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AIM: This study verified the effect of polymerizing cycles on the linear dimensional change, hardness and impact strength of denture acrylic resins. METHODS: One hundred and twenty samples (N.=10) each for the Classico and Vipi acrylic resins were made according to the manufacturers' instructions. The polymerization cycles were: 1- water bath at 74 ºC for 9 hr; 2- water bath at 74ºC for 8 hr and temperature increased to 100 ºC for 1 hr; 3- water bath at 74 ºC for 2 hr and temperature increased to 100 ºC for 1 hr; and 4- water bath at 120ºC and 60 pounds pressure for 1 hr. Samples were deflasked after flask cooling and submitted to finishing. Linear distances between referential points in the samples were measured at deflasking and after water storage for 7 and 30 days with a comparator microscope with an accuracy of 0.0005 mm. Knoop hardness test was accomplished in a durometer with a load of 25 gf for 10 sec and an average of three indentations was considered for the sample hardness. Impact strength (kgf/cm²) was measured by the Charpy system with load of 40 kpcm. Data were submitted to ANOVA and Tukey's test (5%). RESULTS: Dimensional changes in the A-B and A-C distances, hardness values and impact strength for Classico and Vipi resins were differently influenced by the polymerization cycles, when deflasking and water storage for 7 and 30 days were considered. CONCLUSION: Linear dimensional change, hardness and impact strength of denture acrylic resins were differently affected by the polymerization cycles.

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AIM: This study evaluated the temperature change into the pulp chamber during the light curing of composite resin by direct (bovine tooth) and indirect (matrix) methods. METHODS: Direct method: fifty standardized cavities (2x2x2 mm) were prepared in bovine incisors, which were randomly assigned to evaluation of the temperature changes in the pulp chamber. Indirect method: temperature changes were evaluated through a dentine slice of 1.0 mm thickness in a elastomer cubic mold (2x2x2 mm). Filtek Z250 composite resin (3M/ESPE) was photo-activated using three light curing units: quartz-tungsten-halogen (QTH) by continuous, soft-start or intermittent light modulations; light emitting diode (LED); and plasma arc-curing (PAC). Ten groups (N.=10) were established according to technique evaluation and photo-activation methods. All experiments were carried out in a controlled environment (37 °C and 50 ± 10% relative humidity). The temperature changes were recorded using a digital thermometer attached to a type-K thermocouple in contact with the dentin slice (indirect method) or in contact with the axial wall (dentin) of pulp chamber (direct method). The results were submitted to ANOVA and Tukey's test (α=0.05). RESULTS: Temperature changes were statistically higher for the matrix indirect method (2.56 ºC) than bovine teeth direct method (1.17ºC). The change temperature was statistically higher for the PAC (1.77 ºC) when compared to other photo-activation modes in bovine teeth direct method. CONCLUSION: The two methods of temperature evaluation were different, however indirect method detected the higher temperature increase. Higher energy density arising from the light curing units and polymerization techniques promoted higher temperature increase.

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The purpose of this study was to evaluate the influence of height of healing caps and the use of soft liner materials on the stress distribution in peri-implant bone during masticatory function in conventional complete dentures during the healing period by using finite element analysis. Three-dimensional models of a severely resorbed mandible with two recently placed implants in the anterior region were created and divided into the following situations: (i) submerged implants, (ii) healing cap at gingival level and (iii) 1·5-mm supragingival. All these situations were also analysed for a conventional complete denture and a denture relined with a 3-mm-thick layer of soft liner material. The models were exported to mechanical simulation software that presented two simulations, one with load in the inferior right canine (35 N) and the other in the inferior right first molar (50 N). Data were evaluated using Maximum Principal Stress provided by the software. All models showed a stress concentration in the cortical bone corresponding to the cervical part of the implant. The simulations with non-submerged implants showed higher values of stress concentration than those that were submerged. Likewise, soft liner materials presented better results than when the denture base was not relined. The height of the healing caps seems to have a direct influence on the stress distribution in the peri-implant bone during the healing period. Considering the values obtained in this study, the use of soft liners with submerged implants seems to be the most suitable method to use during the period of osseointegration.

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AIM: This study verified the effect of the monomer/polymer proportion on the base adaptation of the complete upper dentures. METHODS: Thirty stone cast-wax baseplate sets were packed in metallic flasks and the acrylic resin polymerized in water at 74 °C for nine hours. Three transverse cuts were made through each stone cast-resin base set, corresponding to regions: A) canines (anterior); B) first molars (median), and C) posterior palate (posterior). Measurements were made using an optical micrometer at five points for each cut to determine base adaptation: left and right marginal limits of the flanges, left and right ridge crests, and midline. Data were analyzed using to ANOVA and Tukey's test (5%). RESULTS: In region A there was significant difference among the monomer-polymer proportions, with a greater value of misfit for the content -25% monomer group and lower for the manufacturer's proportion group. In region B there was significant difference between the manufacturer's content (lowest value) and the monomer contents of +25% and -25% (both statistically similar). In region C there was significant difference among the monomer-polymer proportions, with greater value for the -25% monomer group than for the manufacturer's proportion. There was significant difference when the regions were compared in relation to the same monomer content. The best adaptation was in the region A and the worst in the region C. CONCLUSION: The amount of monomer exerted different effects on the adaptation of the denture base. In all regions, the smallest misfit was observed when the manufacturer's recommended proportion was used and the greatest misfit was observed in the -25% monomer.

