What is Class II (Two) Malocclusion? A primer on some treatment modalities by Dr. Jim Prittinen

Class II malocclusion is a condition characterized by the upper front teeth positioned excessively anterior to the lower front teeth. More than one-third of patients who need orthodontic treatment have a Class II malocclusion. In most Class II cases, both the anterior and posterior upper teeth are anywhere from 4 to 8 mm ahead of their respective lower teeth. Parents describe their child as "having the front teeth sticking out too far" or "not having a good chin". Additionally, many Class II patients also have long, narrow faces. These patients are often very difficult to treat. Long face patients often need extractions to correct Class II problems.

Many orthodontic treatment modalities are used to correct Class II problems. Class II elastics are regarded as the mainstay of Class II correction. They are used with fixed appliances. The classic elastic system involves two fully bracketed arches, with bilateral elastics stretched between the maxillary canines and mandibular molars. Variations on this system include direct attachment of the elastic to an archwire (with a hook, loop, or spur) and an assortment of maxillary and mandibular attachment positions. Although force levels vary greatly depending on the type and placement of the elastic used, forces delivered by a new latex elastic typically range from 50g to 300g.

Class II elastics are widely used because of their simplicity, effectiveness, and the ease with which they can be incorporated into any fixed appliance system. Usually placed after the initial leveling and alignment stages of treatment, Class II elastics can be used with continuous working archwires, as well as partial bracketings (often done in the mixed dentition stage). Primary effects of Class II elastics include forward movement and proclination of the mandibular dentition, along with distal movement and retroclination of the maxillary dentition. Secondary effects include buccal uprighting and widening of the lower molars due to the slight transverse component of force. In the mixed dentition, when Class II malocclusion often is associated with maxillary constriction, elastics can be a useful treatment adjunct as the axial inclination of the posterior teeth is corrected and the curve of Wilson is leveled.

Class II elastics exert a pulling force across the occlusal plane. The vertical component of this pulling force may extrude the maxillary incisors and mandibular molars. Consequently, a downward and backward rotation of the mandible may occur. In patients with long faces (steep mandibular plane angles) mechanics that tend to extrude posterior teeth are contraindicated. Therefore, Class II elastics are used less often and less aggressively in these patients. These patients often benefit form extraction treatment, by using the extraction space to retract the upper anterior teeth and advance the lower posterior teeth. Closing the space also tends to lower the mandibular plane angle, thus preventing long faces from getting longer.

In long faced patients, appliances other than Class II elastics are indicated. The Herbst appliance is a good option because the appliance helps limit molar eruption. The modern Herbst appliance consists of stainless steel crowns over the maxillary first molars, connected to bands on the mandibular first premolars by a rigid plunger-tube system that forces the lower jaw into a forward position during closure. Some designs also use crowns on the lower first molars.

The telescoping mechanism of the Herbst appliance places an upward and posteriorly directed force on the maxillary molars. When the appliance is used during comprehensive orthodontic treatment, the maxillary molars usually move about 1-3mm distally. Additionally, Herbst treatment will either prevent upper molar eruption or (some say) intrude the upper molars. This is why the appliance is used in long faced patients.

In 1987, J.J. Jasper developed and patented the Jasper Jumper, which featured a stainless steel compression spring in a polyurethane sheath. This is a modification of the Herbst "bite-jumping" mechanism that permits greater freedom of mandibular movement. The compression module, which is available in multiple lengths, is anchored to the main archwire and can be incorporated easily into traditional edgewise orthodontic treatment.

Like the Herbst appliance, and unlike Class II elastics, the Jasper Jumper produces intrusive intraarch forces by pushing apart the points of attachment. Because some of the force components are intrusive, these appliances are appropriate for long faced patients. Studies have shown the Jasper Jumper produces a surprising amount of skeletal Class II correction in growing patients. However, breakage is a big problem with this appliance. To mitigate this problem, manufacturers have developed Jasper like appliances that are more durable. The Forsus Fatigue Resistant Device, developed by Unitek, and the Twin Force Bite Corrector, developed by Ortho Organizers, are two appliances that are conceptually similar, but more durable and easier to use than the Jasper Jumper. They are two-piece telescoping piston assemblies within a stainless steel spring cylinder. As the patient closes in maximum intercuspation, the coil spring is compressed, releasing stored energy. At nearly full compression (10-12mm), they apply approximately 200g of force. Because the springs rarely are compressed fully, the level of force delivery is comparable to that of heavy Class II elastics. Initial studies report breakage rates of these appliances to be significantly less than Jasper Jumpers.

The issue of optimal Class II treatment timing is one of the most studied and widely debated topics in orthodontics. Most studies show that late treatment (after all permanent teeth are erupted) and fixed appliances are more efficient than earlier treatment and removable appliances. Cephalometric studies have shown that the therapeutic effectiveness of most Class II correction appliances is greatest when these appliances are used during the pubertal growth spurt. All of the Class II correction appliances discussed here may be used in the permanent dentition, in conjunction with fixed appliances. The key indicator of success over the long term is holding the Class I relationship once it is achieved. Avoidance of Class II relapse is a challenge, but studies have demonstrated that good cuspal interdigitation is an excellent predictor of stability.

In conclusion, many factors contribute to the success or failure of Class II correction. The original malocclusion, as well as, age, growth pattern, and cooperation of the patient, combined with appliance selection are all vitally important in the delivery of high quality orthodontic results.