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

Intraoral 3-D measurement can obtain digital impressions in real-time. However, owing to saliva, enamel, metallic denture, etc., the quality of the captured 2-D image using the intraoral equipment, which is used for feature measurement and 3-D reconstruction, is usually degraded. In this article, we propose an equipment with high performance for intraoral 3-D measurement. First, group-multiline 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 (CSFE) 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 3-D measurements conducted through the proposed equipment by using novel algorithms increased to 10-20 mu m and the measurement efficiency increased to 30%.