Comparison of Modified Double Tray Method and 3D scanning i prosthodontics

Abstract

The purpose of this in vitro study was to investigate and to compare the precision of two different impression techniques for oral prosthetic construction, namely the analogue modified double tray method, and the digital three-dimensional scanning with Trios 3D shape intraoral scanner. The analog method used was a modified double tray method where the tray had been removed to diminish vertical discrepancies in occlusion. All testing was based on a master model with a prepared acrylic tooth from which a total of 20 milled crowns in polymethylmethacrylate was produced, 10 from each impression method.  The fit of the crowns was evaluated according to a clinical protocol and the cement gap was measured with a measuring microscope. Each crown was fitted on to the master model with Flexitime light body, mimicking a cementing procedure. The resulting “cement layer” was after setting of the silicone impression material removed and divided into 4 equal pieces which subsequently were measured in a measuring microscope. Statistical analysis of the resulting measurements showed no significant differences in precision when comparing the impression methods. Because of a manufacturing error in the milling procedure, all of the milled plastic crowns showed suboptimal fit on the master model. However, it was concluded that no statistical - nor clinical difference between the two methods could be established. Most likely, both methods can be used for fabrication of single unit prosthetic reconstructions with adequate precision for effective treatment.