O Komiyama1, M Kawara. 1. Department of Complete Denture Prosthodontics, Nihon University School of Dentistry at Matsudo, Chiba, Japan.
Abstract
STATEMENT OF PROBLEM: Stress relaxation of polymethyl methacrylate has been reported, but no studies have investigated residual stress relaxation in heat-activated acrylic denture base resin fabricated by the polymer-monomer mixture method. PURPOSE: This study evaluated the development of residual stress relaxation and clarified how restricted time in the stone mold influenced stress relaxation of heat-activated acrylic denture base resin after processing. MATERIAL AND METHODS: Flat, dumbbell-shaped specimens were used. Thermocouples and strain gauges were embedded in resin for measuring temperature and strain at the dough-stage of resin packing. To clarify the stress relaxation in the stone mold, specimens were removed from the mold by deflasking at 4 hours after from the start of bench cooling (immediately after reaching room temperature; control), and 1 day, 3, 5, and 10 days from the start of bench cooling. RESULTS: Shrinkage strains at deflasking were two thirds for 1 day restriction, one half for 3 and 5 days restriction, as compared with the control. CONCLUSIONS: This study suggested that removing a denture base fabricated by heat-activated acrylic denture base resin from the stone mold only after keeping it in stone mold for at least 1 day or more was effective for reducing deformation of the denture base.
STATEMENT OF PROBLEM: Stress relaxation of polymethyl methacrylate has been reported, but no studies have investigated residual stress relaxation in heat-activated acrylic denture base resin fabricated by the polymer-monomer mixture method. PURPOSE: This study evaluated the development of residual stress relaxation and clarified how restricted time in the stone mold influenced stress relaxation of heat-activated acrylic denture base resin after processing. MATERIAL AND METHODS: Flat, dumbbell-shaped specimens were used. Thermocouples and strain gauges were embedded in resin for measuring temperature and strain at the dough-stage of resin packing. To clarify the stress relaxation in the stone mold, specimens were removed from the mold by deflasking at 4 hours after from the start of bench cooling (immediately after reaching room temperature; control), and 1 day, 3, 5, and 10 days from the start of bench cooling. RESULTS: Shrinkage strains at deflasking were two thirds for 1 day restriction, one half for 3 and 5 days restriction, as compared with the control. CONCLUSIONS: This study suggested that removing a denture base fabricated by heat-activated acrylic denture base resin from the stone mold only after keeping it in stone mold for at least 1 day or more was effective for reducing deformation of the denture base.