Innovations in Orthodontics: Skeletal Versus Dentoalveolar Expansion Utilizing Clear Aligners and TAD-Assisted Expanders
Marianna Evans, DMD; and Daniel Berant, DMD
Hypoplastic maxilla is a common skeletal anomaly that compromises function and esthetics. Beyond just a narrow-appearing smile, this abnormality presents significant restorative challenges in adult patients as it is often associated with crowding, compromised axial inclination of the teeth, lack of alveolar bone support, root proximity, and occlusal trauma.1 Recent research also confirms association of maxillary deficiency with nasal stenosis and a predisposition to compromised nasal airflow and pharyngeal collapse during sleep.2,3 Maxillary transverse skeletal deficiency is often but not always associated with posterior dental cross-bite. In most cases, maxillary posterior teeth are flared buccally and mandibular posterior teeth are excessively lingually inclined masking the underlying skeletal problem.4 Advances in 3D imaging in dentistry, namely ultra-low radiation cone-beam imaging technology, have significantly enhanced clinicians' ability to diagnose and subsequently treat a maxillary transverse deficiency.5
Maxillary Expansion: Skeletal Versus Dental
Maxillary expansion refers to techniques aimed at increasing maxillary skeletal and dental arch widths. This process is crucial for addressing various skeletal and dental orthodontic issues, including dental crowding, correction of occlusion, esthetic concerns, and even compromised nasal breathing.It is vitally important to understand that maxillary constriction/hypoplasia is a basal bone problem and cannot be resolved with tooth movement alone.1 In children, due to sutural patency, maxillary basal bone can be easily stretched utilizing orthopedic palatal expanders that anchor on permanent or primary teeth. However, in adult patients, application of orthopedic heavy forces to the teeth often lead to dental tipping with formation of periodontal dehiscences and fenestrations with increased risks of gingival recession and orthodontic relapse (Figure 1).1 Historically, maxillary deficiency in skeletally mature patients could only be addressed with surgical techniques, such as surgically assisted rapid palatal expansion.6 Most patients, however, often declined surgical expansion because of the invasiveness of the surgery and in turn accepted compromised orthodontic, periodontal, and restorative treatment outcomes.
Clear Aligners and Dental Arch Expansion - What Are the Limitations?
Aligners have revolutionized orthodontic treatment by offering a clear, comfortable, and removable alternative to traditional braces. The technology behind aligners has continuously evolved. As a result of their increased effectiveness clinicians are able to use them in increasingly complex cases. The development of more sophisticated 3D printing and digital scanning technologies has greatly enhanced the customizability and fit of aligners. Moreover, software algorithms have become more advanced and by incorporating cone-beam computed tomography (CBCT) scans have allowed for more accurate prediction of tooth movement and treatment outcomes.
Aligners can be effective tools to accomplish buccolingual tooth movement and to close open bites. Nevertheless, skeletal sutural expansion is not achievable with either aligners or braces alone in skeletally mature patients. Even in growing children, CBCT-based evidence has yet to demonstrate that maxillary sutural opening can be achieved solely with aligners. Dentoalveolar expansion, easily achievable with aligners, unfortunately does not resolve the underlying basal bone deficiency. Furthermore, it can introduce significant occlusal instability with subsequent high risks of orthodontic relapse and periodontal compromises in the form of alveolar bone dehiscences and gingival recessions. To minimize these periodontal complications and improve long-term stability, bone augmentation periodontal surgeries, such as surgically facilitated orthodontic therapy, have been recommended prior to initiating dentoalveolar expansion with aligners or fixed orthodontic appliances.7
Skeletal Expansion in Adults Without Traditional Surgery - Myth or Reality?
The well-established belief that mid-palatal suture fuses with age has been disproved with histological and computer tomography studies.8 Research shows increased interdigitation in the mid-palatal suture with age that makes it difficult to open utilizing traditional tooth-supported expanders.8 Tooth-supported expanders alone are simply too weak to open up the mid-palatal suture in adult patients without compromising the periodontal integrity of the anchoring teeth.
