This study investigated the diffusion kinetics of a nanofilled (Filtek Z350) and a midifill (Filtek P60) resin composite immersed in distilled water, artificial saliva and lactic acid. Resin composite specimens were desiccated, immersed in the media, weighed at suitable time intervals until they reached sorption equilibrium and were then desiccated again. Sorption and solubility (µg/mm(3)) were calculated based on ISO 4049:2000(E). The diffusion coefficient (m(2).s(-1)) was determined according to Flick's second law. The degree of conversion (DC%) was evaluated by FT-IR and the action of the media on the surfaces of the resin composite was evaluated by SEM. Z350 immersed in lactic acid presented the highest sorption (25.9 ± 1.3). The highest solubility was presented by Z350 immersed in lactic acid (5.6 ± 0.9), followed by P60 immersed in lactic acid (4.4 ± 0.5). The other groups presented no significant difference among them. The diffusion coefficients of both resin composites immersed in lactic acid and that of Z350 immersed in artificial saliva were significantly higher. The lowest diffusion coefficient was presented by P60 immersed in distilled water. The DC% was not significant, (p > 0.05). The SEM analysis showed that the effect of lactic acid on the resin composites was more deleterious than those of water and artificial saliva.
This study investigated the relationship between the solubility, salivary sorption, and degree of conversion of dimethacrylate-based polymeric matrixes. Six polymeric matrixes produced by mixing bis-GMA, TEGDMA and UDMA dimethacrylate monomers were studied. Photoactivation was induced by camphoroquinone/ethyl N,N-dimethyl-4-aminobenzoate. The specimens were light-cured using an irradiance of 850 mW/cm(2) for 20 s. The solubility and sorption (microg/mm(3)) were measured after immersion in artificial saliva (neutral pH) for 7 days. The degree of conversion (%) was obtained by using a FT-IR spectrometer equipped with an attenuated total reflectance crystal (ATR). The degree of conversion varied from 39.15 +/- 6.30 to 65.57+/- 4.80, and was influenced by the viscosity of the monomers present in the polymeric matrixes. The solubility of polymeric matrixes varied between 13.64 +/- 0.39 and 25.08 +/- 0.83, and was strongly influenced by the degree of conversion (Pearson, r = -0.9587, p < 0.01). No correlation was found between salivary sorption and the degree of conversion (p = 0.3918). Salivary sorption was only dependent on the chemical and physical structures of the monomers presented in the polymeric matrixes.
The aim of this study was to analyze the sorption and solubility of a nanofilled (Filtek Z350) and a midifilled (Filtek P60) resin composite in oral environment-like substances, in a simulated deep cavity. A cylindrical cavity prepared in a bovine incisor root was incrementally filled with resin composites. The obtained resin composite cylinders were cut perpendicularly to the axis to obtain 1-mm-thick discs that were divided into fifteen groups (n=5) according to depth (1, 2, 3, 4 and 5 mm) and immersion media (distilled water - DW, artificial saliva - AS and lactic acid - LA). The sorption and solubility were calculated based on ISO 4049:2000. Additionally, the degree of conversion (DC%) was calculated by FT-IR spectroscopy. Data were analyzed using multifactor analysis of variance (MANOVA) followed by Tukey's HSD post-hoc test and linear regression analysis (a=0.05). The DC% was higher for the midifilled resin composite and was negatively influenced by cavity depth (p<0.05). The nanofilled resin composite presented higher sorption and solubility than did the midifilled (p<0.05). The immersion media influenced the sorption and the solubility as follows: LA>AS>DW, (p<0.05). Both phenomena were influenced by cavity depth, with the sorption and solubility increasing from 1 to 5 mm (p<0.05). The degradation of resin composite restorations may be greater in the deepest regions of class II restorations when the composite is exposed to organic acids present in the oral biofilm (lactic acid).
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