Water sorption/desorption in polyacid-modified composite resins for dentistry

Area of Science:

• Dental Materials Science
• Polymer Chemistry
• Physical Chemistry

Background:

• Polyacid-modified composite resins are widely used in restorative dentistry.
• Understanding their water sorption and desorption is crucial for predicting clinical performance and longevity.
• Previous research has focused on conventional composites, but less is known about polyacid-modified variants.

Purpose of the Study:

• To investigate the water sorption and desorption characteristics of three commercial polyacid-modified composite resins.
• To compare the diffusion rates and equilibration times between initial and subsequent water uptake cycles.
• To determine if hydrophilic components enhance water transport compared to conventional composites.

Main Methods:

• Cured specimens of three polyacid-modified composite resins were subjected to controlled water uptake and desorption cycles.
• Water sorption was conducted at 93% relative humidity, and desorption occurred over concentrated sulfuric acid.
• Specimen weight changes were monitored to determine diffusion rates and equilibration times, analyzed using Fick's law.

Main Results:

• Specimens followed Fick's law for water sorption and desorption up to approximately 0.5 of equilibrium moisture content.
• Second water uptake cycles showed significantly higher diffusion rates (0.85–2.72 x 10⁻⁸ cm²/s) compared to the first cycle (2.37–4.53 x 10⁻⁹ cm²/s).
• Desorption rates were comparable to second cycle sorption rates, and equilibration times were shorter for subsequent cycles.

Conclusions:

• The water transport behavior of polyacid-modified composites in high humidity is similar to conventional composites in water.
• The hydrophilic components in these materials do not appear to accelerate the rate of water transport.
• The findings suggest that water diffusion is not significantly enhanced by the polyacidic nature of these resins.