Effect of organic acids in dental biofilm on microhardness of a silorane-based composite

OBJECTIVES: This study evaluated the effect of lactic acid and acetic acid on the microhardness of a silorane-based composite compared to two methacrylate-based composite resins. MATERIALS AND METHODS: Thirty disc-shaped specimens each were fabricated of Filtek P90, Filtek Z250 and Filtek Z350XT. After measuring of Vickers microhardness, they were randomly divided into 3 subgroups (n = 10) and immersed in lactic acid, acetic acid or distilled water. Microhardness was measured after 48 hr and 7 day of immersion. Data were analyzed using repeated measures ANOVA (p < 0.05). The surfaces of two additional specimens were evaluated using a scanning electron microscope (SEM) before and after immersion. RESULTS: All groups showed a reduction in microhardness after 7 day of immersion (p < 0.001). At baseline and 7 day, the microhardness of Z250 was the greatest, followed by Z350 and P90 (p < 0.001). At 48 hr, the microhardness values of Z250 and Z350 were greater than P90 (p < 0.001 for both), but those of Z250 and Z350 were not significantly different (p = 0.095). Also, the effect of storage media on microhardness was not significant at baseline, but significant at 48 hr and after 7 day (p = 0.001 and p < 0.001, respectively). Lactic acid had the greatest effect. CONCLUSIONS: The microhardness of composites decreased after 7 day of immersion. The microhardness of P90 was lower than that of other composites. Lactic acid caused a greater reduction in microhardness compared to other solutions.

Comparison of Silorane and Methacrylate-Based Composites on the Polymerization Heat Generated with Different Light-Curing Units and Dentin Thicknesses

This study evaluated the temperature variation in the pulp chamber during photoactivation of two restorative composite resins (Filtek P90 silorane-based composite and Heliomolar methacrylate-based composite) with either a quartz-tungsten-halogen (QTH) or light-emitting diodes (LED) light-curing unit (LCU) and using dentin thicknesses (0.5 and 1.0 mm). Standardized cavities (2x2x2 mm) were prepared in 80 bovine incisors, which were randomly assigned to 8 groups according to the photoactivation method and dentin thickness. Filtek P90 and Heliomolar (both in shade A3) were used with their respective adhesive systems (P90 self-etch primer / P90 adhesive bond and Excite adhesive). All experiments were carried out in a controlled environment (37°C). The temperature variations (°C) were recorded using a digital thermometer attached to a K-type thermocouple. The results were analyzed statistically by ANOVA and Tukey's test (α=0.05). For composite/dentin thickness interaction, temperature increase was significantly higher in 0.5 mm dentin thickness (40.07°C) compared with 1.0 mm dentin thickness (39.61°C) for Filtek P90. For composite/LCU interaction, the temperature increase was significantly higher for Filtek P90 (39.21°C - QTH and 40.47°C - LED) compared with Heliomolar (38.40°C - QTH and 39.30°C - LED). The silorane-based composite promoted higher temperature increase in the pulp chamber than the methacrylate-based composite.

Este estudo avaliou a variação de temperatura na câmara pulpar durante a fotoativação de duas resinas compostas (Filtek P90 – compósito à base de silorano e Heliomolar – compósito à base de metacrilato) com as unidades foto-ativadoras (UFs) luz de quartzo-tungstênio-halogênio (QTH) ou diodo emissor de luz (LED) e utilizando espessuras de dentina (0,5 e 1,0 mm). Cavidades padronizadas (2×2×2 mm) foram preparadas em 80 incisivos bovinos, as quais foram aleatoriamente divididas em 8 grupos de acordo com os métodos de fotoativação e espessura da dentina. Filtek P90 e Heliomolar (ambos na cor A3) foram utilizadas com seus respectivos sistemas adesivos (Primer P90 auto-condicionante / adesivo P90 e adesivo Excite). Todos os experimentos foram realizados em um ambiente controlado (37°C). As variações de temperatura (°C) foram mensuradas usando um termômetro digital conectado a um termopar tipo-K. Os resultados foram analisados estatisticamente por ANOVA e teste de Tukey (α=0,05). Para interação compósito/espessura de dentina, o aumento da temperatura foi estatisticamente superior para a espessura de dentina de 0,5 mm (40,07°C) quando comparado com a espessura de dentina de 1,0 mm (39,61°C) para a Filtek P90. Para a interação compósito/UFs, o aumento de temperatura foi estatisticamente superior para o Filtek P90 (39,21°C – QTH e 40,47°C – LED) quando comparado ao Heliomolar (38,40°C – QTH e 39,30°C – LED). Compósitos à base de silorano promovem maior aumento da temperatura na câmara pulpar em relação aos compósitos à base de metacrilato.

Comparison of silorane and methacrylate-based composite resins on the curing light transmission

The aim of this study was to investigate the influence of different composite resins - Filtek P90 (silorane-based composite) and Heliomolar (methacrylate-based composite) - on light transmission and decrease in Knoop hardness between the bottom and top of cured specimens. The irradiance of a light-curing unit (LCU) was measured with a power meter (Ophir Optronics; 900 mw/cm2) and spectral distributions were obtained using a spectrometer (USB 2000). Twenty standardized cylindrical specimens (2 mm thick x 7 mm diameter) of each composite resin were obtained by curing using the LCU for 40 s. Light energy transmission through the composite was calculated (n=10). The Knoop hardness number for each surface was recorded as the mean of 3 indentations. The difference in Knoop hardness between the top and bottom (DKH) of the same specimen was calculated (n=10). The irradiance of light that passed through Filtek P90 (272 mW/cm2) was not significantly greater than that the passed through Heliomolar (271 mW/cm2). The DKH of Filtek P90 (25 percent) was significantly higher than that of Heliomolar (12 percent). There was a greater degree of subsurface polymerization of the methacrylate-based composite compared to the silorane-based composite.

O objetivo deste estudo foi avaliar a influência da diferença entre a dureza do topo e da base em compósitos restauradores. Foram utilizados os compósitos restauradores Filtek P90 (compósito à base de silorano) e Heliomolar (compósito à base de metacrilato). A irradiância da unidade foto-ativadodora (UF) foi mensurada com um potenciômetro Ophir Optronics (900 mw/cm2) e o espectro de luz foi obtido usando um espectrofotômetro (USB 2000). Vinte espécimes cilíndricos padronizados (2 mm de espessura por 7 mm de diâmetro) foram obtidos pela fotoativação utilizando UF (40 s) para cada compósito. A irradiância que passou através do compósito foi mensurada (n=10). O número de dureza Knoop para cada superfície foi calculado pela média de 3 penetrações. A diferença da dureza Knoop entre o topo e base (DDK) de um mesmo espécime foi calculada (n=10). A irradiância que passou através da Filtek P90 (272 mW/cm2) não foi estatisticamente superior a Heliomolar (271 mW/cm2). A DDK da Filtek P90 (25 por cento) foi estatisticamente superior a Heliomolar (12 por cento). O compósito a base de metacrilato apresentou melhor grau de polimerização na base quando comparado ao compósito à base de silorano.