title: Stress relaxation of heat-activated acrylic denture base resin in the mold after processing.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  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.
  
  
  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.
authors.affiliation: Department of Complete Denture Prosthodontics, Nihon University School of Dentistry at Matsudo, Chiba, Japan.
authors.forename: O
authors.initials: O
authors.lastname: Komiyama
authors.forename: M
authors.initials: M
authors.lastname: Kawara
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D000704:Analysis of Variance; D003799:Dental Stress Analysis; D003819:Denture Bases; D004548:Elasticity; D006358:Hot Temperature; D003765:Models, Dental; D013314:Stress, Mechanical; D013674:Technology, Dental; D013997:Time Factors; D014867:Water
chemical_list: D000180:Acrylic Resins; D014867:Water