About Class 1, 2 and 3 Growth Types
Class 1 – Orthognathic
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.
The rotation of the jaws is shown on the left. 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 2 – Retrognathic
This classification can be affected by personal preference. It may be preferable in certain cases. These are 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. Others will exhibit a moderate/”normal” amount of growth. Finally, there are 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 obtained 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 protrusive Class II is believed 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 2 Correction
Class II malocclusion is defined by a molar tooth relationship where the lower mandibular molar is back relative to the upper maxillary molar.
There are 15 types of Class II.
The maxillary teeth can be protrusive, the maxilla can be protrusive, the mandible can be retrusive, the mandibular teeth can be retrusive, the maxilla can be retrusive and the mandible can be retrusive, etc… , and vertical dimension can affect these relationships as well.
Treatment can vary depending on the tooth positions, jaw bone positions and availability of growth in the appropriate direction.
Not all Class 2’s are alike by Dr. Standerwick (AJODO Vol. 136, Issue 2, Page 143)
Headgear is useful when lower incisors are inclined forward or if the bite plane displays a significant curve. It is good for reducing a gummy smile or and probably the best option for increasing the vertical height. Growth is necessary. Compliance can be an issue. Required wear is approximately 12-16 hours per day to obtain approximately 1mm per month of movement.
Various named functional appliances do basically the same thing. The push the lower mandible jaw forward in an attempt to stimulate growth; there is also a “headgear effect”. The more growth available, the more lower mandible jaw movement occurs and with less growth the lower mandibular teeth will move forward relative to the lower jaw. This can force the mandibular teeth forward, stressing the gum tissues enough to risk the need for gum grafting (take a patch of tissue from the palate to be placed over the lower mandibular anterior teeth roots.
Elastic bands are useful for short periods with certain facial types. They can make long faces longer and increase the gumminess of smiles. Compliance can be an issue.
With less available growth, one must consider the extraction of permanent teeth, TADs or surgery depending on esthetic demands and boney confines.
Mini-implants (TADs) require minor surgery for placement and they can become loose and require replacement. Besides that, all patients have stated they are fine and do not bother them. Occasionally, 3rd molars (wisdom teeth) may need to be extracted. Tooth movements can be slow and increase treatment time. They do not require the cooperation needed for headgear.
Class 3 – 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.