Recent introduction of temporary anchorage device (TAD)-supported 3D-printed palatal expanders together with CBCT-based digital planning revolutionized the envelope of nonsurgical maxillary expansion (Figure 2 through Figure 4). These advancements have allowed clinicians to correct even severe skeletal surgical malocclusions in non-growing patients.9 Suddenly, what was only possible with osteotomies and invasive surgery can now be achieved with less invasive procedures to correct a patient's maxillary constriction.10 The utilization of TAD-supported palatal expanders offers less invasive treatment options to many adults who otherwise would have to either live with a compromised maxillary anatomy or undergo an invasive complex surgery to resolve the problem.
TAD-Assisted Expanders in Conjunction With Clear Aligners
Today, clear aligners can be used in combination with TAD-supported palatal expanders in the adult population. This fully digitally planned and customized high-precision approach offers solutions to both skeletal maxillary deficiencies and dental malpositions. For the first time in the history of dentistry, basal bone deficiency correction may be achieved without surgery in non-growing patients while teeth are simultaneously uprighted in the alveolar bone to receive axial loading with the use of clear aligners.
Limitations and Challenges
Despite these advancements that have been achieved and the research, albeit limited, that has been done, there remains limitations and challenges to each case. Further research is pending on specific contraindications, possible complications, and long-term stability of expansion outcomes when utilizing aligners and nonsurgical TAD-assisted skeletal expansion protocols.
Conclusion
The advancements in TAD-assisted skeletal expansion and the use of aligners represent significant steps forward in orthodontics and interdisciplinary treatment. While challenges and limitations exist, the ongoing research and technological developments in these areas continue to expand less invasive treatment possibilities for patient care.
ABOUT THE AUTHORS
Marianna Evans, DMD
Adjunct Professor, University of Pennsylvania Sleep Surgery Department, Philadelphia, Pennsylvania; Board-Certified Orthodontist and Periodontist; Private Practice, Newtown Square and Glen Mills, Pennsylvania
Daniel Berant, DMD
Double Board-Certified Specialist in Periodontics and Implant Surgery and Orthodontics and Dentofacial Orthopedics; Private Practice, Manhattan, New York
REFERENCES
1. Vanarsdall RL Jr. Transverse dimension and long-term stability. Semin Orthod. 1999;5(3):171-180.
2. Thuler E, Seay EG, Woo J, et al. Transverse maxillary deficiency predicts increased upper airway collapsibility during drug-induced sleep endoscopy. Otolaryngol Head Neck Surg. 2024. doi: 10.1002/ohn.684.
3. Thuler E, Rabelo FA, Yui M, et al. Correlation between the transverse dimension of the maxilla, upper airway obstructive site, and OSA severity. J Clin Sleep Med. 2021;17(7):1465-1473.
4. Miner RM, Al Qabandi S, Rigali PH, Will LA. Cone-beam computed tomography transverse analysis. Part 1: normative data. Am J Orthod Dentofacial Orthop. 2012;142(3):300-307.
5. Miner RM, Al Qabandi S, Rigali PH, Will LA. Cone-beam computed tomography transverse analyses. Part 2: measures of performance. Am J Orthod Dentofacial Orthop. 2015;148(2):253-263.
6. Betts NJ, Vanarsdall RL, Barber HD, et al. Diagnosis and treatment of transverse maxillary deficiency. Int J Adult Orthod Orthognath Surg. 1995;10(2):75-96.
7. Evans M, Tanna NK, Chung CH. 3D guided comprehensive approach to mucogingival problems in orthodontics. Semin Orthod. 2016;22(1):52-63.
8. Wehrbein H, Yildizhan F. The mid-palatal suture in young adults: a radiographical-histological investigation. Eur J Orthod. 2001;23(2):105-114.
9. Evans M. Three-dimensional control with TAD-tissue supported rapid palatal expander: an overview of clinical applications and biological advantages. Orthod Clin Rev. 2013;22:22-31.
10. Cantarella D, Dominguez-Mompell R, Moschik C, et al. Midfacial changes in the coronal plane induced by microimplant-supported skeletal expander, studied with cone-beam computed tomography images. Am J Orthod Dentofacial Orthop. 2018;154(3):337-345.
