Accuracy of 3D white light scanning of abutment teeth impressions: evaluation of trueness and precision

Abstract

Purpose: This study aimed to evaluate the accuracy of digitizing dental impressions of abutment teeth using a white light scanner and to compare the findings among teeth types.

Materials and methods: To assess precision, impressions of the canine, premolar, and molar prepared to receive all-ceramic crowns were repeatedly scanned to obtain five sets of 3-D data (STL files). Point clouds were compared and error sizes were measured (n=10 per type). Next, to evaluate trueness, impressions of teeth were rotated by 10°-20° and scanned. The obtained data were compared with the first set of data for precision assessment, and the error sizes were measured (n=5 per type). The Kruskal-Wallis test was performed to evaluate precision and trueness among three teeth types, and post-hoc comparisons were performed using the Mann-Whitney U test with Bonferroni correction (α=.05).

Results: Precision discrepancies for the canine, premolar, and molar were 3.7 µm, 3.2 µm, and 7.3 µm, respectively, indicating the poorest precision for the molar (P<.001). Trueness discrepancies for teeth types were 6.2 µm, 11.2 µm, and 21.8 µm, respectively, indicating the poorest trueness for the molar (P=.007).

Conclusion: In respect to accuracy the molar showed the largest discrepancies compared with the canine and premolar. Digitizing of dental impressions of abutment teeth using a white light scanner was assessed to be a highly accurate method and provided discrepancy values in a clinically acceptable range. Further study is needed to improve digitizing performance of white light scanning in axial wall.

Keywords: 3D shape data; Accuracy; Impression scanning; Point cloud; Precision and trueness; White light scanner.

Fig. 1

Precision evaluation for the canine: Ten color-difference maps (A-J) of scans of the canine impression showing fit alignment of digital impression data compared among each other (C_pre1 through C_pre5). Trueness evaluation for the canine: Five color-difference maps (K-O) of scans of the canine impression showing fit alignment of digital impression data compared with the reference model data (C_tru1 to C_tru5). Green represents the exact fit, yellow to red represents a positive discrepancy, and turquoise to blue represents a negative discrepancy.

Fig. 2

Precision evaluation for the first premolar: Ten color-difference maps (A-J) of scans of the first premolar impression showing fit alignment of digital impression data compared among each other (P_pre1 through P_pre5). Trueness evaluation for the first premolar: Five color-difference maps (K-O) of scans of the first premolar impression showing fit alignment of digital impression data compared with the reference model (P_tru1 to P_tru5). Green represents the exact fit, yellow to red represents a positive discrepancy, and turquoise to blue represents a negative discrepancy.

Fig. 3

Precision evaluation for the first molar: Ten color-difference maps (A-J) of scans of the first molar impression showing fit alignment of digital impression data compared among each other (M_pre1 through M_pre5). Trueness evaluation for the first molar: Five color-difference maps (K-O) of scans of the first molar impression showing fit alignment of digital impression data compared with the reference model (M_tru1 to M_tru5). Green represents the exact fit, yellow or red represents a positive discrepancy, and turquoise to blue represents a negative discrepancy.

Fig. 4

Boxplot of discrepancies (precision and trueness) for the digitized impressions of the three types of abutment teeth obtained using a white light scanner: Precision (n=10 per type), trueness (n=5 per type).