Prognathism is a term used to describe the positional relationship of the mandible and/or maxilla

Maxilla

The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...

 to the skeletal base where either of the jaws protrudes beyond a predetermined imaginary line in the coronal plane of the skull. In general dentistry, oral and maxillofacial surgery and orthodontics this is assessed clinically or radiographically (cephalometrics

Cephalometry

Cephalometry is the measurement of the human head by imaging, traditionally from x-ray films.-Dentistry:Cephalometric analysis is used in dentistry, and especially in orthodontics, to gauge the size and spacial relationships of the teeth, jaws, and cranium...

).