Tadashi Hirasawa

Materials Science Initial Dimensional Change of Composites in Dry and Wet Conditions

A study of the expansion of restorative composite resins associated with water sorption was conducted. The results show that this expansion depends upon the mass of water absorbed by the composite restorative. Although polymerization shrinkage can be compensated by expansion due to water sorption, the length of time involved in achieving this compensation is approximately seven d.

Structure and Adhesion of Closs-linked Plastic Denture Tooth.

The purpose of this investigation was to study the Knoop hardness test, absorption and solubilityin MMA, and filler contents of the commercially available several cross-linked plastic denture teeth.In addition, tensile bonding strength of three denture base resins, heat-cured resin, heat-shock resin, andauto-cured resin, bonded to the artificial teeth was measured. Four cross-linked plastic denture teeth and oneconventional acrylic denture tooth were studied.Knoop hardness in the enamel of the specimens was as hard as the commercially available compositeresins for crown and bridge.The enamel contained 25-45% filler. The enamel had high cross-linked polymer, so the rates of swellingand solubility in MMA of the enamel were lower than the body of the specimens and the enamel and body ofplastic denture teeth.The body and dentin of the specimens showed better tensile bond strength than the enamel. Tensile bondstrength of the heat-cured resin and the heat-shock resin bonded to the body was better than the auto-curedresin bonded to the body.There was no difference in results between the body and the conventional acrylic tooth in all examinations.