Three-dimensional evaluation of the reproducibility of presintered zirconia single copings fabricated with the subtractive method

Abstract

Statement of problem. Reproducibility is an important factor determining the success of a prosthesis. However, no studies have focused on identifying the location of errors on prostheses fabricated with the subtractive method, leading to a lack of standards for reproducibility evaluations. Purpose. The purpose of this in vitro study was to evaluate the reproducibility of the subtractive method by conducting 3-dimensional assessments of presintered single-tooth zirconia copings for different teeth. Material and methods. Acrylic resin tooth molds for the canine (CAN), premolar (PRE), and molar (MOL) were used to prepare stone casts, and copings were designed and fabricated with the subtractive method. The intaglio surfaces of corresponding presintered zirconia copings were scanned with a blue light scanner. Initial scan data were used as a reference for comparisons with subsequent data for the measurement of errors. Nine color-difference maps were created for each of the 3 groups and used to calculate root-mean-square (RMS) error values. One-way analysis of variance and the Tukey honestly significant difference tests were used for statistical evaluations (alpha=.05). Results. MOL copings exhibited the highest RMS error value (9.22 +/- 1.56 mu m), which was significantly different from values for CAN (3.33 +/- 2.65 mu m) and PRE (4.00 +/- 2.40 mu m; P<.001) copings. Color-difference maps revealed maximum errors in the line angles. Conclusions. The highest reproducibility was observed for the CAN copings. The clinical reproducibility of the subtractive method can be improved by avoiding sharp angles during abutment preparation and careful reproduction of angles during prosthesis fabrication.