Early Treatment in Preteens and Teenagers Using Aligners
Eugene K. Chan and M. Ali Darendeliler
Summary
Clear aligner therapy has always been reserved for adults and/or the esthetically conscious patient. Historically, clear aligners did not work well with younger patients, or patients with primary or mixed dentition. The digital platform could not work out the necessary differentiation between the biology of tooth movement between primary and permanent dentition. The constant dental exfoliation and dynamic growth changes may also be harder to track as the case progresses. The lack of compliance in younger patients often led to nonideal clinical finish, prolonged treatment duration, and inefficient treatment. New advances in digital algorithm allowing biomaterials, attachment designs, and optimized velocity of the movement of both primary and permanent teeth within the same subject has opened up a new option for selected young patients. Both early interceptive phase I treatment and full comprehensive orthodontic treatment in children using the clear aligners have become a reality.
Introduction
Patients may be referred early to the orthodontist for interceptive treatment for various reasons. Major reasons include the presence of supernumerary teeth disrupting routine dental eruption, disparity in jaw growth, the presence of parafunctional habits that may have disturbed the equilibrium of dental positioning, missing or early loss of deciduous teeth leading to the early loss of space, or anterior or posterior crossbites that may hinder the symmetry and/or dentoalveolar development. Other reasons may also include trauma, soft-tissue abnormalities, variations in dental anatomy, or transposition of teeth.
Commencing early orthodontic treatment appears logical as it enables the complete or partial correction of many incipient discrepancies or, at least, a reduction in their capacity to become worse. Interception, or early intervention, employs simple therapeutic techniques that do not strain the limited stores of cooperation young patients can bring to the therapeutic encounter. Its objective is to eliminate or minimize dentoalveolar and skeletal disorders that may interfere with growth, function, esthetics, and the psychological well-being of the child.1
For a long time, early interceptive treatment involved various fixed and/or removable appliances such as the headgears, removable or fixed expanders, bite planes, habit breakers, functional appliances such as twin or mono blocks, or fixed partial preadjusted bracket systems.
Recent improvements in aligner therapy have allowed this appliance, historically used for adult esthetic orthodontic treatment, to be considered for such early interceptive treatment.
The success of early interceptive treatment lies within the thorough understanding of the cause of the problem, the knowledge of the patients’ potential growth, the deciduous and permanent dentitions’ biological response to orthodontic intervention, and good patient compliance. Appliance design in early interceptive orthodontic treatment is rather complex. It has always been varied with many modifications to accommodate for differently timed treatment, targeting different needs and purposes of the interception. The management of the developing dentition is tricky. While early treatment may be indicated dentally, patient maturity and psychological readiness may not be. The window period of treatment in both genders vary quite a fair bit, and also varies within the gender group itself.
Traditional appliances used in interceptive treatment could mostly treat one problem but not the other.
Fixed Expansion
Transverse expansion required in cases that demonstrate bilateral posterior crossbites (Fig. 3.1a) can often be easily corrected with a fixed expansion device. The case shown had the transverse discrepancy corrected in 2 months with a Hyrax fixed expander (Fig. 3.1b). The expander was left in place for a further few months before it was removed to commence a stage II treatment with the Invisalign appliance. This fixed preliminary treatment, although effective in achieving phase I treatment objectives, can only correct the transverse discrepancy. Dental alignment, anteroposterior changes, arch coordination, and dental interdigitation cannot be achieved using this same appliance (Fig. 3.1c).
Removable Anterior Bite Plate Appliance
Increased dental overbites in mixed dentition may lead to increased attrition and wear to the anterior teeth, and may further contribute to a more complex dental malocclusion later (Fig. 3.2a). A typical treatment modality is a removable upper anterior bite plane appliance (Fig. 3.2b). This appliance is usually worn full time for a period of 6 to 9 months. Incorporating the young patient’s vertical dentoalveolar growth, the appliance disocclude the posterior segment and encourages the lower molars to overerupt, hence opening the vertical dimension and correcting the dental overbite (Fig. 3.2c). Although other auxiliaries such as screws (for transverse or anteroposterior corrections), finger, and/or Z-springs may be incorporated into these removable appliances, individual tooth movements still cannot be achieved with this appliance unless partial fixed appliances are placed. The patient is usually retained and monitored closely thereafter as they transit into permanent dentition before comprehensive orthodontic treatment may be indicated once again.
