Intraoral 3-D Measurement by Means of Group Coding Combined With Consistent Enhancement for Fringe Projection Pattern

Abstract

Intraoral 3D measurement can obtain digital impressions in real time. However, owing to saliva, enamel, metallic denture, etc., the quality of the captured 2D image using the intraoral equipment, which is used for feature measurement and 3D reconstruction, is usually degraded. In this paper, we propose a equipment with high performance for intraoral 3D measurement. First, group-multi-line coding algorithm instead of sinusoidal or gray code for fringe projection profilometry (FPP) was applied for stripe pattern decoding. The distance between adjacent stripes was large enough to avoid the scatter of the tooth. It can also overcome the shortcoming of sinusoidal-based phase computing, leading to accuracy degradation owing to scanner jittering. Second, a consistent stripe feature enhancement method is proposed. The stripe feature in the mirror, exposure, and low-contrast area was homogeneously enhanced. Consequently, an individual scene is reconstructed using more effective and accurate points. This not only improves the precision of point cloud registration, it also reduces the probability of mismatch and shortens the scanning time for a full-arch. Our results showed that the accuracy of intraoral 3D measurements conducted through the proposed equipment by using novel algorithms increased to 10 - 20 μm and the measurement efficiency increased to 30%.