The Accuracy of Optical Scanning: Influence of Convergence and Die Preparation

Abstract

SUMMARY The purpose of this study was to determine the reliability of the data acquisition and modeling process of laser and white light scanners by evaluating the reproducibility of digitized simulated crowns with different convergences. A secondary purpose was to analyze the influence of die preparation by testing this hypothesis with a set of dies without ditching compared with a set with well-defined margins. Ditching or trimming the die defines the position of the margin and acts as a guide to gingival contour when the restoration is being waxed. Two light scanners (a white light optical scanner [Steinbichler Gmbh, Neubeuern, Germany] and red laser light scanner [TurboDent System, Taichung, Taiwan]) were evaluated. Two sets of simulated crowns were fabricated as cone frustrum models with a total occlusal convergence (TOC) of 0°, 5°, 10°, 15°, 20°, and 25° and a 9-mm base and 3-mm height using a precision milling machine and computer-aided design/computer-aided manufacturing (CAD/CAM) technique. One set of the dies was ditched immediately below the finish line to enhance marginal definition. Each die was optically digitized five times directly with the two different measuring systems. The area of each triangle in the scan that is occlusal to the margin line was calculated and summed to produce the final surface area measurement provided. The digitizing error was compared with the computed surface area of the original master die sets and compared with a paired t-test (df=4; 95% CI). There was no difference in accuracy of the untrimmed dies between the two systems evaluated. We also did not find any difference in the 0° (p=0.12) and 5° degree (p=0.21) groups among the ditched dies. However, when the TOC exceeded 5°, there was a significant difference between the two groups, with the laser groups having a smaller error percentage. Three-dimensional light scanning was not affected by the convergence angle except in the 0°-5° range. Trimming the dies greatly affected the accuracy of scanning.

The accuracy of the CAD system using intraoral and extraoral scanners for designing of fixed dental prostheses

“…The D810, an EAT scanner from 3Shape, is also one of the most popular scanners for the same reasons. These methods of scanning systems have been used to fabricate prostheses in clinics, and earlier studies have shown that their accuracy is acceptable for longterm clinical success [18][19][20] . These scanners were selected for this study as representative systems.…”

Marginal Accuracy and Internal Fit of 3-D Printing Laser-Sintered Co-Cr Alloy Copings

“…It can be both time-saving and cost-effective, when compared to conventional casting technology, and many studies have been reported [12,13,14]. Laser sintering is a type of additive manufacturing and a relatively new method compared to both casting and CAD/CAM milling techniques [15,16,17]. This is also called three-dimensional (3-D) printing, or rapid prototyping (RP).…”

Biomedical Optics and Lasers

“…Laser scans at micro-scale can be valuable for production of dental restorations. Impressions taken from dental arch can be scanned entirely or partially with laser or ordinary light at micro-scale to produce die used preparation of dental restoration precisely [24].…”