Achieving Predictable Class II Correction with Clear Aligner Therapy – Keys to Success

Clear aligner therapy has evolved significantly, particularly in its ability to address more complex cases like Class II malocclusions. While clear aligners offer many advantages for patients, achieving predictable Class II correction requires careful planning and understanding of this treatment modality’s opportunities and limitations.

Background on Class II Treatment

Class II malocclusions can present as a sagittal discrepancy on molars and canines. A retrognathic mandible, protrusive maxilla, or both characterize a skeletal Class II problem. Treatment approaches generally fall into three categories: growth modification, dentoalveolar camouflage, or surgical intervention. For growing patients, functional appliances like the Herbst or Twin Block aim to improve mandibular growth and the skeletal relationship. In non-growing patients, camouflage treatment often involves maxillary molar distalization and/or mandibular incisor proclination to correct the dental relationship. Traditionally, Class II correction has relied heavily on patient compliance with removable functional appliances or Class II elastics. Fixed functional appliances like the Herbst aimed to reduce compliance issues. More recently, clear aligner therapy has emerged as another option for treating Class II cases.

Clear Aligner Therapy for Class II Correction

We can use clear aligners to address Class II malocclusions through several mechanisms. Studies have shown that clear aligners can effectively distalize maxillary molars. Ravera et al. found that maxillary first molars could be distalized an average of 2.25 mm without significant tipping or vertical movements. Invisalign’s Mandibular Advancement (MA) and the Mandibular Advancement Occlusal Block (MAOB) feature use precision wings or bite blocks to position the mandible forward, similar to other functional appliances. Clear aligners have also demonstrated high efficacy in dental arch expansion, which can create additional space for Class II correction (Morales-Burruezo et al.). Additionally, Class II elastics can be used with clear aligners to aid in sagittal correction, similar to fixed appliances (Giancotti et al.).

Opportunities and Limitations

Clear aligners offer several opportunities for Class II correction. They are removable, which can enhance patient comfort and hygiene, making them preferable for many adult patients. The full occlusal coverage of aligners may provide better control of vertical dimension than other treatment modalities. Clear aligner therapy allows for simultaneous arch expansion, molar distalization, and mandibular advancement in growing patients.

However, there are limitations to consider. Anchorage control during molar distalization and anterior retraction remains a significant challenge. Li et al. found that molar distalization efficacy was only 36.48% for the first molars and 41.94% for the second molars. The same study found that molar distalization efficacy was significantly lower in cases requiring anterior retraction than in non-retraction cases.

Mechanism of Action and Occlusal Plane Changes

Class II elastics, often used with clear aligners, can have some unwanted effects. Li et al. found that the bisected occlusal plane angle increased by 1.51° in Class II patients treated with clear aligners and elastics, likely due to extrusion of molars and incisors. If not properly controlled, the mesial force on the lower arch can lead to the proclination of mandibular incisors. The distal force on the upper arch can cause extrusion of maxillary incisors, potentially worsening gummy smiles. It is critical to consider these effects and, in the ClinCheck design, vertical movements to counteract these effects if they are undesirable. 

Keys to Success

We should consider several key elements to achieve predictable Class II correction with clear aligners. Realistic treatment planning is crucial, and overcorrection in the ClinCheck may be necessary, especially for molar distalization. Employing a V-shaped distalization pattern, starting with the second molars, then the first molars, followed by premolars and anterior teeth, can improve efficiency. Simon et al. found that attachments on the tooth surface improved the accuracy of tooth movements, particularly for molar distalization.

Regular monitoring of tooth movements and willingness to refine treatment as needed are essential for achieving desired outcomes. Careful case selection is crucial, as mild to moderate Class II cases are more predictably treated with aligners than severe cases. It’s important to be mindful of the potential for posterior bite opening during Class II correction by ensuring proper anterior torque and leveling of the lower curve of Spee. In some cases, consider distalizing molars first before attempting anterior retraction to maximize distalization efficacy and reduce anterior roundtripping. In growing patients, leverage Class II elastics for occlusal plane changes or utilize the MA feature to potentially harness mandibular growth and improve skeletal relationships.

Conclusion

While clear aligner therapy offers a promising approach to Class II correction, it requires a nuanced understanding of biomechanics and aligner capabilities. The discrepancy between predicted and achieved tooth movements highlights the importance of careful treatment planning and monitoring. By incorporating these key elements into your treatment planning and execution, you can enhance the predictability of Class II correction with clear aligners. Staying current with the latest improvements in the appliance and research and continuously refining your approach based on clinical experience will lead to the best outcomes for your patients.

References:

1. Ravera S, et al. Maxillary molar distalization with aligners in adult patients: a multicenter retrospective study. Prog Orthod. 2016;17:12.
2. Li L, et al. Maxillary molar distalization with a 2-week clear aligner protocol in patients with Class II malocclusion: A retrospective study. Am J Orthod Dentofacial Orthop. 2023.
3. Simon M, et al. Treatment outcome and efficacy of an aligner technique–regarding incisor torque, premolar derotation, and molar distalization. BMC Oral Health. 2014;14:68.
4. Morales-Burruezo I, et al. Arch expansion with the Invisalign system: efficacy and predictability. PLoS One. 2020;15:e0242979.
5. Giancotti A, et al. Correction of Class II Malocclusions in Growing Patients by Using the Invisalign Technique: Rational Bases and Treatment Staging. J Orthod Endod. 2017;3(3):12.
6. Hosseini HR, et al. A comparison of skeletal and dental changes in patients with a Class II relationship treated with clear aligner mandibular advancement and Herbst appliance followed by comprehensive orthodontic treatment. Am J Orthod Dentofacial Orthop. 2024;165:205-19.
7. Li J, et al. Changes of occlusal plane inclination after orthodontic treatment in different dentoskeletal frames. Progress in Orthodontics. 2014;15:41.