Affiliations: Dental Materials, Department of Restorative Dentistry, Indiana University School of Dentistry, Indianapolis, IN, USA | Operative Dentistry, Department of Restorative Dentistry, Indiana University School of Dentistry, Indianapolis, IN, USA
Note: [] Corresponding author: Professor Yoshiki Oshida, Ph.D., 1121 West Michigan Street, Indianapolis, IN 46202‐5186, USA. Tel: +1 317 274 3725; Fax: +1 317 274 2419; E‐mail: [email protected].
Abstract: Water sorption tests were conducted on unfilled poly(methyl methacrylate) samples in distilled water at 5, 37, and 60\,^{\circ}C under three different tensile stress ratios (\sigma_{\rm appl}/\sigma _{\rm ys}= 0%, 5%, and 10%). Each sample was placed in a modified Hoffman open‐side tubing clamp and subjected to four‐point bending at pre‐determined stress level for 1 day, 3 days, 1 week, 2 weeks, and 4 weeks. Water sorption was measured by weight change calculations, without accounting for any weight loss due to solubility of uncured monomer. A generalized diffusion equation can be used to express both stress‐free and stress conditions; D=D_{\rm o}\exp[-E(\sigma)/kT]. It was found that the activation energy for water sorption diffusion was linearly related to applied stress ratios; i.e., E=1.15\ \sigma_{\rm appl}/\sigma_{\rm ys} + 10.76 (kJ/mol), with the correlation coefficient r =0.97. Since the proportional pre‐exponential constant, D_{\rm o}, is independent of temperature, it is speculated that the loading percentage of reinforcing filler elements in composite resin materials can be related to this constant.
