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Abstract
The influence of curing tip distance and storage time in the kinetics of water diffusion (water sorption-W SP, solubility-W SB, and net water uptake) and color stability of a composite were evaluated. Composite samples were polymerized at different distances (5, 10, and 15 mm) and compared to a control group (0 mm). After desiccation, the specimens were stored in distilled water to evaluate the water diffusion over a 120-day period. Net water uptake was calculated (sum of WSP and WSB). The color stability after immersion in a grape juice was compared to distilled water. Data were submitted to three-way ANOVA/Tukey's test (α = 5%). The higher distances caused higher net water uptake (p < 0.05). The immersion in the juice caused significantly higher color change as a function of curing tip distance and the time (p < 0.05). The distance of photoactivation and storage time provide the color alteration and increased net water uptake of the resin composite tested.
Highlights
Recent improvements in resin-based dental materials have focused on the longevity of restorations considering the mechanical resistance and their chemical stability
This study evaluated the influence of different curing tip distances in the kinetics of water diffusion and in the color stability of a commercial BisEMA-based resin composite
No significance was noted when the polymerization was performed at 5 mm in comparison to the control group (p > 0.05)
Summary
Recent improvements in resin-based dental materials have focused on the longevity of restorations considering the mechanical resistance and their chemical stability. Water absorption was previously deemed beneficial to filling materials, as the consequent swelling was believed to compensate for polymerization shrinkage[6]. Absorbed water is known to result in internal strains, facilitating the extraction of free monomers or polymerization residues in resin-based materials. Water molecules can be clustered[7,8] inducing a plasticization effect and softening of the surrounding matrix (that is, a lowering of the elastic modulus)[9]. Water is responsible for chemical decomposition, such as the oxidation and hydrolysis of the resin matrix[10]. Hardness was found to be negatively influenced by both curing tip distance and storage time[11]
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