9: Open-bite treatment with aligners

Aldo Giancotti, Gianluca Mampieri

In recent years, aligners have shown to be an extraordinary and effective tool to correct open-bite cases. Such unexpected results make them the gold standard in the treatment of malocclusions characterized by vertical excess as in open-bite cases. Open bite is challenging to treat for its multifactorial etiology and for high incidence of relapse.

The aim of this chapter is to show strategies and protocols for the treatment of anterior open bite by clear aligners.

Diagnosis of anterior open bite

Obviously, a proper diagnosis is essential in determining the appropriate corrective measures. It is possible to classify three types of open bite:

1. Dental
2. Dentoskeletal
3. Skeletal

Generally, skeletal open bite requires an orthosurgical approach. Instead, dental and dentoskeletal open-bite cases can be treated only by means of orthodontics.¹^,²

Biomechanics for anterior open-bite correction

The biomechanics for anterior open-bite correction can be achieved either by extruding the incisors or intruding the posterior teeth, or by a combination of both. For the nonsurgical treatment of adult patients, some guidelines consider extraction and retraction for dental open-bite correction.³ A limited number of open-bite cases is suitable for such type of treatment.

Dental open-bite cases are mostly associated with the following characteristics:

■ Normal craniofacial pattern
■ Incisor proclination
■ Undererupted anterior teeth
■ Little or no gingival display on smile
■ No more than 2 to 3 mm of upper incisor exposure at rest

If the anterior open bite depends only on tooth position, it is a relative open bite; the biomechanics for the correction are easy, as follows:

■ Reducing incisor proclination to produce a relative extrusion
■ Pure extrusion of incisors by extrusive attachments

The amount of incisal and gingival display needs to be assessed clinically prior to deciding if pure extrusion is desired from a smile esthetics point of view.

When dentoskeletal factors are important in determining the cause of open bite, it is often caused by posterior dentoalveolar excess as well as by both downward and backward mandibular rotation.^4–10 These types of open bite with a skeletal component caused by heredity and/or supererupted posterior teeth require complex orthodontic treatments with active molar intrusion or even major orthognathic surgery.³^,¹¹

In case of a dentoskeletal open bite, specific procedures have been designed to intrude posterior teeth or, at least, prevent molar eruption or extrusion in the attempt to reduce or control anterior facial height, especially during the growing age (high-pull headgear, lower transpalatal arch with resin button, and posterior bite blocks). The introduction of temporary anchorage devices (TADs) has allowed an active intrusion of posterior teeth also in adult patients with a consequent mandibular counterclockwise rotation and improvement of anterior open bite.

Extraction of posterior teeth is another strategic approach to correct anterior open bite. Indeed, when indicated, molar extraction for caries or periodontal reasons could be highly effective in reducing facial height. Forward movement of the terminal molars allows the mandible to hinge upward and forward. It has been postulated that 1 mm of intrusive vertical movement of the molars results in approximately 2 to 3 mm of bite closure by mandibular counterclockwise rotation.¹²

In the treatment of a dentoskeletal open-bite case, one shall observe some biomechanical principles. Any procedure meant to increase facial height by means of extrusion of posterior teeth must be avoided. Leveling the arches is usually not to be considered appropriate, and the maintenance or creation of a curve of Spee would be desirable. Furthermore, banding of second molars should be avoided to prevent any extrusion movement when molars are engaged on the arch wire.¹³

The abovementioned scenario can be easily avoided by using aligners, which allow for nonextrusion and represent a great advantage during open-bite treatment. This is why a number of researchers consider aligners as the gold standard.¹⁴

Aligner protocols for open-bite treatment

Clincheck software design

The clear aligner treatment of open-bite cases depends on the type of malocclusion requiring correction, and specific biomechanics have to be requested by checking the appropriate boxes on the prescription form of the ClinCheck software program to generate a predictable ClinCheck plan.

Dental open bite, also known as relative open bite, clinically features excessive incisor proclination; it can be treated only by reducing incisor proclination, producing a relative extrusion of anterior teeth. For these movements, attachments are not strictly required.

