Difference in water accumulation patterns between solid and closed hollow obturators under a thermal cycle

Water accumulation in the hollow space of a maxillary obturator is a continuing problem, and it is unclear whether the porosity of acrylic resin is involved in the mechanism. The purposes of the study were to evaluate the effect of a hollow space in the resin obturator on water sorption under a thermal cycle and to determine factors associated with water accumulation in the obturator. Twenty solid spheres (30-mm diameter) and 40 hemispheres (30-mm diameter, 1.5 mm thickness) were fabricated from heat-polymerized acrylic resin. Closed hollow specimens consisted of 2 hemispheres joined with autopolymerizing resin. Ten solid and 10 closed hollow specimens were immersed in distilled water, whereas the other specimens were stored at 100% relative humidity. Each specimen was thermocycled (5°CY37°C) with a dwell time of 12 hours and weighed every 12 hours for 180 days. Of the 20 closed hollow specimens, 16 showed no water accumulation (8 in distilled water, 8 at 100% humidity). The weight of these specimens became saturated by day 90, with increases fromthe initialweight of 1.41%at 5°Cand 1.36%at 37°C. By day 180, the weights of the solid specimens had increased by 0.96% at 5°C and 0.94% at 37°C. Weight fluctuation associated with temperature was observed for both types of specimens and for all storage conditions. It is concluded that water accumulation inside a closed hollow obturator is not directly related to thewater absorption properties of the acrylic resin but is related to thermal damage of the obturator.