósito de determinar a alteraçäo dimensional porcentagem e porosidade de resina acrílica para bases de dentaduras. Para a alteraçäo dimensional as variáveis foram: 1) iniciar a polimerizaçäo imediatamente após a prensagem ou 24 horas após; 2) condensar a resina nas fases borrachóide, plástica e pegajosa; 3) determinar as alteraçöes após desinclusäo, e 2 e 8 semanas após imersäo em água; 4) medidas feitas ao longo de diferentes locais entre dentes. Para o estudo da porosidade foram empregadas as variáveis (1) e (2) e mais as espessuras dos blocos polimerizados (0,5; 1,0; 2,0 e 3,0cm). Dos resultados foi possível concluir que: iniciar a polimerizaçäo imediatamente após a prensagem ou 24 horas depois, näo influiu na magnitude da contraçäo, mas a imediata conduz mais facilmente à formaçäo de porosidade; a fase borrachóide näo conduziu a maior contraçäo que a plástica e quanto à porosidade tende a diminuí-la; a imersäo após semanas recupera parte da contraçäo de polimerizaçäo; a contraçäo varia com o local entre dentes; com polimerizaçäo após 24 horas, a manifestaçäo de porosidade é menor

Polimento químico e desgaste superficial de bases de resina acrílica para dentaduras / Chemical polishing and wear on the superfical basic of acrilic resins for dentures

The influence of the chemical polishing on superficial wear acrylic resin samples was observed. Denture bases and total crowns polished samples were analysed by comparison microscope. The results showed there were superficial wear significant in every samples, independently of the materials activations type