title: The dimensional stability of impression materials and its effect on in vitro tooth wear studies.
abstract: OBJECTIVE
  To assess the dimensional stability of 8 impression materials over 12 weeks relevant to in vitro tribology studies.
  
  
  METHODS
  Ten impressions from eight impression materials were taken of a metal block (ADA block) conforming to the American Dental Association specification for impression materials and of another metal block (custom block) which allowed measurements over a larger surface area. The impressions and blocks were scanned on a non-contacting laser profilometer (Taicaan® - Southampton, UK) and using surface metrology software Boddies® (Taicaan® - Southampton, UK) measurements were made at 24h, 2, 4, 8 and 12 weeks. The impression materials tested were [1] Aquasil®, [2] Aquasil® DECA, [3] Affinis®, [4] Express®, [5] Extrude®, [6] Impregum®, [7] President® and [8] Take 1®.
  
  
  RESULTS
  Seven addition silicones and one polyether [6] were tested. [2] and [6] were monophasic, the rest were putty-wash. The results from impressions of the ADA block showed that all materials contracted compared to measurements obtained directly from the block [1] expanded over time (+31.5 μm) (p<0.05). The results from the custom block showed that all materials contracted compared to direct measurements of the block. [4] and [7] expanded over time (+62 μm and +63.8 μm respectively). [8] contracted over time (-54.7 μm) (p<0.05).
  
  
  CONCLUSIONS
  No material showed linear changes >1.5% and were stable for 12 weeks. Nevertheless, the range of changes would affect tribology studies were cut-offs lesser than the reported changes are selected. All impressions should be processed after similar time delays to reduce the errors introduced by dimensional changes.
authors.affiliation: UCL Eastman Dental Institute, Prosthodontics, 256 Gray's Inn Road, London WC1X 8LD, UK.
authors.forename: Jose M
authors.initials: JM
authors.lastname: Rodriguez
authors.forename: David W
authors.initials: DW
authors.lastname: Bartlett
mesh_terms: D003760:Dental Impression Materials / Q000737:chemistry*; D004355:Drug Stability; D020724:Elastomers / Q000737:chemistry; D008422:Materials Testing; D013997:Time Factors; D057085:Tooth Wear / Q000175:diagnosis
chemical_list: D003760:Dental Impression Materials; D020724:Elastomers