Comparison and Reproducibility of Two Maxillary Regional Registration Methods

Objectives: The aim was to evaluate the differences between 2 methods of maxillary voxel-based registration and to test the interobserver reproducibility of the methods.
Methods: 3D models were built using the cone-beam computed tomography scans of two time-points from a sample of 12 growing subjects. One observer labeled six landmarks in all T2 models, in different regions of the maxilla, in order to evaluate errors of pitch, roll and yaw, and to avoid any landmark identification errors. The T2 models pre-labeled were cropped by two previously calibrated observers, working independently, and two different regions of reference were defined for the voxel-based registration: Method 1) the Maxilla (MAX) region of reference included the maxillary bone cropping inferiorly the dentoalveolar processes; superiorly, regions above the plane passing through the right and left orbitale point; laterally, zygomatic processes at orbitale point; and posteriorly at a plane passing through the distal surface of the second molars. Method 2) the Palate and infra-zygomatic region of reference (PIZ), had different posterior and anterior limits (respectively, plane passing through the distal of the first molar and distal of the canines). Automated voxel-based registrations were performed by both observers. The distance between correspondent landmarks and their x,y,z coordinates were calculated . One-sample t test was applied to compare both methods. The difference between the 2 observers was assessed with paired sample t test. Bland-Altman method was used as measure of agreement.
Results: The mean of the differences between landmarks was 0.33 mm (CI= 0.26-0.39). The differences between the two methods were not clinically relevant. The difference between observers was not significant (p-values 0.99, 0.88, 0.32, respectively for x,y,z coordinates). The Bland-Altman plot indicated adequate concordance between the two observers.
Conclusions: both methods of regional maxillary registration (MAX and PIZ) showed similar results and adequate interobserver reproducibility.