There are basically 3 horizontal facial types; of which, any one of the 3 types can have an increased, neutral or decreased vertical facial height component.  Being 3-dimensional the final consideration is the transverse (width). 



Class I/Orthognathic: (float the mouse cursor over the illustrations for help with determining the correct illustration)

Normal variation is based on 1 standard deviation  determined statistically based on ethnic type.

Crowding in these individuals usually requires orthodontic movement while maintaining the position of the jaws.  Vertical tendencies can develop to Class II or Class III depending on  rotation of the jaws with treatment.

(Rotation of the jaws shown.  There is variation in the point of rotation depending on facial growth patterns and tooth contact; illustration from Bjork A. Facial growth in man, studied with the aid of metallic implants. Acta Odontol Scand 1955;13:9-34.)

Class II/Retrognathic:                                                                                                                                                            
    
This classification can be affected by personal preference, and may be preferable in certain but mostly female cases.  It can be a relative retrognathia (retrusion) of the mandible.

 

   There are arguably 12 to 18 combinations of Class II which include:

Protrusion of the maxilla (upper jaw) or the maxillary teeth (upper teeth)

Retrusion of the mandible (lower jaw) and/or mandibular teeth.

A clockwise rotation of the mandible with increased vertical component can create a Class II skeletal arrangement.

In the most difficult cases, the retrusion of the mandible occurs with retrusion of the maxilla.
 

Functional Appliances position the mandible forward allowing the articulation with the base of the skull to adapt and arguably allows the mandible to grow.  There are individuals who will exhibit a lot of growth, those who will exhibit a moderate/"normal" amount of growth and then some for whom growth doesn’t seem affected; however, there is not yet a genetic test available to assess which individual with exhibit the best/worst response.  It is also unknown whether the individuals that exhibit poor growth are not just a group who are hypo-responsive (low responsiveness) and therefore just need more time for the desired effect.  Parents should reasonably assess the level of compliance of their child as many therapies in the mixed dentition (having baby and permanent teeth) are removable appliances. 

In a non-growing or possibly hypo-responsive individual, the orthodontic correction may need to be supplemented with orthognathic surgery.

Studies have shown that a comparable dental result can be obtain for a Class II caused by maxillary dental protrusion when treated with 1-phase versus 2-phases (a functional appliance to position the jaws and then braces); however, this study should not be applied to the at least 11 other types of Class II.  This protusive Class II is believe to represent 15% of Class II's. The functional appliance group in these 1-phase versus 2-phase studies were less likely to seek surgical correction as a trend; the number of subjects did not allow for a statistically significant observation. The risk of root resorption may be decreased by the use of functional appliances in the mixed dentition.
 

Class III/Prognathic

This classification is exhibited as either:

Restricted growth of the maxilla;  considered genetically linked to suture growth.

Extra growth of the mandible; also considered genetically linked but to cartilage on the mandible.

 

This classification is difficult to assess as the growth is unpredictable, and it is essential that these individuals be evaluated early.

The craniofacial sutures are manipulated more efficiently in younger individuals, and become increasingly difficult to manipulate after 8 years of age.  

In a non-growing or possibly hypo-responsive individual, the orthodontic correction may need to be supplemented with orthognathic surgery.

 

 
These opinions are meant for educational purposes and are in no way an exhaustive explanation of orthodontic diagnosis.  Any suspicion of a condition mentioned should be confirmed with a certified specialist in orthodontics.