For orthodontic treatments of teens, the same fundamental considerations apply whether the treatment is performed with aligners or with fixed appliances. However, the planning of teen cases with aligners, the definition of treatment strategies, the anchorage situation, and both the possibilities and the restrictions for tooth movements are different between treatments with aligners and treatments with fixed appliances. Therefore, when treating teens with aligners, these different factors and considerations have to be taken into account for a successful treatment. This chapter describes fundamental issues of aligner orthodontics and points out particularities of teen treatments compared to treatments of adults and treatments with fixed appliances.
Aligners can be as effective as brackets and wires for treating patients, both teens and adults, with various kinds of malocclusions. Not all aligner systems on the market show the same range of performance. The following checklist can be a helpful means in determining which aligner system is most appropriate and allows to compare them according to different parameters:
Mixed dentition: we might start with deciduous teeth in situ and will have to deal with erupting permanent teeth during the treatment. In almost all cases with erupting teeth, an MCC will be necessary during treatment (Fig. 4.1).
Enamel: in many countries, the prevalence of molar incisor hypoplasia is increasing. Patients who have less resistant enamel can benefit from removable appliances and still all types of malocclusions can be treated.
In most cases, Class II malocclusion therapy consists of both growth modification and dentoalveolar correction. The ideal time for growth modification is mainly in the mixed dentition. The treatment has to start early enough to benefit from the pubertal growth peak. For the treatment of patients with dental and/or skeletal Class II, there are the following options.
Phase 1 usually consists of activator (any type), plate-headgear, headgear, any type of distalizing devices (Carriere, Beneslider, Pendulum, distal-jet, etc.), maxillary expansion (forced/rapid), extraction of premolars, etc. Subsequently, this Phase 1 is followed by Phase 2 by means of aligner treatment.
Parallel to the initial sagittal correction, movements which are less predictable with aligners alone, such as correction of severe deep bites or transversal discrepancies, can be improved simultaneously. The subsequent Phase 2 with aligners will be easier, more predictable, and shorter.
Starting Phase 1 during mixed dentition allows starting the aligner treatment in the permanent dentition and, therefore, the necessity of an MCC is significantly reduced. Almost all patients starting the aligner treatment during mixed dentition will need an MCC, whereas an MCC after start in the permanent dentition is rare when the planning was correct.
With a sophisticated aligner system, the distalization of upper posterior teeth can be performed in a very predictable way. Studies have shown that no significant tipping of teeth will occur when the distal movement of molars is up to 2.5 mm. Clinical experience shows that even movements up to 4.5 mm can routinely be performed successfully. It is recommended to place rectangular vertical attachments on the molars in order to prevent tipping if the distalization exceeds 2.5 mm.
In all cases, use of Class II elastics is mandatory. The standard procedure is to fix buttons on the lower first molars and attach the elastics from these points to hooks located at the upper canines, which are cut directly into the aligners (Fig. 4.2). On both sites, it is possible to place buttons or cuts in order to attach the elastics. The inclination of the incisors will remain very stable for both kinds of attachments of the elastics, cuts and buttons. The decision whether to put cuts or buttons is influenced mainly by the form and the height of the clinical crown of the teeth and by personal preference.
If the skeletal base is only moderate Class II, 12 hours/day of elastic wear can be sufficient for anchorage. Generally, it is recommended to always start with Class II elastics which are worn full-time (24 hours/day). Depending on the progress, the duration can be reduced during treatment. Careful monitoring is always required for both tipping of teeth and sagittal relation.
The final result of growth modification alone, in order to correct Class II malocclusions, is highly dependent on the compliance to wear Class II elastics and on growth itself. Both factors are difficult to foresee, and careful steady monitoring is mandatory.
While the inclination of the lower incisors remains very stable, this force system will produce a slight posterior rotation of the maxilla (comparable to a Herren-type activator). Probably, when attaching the elastics on buttons on the teeth, the inclination of the incisors will remain more stable compared to the attachment of the elastics directly on the aligners. However, no scientific data covering this topic are available yet.
The amount of distalization of the upper posterior teeth could be too much if the effect of the elastics is higher than planned or if more sagittal growth occurs than included in the treatment plan. Should this be the case, it is necessary to undertake an MCC.
It is recommended to correct Class II malocclusion 2/3 by distalization in the maxilla and 1/3 by effect of Class II elastics. If the treatment plan is designed accordingly, the clinician has more flexibility during the treatment phase.
In cases with severe crowding, the extraction of upper first and lower second premolars can be useful in order to obtain a Class I molar and canine relationship. This treatment will require attachments and auxiliaries to prevent undesired molar tipping, particularly in the mandible (see Section 4.3 and Section 4.6.1).
The precision wings (Fig. 4.3) keep the mandible in a slightly protruded position.
The treatment of Class III patients almost always consists of a two-phase therapy: the first phase consists of growth modification in preadolescent age and the second phase will follow afterward in the permanent dentition (camouflage or surgery).
According to the present skeletal pattern, either maxillary deficiency or mandibular protrusion or a combination of both, different appliances have been designed. Clinically and cephalometrically, it is difficult, however, to separate the effects of an appliance, for example, the Delaire face mask, to the jaws. We will always find effects in both dental arches/jaws.
Clinically, the focus should be on growth modification (skeletal effect) and avoiding camouflage or compensation. It is important not to protrude the upper incisors when trying to obtain or keep a positive overjet.
Aligner treatment in this phase consists of a pair of passive aligners provided with buttons for the application of Class III elastics. In the lower jaw, it is recommended to bond buttons or hooks directly on to the first primary molars. This prevents the lower aligner from disconnecting. In the upper jaw, alternatively, a palatal plate can be used. This device has the advantage that the position of the upper incisors can simultaneously be improved (mainly derotation of lateral incisors) and some expansion can be done when needed. Poncini clasps are strong enough to keep the plate in place with the elastics hooked directly on them. To improve compliance, the labial arch can be left out.