Accuracy of newly formulated fast-setting elastomeric impression materials

STATEMENT OF PROBLEM: Elastomeric impression materials have been reformulated to achieve a faster set. The accuracy of fast-setting elastomeric impression materials should be confirmed, particularly with respect to disinfection. PURPOSE: The purpose of this study was to assess the accuracy of 2 types of fast-setting impression materials when disinfected with acid glutaraldehyde. MATERIAL AND METHODS: Impressions of the mandibular arch of a modified dentoform master model were made, from which gypsum working casts and dies were formed. Measurements of the master model and working casts included anteroposterior (AP) and cross-arch (CA) dimensions. A stainless steel circular crown preparation incorporated within the master model was measured in buccolingual (BL), mesiodistal (MD), and occlusogingival (OG) dimensions and compared to measurements from recovered gypsum dies. The impression materials examined were a fast-set vinyl polysiloxane (VPS-FS, Aquasil Ultra Fast Set), a fast-set polyether (PE-FS, Impregum Penta Soft Quick Step), and a regular-setting polyether as a control (PE, Impregum Penta). Disinfection involved immersion in 3.5% acid glutaraldehyde (Banicide Advanced) for 20 minutes, and nondisinfected impressions served as a control. Linear measurements were made with a measuring microscope. Statistical analysis utilized a 2-way and single-factor analysis of variance with pair-wise comparison of mean values when appropriate. Hypothesis testing was conducted at alpha = .05 RESULTS: No differences were shown between the disinfected and nondisinfected conditions for all locations. However, there were statistical differences among the 3 materials for AP, CA, MD, and OG dimensions. AP and CA dimensions of all working casts were larger than the master model. Impressions produced oval-shaped working dies for all impression materials. PE and PE-FS working dies were larger in all dimensions compared to the stainless steel preparation, whereas VPS-FS-generated working dies were reduced in OG and MD dimensions. Differences detected were small and may not be of clinical significance. CONCLUSIONS: Impression material accuracy was unaffected by immersion disinfection. The working casts and dies were similar for PE and PE-FS. VPS-FS generated gypsum dies that were smaller in 2 of the 3 dimensions measured and may require additional die relief. Overall accuracy was acceptable for all 3 impression materials.