Accuracy of a separating foil impression using a novel polyolefin foil compared to a custom tray and a stock tray technique

Abstract

Purpose: To compare the dimensional accuracy of three impression techniques- a separating foil impression, a custom tray impression, and a stock tray impression.

Materials and methods: A machined mandibular complete-arch metal model with special modifications served as a master cast. Three different impression techniques (n = 6 in each group) were performed with addition-cured silicon materials: i) putty-wash technique with a prefabricated metal tray (MET) using putty and regular body, ii) single-phase impression with custom tray (CUS) using regular body material, and iii) two-stage technique with stock metal tray (SEP) using putty with a separating foil and regular body material. All impressions were poured with epoxy resin. Six different distances (four intra-abutment and two inter-abutment distances) were gauged on the metal master model and on the casts with a microscope in combination with calibrated measuring software. The differences of the evaluated distances between the reference and the three test groups were calculated and expressed as mean (± SD). Additionally, the 95% confidence intervals were calculated and significant differences between the experimental groups were assumed when confidence intervals did not overlap.

Results: Dimensional changes compared to reference values varied between -74.01 and 32.57 µm (MET), -78.86 and 30.84 (CUS), and between -92.20 and 30.98 (SEP). For the intra-abutment distances, no significant differences among the experimental groups were detected. CUS showed a significantly higher dimensional accuracy for the inter-abutment distances with -0.02 and -0.08 percentage deviation compared to MET and SEP.

Conclusion: The separation foil technique is a simple alternative to the custom tray technique for single tooth restorations, while limitations may exist for extended restorations with multiple abutment teeth.

Keywords: Accuracy; Custom tray; Dental impression; Separating foil; Stock tray.

Fig. 1. (A) Machined mandibular complete-arch metal model with special modifications before replacement of the right second premolar, (B) Second premolar with modified overlay preparation with reference lines on the occlusal plane.

Fig. 2. Distances measured on the master model and on the casts in the 3 different groups. (A) Intra-abutment distances (d1 - d4), (B) inter-abutment distance ×1, (C) inter-abutment distance ×2.

Fig. 3. Deviation of the measured intra-abutment (d1 - d4) and inter-abutment distances (x1 and x2) in the 3 experimental groups (CUS: custom tray, MET: stock metal tray, SEP: separating foil technique) compared to the master model (reference). Each error bar represents the 95% confidence interval of the mean.