Dimensional Accuracy of a New Polyether Impression Material

Objectives: To evaluate the dimensional accuracy of stone dies produced from standardized impressions taken with a new and a conventional polyether impression material and a vinyl polysiloxane reference material. Methods: Impressions with the light and heavy-bodied types of the polyether materials P2 (P2L/H; Heraeus Kulzer) and Impregum (IML/H; 3M ESPE) and with the vinyl polysiloxane Flexitime (FLC/H; Heraeus Kulzer) were produced from a truncated chromium steel cone (8 mm height and base diameter, 10^o convergence) in cylindrical perforated steel trays giving an impression layer thickness of 4 mm at the prominence line. Impressions were taken at 23^o or 37^o C. Dies were poured in Type 4 stone after 1 or 24 hours storage at ambient atmosphere. In a second series impressions were stored at different relative humidity (0, 33, 50, 75, or 100%) for 24 h prior to die pouring. The accuracy of the stone dies was determined as discrepancy between a steel ring, fitting perfectly on the steel die, and the occlusal die surface. The base diameter deviation Δd (μm) was calculated. Statistical data treatment with regression analyses and ANOVA (p<0.05). Results: After 1 h minor differences in Δd were noticed between the impression materials only. Impressions taken at 37^o C exhibited significantly higher &Δd than at 23^o C. P2L showed the highest Δd increase from impressions taken both at 23^o or 37^o C and die pouring after 24 h (p<0.05). Flexitime showed moderate Δd differences at the two pouring times. The Δd of dies made from polyether materials decreased significantly with increasing humidity (r²>0.89) whereas Flexitime was not adversely affected (r²<0.32). Conclusion: In contrast to conventional polyether, P2L shows less dimensional stability upon prolonged storage. Polyethers absorb water that compromises die accuracy significantly upon storage at high humidity.