The stability of temporary prosthetic base materials. II: Water sorption and its effects

The bases of occlusal rims and trial dentures may sorb water during disinfection procedures, adjustment in the mouth and rinsing and cooling under running water. Such sorped water may adversely affect the properties of the baseplate materials. The room temperature water sorption of sheets of grey and pink shellac and cold cure acrylic resin was determined over 10 weeks by weighing. The Wallace surface hardness, linear dimension and transverse strength were also measured each week. Specimens were reweighed each week as they dried at room temperature. At the conclusion of the tests, the materials showed a change after soaking in weight, hardness, linear dimension and transverse strength, and change after drying relative to original mass for grey shellac of +1.5%, -48%, +0.7%, -58%, +0.33%; for pink shellac of +2.0%, -56%, +0.9%, -65%, +0.4%; and for acrylic resin of +1.2%, +10%, +0.4%, -30%, -2.1% respectively. The acrylic resin material was thus less affected by water sorption than the grey and pink shellac materials.