A Landmark-based Analysis of Three-dimensional Images in Class II Patients

Objectives: Traditionally, the cranio-mandibular morphology of class II patients has been mainly examined based on two-dimensional (2D) radiographs in the lateral view. The present study evaluated the three-dimensional (3D) cranio-mandibular features using a landmark-based analysis and examined whether or not a 3D analysis is needed in class II patients.
Methods: Thirty 3D cone beam computed tomography (CBCT) images of Japanese patients (18 to 35 years old) showing class I malocclusions (sk1 group; n=15) and class II malocclusions (sk2 group, n=15) were used in this study. After cranial and mandibular images were generated via surface rendering of the CBCT images, 105 landmarks were identified per image. Based on these landmarks, 53 angular and linear measurements were extracted and compared between the 2 groups using a t-test. The coordinate values of the landmarks were then analyzed through a principle component (PC) analysis using a geometric morphometrics software program (MorphoJ 1.07a, Klingenberg).
Results: Of the 53 total measurements, 26 showed significant differences (p<0.05). The sk2 group showed a narrow zygomatic arch with a small mandibular length and high mandibular plane angle. The first 8 significant PCs, which explained 73.1% of the total variance, were determined to be significant. The first and second components showed the most notable difference between groups (PC1, p=0.043; PC2, p=0.006). In the sk2 group, PC1 indicated a smaller zygomatic arch width, high mandibular plane angle and forward position of the condylar head, while PC2 indicated a narrow nasal and intergonial width.
Conclusions: A landmark-based analysis revealed the 3D cranio-mandibular features of class II patients. Class II patients were characterized by two orthogonal PCs including the width, depth, and height of the anatomical structures. These findings indicate that a 3D analysis is indispensable when evaluating the cranio-mandibular morphology of class II patients.