One way in which a vertical jaw abnormality can occur is if the condylar growth process is damaged, and thus the intramembranous growth continues along the posterior condylar margin, becoming predominant, thus resulting in a high angle type.Assessing a patient for vertical and horizontal excess
The Maxillary Mandibular Plane Angle (MMPA) is important in assessing a patient for vertical jaw abnormality. The important landmarks are the Frankfurt plane and the Mandibular plane. The Frankfurt plane is a line charted from the upper border of external auditory meatus to the lower border of the orbit. It is similar to the ala-tragus line however should not be confused with it. Whereas the Mandibular angle is a line measured along the natural lower border of the patients mandible. The intersection of the Frankfurt and Mandibular plane is what determines the pattern of vertical growth. If the intersection occurs behind the occiput i.e. decreased angle, then the patient is considered to have horizontal growth. On the other hand, if the intersection occurs in front of the occiput, then the patient is considered to have vertical growth. The normal range is considered to be between 25 and 30 degrees in a typical Caucasian person. Those with excess vertical jaw growth are most often seen having an anterior open bite, as the mandible is growing away from the maxilla. Whereas those with excessive horizontal growth are seen as having an overbite.
Excessive Downward Displacement and Insufficient Downward Displacement
Here on, we will use interchangeably the terms vertical maxillary excess and deficiency with excessive and insufficient downward displacement. In order to understand its manifestations, we need to account for key landmarks such as:· Columella (CM)– The tissue that links the nasal tip to the nasal base, separating the nares. The inferior margin of the nasal septum
· Subnasale (SN) – the junction of the upper lip and the columella
· Stomion Superios (Sts) – the lower most point on the vermillion of the upper lip
· Stomion (Sto) – The point of contact, when lips are competent, in the midline, between the top and bottom lip
· Stomion Inferious (Sti) – the upper most point on the vermillion of the lower lip
· Soft tissue mention (Me) – The most inferior point on the soft tissue outline of the chin
The measurements of the upper lip and lower lip for each patient are ascertained by using the aforementioned landmarks. The length of the upper lip is measured from Sn to Sts. In a typical male and female this measures to 24mm and 21mm respectively (REF). The length of the lower lip is measured from Sti to Me. In a typical male and female this measures to 50mm and 46.5mm respectively.When considering EDD and IDD, the class of the skeletal base is a good adjunct. In other words, EDD and IDD can either appear camouflaged or apparent given the skeletal base and the soft tissue profile accompanying it.