The first step consists of recovering the needed space in both arches. Space can be gained by arch expansion and/or interproximal reduction (IPR). The decision depends on the shape of the arches, tooth dimension, periodontal structure, and condition. Aligners can easily modify the shape of the arch, and it is later possible to retract the incisors obtaining enough relative extrusion in mild open bite to solve the issue.

Attachments in open-bite correction

In case of more severe dental open bites, anterior teeth extrusion can be strategic. Undoubtedly, extrusion is the most difficult movement to reproduce with aligners. In such conditions, attachments play an important role to determine tooth extrusion. Attachments and anchorage optimized anterior extrusive attachments are automatically placed on the incisors by the software when pure extrusion of 0.5 mm or more is detected (Figs. 9.1 and 9.2). Conventional extrusion attachments have a rectangular shape with beveled edge toward the gingiva to allow for optimal pressure from the aligner and then achieve proper extrusion (Fig. 9.3). These attachments could be positioned also on the palatal surface if aesthetic reasons are a priority (Fig. 9.4). Our experience suggests that the use of rectangular-shaped attachments with beveled edge toward the gingiva with the largest possible dimensions in relation to the incisor and most incisal possible allowed for an optimal control of relative and absolute incisor extrusion.

Fig. 9.1Optimized extrusive attachments of the Invisalign system.

Fig. 9.2The anterior extrusive forces and reciprocal posterior intrusive forces work in synergy to correct the anterior open bite.

Fig. 9.3Rectangular shape attachments with beveled edge toward gingiva.

Fig. 9.4Palatal attachments and occlusal attachments on upper molars.

Anchorage attachments can have different shapes and dimensions, according to the type and/or number of teeth involved.

The dentoskeletal open-bite treatment complies to a more complex protocol to correct the malocclusion. Indeed, in this type of open bite, the skeletal structure shows a dentoalveolar posterior vertical excess, which is responsible for an increased lower facial height.

For this reason, anterior tooth extrusion alone is not enough for correction, and one shall reduce the posterior vertical excess by dental intrusion.

Posterior dental intrusion results in a mandibular counterclockwise rotation mainly responsible for the open bite’s correction, which can be verified by final cephalometric values. The anterior extrusive forces and reciprocal posterior intrusive forces work in synergy to close the anterior open bite (see Fig. 9.2).

The amount of posterior intrusion may range from less than 0.5 mm to a maximum of 1.0 mm. Beyond the range of predictability for aligner movements, it may be necessary to use TADs.

Molar intrusion can be planned with aligners, and therefore we define it as selective intrusion. The first and second molars in the upper arch and first molars and bicuspids in the lower arch are involved in the plan. The protocol related to attachment placement for anchorage usually envisages rectangular attachments on the molars and optimized ones on bicuspids. As for intrusion teeth, the official Invisalign protocol does not include the use of attachments. Some experienced clinicians prefer to add occlusal rectangular attachments to increase intrusive components and thus increase effectiveness (see Fig. 9.4).

In more severe open-bite malocclusions, some clinicians prefer to stage posterior intrusion sequentially for a more predictable clinical outcome: first the maxillary second molars, then the first molars, and then the second premolars.¹⁵

An important aspect to make predictable planning with aligners is to design an overcorrection. In the ClinCheck we have to see the final virtual occlusion with heavy anterior occlusal contacts and at least 2 mm of positive overbite.

Our point of view concerning dental intrusion is that the most important effect of aligners in reducing posterior vertical excess is the bite-block effect, which is caused by two layers of aligner material between posterior teeth.¹⁴ It allows to effectively intrude posterior teeth, hence enabling subsequent autorotation of the mandible and reducing anterior facial height.

The bite-block effect cannot be quantitatively priorly planned or displayed in the virtual digital setup by ClinCheck, but we can routinely observe it clinically, especially in patients with a normal or larger mandible.

In final, to guarantee the maintenance of the result over time, it is essential to use Vivera, the clear retainer produced by Align, because the posterior occlusal coverage will prevent the reeruption of posterior teeth.