Is a Wiggling-Motion Modified Two-Step Impression Technique as Accurate as Conventional Techniques in Restorative Dentistry?

Abstract

Background: The purpose of this study was to evaluate dental impression accuracy of one-step and two-step techniques compared to a modified two-step technique.

Methods: Four impression techniques were compared: (1) a one-step double mix (DM) technique, (2) a cut-out (CO) technique, in which space relief was created using a blade and a laboratory bur, (3) a membrane (ME) technique, in which space relief was created by placing a PVC membrane on top of the putty material during the primary impression, and (4) a wiggling motion (WI) technique, in which PVC membrane was placed and additional wiggling movements were performed during the first 20 s when the primary impression was seated upon the master model (MM). Impressions were poured with type IV stone. Casts were scanned with a laboratory scanner and measurements were made for each cast using three-dimensional analysis software.

Results: All groups presented differences compared to MM group, in at least one intra-abutment distance. Groups DM and ME presented the most significant differences, in three and two distances, respectively, whereas CO and WI presented one significant different distance compared to MM. There were no differences between MM and the four techniques for inter-abutment distances.

Conclusions: WI yielded similar results with CO technique. Both performed better than the other groups.

Keywords: dental impression technique; double mix two-step technique; polyvinylsiloxane; wiggling motion technique.

Figure 1

Master model with three metal dies (A, Β₁, Β₂), representing one full-crown preparation for a single crown (first molar-A) and two prepared teeth for a three-unit FPD (right second premolar-B₁ and second molar-B₂) at the opposite site.

Figure 2

Design of metal dies, where grooves that represent height (H) (left), mesiodistal (MD), and buccolingual (BL) distances (right) are highlighted.

Figure 3

The point where BL and MD grooves met was referred to as the center of each die (point A, B₁, B₂). Three inter-abutment measurements (AB1, AB2, B1B2) were obtained, using the center of each metal die as reference point.

Figure 4

A custom-made apparatus was used in order to achieve repeatable positioning of the tray. (a). Front view and (b). Top view of the apparatus, the tray, and the master model.

Figure 4

A custom-made apparatus was used in order to achieve repeatable positioning of the tray. (a). Front view and (b). Top view of the apparatus, the tray, and the master model.