Anterior open bite – diagnostics and therapy

Introduction

An open bite is defined as an occlusal condition in which opposing teeth do not come into contact. It is clinically manifested in the frontal or lateral part of the jaws. Our article focuses on the treatment modalities of an anterior open bite (AOB).

AOB brings complications for patients, which are both aesthetic and functional. Patients with AOB cannot properly use their front teeth. In extreme cases, we see bruxism issues in the posterior segment.

A frontal open bite is characterized as a condition with larger eruption of distal teeth and oval facial phenotype (long face). These patients may have an incompetent lip seal and there are changes in the sense of "clockwise" rotation on the cephalogram. The treatment is perceived in orthodontics as one of the most complex [1–6]. It is not only a complexity in terms of therapy, but also in the retention of the result. There are often various forms of recurrence of the defect with a reduction of the overbite in the area of upper incisors and the relapse of the negative depth of the occlusion.

Etiologically, it is a very heterogeneous unit. Reyneke and Ferreti [7] define two mechanisms of AOB formation: morphogenetic and adaptive theories. The morphogenetic theory is a growth disorder in the sense of the deviation of genetically conditioned control of the growth pattern with the occurrence of abnormal occlusion. In the adaptive theory, disrupted occlusion is caused by secondary adaptation to functional anomalies at the naso-oropharyngeal level.

Evaluation

There is no clear consensus on optimal AOB therapy [1]. Many articles focus on the effect of the treatment itself. However, it is very important to focus on the long-term stability of the outcome [8]. Unfortunately, relevant studies and meta-analyses do not provide a clear answer to the stability of the outcome [1,8]. As the group of patients is highly heterogeneous, there are often inconsistencies in baseline pre-treatment descriptions of the studies, as reported by Greenlee [1,9–16]. This applies in the surgical patients’ group in particular, where it is often unclear whether the presence of an open bite was present prior to orthodontic treatment or occurred as a result of orthodontic decompensation.

Diagnostics

The incidence of AOB shows large variance among different ethnicities, which supports the theory of genetic influence on the development of the skeletal defect. According to Proffit et al [14], the incidence of AOB in the Caucasian population in the USA is 2.9%.

The phenotype of a patient with AOB is as follows: the vertical component of the growth can cause a narrowing of the palatal arch and the formation of crossbite. The incisors cannot compensate for the vertical direction of the growth and the space between the upper and lower incisors begins to open, causing a negative overbite. An insufficient lip seal then leads to the tongue thrust in order to close the gap between the lips during swallowing. This mechanism of action applies pressure on the incisors which then leads to a further open bite.

The lateral cephagram shows posterior rotation, the angle formed by the lines Nasion – Sella (NS) and the mandi­bular line (ML) is increased, the so-called high angle of the mandibular line. We also find a significant antegonal notching on the lower edge of the mandible, receding chin, larger inter-incisal angle, smaller inter-molar angle and an enlarged lower third of the face.

For proper diagnosis, we focus on the location of the defect, whether it is located in the maxilla or mandible or whether it is a combination of both. The age of the patients is very important. In children, we focus on habits, such as thumb sucking. Sucking is a physiological phenomenon in children that should disappear by the age of 6. If present beyond the age of 6, it becomes a risk factor in terms of AOB [16] development. Airway obstructions at the level of the oropharynx and nasopharynx [17] is another causal factor, especially in the presence of hypertrophic adenoids. In patients with allergic rhinitis, there is an activation of adaptive neuromuscular compensation with the development of AOB as part of the image of the so-called “facies adenoidea“. Masticatory palsy is considered as another risk factor for the development of an anterior open bite. Reduced muscle strength will allow molar eruption into supraocclusion [18] and thus may lead to the development of AOB.

In adult patients, the onset of AOB is due to excessive vertical growth of the upper jaw, shortening the ramus of the lower jaw, or a combination of both. Clinically, we find an extension of the vertical height of the face, paranasal flattening, a convex profile, a narrow base of the nose and incompetent lips [7].

Therapy

The treatment varies according to age of the patient.

If the cause of an open bite is a habit or airway obstruction as described in the previous section, stopping the habit (e.g. by wearing a ready-made vestibular veil), or removing the obstruction can lead to a causal adjustment of the condition without the need for further therapeutic intervention.

If an open bite is present even without an obvious cause, then we choose the "wait and see" method in deciduous dentition. In mixed dentition, orthodontic removable devices are a preferred method of treatment.

