Determining the sagittal relationship between the maxilla and the mandible: a cephalometric analysis to clear up the confusion.

Unlabelled: Establishing the sagittal jaw relationship is a key component to developing a diagnosis when treating an orthodontic patient. Several measurements, including the Wits Appraisal, ANB angle and nasion perpendicular have been and are currently used by practitioners to diagnose the sagittal jaw relationship. Unfortunately, all of these measurements have their limitations. The Cannon Analysis was created in an attempt to help overcome these limitations.

Methods: One hundred untreated patients from the Vanderbilt University Medical Center database were selected, and their initial lateral cephalometric radiographs were digitally traced utilizing the Cannon Cephalometric Analysis. All of these patients had an orthognathic profile, a Class I occlusion and a good skeletal balance as judged by the authors. Normative values were established for the Cannon Analysis and then broken down by sex and age (8-11, 12-18, 19 and over). An example case was analyzed using the Cannon Analysis and several diagnostic scenarios were reviewed.

Results: The variance or difference between Porion to A Point (Po-A) and Porion to B Point (Po-B) was found to be 12.6 mm. This value remained relatively constant throughout life, with only slightly higher values for males versus females.

Conclusion: The Cannon Analysis is an effective way to accurately establish the sagittal jaw relationship since it is not affected by the anterior / posterior position of nasion, the steepness of the mandibular plane angle, nor an improperly drawn occlusal plane.