Removable Posterior Bite Plate Appliance
Young patients with a digit sucking habit develops a malocclusion with an anterior open bite, commonly also associated with a constricted upper arch and posterior crossbites (Fig. 3.3a). Treatment usually takes about 6 to 9 months with a removable upper dental arch appliance designed with bilateral posterior bite planes. An expansion screw is also incorporated into the palatal aspects of the appliance (Fig. 3.3b). The primary treatment objectives are to allow the canting of the occlusal plane to normalize the occlusion, achieve a positive overbite, and expand the upper dental arch to correct the posterior crossbites (Fig. 3.3c). Further dental alignment, arch coordination, and anteroposterior changes were corrected later usually in the permanent dentition using clear aligner therapy (Fig. 3.3d).
Fig. 3.3 (a)An early mixed dentition case with a severe anterior open bite (patient was 8 years 7 months old). (b)Typically corrected using an upper removable appliance with posterior bite plane or posterior occlusal coverage and expansion screw incorporated. (c)Interceptive treatment corrected over a period of 12 months. (c)Full comprehensive treatment completed using clear aligner therapy.
Functional Appliance
Early treatment in patients with a Class II malocclusion with skeletal discrepancy needs to be timed well. Monitoring growth parameters such as secondary growth characteristics and charting changes in cervical vertebrae in lateral cephalometric radiographs is useful2 , 3 (Fig. 3.4a, b). Young patients with a severe skeletal II growth pattern are usually treated just before they hit their growth spurt (Fig. 3.5a–c). With good compliance in wearing a functional appliance, the dentofacial discrepancy can usually be corrected within 9 to 12 months (Fig. 3.5d–g). The functional appliance used in this case was a Clark twin block. An expansion screw is usually incorporated into this appliance and transverse correction can be achieved together with the anteroposterior discrepancy. After sagittal splinting is achieved, selective grinding of the acrylic of the appliance is done to allow vertical eruption to further correct vertical discrepancies. Despite the ability to correct the dentofacial and malocclusion in all three planes, the typical functional appliance is still not able to individually correct dental alignment problems and complete the case to a high-quality finish with good interdigitation. Fixed appliances or clear aligners are usually necessary to complete the case thereafter.
Fig. 3.4 (a)Physical growth evaluation with leading questions supporting known growth parameters. How rapidly the child has grown recently? Have clothes and shoe sizes changed? At what age did sexual maturation occur in older siblings? What is the child’s height–weight when compared with parents/older siblings? (b) Timing for orthopedic treatment planned around peak mandibular growth looking at cervical vertebrae .
Fig. 3.5 (a)Early interceptive treatment of a 10-year 1-month old child with a removable functional appliance. (b)Pretreatment panoramic radiograph. (c)Pretreatment lateral cephalometric radiograph. (d)Interceptive treatment completed in 10 months. (e)Post stage I treatment panoramic radiograph. (f)Post stage I treatment lateral cephalometric radiograph.
Invisalign First
Two-phase treatments using aligners for both phases I and II have not been considered until recently (Fig. 3.6). Aligner therapy has always been reserved for the adult, esthetically conscious patient. The fact that they are less visible has that big advantage over conventional fixed appliances, and remains a large drawcard. However, its close to full time, 22-hour daily wear routine has made the patient’s compliance of aligner wear paramount in the success of the orthodontic treatment. Younger patients may not be as responsible or compliant; hence, most parents and clinicians have not considered aligner therapy as their appliance of choice for them.
The recent introduction of new features in aligner therapy has tried to negate such problems. The placement of compliance indicators (Fig. 3.7) on the aligners has given the parent and/or clinician a chance to ensure aligners are worn sufficient hours. Optimized attachments designed for deciduous teeth and specifically designed staging protocols for mixed dentition have allowed vertical and transverse dentoalveolar problems to be addressed with aligner treatment, and also precise individual dental movements may be planned With close monitoring and good patient encouragement, these new features may outweigh the risks of noncompliance and have given the clinician another reason to consider using aligner therapy for the child with mixed dentition.
Unlimited number of aligners may be ordered over an 18-month period; therefore, quite a variety of cases can be treated using the Invisalign First appliance. The ability to incorporate and maximize these features, such as precision bite ramps, posterior occlusal coverage, individual optimized tooth movements, dental arch expansion, eruption compensators, and anteroposterior correction with elastics, has broadened the treatment aspects of phase I therapy beyond just addressing one or two problems.
Younger patients may not cope well with the procedure of obtaining alginate dental impressions. Overly sensitive gag reflexes have deterred many early orthodontic interventions. With digital intraoral scanner (such as iTero element scanner) getting more popular, the ease of obtaining a digital “impression” of the intraoral hard and soft tissues has made this step a lot more pleasant to both the patient and the clinician. This has enabled the prescription of early treatment more feasible.
