Class II malocclusion is one of the most common malocclusions among orthodontic patients. Within Class II, we have two different types, division 1 and division 2. Each of them has specific dental and facial characteristics that must be taken into account when designing our treatment plan. For example, in patients with Class II division 2 it is common to observe that they are patients with a concave profile, retruded lips, a reduced lower facial third and a prominent chin. Intraorally, we usually find narrow arches, retroinclined incisors and increased overbite.
Class II division 2 can be treated either with aligners or with brackets, achieving similar results. However, the biomechanics of each system are different. Studies show that the effectiveness of both devices in correcting this type of malocclusion is similar . In my opinion, or at least in my hands, torque correction is easier to achieve (or faster) with fixed orthodontics compared to aligners. When a patient comes with negative torque on incisors and a complete overbite, treating this type of problem with aligners is more difficult for me than, for example, solving it with brackets and a pair of Australian archwires with tip-back bends.
Although the mechanics of fixed orthodontics have an earlier origin than the mechanics with aligners, they are still more effective for some movements. Proof of this can be seen in those cases of aligners where we need to place sectional archwires to improve the tip or root inclination of the teeth or when we place buttons and power-chains to derotate a tooth that has not moved as planned. The ease with which we can change the torque and improve the overbite with fixed orthodontics is not possible with aligners because they are removable. For that reason, when we face very complex cases of class II division 2, sometimes we will need auxiliary techniques to the aligners, such as micro-screws, which will help us to achieve the desired torque.
However, although brackets may be more effective than aligners in correcting this type of malocclusion, this does not mean that they are the best option in all cases.
One of the unwanted effects caused by almost all orthodontic treatments is the root resorption associated to the movement of the teeth. The specific cause of this is difficult to determine, as there are numerous factors that can cause this root resorption: from sex, age, race, type of movement, the amount of force applied, the duration of orthodontic treatment... and there is also another variable that we should not forget: the type of appliance we use. And, in this aspect, aligners outperform braces (by a little).
A recent study has shown that root resorption caused in Class II division 2 treatments with aligners is less than that caused by braces. Why is this? We can identify two main reasons:
- The type of force applied: Aligners, being removable appliances, do not apply a continuous force as brackets do, but apply a discontinuous and controlled force, normally within the biological range of movement. The fact that the forces are intermittent and are within reasonable values to facilitate the adaptation of the periodontal structures to tooth movement means that the risk of affecting the root cementum and thus causing root resorption is lower
- Greater control of movements thanks to digital planning: when we move teeth with braces, we do not have the same control over root movement that we do with aligners. On ClinChecks, Approvers, or any other software for digital planning, we can decide what sequences we want to do, how many millimeters we can proincline, verify if we are moving the roots outside the cortical bone with the CBCT tool... All this makes the movements made with aligners, if they are well planned, "safer" than with braces. This may be one of the reasons why less root resorption has been detected in treatments with aligners in patients where a considerable torque change has to be made.
And so, in cases of Class II division 2, the following dilemma arises: Which option do we choose, to correct the malocclusion with brackets with proven mechanics or to treat the patient with aligners, knowing that it may be a more complex treatment but that it can reduce the amount of root resorption? As always, there is no clear answer to the question. It will depend on the case.
Chen H et al. Changes of maxillary central incisor and alveolar bone in Class II Division 2 nonextraction treatment with a fixed appliance or clear aligner: A pilot cone-beam computed tomography study. Am J Orthod Dentofacial Orthop 2022.