Variations in Horizontal Angulation and Vertical Measurements With CBCT

Objectives: The purpose of this in-vitro study was to determine the effect of variations in horizontal mandibular angulation and vertical measurements with Cone Beam Computed Tomography (CBCT).
Methods: We used four foam edentulous mandibles. The mandibles was mounted on a wooden plate for imaging. In each mandible five tooth locations were identified. Premeasured gutta percha (GP) sticks were attached on buccal, central and lingual positions at each tooth location and measurements were made. Using Iluma CBCT machine, we imaged each mandible with different horizontal angulations. Pre-marked angulations on the tripod and CBCT machine laser lights were used for positioning: Correct position: Each mandible was scanned with 0 degree horizontal angulation. Mid sagittal plane was centered and the lower border of the mandible was kept parallel to the floor. Upward extension: Mid sagittal plane was centered. Wooden platform with mandible was tilted upwards to 5 degrees. Lateral flexion: 5 and 10 degree angulations were obtained by tilting the wooden platform with each mandible toward the left side. Software correction: Mandible orientation was corrected to make the inferior border of the mandible parallel to the floor using the CBCT orientation correction software (from 5 to 0 degrees). We compared the measurements from the corrected scan with the 0 degree and actual GP measurements. CBCT DICOM data was reconstructed (0.3mm voxel size) and viewed by Iluma vision software. Vertical measurements were made on cross-sectional images (2mm thickness & 1mm spacing).
Results: Multiple t-tests were done.Statistical analysis revealed a significant interaction between tooth locations (P<0.005) and angulations (p value<0.0001). However, statistical analysis failed to yield any significant interaction between tooth location and GP position.
Conclusions: Improper head orientation could lead to signification variation on vertical measurements. It is recommended that clinicians evaluate head positioning before making any measurements and make any needed orientation corrections within the CBCT viewing software.