Effect of storage period on the accuracy of elastomeric impressions.
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.
Franco
Eduardo Batista
EB
Department of Operative Dentistry, Endodontics, and Dental Materials, Bauru School of Dentistry, University of São Paulo, Bauru, SP, Brazil.
da Cunha
Leonardo Fernandes
LF
Benetti
Ana Raquel
AR