Comparison of the reliability of craniofacial anatomic landmarks based on cephalometric radiographs and three-dimensional CT scans.

OBJECTIVE

Conventional cephalometry is an inexpensive and well-established method for evaluating patients with dentofacial deformities. However, patients with major deformities, and in particular asymmetric cases are difficult to evaluate by conventional cephalometry. Both two- and three-dimensional computed tomography (CT) have been proposed to alleviate some of these difficulties. Only a few studies using metallic markers have indicated 3-D CT to be a useful diagnostic method, whereas no studies have evaluated the reliability of the anatomic cephalometric points used in 3-D CT. The aim of our study therefore was to compare the reliability of anatomic cephalometric points from conventional cephalograms and 3-D CT.

METHODS

Nine human dry skulls were CT scanned. In addition standard lateral and frontal cephalograms were obtained. The CT scans were 3-D image reconstructed, and the cephalometric points were recorded as x, y, and z co-ordinates by two investigators. Computerized cephalometrics were performed-on the lateral and frontal cephalograms. Intra- and interindividual variations were calculated for each method and tested for statistical significance.

RESULTS

Lateral cephalogram measures were more reliable than 3-D CT, with interobserver variations less than 1 mm for most points compared to about 2 mm for 3-D CT. Lateral cephalometrics also showed significantly less interobserver variation for six variables. This was, however, less obvious when 3-D CT was compared to frontal cephalograms. Frontal cephalometrics showed significantly less interobserver variation for three of the investigated variables.

CONCLUSIONS

For standard lateral and frontal cephalometric points, there is no evidence that 3-D CT is more reliable than the conventional cephalometric methods in normal skull, and the benefit of 3-D CT cephalometric is indicated to be in the severe asymmetric craniofacial syndrome patients, as conventional cephalometrics is known to be inferior in these cases.