We have traditionally managed extraction cases with fixed appliances, but as clear aligner therapy continues to evolve, orthodontists are increasingly utilizing this treatment modality for more complex cases, including those requiring premolar extractions. Advances in aligner technology and biomechanical understanding have opened new possibilities, yet challenges remain in achieving predictable outcomes.
Orthodontists typically decide to extract teeth in orthodontic treatment based on factors such as crowding, incisor protrusion, facial profile concerns, and the need for stability [7]. Extraction treatment aims to create space for alignment, improve occlusion, and enhance facial aesthetics. However, managing extraction spaces and controlling tooth movements present unique challenges, particularly with clear aligner therapy.
Clear Aligner Therapy for Extraction Cases
Clear aligners can address extraction cases through several mechanisms:
- Controlled retraction of anterior teeth
- Maintenance of posterior anchorage
- Management of root angulation and torque
- Vertical control during space closure
- Transverse coordination of the arches
Studies have shown that clear aligners can effectively manage these tooth movements, although the efficacy may vary depending on the severity of the malocclusion and the specific movements required [1,6].
Opportunities and Limitations
Clear aligners offer several opportunities for extraction treatment. They are removable, enhancing patient comfort and hygiene. Visualizing and planning tooth movements digitally allows for precise treatment planning. Additionally, clear aligner therapy allows for simultaneous management of multiple aspects of tooth movement during space closure [2].
However, there are limitations to consider. Achieving adequate anchorage control can be challenging, often resulting in more mesial movement of molars compared to fixed appliances [6]. Root control and bodily movement are difficult to achieve, with a tendency for uncontrolled tipping of teeth adjacent to extraction sites [1]. Maintaining proper incisor torque during retraction is crucial but can be challenging with aligners [6]. The “roller coaster effect” (extrusion of incisors and intrusion of posterior teeth) can also be difficult to manage [5].
Mechanism of Action and Biomechanical Considerations
The biomechanics of space closure with clear aligners differ from those of fixed appliances. We develop force systems through the elasticity of the aligner material, force features built into the aligner, and the design of attachments. Recent finite element analysis studies have provided insights into these force systems [8].
During space closure, the strain in the aligner material increases as the extraction space decreases, leading to enhanced space closure forces. However, this can also result in unwanted tipping and rotation of teeth adjacent to the extraction sites [8]. The center of rotation of anterior teeth tends to move labially and apically during retraction, affecting torque control [5].
Keys to Success
To achieve predictable outcomes in extraction cases with clear aligners, orthodontists should consider several key elements:
- Careful case selection, focusing on cases with 9-10 mm of crowding or greater [7]. Greater crowding tends to reduce posterior tipping [10].
- Realistic treatment planning with overcorrection in the virtual setup [1]. The design digitally must compensate for lag and incorporate reverse curve mechanics plus overtreatment of challenging movements
- Strategic use of attachments to improve the accuracy of tooth movements [9]. Attachments are critical for root control, and optimized attachments tend to have greater control of distal movements and reduce mesial tipping of the posterior teeth [10, 11].
- Proper anchorage planning, determining whether minimum, moderate, or maximum anchorage is required [4].
- Implementation of specific force systems for posterior anchorage, canine root control, incisor torque, and vertical dimension management [3,4,5,9].
- Utilization of a proper staging, focusing on vertical and root control of the posterior and anterior teeth, followed by space closure [8].
- Regular monitoring and refinement of treatment as needed [6].
Outcome Comparison
Studies comparing clear aligner therapy to fixed appliances in extraction cases have shown that while both can achieve similar amounts of incisor retraction, clear aligners tend to result in greater increases in overbite, more lingual tipping of maxillary incisors, and more mesial tipping of molars [2,6]. Understanding these tendencies is crucial for treatment planning and implementing appropriate compensations. Consider temporary skeletal anchorage, optimized attachments, overcorrection, and careful biomechanics to improve outcomes when treating extraction cases with clear aligners.
