Calibration of Intraoral 3-D Measurement System With Using Consummated Model Combined With Highly Accurate Data Pairs

Direct digital impressions can be obtained using intraoral 3-D scanners. Among them, the fringe projection profilometry (FPP)-based intraoral scanner serves as a micro-3D imaging system. Here, proper calibration is critical for highly accurate digital impressions. However, due to its miniaturized structure, some of the designed geometric parameters are difficult to be attained in factory assembly using model-based reconstruction. Moreover, the angle of the structured light is typically small to avoid shadows of the dental sulcus. Consequently, even a small error in detecting stripe feature within the FPP image is magnified in the reconstructed 3-D point. Thus, it is challenging to achieve proper calibration and meet the accuracy requirements of an intraoral 3-D scanner. In this study, we introduce a consummated calibration model, by importing all the geometric parameters to compensate for assembly errors. A subpixel cross-center detection algorithm is proposed to prepare the data pairs for optimization of parameters in the calibration model. All parameters are optimized using the Levenberg–Marquardt algorithm. A 3-D lookup table (LUT) is used to refine the reconstructed 3-D points. Excellent calibration results were achieved, demonstrating a precision of
$15 \mu \text{m}$
for 3-D teeth impression.