It checks for the alignment of the soft tissue nasion, the middle part of the upper lip at the vermillion border, and the chin point. If present, it is necessary to distinguish between a false and true asymmetry. A false asymmetry arises due to occlusal interferences, which results in a lateral displacement of the mandible, producing a cross-bite in the anterior/buccal region. Elimination of the displacement will return the mandible to a centric position. On the other hand, a true asymmetry indicates unequal facial growth on the left or right side of the jaws. Elimination of any occlusal cross-bites is not only difficult, but unlikely to improve the facial asymmetry. The assessment of the transverse components of the facial width is best described by the "rule of fifths", which sagittally divides the face into five equal parts:
Each transverse fifth should be an eye distance in width. The middle fifth is marked by the inner canthus of both eyes. The medial three-fifths of the face is marked from the outer canthus of the eye frames
The outer two-fifths of the face is measured from the lateral canthus to lateral helix of the ear, which represents the width of the ears. Tests
It is insufficient to derive at a diagnosis of jaw deformity solely based on the clinical examination. Hence, additional information is gathered from diagnostic tests, which may include dental model analyses and radiographic imaging studies. Dental Model Analyses - Study models for analysis can be made by taking dental impressions, or by 3D intra-oral scanning.
A lack of bony support for the soft tissues in this region will subsequently produce the depression, known as paranasal hollowing. This indicates a low level antero-posterior maxillary deficiency. Maxillary deficiency usually manifests as an increased naso-labial angle, although this is not a credible indication due to factors such as a short upper lip and/or proclined incisors. Another method to predict if a patient has maxillary deficiency is by the ‘scleral show and eyelid shape.’ The lower eyelid normally rests at the inferior border of the iris, without any sclera showing. If there is any sclera showing, then this is a good sign of infraorbital rim deficiency and maxillary antero-posterior deficiency, two manifestations that are usually seen in Class III patients. Orientation
When a jaw is abnormally oriented, malrotations occur. These malrotations are classified according to the axis on which the abnormal rotation occurs. When a jaw is malrotated around the transverse facial axis, it is said to have abnormal pitch. When malrotated around the anteroposterior axis, the jaw has an abnormal roll, a condition also known as cant. Finally, when a jaw is malrotated around the vertical axis, it has abnormal yaw. It can occur in maxilla and/or mandible and could result due to abnormal growth of the jaws in itself or as compensatory growth. Shape
Shape refers to figure, the geometric characteristic of an object that is not size, position, or orientation 5. A jaw with abnormal shape is said be distorted. Completeness
Completeness means the wholeness of the jaw.