title: Comparison of the dimensional accuracy of injection-molded denture base materials to that of conventional pressure-pack acrylic resin.
abstract: OBJECTIVE
  This study compared the linear dimensional changes of 3 injection-molded denture base materials to that of conventionally processed polymethylmethacrylate (PMMA) resin.
  
  
  METHODS
  An impression of an aluminum maxillary edentulous arch was made with a condensation silicone impression material (Denture Elasticon) to fabricate a gypsum master cast that was replicated as a silicone mold. A maxillary complete denture with acrylic teeth was waxed to full contour on the master cast and replicated to make 40 wax dentures. ERA attachments cast in metal (Rexillium) with indices milled into the centers were waxed into 3 positions in each denture for recording dimensional measurements of the wax denture. Ten dentures were allocated to each of 4 groups; Group 1 was processed using conventionally processed PMMA (Microlon), Group 2 used injection-molded PMMA (SR-lvocap), Group 3 employed injection-molded nylon (Valplast), and Group 4 used injection-molded styrene (Northern). All processed specimens were stored at room temperature (25 degrees C, ambient humidity) for 1 week (while still on the master cast) before anteroposterior and cross-arch measurements were made using the ERA reference points with a digital caliper. After separation from the master cast and following water storage at 37 degrees C for 7 days additional measurements were made.
  
  
  RESULTS
  An analysis of the results showed that the effect of processing was not the same for the 3 dimensions studied, regardless of which dimension was considered (p < 0.0001). The pattern of dimensional changes associated with the material type was not the same between the wax and processing stages as it was for the change between the processing and decasting stages (p < 0.0001).
  
  
  CONCLUSIONS
  Processing the denture base materials produced unequal deformation in different dimensions (anterior-posterior and cross-arch). Each material tested also responded differently to the processing stages.
authors.affiliation: King's College of Medicine and Dentistry, London, UK.
authors.forename: Ali
authors.initials: A
authors.lastname: Parvizi
authors.forename: Terry
authors.initials: T
authors.lastname: Lindquist
authors.forename: Robert
authors.initials: R
authors.lastname: Schneider
authors.forename: Derrick
authors.initials: D
authors.lastname: Williamson
authors.forename: Daniel
authors.initials: D
authors.lastname: Boyer
authors.forename: Deborah V
authors.initials: DV
authors.lastname: Dawson
mesh_terms: D000180:Acrylic Resins; D003799:Dental Stress Analysis; D003819:Denture Bases; D003779:Denture Design / Q000379:methods*; D003827:Denture, Complete, Upper; D006801:Humans; D016014:Linear Models; D008422:Materials Testing; D003765:Models, Dental; D009757:Nylons; D019904:Polymethyl Methacrylate; D011137:Polystyrenes; D015203:Reproducibility of Results; D014885:Waxes
chemical_list: D000180:Acrylic Resins; C076183:Microlon; D009757:Nylons; D011137:Polystyrenes; C077042:SR-Ivocap; D014885:Waxes; D019904:Polymethyl Methacrylate