title: Abrasion resistance of a resin-impregnated type IV gypsum in comparison to conventional products.
abstract: BACKGROUND
  Limited abrasion resistance is one of the disadvantages of gypsum materials. One means to improve these properties may be the addition of various polymers to reinforce surface and subsurface wear resistance.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the abrasion resistance of 3 types of gypsum materials with a novel abrasion wear device.
  
  
  METHODS
  A standard test specimen (50 x 50 x 8 mm) with repeating 1 mm, 45 degrees -angle vertical ridges was used as the test surface. Three types of gypsum materials were evaluated: a type III stone, a conventional type IV stone, and a resin-impregnated type IV stone. Specimens of each material (n = 30) were poured in a vinyl polysiloxane impression of the standard test specimen with the use of an acrylic resin custom tray. Each gypsum product was mixed according to the manufacturer's instructions, poured, and separated 1 hour later. Specimens were trimmed and allowed to bench set for 24 hours (n = 15) or 7 days (n = 15). Abrasion was evaluated with the use of a reciprocal moving stage positioned below a weighted stylus. The stylus was loaded with 3 different weights (15, 50, and 75 g), and the individual gypsum specimens were moved reciprocally for 10 passes. Before and after each set of passes, the specimen was measured on an analytical balance to determine material loss. Three-way ANOVA and Scheffe's multiple comparisons test were used to analyze the data (P<.05).
  
  
  RESULTS
  Type III gypsum at 24 hours exhibited significantly greater material loss than type IV stones at both 7 days and 24 hours (P<.001). Type III gypsum specimens exhibited significantly greater material loss at 24 hours than at 7 days (P<.001). There was no significant difference in the abrasion resistance of type IV specimens at 24 hours and 7 days.
  
  
  CONCLUSIONS
  Within the limitations of this study, no significant differences in abrasion resistance were found between specimens fabricated with resin-impregnated and conventional type IV stones, although the former exhibited the least material loss.
authors.affiliation: Department of Prosthodontics, College of Dentistry, University of Iowa, Iowa City, Iowa 52242, USA. terry-lindquist@uiowa.edu
authors.forename: Terry J
authors.initials: TJ
authors.lastname: Lindquist
authors.forename: Clark M
authors.initials: CM
authors.lastname: Stanford
authors.forename: Homan
authors.initials: H
authors.lastname: Mostafavi
authors.forename: Xian-Jin
authors.initials: XJ
authors.lastname: Xie
mesh_terms: D000180:Acrylic Resins; D000704:Analysis of Variance; D002133:Calcium Sulfate / Q000737:chemistry*; D003760:Dental Impression Materials / Q000737:chemistry; D003761:Dental Impression Technique / Q000295:instrumentation; D003764:Dental Materials / Q000737:chemistry*; D006801:Humans; D008422:Materials Testing; D011108:Polymers / Q000737:chemistry; D011145:Polyvinyls / Q000737:chemistry; D012117:Resins, Synthetic / Q000737:chemistry*; D012833:Siloxanes / Q000737:chemistry; D013223:Statistics as Topic; D013499:Surface Properties; D013997:Time Factors
chemical_list: D000180:Acrylic Resins; D003760:Dental Impression Materials; D003764:Dental Materials; D011108:Polymers; D011145:Polyvinyls; D012117:Resins, Synthetic; D012833:Siloxanes; C034183:vinyl polysiloxane; D002133:Calcium Sulfate