Water absorption characteristics of two types of acrylic resin obturators

The mechanisms of water accumulation in the inner space of a closed hollow obturator are not understood, and it is not known whether the porosity of acrylic resin is involved in these mechanisms.

The purpose of this study was to evaluate water absorption by solid and closed hollow obturators and to determine the mechanisms of water accumulation in the inner space of the closed hollow obturator.

Twenty solid and 20 closed hollow spherical specimens (30 mm in diameter) were fabricated from heat-polymerized acrylic resin (Acron Clear). Closed hollow specimens consisted of 2 hemispheres (30 mm in diameter, 1.5 mm in thickness) joined with autopolymerizing resin (Unifast II). Ten solid and 10 closed hollow specimens were immersed in distilled water at 37 degrees C, while the other specimens were stored in an atmosphere of 100% relative humidity at 37 degrees C. Each specimen was weighed every 24 hours for 180 days, and weight changes between each group were compared by 2-way ANOVA and the Tukey HSD test. Split-plot design ANOVA was used to compare the course of the weight change over 180 days (alpha=.05).

The weight of the closed hollow specimens increased immediately and became saturated by day 30, with an increase of 1.44% from the initial weight. Water accumulation was not observed inside the closed hollow specimen during the 180-day storage period. The weight of solid specimens increased more slowly than that of closed hollow specimens; by day 180 the weight of the latter had increased by 1.16%. However, no significant difference in changes in mean mass of the same type of specimen was observed between the 2 storage conditions.

These results suggest that water accumulation inside a closed hollow obturator is unrelated to the water absorption properties of the acrylic resin.