John K. Harcourt

Fracture toughness of water-aged resin composite restorative materials

OBJECTIVES The purpose of this study was to assess the effects of aging experimental dimethacrylate resin composites in water at 37 degrees C for periods up to 6 wk by measuring the variations in fracture toughness (K(c)), elastic modulus (E), fracture energy (G(c)), and water sorption. METHODS Six experimental resins were formulated from dimethacrylate resins, and were filled to 86 wt% (ca. 70 vol%) with treated inorganic filler to form six experimental composites. The fracture toughness was determined using a double torsion technique, the elastic modulus was measured in flexure, and the fracture energy was calculated from the fracture toughness and elastic modulus. RESULTS As a result of aging in water, K(c) and the G(c) increased, and the elastic modulus decreased, but all values approached a plateau near 6 wk. Water sorption also occurred during this period, mainly during the first 2 wk. SIGNIFICANCE Variations in the mechanical properties are interpreted as being due to plasticization of the resin matrix by water, which appears to lower the yield stress and increase in the size of the plastic zone ahead of the crack, thereby causing the observed increase in G(c) and K(c). After approximately 6 wk, no further changes in properties occurred.

Accuracy in registration and transfer of prosthetic records

Abstract— A review of the mandibular movements and a definition of functional positions provides an introduction to understanding the problems to be overcome in correctly recording the proper relationship of the mandible to the maxilla. Despite accurate registration techniques sources of error arise in laboratory procedures because of instability of materials and changes during their setting or polymerization.

Australia-New Zealand Division of the International Association for Dental Research-Abstracts of Papers Presented at the Twelfth Annual Meeting

S AND TITLES Australia-New Zealand Division of the International Association for Dental Research-Abstracts of Papers Presented at the Twelfth Annual Meeting

Retention of alginate impression material using a polyester fibre-mat textile

Abstract To ensure accuracy, alginate, impression materials must be firmly retained in the impression tray. This short report compares the effectiveness of perforated trays with a newly developed self-adhesive polyester fibre mat material which can be used to line the inner surface of stock and custom made impression trays. In all cases, the fibre mat was much more effective as a retention medium when compared with perforations. Also, small perforations proved more effective than larger ones for alginate retention.