Long-term Stability and Treatment Duration
Further research is required on the long-term stability of extraction treatment with clear aligners. Some studies have indicated that aligner treatment in extraction cases may take longer than fixed appliances to achieve comparable results [6]. Orthodontists should consider regular follow-up and appropriate retention strategies to maintain treatment outcomes.
Conclusion
Clear aligner therapy offers a promising approach to extraction treatment, particularly for carefully selected cases. It requires a nuanced understanding of biomechanics, aligner capabilities, and individual patient factors. By incorporating the key elements discussed into treatment planning and execution, clinicians can enhance the predictability of extraction treatment with clear aligners.
As clear aligner technology advances, we expect further improvements in managing these complex cases. Staying current with the latest research and continuously refining clinical approaches will be key to achieving optimal results for patients requiring extraction treatment with clear aligners.
References:
1. Dai, F. F., Xu, T. M., & Shu, G. (2021). Comparison of achieved and predicted crown movement in adults after 4 first premolar extraction treatment with Invisalign. American Journal of Orthodontics and Dentofacial Orthopedics, 160(6), 805-813.
2. Gaffuri, F., Cossellu, G., Lanteri, V., Brotto, E., & Farronato, M. (2020). Comparative effectiveness of Invisalign and fixed appliances in first-premolar extraction cases. J Clin Orthod, 52(5), 294-301.
3. Hong, Y. Y., Kang, T., Zhou, M. Q., Zhong, J. Y., & Chen, X. P. (2024). Effect of varying auxiliaries on maxillary incisor torque control with clear aligners: A finite element analysis. American Journal of Orthodontics and Dentofacial Orthopedics.
4. Liu, J. Q., Zhu, G. Y., Wang, Y. G., Zhang, B., Yao, K., & Zhao, Z. H. (2023). Different biomechanical effects of clear aligners in closing maxillary and mandibular extraction spaces: Finite element analysis. American Journal of Orthodontics and Dentofacial Orthopedics, 163(6), 811-824.
5. Liu, L., Song, Q., Zhou, J., Kuang, Q., Yan, X., Zhang, X., … & Lai, W. (2022). The effects of aligner overtreatment on torque control and intrusion of incisors for anterior retraction with clear aligners: A finite-element study. American Journal of Orthodontics and Dentofacial Orthopedics, 162(1), 33-41.
6. Song, J. H., Lee, J. H., Joo, B. H., Choi, Y. J., Chung, C. J., & Kim, K. H. (2024). Treatment outcome comparison of Invisalign vs fixed appliance treatment in first premolar extraction patients. American Journal of Orthodontics and Dentofacial Orthopedics, 165(4), 399-413.
7. Tom, K., Mancl, L., Woloshyn, H., Khosravi, R., & Bollen, A. M. (2024). Association between crowding estimation and extraction recommendations in orthodontics. American Journal of Orthodontics and Dentofacial Orthopedics, 165(1), 64-72.
8. Wang, Y. G., Zhu, G. Y., Liu, J. Q., Wang, Y. F., & Zhao, Z. H. (2024). Dynamic biomechanical changes of clear aligners during extraction space closure: Finite element analysis. American Journal of Orthodontics and Dentofacial Orthopedics, 165(3), 272-284.
9. Yang, Y., Yang, R., Liu, L., Zhang, X., Jiang, Q., Fan, Q., … & Lai, W. (2023). The effects of aligner anchorage preparation on mandibular first molars during premolar-extraction space closure with clear aligners: A finite element study. American Journal of Orthodontics and Dentofacial Orthopedics, 164(2), 226-238.
10. Dai, Fan-Fan, Tian-Min Xu, and Guang Shu. “Comparison of achieved and predicted tooth movement of maxillary first molars and central incisors: first premolar extraction treatment with Invisalign.” The Angle Orthodontist 89.5 (2019): 679-687.
11. Comba, Benedetta, et al. “A three-dimensional finite element analysis of upper-canine distalization with clear aligners, composite attachments, and class II elastics.” J Clin Orthod 51.1 (2017): 24-28.
