Resistencia a la compresión de resinas compuestas a base de metacrilato y de silorano / Compressive strength of a silorane-based and a methacrylate-based composite resin

Objetivo: el objetivo de este estudio fue comparar la resistencia a la compresión de resinas compuestas a base de silorano y a base de metacrilato. Materiales y métodos: treinta muestras con formato de disco, fueron confeccionadas insertando las resinas, de forma incremental, en una matriz de aluminio (10 cm de diámetro x 15 mm de alto). El tiempo de fotoactivación de cada incremento fue de 20 segundos (Filtek P60, 3M ESPE) y 40 segundos (Filtek P90, 3M ESPE), utilizando una lámpara de luz halógena a 500 mW/cm2. LUego de ser almacenadas en agua destilada a 23 +- 2ºC y 50 +-5 por ciento de humedad relativa durante 40 horas, las muestras fueron sometidas al test de resistencia a la compresión, en una máquina de ensayos universal (1,3 mm/min). Los datos (en MPa) fueron analizados estadísticamente mediante ANOVA y prueba de Tukey (alfa=0,05). Resultados: los valores de resistencia a la compresión de P60 fueron estadísticamente superiores a los de P90 (P60=371,91 +- 58,76; P90=264,41+-30,33). Conclusión: las resinas compuestas a base de silorano presentaron los valores más bajos de resistencia a la compresión.

Resistencia a la compresión de resinas compuestas a base de metacrilato y de silorano / Compressive strength of a silorane-based and a methacrylate-based composite resin

Objetivo: el objetivo de este estudio fue comparar la resistencia a la compresión de resinas compuestas a base de silorano y a base de metacrilato. Materiales y métodos: treinta muestras con formato de disco, fueron confeccionadas insertando las resinas, de forma incremental, en una matriz de aluminio (10 cm de diámetro x 15 mm de alto). El tiempo de fotoactivación de cada incremento fue de 20 segundos (Filtek P60, 3M ESPE) y 40 segundos (Filtek P90, 3M ESPE), utilizando una lámpara de luz halógena a 500 mW/cm2. LUego de ser almacenadas en agua destilada a 23 +- 2ºC y 50 +-5 por ciento de humedad relativa durante 40 horas, las muestras fueron sometidas al test de resistencia a la compresión, en una máquina de ensayos universal (1,3 mm/min). Los datos (en MPa) fueron analizados estadísticamente mediante ANOVA y prueba de Tukey (alfa=0,05). Resultados: los valores de resistencia a la compresión de P60 fueron estadísticamente superiores a los de P90 (P60=371,91 +- 58,76; P90=264,41+-30,33). Conclusión: las resinas compuestas a base de silorano presentaron los valores más bajos de resistencia a la compresión.(AU)

Color stability of resins and nylon as denture base material in beverages.

PURPOSE: Staining of prosthodontic materials may result in patient dissatisfaction and additional expense for replacement. This study aimed to determine the color stability of two heat-cured denture base acrylic (Lucitone 550, Vipi Cril) and one nylon denture base resin (Transflex) after immersion in beverages. MATERIALS AND METHODS: Forty disks of each resin (20.0-mm diameter, 3.0-mm thick) were prepared and stored in distilled water for 24 hours at 37°C. During that time (T(0) ), the color of all specimens was spectrophotometrically measured. Each specimen was immersed in coffee, cola, red wine, and distilled water as a means of control. After 15-day (T(1) ) and 30-day (T(2) ) periods of immersion, the color of the specimens was measured again. The CIE (Commission Internationale de L' Eclairage) L*a*b* system was used to determine mean ΔE (color changes) values for each material and compared statistically with two-way ANOVA and Bonferroni intervals at 0.95. RESULTS: In ΔET(0) T(1) and ΔET(0) T(2) the most severe staining was apparent with red wine (p < 0.001), followed by coffee (p < 0.01), when compared to the specimens stored in distilled water. Transflex also showed significant color change after immersion in cola (p < 0.01). In ΔET(1) T(2) only red wine promoted significant staining of all resins (p < 0.0001). CONCLUSION: Chromatic changes were exhibited by specimens immersed in red wine, followed by coffee. For Transflex, cola also promoted color changes. The values of color changes converted to National Bureau of Standard units showed them to be perceivable to the human eye.

Reducing the incompatibility between two-step adhesives and resin composite luting cements.

PURPOSE: To determine whether the adverse interaction between a two-step/acidic etch-and-rinse adhesive (One-Step Plus [OS], Bisco) and chemically cured resin luting cement [Variolink II, Ivoclar Vivadent] can improve adhesive coupling by reducing the dentin permeability with an oxalate desensitizer (BisBlock, Bisco). MATERIALS AND METHODS: After exposing dentin on the occlusal surfaces of human third molars, bonding was performed on either oxalate treated (BB) or nontreated (NB) demineralized dentin. A resin luting cement was placed in the format of a crown following the light-curing mode (only with the base syringe [LC]) or the chemically curing mode (mixture of base and catalyst syringes [CC]). The activation of the LC or CC cements was either immediately [IM], meaning soon after the placement of LC and the initial set of CC cement (5 min), or after a delay of 20 min [DP] for both modes of polymerization. Five teeth were assigned to each experimental condition. Teeth were sectioned to obtain sticks with a cross-sectional area of 0.95 mm2, which were tested using the microtensile bond strength test soon after the specified periods of polymerization. The bond strength values of each adhesive were analyzed by three-way repeated measures ANOVA and Tukey's tests (α = 0.05). Fractographic analysis of the specimens was performed using SEM. RESULTS: The delayed polymerization (for both LC and CC cements) produced low bond strength values compared to IM activation. When the BB was employed, the bond strength values of the CC cement was approximately doubled, while the BB did not affect the bond strength of the LC cement. Bond strength values of LC cements were higher than CC. The use of BB significantly improved the bond strength of CC cement only. The morphological observations confirmed the bond strength results. A myriad of voids could be detected in the luting cement side when BB was not applied, except for the immediately light-cured group. CONCLUSION: The use of an oxalate desensitizer (BisBlock) reduced the incompatibility between a two-step etch-and rinse adhesive and chemically cured resin cements and light-cured systems in the delayed polymerization mode.

Incompatibilidade entre sistemas adesivos simplificados e cimentos resinosos/resinas compostas / Incompatibility between simplified adhesive systems and resin cement/composite resin

Evidência científica demonstram que, quando sistemas adesivos simplificados são associados a cimentos de ativação química ou de dupla ativação - na qual a ativação química é essencial -, bem como no caso de uso de resinas compostas nas técnicas de polimerização lenta, pode ocorrer incompatibilidade química e física. Várias manobras podem minimizar esta incompatibilidade, entre elas destacam-se: 1) uso de co-iniciadores nas soluções adesivas para polimerização química; 2) uso de agentes que diminuam a permeabilidade dentinária; 3) uso de múltiplas camadas de adesivo; 4) aumento do tempo de fotoativação; 5) conversão de adesivos simplificados em adesivos não-simplificados, por meio do uso de uma camada de adesivo hidrófoba; e 6) uso da técnica de selamento imediato ou técnica da "cobertura com resina". A técnica de selamento imediato é a de melhor custo-benefício, pois bloqueia a incompatibilidade física e química do cimento resinoso utilizado para o procedimento de cimentação e diminui a contaminação bacteriana e irritação da polpa, aumentando a união das peças protéticas à dentina.