Effect of double flasking and investing methods on artificial teeth movement in complete dentures processing.

PURPOSE: The aim of this study was to evaluate linear dimensional alterations of artificial teeth for complete dentures when using different investment and flasking techniques. BACKGROUND: Dimensional changes in the vertical dimension may occur owing to changes in artificial teeth positioning caused by different investing and flasking techniques. MATERIALS AND METHODS: Thirty pairs of the complete dentures were manufactured and randomly divided into three groups (n = 10): (1) invested with type III stone in monomaxillary PVC flask; (2) invested with type III stone in bimaxillary PVC flask; and (3) invested with laboratory silicone in bimaxillary PVC flask. Dentures were polymerised by microwave, and 12 linear distances were measured before and after denture processing. Data were analysed by one-way anova, considering manufacturing technique as the study factor. Tukey's HSD was used as post hoc ANOVA (p = 0.05). RESULTS: Most of the linear distances were comparable for all groups. All transversal maxillary and mandibular distances were higher for group 1 compared with groups 2 and 3 (p < 0.05), except the distance 3-6 for mandibular arch, in which no difference was found between groups (p < 0.05). Both maxillary diagonal distances were higher in group 1 (p < 0.05), and no differences were found among all groups for mandibular measurements. CONCLUSIONS: Double flasking technique independent on the investment material is shown to be the most effective method to reduce changes in artificial teeth positioning.

Water sorption of heat-polymerized acrylic resins processed in mono and bimaxillary flasks.

This study evaluated water sorption in heat-polymerized acrylic resins processed in monomaxillary flasks by water bath and in bimaxillary flasks by microwave energy and water bath. Fifty heat-polymerized acrylic resin specimens were fabricated according to the 12th specification of the American Dental Association and assigned to 3 groups: group 1 was processed by water bath in monomaxillary metallic flask; group 2 was processed by microwave energy in bimaxillary PVC flask; and group 3 was processed by water bath in bimaxillary metallic flask. Specimens were submitted to water sorption test, means were calculated and analyzed statistically by Student's t-test. Means (in g/cm3) were: group 1--0.024085, group 2--0.025312 and group 3--0.022098. Microwave energy processing and the amount of stone and resin used in the bimaxillary PVC flask did not influence water sorption; specimens processed in bimaxillary metallic flask by water bath presented lower water sorption means, suggesting an inadequate polymerization of the acrylic resin mass.

Water sorption of heat-polymerized acrylic resins processed in mono and bimaxillary flasks

A finalidade deste estudo foi avaliar a sorção de água de resinas acrílicas ativadas termicamente quando processada em mufla monomaxilar para banho de água e mufla bimaxilar para banho de água e microondas. Foram confeccionados 50 corpos-de-prova de resina acrílica ativada termicamente de acordo com a especificação nº 12 da American Dental Asociation, divididos em três grupos: no grupo 1, os corpos-de-prova foram processados em mufla monomaxilar metálica para banho de água; no 2 foram processados em mufla bimaxilar de PVC para uso em microondas e no 3 foram processados em mufla bimaxilar metálica para banho de água. Os corpos-de-prova foram submetidos ao ensaio de sorção de água, os valores médios foram calculados e analisados pelo teste t de Student. Os valores obtidos (g/cm3) foram: grupo 1 - 0,024085, grupo 2 - 0,025312 e grupo 3 - 0,022098. A polimerização da resina acrílica por energia de microondas na mufla bimaxilar de PVC não influenciou a sorção de água em relação ao processamento em muflas monomaxilares, enquanto a polimerização feita em muflas bimaxilares metálicas aquecidas em banho de água diminuiu esse índice, sugerindo inadequada polimerização da massa de resina.

Surface roughness of acrylic resins processed by microwave energy and polished by mechanical and chemical process

The aim of this study was to evaluate the influence of polymerization methods (microwave energy - MW, and water bath - WB) and polishing techniques (chemical - C and mechanical - M) on the surface roughness of one heat-polymerized acylic resin (Vipi-Cril). Forty acrylic resin disk-shaped samples were made according to ADA specification nº 12. Half of samples were processed by microwave energy (500W for 3 minutes), and the other half by water bath (74±1 ºC for 9 hours). After deflasking, the samples were trimmed with a sequence of abrasive aluminum oxide sandpapers of different grades (180, 220 and 400) and divided in 4 groups according to polymerization methods and polishing techniques: G1: MW+CP, G2: MW+MP, G3: WB+CP and G4: WB+MP. Surface roughness values were measured using a Surfcorder SE 1700 rugosimeter (Kosaka Laboratory Ltd, Kosaka, Japan). Mann-Whitney test (p=.05) indicated significant differences between polishing methods processed by microwave energy (p= .0018), and between polishing methods processing by water bath (p= .0002). Samples processed by both methods (water bath or microwave energy) showed smoother surfaces when polished by mechanical polishing method, and polymerization methods did not influence in surface roughness.

Influence of mechanical and chemical polishing in the solubility of acrylic resins polymerized by microwave irradiation and conventional water bath.

OBJECTIVES: The aim of this work was to evaluate the solubility of acrylic resin activated by microwave irradiation (MI) or water bath (WB), when submitted to chemical (CP) or mechanical (MP) polishing. METHODS: Forty acrylic resin samples were made and processed either by water bath (74 +/- 1 degrees C, 9 h) or microwave irradiation (500 W, 3 min). After deflasking, the samples were finished with aluminum oxide sandpapers in decreasing granulations till reaching similar dimensions. The samples were divided into four groups according to the association between kind of polymerization and polishing: A (WB + CP), B (WB + MP), C (MI + CP) and D (MI + MP). Solubility test was performed for each group and percentile solubility was calculated. Data were statistically analyzed using variance analysis and Kruskal-Wallis. RESULTS: The average of percentile solubility (%) was obtained: A = 0.07, B = 0.02, C = 0.04, D = -0.14, however, no significant difference was found between types of polishing in the samples polymerized by water bath (A and B). When processed by microwave irradiation (C and D), there was significant difference between the applied methods of polishing, so that mechanical polishing lead to a lower solubility. SIGNIFICANCE: Solubility is a property of acrylic resins, representing not reacted substances releasing that could promote tissular reactions in prosthesis users. The association between polymerization by microwave irradiation and mechanical polishing showed less residual substances releasing for heat-cured acrylic resins, reducing the probability of developing tissular reactions.