title: Effect of storage period on the accuracy of elastomeric impressions.
abstract: OBJECTIVE
  To investigate the effect of the storage period on the accuracy of recently developed elastomeric materials.
  
  
  METHODS
  Simultaneous impressions of a steel die were taken using a polyether (I: Impregum Soft Heavy and Light body, 3M ESPE) and vinyl polysiloxane (P: Perfectim Blue Velvet and Flexi-Velvet, J.Morita). The trays were loaded with the heavy-bodied impression materials while the light-bodied impression materials were simultaneously spread on the steel die. The impressions were poured after 2 hours, 24 hours, and 7 days. Impressions were stored at approximately 55% relative humidity and room temperature. Ten replicas were produced for each experimental condition (n=60). Accuracy of the stone dies was assessed with a depth-measuring microscope. The difference in height between the surface of the stone die and a standard metallic ring was recorded in micrometers at four demarcated points, by two independent examiners. Data were submitted to two-way ANOVA and Tukey test (a = 0.05).
  
  
  RESULTS
  Significant differences were found among the groups. Smaller discrepancies were observed when pouring was performed up to 24 hours (I-2h= 65.0 +/- 15.68 microm; I-24h= 81.6 +/- 11.13 microm) for the polyether, and up to 7 days for the vinyl polysiloxane (P-2h= 79.1 +/- 13.82 microm; P-24h= 96.8 +/- 6.02 microm; P-7d= 81.4 +/- 4.3 microm). Significant dimensional discrepancies, however, were observed when polyether was stored for 7 days (I-7d= 295.3 +/- 17.4 microm).
  
  
  CONCLUSIONS
  Storage may significantly affect the dimensional accuracy of impressions and, thus, a maximum period and storage condition should be specified for the recently developed materials.
authors.affiliation: Department of Operative Dentistry, Endodontics, and Dental Materials, Bauru School of Dentistry, University of São Paulo, Bauru, SP, Brazil.
authors.forename: Eduardo Batista
authors.initials: EB
authors.lastname: Franco
authors.forename: Leonardo Fernandes
authors.initials: LF
authors.lastname: da Cunha
authors.forename: Ana Raquel
authors.initials: AR
authors.lastname: Benetti