For an adult patient, there are two basic therapeutic approaches; orthodontic or combined orthodontic-surgical. The orthodontic closure of an anterior open bite consists of: transverse expansion of the upper dental arch, extrusion of the upper and lower incisors, extractions of the upper and lower premolars with retrusion of the upper and lower incisors. Other treatment options include intrusion of the molars, e.g. by means of temporary anchoring devices [19,20], a miniplate temporarily fixed to the facial bony structures [21], or extraoral traction with class III elastics [22,23]. Some authors argue that the transverse expansion of the distal part of the maxilla has debatable stability, as it may lead to tilting of the teeth rather than to widening of the palate. On the other hand, Angelieri et al presents a classification of the maturation of palatal suture independent on the age, where one can decide between the stable orthodontic expansion by the use of fixed palatal expander (rapid maxillary expansion-RME /HYRAX) or by surgically assisted expansion (SARME or segmental Le Fort I) [24].

Today, combined surgical-orthodontic therapy is the gold standard in anterior open bite therapy. This resolves both occlusion and aesthetic concerns. However, the prerequisite is a terminated growth (usually after 18 years of age in girls and a year later in boys) based on a wrist X-ray.

The treatment consists of four stages: decompensation, surgery, final orthodontic treatment phase and retention.

Decompensation phase

The patients are informed that during the decompensation phase their defect will be significantly overexpressed, as the compensatory mechanisms of their teeth will be reduced. In patients with AOB, we primarily focus on the presence of one or two occlusal planes (biplanar occlusal plane – BPO). In the case of BPO, we try to maintain both planes and place the teeth in the most stable position without trying to level the occlusal plane. We also avoid intrusion of the distal teeth or an attempt at transverse expansion in the distal part of the dental arch. In dental crowding, one of the premolars can be extracted to achieve a stable position of the teeth in the alveolus. If segmental surgery is planned in a patient with BPO, it is necessary to parallelize the roots of the teeth at the site of the intended osteotomy to minimize the risk of the damage to the roots during the surgery. During the orthodontic phase, we place great emphasis on the position of the lower teeth in the dental arch. This serves as a “splint“ to which we adapt the maxillary teeth, especially in the case of segmental surgery [7].

Surgery

AOB can be closed by monomaxillary Le Fort I osteotomy non-segmentally or segmentally (we follow the number of occlusal planes, which is usually two in AOB [20]) and autorotation of the mandible. However, in most cases, bimaxillary segmental surgery is required. For each segmental operation, it is necessary to monitor the vertical position of the incisale (measured to the reference point, e.g. a screw inserted into the glabella area or to the inner corner of the eye). The most common forms of segmental osteotomy on the palate are the so-called: "Y" (Fig. 1) or "H" (Fig. 2) osteo­tomies, obtaining 3, resp. 4 fragments. These parts are then placed in the required vertical and horizontal position.

Final orthodontic treatment

 There are minor adjustments in the position of individual teeth, or closing the gaps between them.

Retention

We perform retention using removable or fixed retainers on lingual surfaces of the frontal teeth in the upper and lower dental arches. In patients with AOB, it is necessary to regularly check the stability of the result due to a great tendency of the defect to relapse [25].

Conclusion

Frontal open bite therapy is the most demanding procedure in combined orthodontic-surgical therapy of this defect. It requires a highly motivated patient and an experienced team of orthodontist and surgeon. Careful case planning is a paramount for success. The experience of the members of the treatment team plays a vital role in choosing an appropriate treatment modality. Some authors describe the combined performance associated with upper jaw floor expansion in combination with BSSO [26]. The financial side of the treatment also plays an important role in author’s opinion. In our region, the surgical portion of this treatment is fully covered by medical insurance; however, orthodontic treatment has a significant out-of-pocket portion.

Role of authors: The authors participated in the creation of the article equally.

Disclosure: The authors have no conflicts of interest to disclose.

Financial support: The authors declare that this study has received no financial support.

Assoc. Prof. Peter Tvrdý, M.D., D.M.D., Ph.D.

Department of Oral and Maxillofacial Surgery

University Hospital and Faculty

of Medicine, Palacky University

I. P. Pavlova 6

779 00 Olomouc

e-mail: peter.tvrdy@fnol.cz

Submitted: 4.7.2021

Accepted: 30.8.2021