The Invisalign First appliance is typically indicated for the early mixed dentition ranging from the age of approximately 6 to 10 years old. However, it is reserved for cases where the permanent first molars have sufficiently erupted, and with at least two incisors that are at least two-thirds erupted (per arch). The case should also have at least two nonmobile primary teeth (C, D, or E), plus a partially erupted permanent tooth (3, 4, or 5) per quadrant in at least three quadrants.
The default velocity of dental movement within the Invisalign First treatment setup is not differentiated between primary and permanent dentition. However, it is essential for the clinician to understand the biology of tooth movement well. Clinicians should study the current orthopantomogram (OPG) radiographs to identify and recognize the state of resorption of the dental roots of the primary dentition and the anatomy of the roots of the permanent dentition as well as to look at the clinical crown heights and thickness of the dentoalveolus to adjust the velocity of dental movement accordingly.
This treatment modality is applicable for developing the arch form and creating space for erupting dentition. Generically, it can be used to address conditions such as dental arch development, dental expansion, spacing/crowding issues, anteroposterior correction, esthetic alignment, dental protrusions, and/or interferences (including elimination of functional shifts).
The appliance utilizes a default staging pattern for dental arch expansion and movements. The permanent first molars are usually expanded and moved first, followed by the incisors before the deciduous teeth (Fig. 3.8). This sequential staging pattern allows the permanent teeth to be well established in the arch before the deciduous teeth are moved. It is logical that with the permanent incisors and molar roots being both wider in girth and longer in length, the resistance to dental movement will be greater. Allowing more aligners and greater pressure expressed on these teeth is necessary to achieve the desired movements. Deciduous teeth have generally shorter clinical crown heights. The propriety software is able to analyze the dental structure, measure the buccal contours and mesiodistal width, understand the direction and type of dental movement required, and design optimized attachments for these primary dentition Fig. 3.9).
Here are some of the recommended setup preferences:
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Interproximal reduction (IPR) is not recommended for the primary dentition. In general, primary teeth are good space maintainers and therefore IPR in primary teeth is rarely required. During dental arch expansion, both permanent and primary teeth will be buccally expanded. This reflects the phase I treatment goals to develop the arch form and also to maintain or increase space for erupting permanent dentition. Predictable dental arch expansion ranges between 4 and 6 mm per arch.
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The sequential staging pattern allows the movement of the permanent molars before the other teeth; thereafter, simultaneous staging of the other teeth follows. This allows differential anchorage from the other dentition to predictably move the permanent molars.
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If there were any Bolton tooth size discrepancies, the extra spacing will be left mesial and distal to the deciduous canines. This allows sufficient space for the larger permanent canines to erupt uneventfully.
Effective anteroposterior correction can also be incorporated within the Invisalign First appliance. Class II or Class III elastics can be prescribed and designed using a mixed dentition grid during the ClinCheck treatment planning process (Fig. 3.10). Buttons and elastics are readily applied clinically where indicated as well (Fig. 3.11). Attachment design is important using the Invisalign appliance in the mixed dentition. Primary teeth have short clinical crown heights and require attachments to increase the retention of the appliance. In the mixed dentition phase, as the child transits into the permanent dentition, there will be a stage where the deciduous teeth have exfoliated, while the permanent teeth are yet to fully erupt. The retention of the appliance on the patient’s dentition can be rather challenging during this time. To improve retention on short clinical crowns, optimized retention attachments are automatically placed by the ClinCheck software (Fig. 3.12). Hence, primarily, the attachments used in the Invisalign First appliance are for (1) rotation, (2) extrusion, and (3) retention purposes. These attachments can be visualized on the ClinCheck treatment plan and may be modified by the clinician as required. Extrusion and rotation attachments are placed on the permanent teeth by default, whereas the retention attachments are placed on the primary teeth (Fig. 3.13).
If the case commences after the exfoliation of the deciduous tooth but before the full eruption of the succedaneous permanent tooth, eruption compensation tabs will be placed. These are visualized as “ghost teeth” on the ClinCheck plans or as a “pontic” clinically (Fig. 3.14). The retention of the appliance during this phase is usually compromised—hence, the necessity to time the active treatment well or have a good retention attachment design. As treatment progresses, the permanent tooth/teeth will erupt into the pontic space. Further in-out and/or rotational corrections will be addressed when new scans or impressions are taken when additional aligners are ordered after the first lot of aligner are exhausted.
