Influence of double flask investing and microwave heating on the superficial porosity, surface roughness, and knoop hardness of acrylic resin.
OBJECTIVE
Simultaneous polymerization of maxillary and mandibular complete dentures with teeth in occlusion through investing in a double special flask has been described as a more rapid and efficient method to polymerize prostheses than the conventional method; however, no study has been done to verify important properties of resin, including superficial porosity, surface roughness, and hardness, when processed by this technique. The purpose of this study was to verify if the simultaneous polymerization associated with microwave heating may alter the superficial porosity, surface roughness, and Knoop hardness of acrylic resin.


METHODS
Resin specimens processed in single and double dental flasks were compared using microwave energy and warm water methods. Four groups were tested according to the investing flask and the method of resin cure: Group I control specimens (n = 15) were invested in single metal flasks and cured by warm water at 74 degrees C for 9 hours. Group II (n = 15) specimens were invested in single polyvinyl chloride flasks and cured by microwave energy at 90 W for 20 minutes plus 450 W for 5 minutes. Group III (n = 30) and Group IV (n = 30) specimens were processed by simultaneous polymerization in double flasks and cured by the same warm water and microwave energy protocols, respectively.


RESULTS
No significant differences were found in mean superficial porosity (8.06 +/- 2.28 pore/cm(2)), surface roughness (0.14 +/- 0.03 mum), or Knoop hardness (19.66 +/- 2.25 kgf/mm(2)) between the control group (GI), and the other three experimental groups (p > 0.05).


CONCLUSIONS
Processing acrylic resin in a double flask heated by either warm water or microwave energy does not alter the resin's superficial porosity, surface roughness, or Knoop hardness; however, other properties of resin should be analyzed using this denture processing technique.
Department of Prosthodontics and Periodontology, Piracicaba Dental School, State University of Campinas, Piracicaba SP 13414 018, Brazil. rizzatti@fop.unicamp.br
Celia Marisa
CM
Rizzatti-Barbosa
Margarete C
MC
Ribeiro-Dasilva
D000180:Acrylic Resins / Q000737:chemistry* / Q000528:radiation effects; D003734:Dental Casting Investment / Q000737:chemistry* / Q000528:radiation effects; D003735:Dental Casting Technique / Q000295:instrumentation*; D003819:Denture Bases; D003779:Denture Design / Q000295:instrumentation*; D003824:Denture, Complete; D006244:Hardness; D006358:Hot Temperature; D006801:Humans; D008872:Microwaves
D000180:Acrylic Resins; D003734:Dental Casting Investment