Accuracy of measurements of mandibular anatomy in cone beam computed tomography images

Abstract

Objectives: Cone beam computed tomography (CBCT) images of ideally positioned and systematically mispositioned dry skulls were measured using two-dimensional and three-dimensional software measurement techniques. Image measurements were compared with caliper measurements of the skulls.

Study design: Cone beam computed tomography volumes of 28 skulls in ideal, shifted, and rotated positions were assessed by measuring distances between anatomic points and reference wires by using panoramic reconstructions (two-dimensional) and direct measurements from axial slices (three-dimensional). Differences between caliper measurements on skulls and software measurements in images were assessed with paired t tests and analysis of variance (ANOVA).

Results: Accuracy of measurement was not significantly affected by alterations in skull position or measurement of right or left sides. For easily visualized orthodontic wires, measurement accuracy was expressed by average errors less than 1.2% for two-dimensional measurement techniques and less than 0.6% for three-dimensional measurement techniques. Anatomic measurements were significantly more variable regardless of measurement technique.

Conclusions: Both two-dimensional and three-dimensional techniques provide acceptably accurate measurement of mandibular anatomy. Cone beam computed tomography measurement was not significantly influenced by variation in skull orientation during image acquisition.

Fig. 1

Modified angle divisor tool with right mandible seated and ready for marking of gonial angle. A pencil will be placed in the groove of the bisector arm to mark gonion.

Fig. 2

Example of 15-mm panoramic image layer used for two-dimensional measures. Condylion, gonion, and mental foramen marks are projections from the axial slice at the center of the image layer location (see Fig. 3). Measurement values: A = gonion-mental foramen distance, B = horizontal reference wire, C = vertical reference wire, D = condylion-gonion distance, E = gonial angle, and F = gonial angle bisector.

Fig. 3

Axial slices and marked measuring points. Red lines are placed perpendicular to the panoramic image path and tangent to the landmark. Crosshairs represent measuring points placed by the three-dimensional measuring tool. Crosshairs are displayed in every axial slice between the actual measurement point locations. A, Marking of superior condylar surfaces bilaterally and measurement of condylion-gonion distance. B, Marking of the ramus cortex at gonion bilaterally. Inner values represent gonion-mental foramen measurements. Outer values depict condylion to gonion measurement distance. C, Marking of the inner cortical surface of the posterior aspect of the right mental foramen. Measurements are gonion to mental foramen measurement distances.