Janalt Damstra

The use of three-dimensional (3D) methods for facial imaging has increased significantly over the past years. Traditional 2D imaging has gradually being replaced by 3D images in different disciplines, particularly in the fields of orthodontics, maxillofacial surgery, plastic and reconstructive surgery, neurosurgery and forensic sciences. In most cases, 3D facial imaging overcomes the limitations of traditional 2D methods and provides the clinician with more accurate information regarding the soft-tissues and the underlying skeleton. The aim of this study was to review the types of imaging methods used for facial imaging. It is important to realize the difference between the types of 3D imaging methods as application and indications thereof may differ. Since 3D cone beam computed tomography (CBCT) imaging will play an increasingly important role in orthodontics and orthognathic surgery, special emphasis should be placed on discussing CBCT applications in facial evaluations.

3D cone beam computed tomography (CBCT) images offer a unique and new appreciation of the anatomical structures and underlying anomalies not possible with conventional radiographs. However, in almost all aspects of CBCT imaging, from utilization to application, inherent limitations and pitfalls exist. Importantly, these inherent limitations and pitfalls have practical implications which need to be addressed before the potential of this technology can be fully realized. The purpose of this review was to explore the current limitations and pitfalls associated with CBCT imaging to allow for better and more accurate understanding of the possibilities this imaging modality could offer, particularly pertaining to 3D cephalometry.

The aim of this study was to evaluate and compare postero-anterior (PA) cephalograms and cone-beam computed tomography (CBCT) images for the detection of mandibular asymmetry. Six asymmetric anonymous dry human skulls with visible chin deviation were available for this study. Metallic markers were glued on the anatomical landmarks to avoid identification error. PA cephalograms and CBCT scans were made by means of a standardized set-up. Each scan and cephalogram was measured three times by a single observer and the means used for analysis. Asymmetry was defined by the subtraction of the left side and right side measurements. CBCT was reliable [intraclass correlation coefficient (ICC) > 0.957] and very accurate (within 0.5 mm) in detection of all asymmetry. PA cephalograms were not accurate in detection of asymmetry of the mandibular ramus length, the mandibular body length, and the total mandibular length. PA cephalograms were the least reliable in determining the mandibular body length asymmetry (ICC = 0.686). The use of CBCT to detect mandibular asymmetry was validated with this study. CBCT images are very reliable and accurate for the detection of asymmetry and should be considered over conventional PA cephalometry when a chin deviation is present.

Morphometric methods are used in biology to study object symmetry in living organisms and to determine the true plane of symmetry. The aim of this study was to determine if there are clinical differences between three-dimensional (3D) cephalometric midsagittal planes used to describe craniofacial asymmetry and a true symmetry plane derived from a morphometric method based on visible facial features. The sample consisted of 14 dry skulls (9 symmetric and 5 asymmetric) with metallic markers which were imaged with cone-beam computed tomography. An error study and statistical analysis were performed to validate the morphometric method. The morphometric and conventional cephalometric planes were constructed and compared. The 3D cephalometric planes constructed as perpendiculars to the Frankfort horizontal plane resembled the morphometric plane the most in both the symmetric and asymmetric groups with mean differences of less than 1.00 mm for most variables. However, the standard deviations were often large and clinically significant for these variables. There were clinically relevant differences (>1.00 mm) between the different 3D cephalometric midsagittal planes and the true plane of symmetry determined by the visible facial features. The difference between 3D cephalometric midsagittal planes and the true plane of symmetry determined by the visible facial features were clinically relevant. Care has to be taken using cephalometric midsagittal planes for diagnosis and treatment planning of craniofacial asymmetry as they might differ from the true plane of symmetry as determined by morphometrics.