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PURPOSE: This study investigated the tooth movement of standardized simulated dentures processed by traditional closure or the new Rafael Saide (RS) tension system when cooled in the curing water itself or in curing water followed by bench storage for 3 hours. MATERIALS AND METHODS: Forty stone casts were formed from a mold of an edentulous maxillary arch. The wax denture record bases were made on the casts; the height of the wax rim occlusion was 20 mm in the labial sulcus of the cast and 10 mm in the posterior region. The upper stone cast was mounted on a Mondial 4000 semi-adjustable articulator with wax rim interocclusal references in relation to the lower stone cast teeth. Metallic pins were placed in the incisal border of the maxillary central incisors (I), labial cusp of the first premolars (PM), and mesiolabial cusp of the second molars (M). The incisor-to-incisor (I-I), premolar-to-premolar (PM-PM), and molar-to-molar (M-M) transversal distances and left incisor-to-left molar (LI-LM), and right incisor-to-right molar (RI-RM) anteroposterior distances were measured before and after denture polymerization with an optical microscope with a tolerance of 0.0005 mm. For traditional closure, the dentures were flasked conventionally in standard metallic flasks, which were afterward placed in spring clamps. For the new RS system closure, the flasks were pressed between the metallic plates of the tension system after the final closure. The Clássico heat-polymerizing acrylic resin dough was packed in the flasks under a final packing pressure of 1.250 kg f. Twelve hours after flask closure, the dentures were polymerized in a moist heat-polymerizing cycle for 9 hours at 74 degrees C. The denture was deflasked after cooling in the water of the polymerizing cycle (groups A and C) or in the water of the polymerizing cycle and then bench-stored for 3 hours (groups B and D). Collected data were analyzed with analysis of variance and Tukey's test (p< 0.05). RESULTS: There was no statistically significant difference (p> 0.05) between the conventional and new RS system closure methods for the transversal distances after polymerization in all studied groups. The anteroposterior distances did not change with deflasking after water bath cooling. There were statistically significant differences (p< 0.05) in the anteroposterior distances with deflasking after water bath cooling and then bench storage for 3 hours. CONCLUSION: Tooth movement was similar in dentures processed by traditional closure and by the new RS tension system, with the exception of the anteroposterior distances when the flasks were cooled in their own curing water and bench-stored for 3 hours.

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O objetivo deste estudo foi avaliar o efeito de duas técnicas de inserção do compósito sobre o nível de infiltração marginal na interface dente/compósito restaurador. Foram preparadas 40 cavidades circulares medindo 4 mm de diamêtro por 3 mm de profundidade em dentes bovinos, que foram divididos em 4 grupos (n=10): Grupo 1 - Único encremento + P60; Grupo 2 - Único encremento + Definite; Grupo 3 - Três incrementos + P60 ; e Grupo 4 - Três incrementos + Definite. Todas as amostras foram armazenadas em água destilada a 37°C, por 24 horas e submetidas a 500 ciclos térmicos (5° e 55°) por 30 segundos em cada banho. Em seguida, os dentes foram imersos em solução de azul de metileno a 2 por cento, por 4 horas, e a microinfiltração avaliada. Os resultados submetidos ao teste estatístico de Kruskal-Wallis mostraram que a técnica de inserção em 3 incrementos para o Definite com 1 incremento; o P60 com 3 incrementos apresentou níveis de infiltração marginal estatisticamente menores em relação ao P60 e Definite, ambos com 1 incremento

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The dimensional alterations of denture bases were verified in function of the acrylic resin post-pressing time. Twenty stone cast/wax base sets were confected for routine flasking procedure. Thermosetting acrylic resin (Clássico) was prepared according to the instructions of the manufacturer. After final pressing, the acrylic resin was submitted to polymerization in water at 74 degrees C during 9 hours, following the immediate, 6-, 12-, and 24-hour post-pressing times. The resin bases were fixed on the casts with instantaneous adhesive and the sets were laterally sectioned in the regions corresponding to the distal aspect of canines (A), mesial aspect of first molars (B), and posterior palatal zone (C). The gap between the stone cast and the resin base was measured with a comparative microscope at five referential positions for each kind of sectioning. Data submitted to ANOVA and Tukey's test showed that there was no statistically significant difference between the immediate and the 6-hour post-pressing times as well as between the 12- and the 24-hour post-pressing times. However, there was statistically significant difference between the immediate/6-hour groups and the 12-/24-hour groups.

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