Summarized by Dr. Hani Alhebshi.
Class II subdivision cases were defined as patients who have complete class II molar relationship on one side and class I on the other side.
One Study considered that a Class II subdivision required at least a half cusp difference between the right and left sides (For example, a full cusp Class II relationship on the right side and a half cusp Class II relationship on the left side).
Many orthodontists from British schools do not consider a subdivision case as a type in the classification. However they just see cases of class II as division one or two and treat each case separately according to the clinical situation.
Sanders et al., stated that the primary contributing factor responsible for a Class II subdivision malocclusion is a deficient mandible, due to either reduced ramus height or mandibular length, on the Class II side. However, other studies have reported that the main factor contributing to the asymmetric anteroposterior relationships in Class II subdivision malocclusions is the dentoalveolar component
Dentally , most studies show that class II subdivision malocclusion is primarily caused by distal positioning of the mandibular first molar in relation to the maxillary first molar, on the class II side.
Secondarily, it can be consequent to mesial positioning of the maxillary first molar, in relation to the mandibular first molar, on the class II side.
As a result, most class II subdivision malocclusion patients present the mandibular dental midline displaced toward the class II side associated to the maxillary dental midline coincident to the midsagittal plane or with a mild deviation, which require asymmetric orthodontic approaches.
Sara E. Cassidy et al, placed the subjects in their study into 4 groups based on similarities in their midline relationships , and the etiology of their asymmetries :
GROUP 1 – maxillary and mandibular midlines on with facial midline.
GROUP 2 – maxillary midline off from facial midline.
GROUP 3 – mandibular midline off from facial midline. ( Has tendency to be skeletal in origin).
GROUP 4 – Other midlines such as midlines both deviated to the same or opposite sides. They are small in numbers.
The treatment strategies include:
1- Orthognathic surgery to correct mandibular deviation with or without maxillary surgery but very few patient who accept this option because they don’t see their occlusion so severe to take the risk of surgery.
2- Extractions : is a good for camouflage if the profile of the patient can tolerate it.
- When Maxillary midline is off , then an extraction of one upper premolar on the class II side will correct the subdivision.
- When Lower midline is off while upper is on , Extraction of 4 premolars or 3 premolars ( 2 upper premolars and one lower on the class I side). Guilherme Janson et al, concluded that Treatment of class II subdivision malocclusion with 3 and 4 premolar extractions have a similar long-term posttreatment occlusal stability.
- It was not surprising to find that treatment time tended to increase with extractions. This study agrees with Fink and Smith , who also found the number of extracted premolars has a direct relationship to treatment time, with treatment time increasing by 0.9 months for each extracted premolar. These results are also similar to those of Alger, who found extraction cases to average 4.6 months longer than non-extraction cases.
- An interesting conclusion of Cassidy paper is Complete correction of midlines is not always achieved, especially in the case of mandibular skeletal asymmetry.
3- Headgears with asymmetric force activations. Brosh et al, concluded the following : For a bilateral unequal Class II relationship, the system of choice is outer-bow asymmetric headgear. For a unilateral Class II relationship with 1 side in a Class I molar relationship (Class II subdivision), inner-bow asymmetric headgear is recommended.
4- Fixed functional appliance like herbst or unilateral Forsus appliance. The entire lower arch should be continuously ligated with stainless steel ligature wire to prevent spacing and excessive proclination of the mandibular arch. Lingual crown torque may be incorporated into the mandibular arch as an additional step in preventing excessive proclination of incisors. If additional maxillary molar distalization is desired, a 0.018 stainless archwire may be placed in the upper arch to decrease frictional forces during translation and a lower lingual arch may be utilized. If less maxillary molar movement had been desired, a fixed transpalatal arch (TPA) would be placed. Close monitoring within 6 weeks is advisable to check any lateral open bite or canting in the occlusal plane.Lower incisor proclination was increased when fixed functional appliances were used, as well as when a Class I molar relationship was the target for the Class II side.
1- Classification and Treatment of Angle Class II Subdivision Malocclusions , Sara E. Cassidy.
2- Stability of class II subdivision malocclusion treatment with 3 and 4 premolar extractions. By Guilherme Janson1et al.
3- Unequal outer and inner bow configurations: comparing 2 asymmetric headgear systems. By Brosh et al.
4- Correction of Class II Subdivision Malocclusion with the Forsus™ Appliance
5- Different Seminars in Orthodontic department in King Abdulaziz University with Prof. Ali Habeeb ( Head of Orthodontics program ).