The Class II Malocclusion by Dr J W "Skip" Truitt B.S. D.D.S
The Class II malocclusion is the most common malocclusion to be seen in the Western world. To correctly treat this malocclusion, it is critical the clinician is able to make the differential diagnosis between the trapped retrognathic mandible (a skeletal Class II), and maxillary arch length loss (a dental Class II). The diagnosis can be complicated by the patient having both the dental and skeletal components in their malocclusion. To further complicate the issue, it is possible to have either component in a unilateral configuration.
The use of an orthopedically orientated cephalometric analysis plays a vital role in establishing the correct diagnosis and treatment plan. This clinician’s preference is the Bimler analysis as it can accurately assess both the dental and skeletal components of the Class II malocclusion, as well as determine the magnitude of the imbalances.
Once the diagnosis has been established, the next step is to formulate a treatment plan that addresses each component in the appropriate sequence. Failing to establish this correct sequence will result in a compromised result.
Skeletal Class II
If the patient suffers from the skeletal Class II (a trapped mandible), and has not completed the final pubertal growth, total resolution of the malocclusion is possible. If the mandibular epiphyseal growth plates have closed, the correction will be compromised to some degree. Orthognathic advancement surgery is frequently the best option for the severe skeletal Class II post pubertal patient.
The first step in treating the skeletal Class II is to determine exactly what is trapping the mandible and preventing it from attaining its genetic Class I relationship to the anterior cranial base. There are five things that can trap the mandible and prevent the normal growth. These five things, in the most common order they occur, are the following:
Some patients have only one of these preventing the mandible from growing to its genetic potential. Some patients have all five resulting in a very severe skeletal Class II malocclusion.
The skeletal Class II malocclusion is not a direct genetic transfer like the skeletal Class III malocclusion. Rather the patient inherits the location of the glenoid fossa more posteriorly than average relative to the anterior base. This in turn increases the propensity for the entrapment.
All of the factors trapping the mandible must be eliminated before the mandible can be fully distracted into the skeletal Class I relationship, with the exception of the deep bite. The vertical entrapment is eliminated when the mandible is distracted down and forward with appliances such as the Bionator, or the Walters Twin-Block.
The distraction can be done as the final phase in the treatment sequence, or it can be done incrementally as the entrapment is being eliminated. When both options are open, the incremental distraction is the better of the two options in the permanent dentition. The incremental distraction is usually accomplished using a RN-Sagittal appliance modified with an anterior bite ramp, Class II elastics holding the mandible forward in the distracted position, and vertical elastics posteriorly to erupt the deep Curve of Spee.
Full correction of the skeletal Class II can be achieved if the distraction occurs prior to the closure of the mandibular epiphyseal growth plates. Beyond this point the correction is obtained by remodeling of the glenoid fossa and the mandibular condyles, eliminating any posterior displacement of the condyles, and remodeling of the dental alveolar bases. Orthognathic surgery is usually the best option for the complete correction of a severe skeletal class II in the adult patient.
Dental Class II
Treatment of the dental Class II (maxillary arch length loss), usually depends upon the amount of arch length loss, and the age of the patient. For example, the lost arch length caused by the premature loss of a deciduous second molar can be easily treated using a simple plate with a screw mesial to the first permanent molar.
The same arch length loss in the older patient who has erupted permanent second molars will require more sophisticated mechanics. These may include recovering the lost arch length, or compensating for the lost arch length with either mid arch or terminal arch extractions. Dental Class II malocclusions in the permanent dentition almost always require the use of fixed appliance therapy.
Skeletal & Dental Class II
If the patient has both the trapped mandible and the arch length loss, the sequence of therapy is to establish the skeletal Class I before recovering the lost arch length. The exceptions to this are the lost E space in the mixed dentition, and the final repositioning of the mandible with a Rick-a-nator appliance or composite tripod bonding.
Correct diagnosis followed by a properly sequenced treatment are the keys to successfully resolving the Class II malocclusion. While appliance selection is the prerogative of each individual clinician, diagnosis and treatment sequence should always be consistent.