Newly defined landmarks for a three-dimensionally based cephalometric analysis: a retrospective cone-beam computed tomography scan review

Abstract

Objectives: To identify two novel three-dimensional (3D) cephalometric landmarks and create a novel three-dimensionally based anteroposterior skeletal measurement that can be compared with traditional two-dimensional (2D) cephalometric measurements in patients with Class I and Class II skeletal patterns.

Materials and methods: Full head cone-beam computed tomography (CBCT) scans of 100 patients with all first molars in occlusion were obtained from a private practice. InvivoDental 3D (version 5.1.6, Anatomage, San Jose, Calif) was used to analyze the CBCT scans in the sagittal and axial planes to create new landmarks and a linear 3D analysis (M measurement) based on maxillary and mandibular centroids. Independent samples t-test was used to compare the mean M measurement to traditional 2D cephalometric measurements, ANB and APDI. Interexaminer and intraexaminer reliability were evaluated using 2D and 3D scatterplots.

Results: The M measurement, ANB, and APDI could statistically differentiate between patients with Class I and Class II skeletal patterns (P < .001). The M measurement exhibited a correlation coefficient (r) of -0.79 and 0.88 with APDI and ANB, respectively.

Conclusions: The overall centroid landmarks and the M measurement combine 2D and 3D methods of imaging; the measurement itself can distinguish between patients with Class I and Class II skeletal patterns and can serve as a potential substitute for ANB and APDI. The new three-dimensionally based landmarks and measurements are reliable, and there is great potential for future use of 3D analyses for diagnosis and research.

Keywords: CBCT; Cephalometric analysis; Cephalometric landmarks.

Figure 1.

(a) The Anatomage area measurement tool was used to outline the premaxillary bone anterior to the premaxillary suture to form a closed polygon. The y and z coordinates of each vertex were recorded and used to calculate the maxillary sagittal centroid. (b) The axial slice through the z coordinate of the maxillary centroid that was calculated in the sagittal plane was viewed, and the Anatomage area measurement tool was used to outline a closed polygon. The x and y coordinates of each vertex were recorded and used to calculate the maxillary axial centroid.

Figure 2.

(a) The Anatomage area measurement tool was used to outline the visible mandibular symphysis to form a closed polygon. The y and z coordinates of each vertex were recorded and used to calculate the mandibular sagittal centroid. (b) The axial slice through the z coordinate of the mandibular centroid that was calculated in the sagittal plane was viewed, and the Anatomage area measurement tool was used to outline a closed polygon. The x and y coordinates of each vertex were recorded and used to calculate the mandibular axial centroid.

Figure 3.

The overall maxillary and mandibular centroids were projected onto the midsagittal plane. True vertical lines were drawn from each centroid, and the linear distance between the two lines was calculated along the true horizontal (M measurement).

Figure 4.

The M measurement for each patient was plotted against (a) the corresponding ANB angle and (b) against the APDI angle. The correlation coefficient (r) was calculated to be 0.88 and −0.79, respectively.

Figure 5.

The average M measurement (mm) was plotted against the difference to demonstrate intraexaminer “o” (T₁-T₂) and interexaminer “x” (T₁-T_GK) reliability.

Figure 6.

A three-dimensional scatterplot was used to visualize the intraexaminer reliability of (a) the average maxillary and (b) the average mandibular centroid. The blue circle represents T₁; the red circle represents T₂.

Figure 7.

A three-dimensional scatterplot was used to visualize the interexaminer reliability of (a) the average maxillary and (b) the average mandibular centroid. The blue circle represents T₁; the green circle represents T_GK.