title: Pressure and temperature changes in heat-cured acrylic resin during processing.
abstract: OBJECTIVE
  The aims of this study were to measure the pressure and temperature changes of acrylic resin during processing, to record the highest temperature reached when fast cured in boiling water and to determine the elevated boiling point of monomer under high pressure.
  
  
  METHODS
  A subminiature pressure transducer (temperature compensated to 94 degrees C) and a thermocouple were placed on the palate of a standardized maxillary complete denture base. A heat-cured resin (Trevalon C) was polymerized by a long heating cycle (72 degrees C for 6.5 h and 92 degrees C for 1.5 h). Recordings of pressure and temperature (n=6) were made at initial clamping of denture flasks and throughout the processing cycles of resin. The temperature of the resin was also monitored during a fast cycle, which was accomplished by placing the flask directly into boiling water for 40 min.
  
  
  RESULTS
  The pressure of acrylic dough inside the clamped flask was initially 11.5 atm (SD=3.2) and reached a peak of 22.0 atm (SD=3.5) during the long heating cycle. The elevated boiling point of monomer at increased pressure was calculated to be about 193 degrees C (at 11.5 atm) and 228 degrees C (at 22.0 atm). These elevated boiling points are higher than the maximum temperature 131 degrees C (SD=6.6) reached during the fast curing cycle. No porosity was observed even in the denture bases heat-cured by the fast cycle.
  
  
  CONCLUSIONS
  The highest temperature reached by heating of resin during processing is well below the elevated boiling point of monomer. Monomer therefore does not boil in clamped denture flasks under sufficient pressure. Thus adequate clamp pressure prevents gaseous porosity irrespective of curing cycle used.
authors.affiliation: 4F, Oral Rehabilitation, Faculty of Dentistry, The University of Hong Kong, The Prince Philip Dental Hospital, 34 Hospital Road, Hong Kong, People's Republic of China.
authors.forename: W F E
authors.initials: WF
authors.lastname: Yau
authors.forename: Y Y
authors.initials: YY
authors.lastname: Cheng
authors.forename: R K F
authors.initials: RK
authors.lastname: Clark
authors.forename: T W
authors.initials: TW
authors.lastname: Chow
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003819:Denture Bases; D004055:Differential Thermal Analysis; D008422:Materials Testing; D008768:Methylmethacrylates / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D016062:Porosity; D011312:Pressure; D013696:Temperature
chemical_list: D000180:Acrylic Resins; D008768:Methylmethacrylates; D011108:Polymers; C029883:Trevalon universal