Validation of conventional 2D lateral cephalometry using 3D cone beam CT

Abstract

Objective: To determine if two-dimensional (2D) measurements from conventional cephalometric lateral skull radiographs are comparable to those derived from three-dimensional (3D) cone beam computed tomography (CBCT) images.

Design: In vitro laboratory study.

Setting: University Dental Hospital.

Method: A sample size calculation determined that 14 dried skulls were required to detect a 2° difference in angular measurements. The skulls were scanned at 0·3 mm³ voxel size. Maximum intensity projection (MIP) views were uploaded into OPAL cephalometric software (British Orthodontic Society, London, UK) for 2D analysis. CBCT data was uploaded into Mimics (Materialise, Leuven, Belgium) with 3D reconstructed and sagittal slice views being used. An Eastman analysis was carried out for the 2D and 3D images with the data compared using two-sample t-tests at P<0·05. Measurements greater than 2° between the 2D and 3D data were considered clinically significantly different. Intra-observer reproducibility was assessed by calculating random and systematic error using the Dahlberg formula and a two-sample t-test (P<0·05).

Results: The random error was below 0·5° and the systematic error was acceptable (P<0·05). There were no statistically significant differences between the measurements from the 2D and 3D images for any variable (P<0·05). However, the mean SNB value and the mean value for the angle between the lower incisor and mandibular plane differed by greater than 2° between the 2D and 3D data. The latter was thought to be due to limitations of the definition of Gonion for 3D images and the precision of locating the lower incisor apex in 2D.

Conclusion: Measurements used in the Eastman cephalometric analysis derived from 2D cephalometric lateral skull images are comparable to those derived from 3D CBCT images.

Keywords:

• Cone beam CT
• cephalometry
• MIP view

Acknowledgments

The authors thank Lynda Cochrane for her assistance with the Bland and Altman plots.