Comparison of Accuracy of Intra-oral Scanners according to Scanning Distance

Abstract

Objectives: The aim of this study was to evaluate the factors affecting intra-oral scanner accuracy by analyzing variation in measurements of a dental model according to scanning distance.

Methods: A dental cast, including a prepared left mandibular first molar, was used as a reference model. Rectangular resin frames measuring 20 mm × 30 mm with heights of 2.5 mm, 5.0 mm, and 7.5 mm were made with a three-dimensional (3D) printer to achieve uniform scanning distances between the teeth and the scanner tip. The model was scanned 10 times with a laboratory reference scanner (Identica Hybrid

MEDIT, Seoul, Korea) to obtain the true value. Scanning was performed 10 times at four distances of 0 mm, 2.5 mm, 5.0 mm, and 7.5 mm with the frame of each height using the following three different intra-oral scanners: TRIOS (3Shape, Copenhagen, Denmark)

CS 3500 (Carestream Health, NY, USA)

and PlanScan (Planmeca, Helsinki, Finland). The linear distance measurement method (2D) and the best-fit alignment method (3D) were used to analyze and evaluate the accuracy of the intra-oral scanners. In the linear distance measurement method (2D), the scan image was aligned to the same position using the Rapidform 2004 software (INUS Technology, Seoul, Korea). Measurements were taken at five different parameters (i.e., between the canines [3D], the first molars [6BD and 6LD], and the canine and the first molar [46D and 36D]) and the results were compared. In the best-fit alignment method (3D), using the Geomagic Control X 2017 (3D Systems, Rock Hill, SC, USA) program, the root mean square (RMS) values of the two scan images were calculated. Differences were analyzed using a Friedman test and post hoc Wilcoxon signed-rank test (p < 0.05).

Results: In the 2D comparison, the different from the reference value was the smallest at 2.5 mm and 5.0 mm. In the 3D comparison, 2.5 mm and 5.0 mm were the most accurate, and 0 mm was the least accurate among the four distances. The two methods showed similar results. The accuracy of the scanners used from most accurate to least accurate was as follows: Identica Hybrid, TRIOS, CS 3500, and PlanScan.

Conclusions: To our knowledge, this study was the first to evaluate the accuracy of scanning distances, and found a difference between the accuracy of the scanning distance and the accuracy of the scanner. Moreover, the results of this study indicated that the scanning distance was a variable affecting accuracy. Therefore, the results of this study will improve the accuracy of intra-oral scanners in various oral environments, and provide guidelines for developing new intra-oral scanners.