Anterior open bite and posterior open bite

16 May

12.1. DEFINITIONS
  • Anterior open bite (AOB): there is no vertical overlap of the incisors when the buccal segment teeth are in occlusion (Fig. 12.1).
  • Posterior open bite (POB): when the teeth are in occlusion there is a space between the posterior teeth (Fig. 12.2).
  • Incomplete overbite: the lower incisors do not occlude with the upper incisors or the palatal mucosa (Fig. 12.3). The overbite may be decreased or increased.

Anterior open bite and posterior open bite

12.2. AETIOLOGY OF ANTERIOR OPEN BITE
In common with other types of malocclusion, both inherited and environmental factors are implicated in the aetiology of anterior open bite. These factors include skeletal pattern, soft tissues, habits, and localized failure of development. In many cases the aetiology is multifactorial, and in practice it can be difficult to determine the relative roles of these influences as the presenting malocclusion is similar. However, a thorough history and examination, perhaps with a period of observation, may be helpful.
12.2.1. Skeletal pattern
Individuals with a tendency to vertical rather than horizontal facial growth exhibit increased vertical skeletal proportions (see Chapter 4). Where the lower face height is increased there will be an increased inter-occlusal distance between the maxilla and mandible. Although the labial segment teeth appear to be able to compensate for this to a limited extent by further eruption, where the inter-occlusal distance exceeds this compensatory ability an anterior open bite will result. If the vertical, downwards, and backwards, pattern of growth continues, the anterior open bite will become more marked.
In this group of patients the anterior open bite is usually symmetrical and in the more severe cases may extend distally around the arch so that only the posterior molars are in contact when the patient is in maximal interdigitation (Fig. 12.4). The vertical devlopment of the labial segments results in typically extended alveolar processes when viewed on a lateral cephalometric radiograph (Fig. 12.5).
12.2.2. Soft tissue pattern
In order to be able to swallow it is necessary to create an anterior oral seal. In younger children the lips are often incompetent and a proportion will achieve an anterior seal by positioning their tongue forward between the anterior teeth during swallowing. Individuals with increased vertical skeletal proportions have an increased likelihood of incompetent lips and may continue to achieve an anterior oral seal in this manner even when the soft tissues have matured. This type of swallowing pattern is also seen in patients with an anterior open bite due to a digit-sucking habit (see Section 12.2.3). In these situations the behaviour of the tongue is adaptive. An endogenous or primary tongue thrust is rare, but it is difficult to distinguish it from an adaptive tongue thrust as the occlusal features are similar (Fig. 12.6). However, it has been suggested that an endogenous tongue thrust is associated with sigmatism (lisping), and in some cases the both the upper and lower incisors are proclined by the action of the tongue.
12.2.3. Habits
The effects of a habit depend upon its duration and intensity. If a persistent digit-sucking habit continues into the mixed and permanent dentitions, this can result in an anterior open bite due to restriction of development of the incisors by the finger or thumb (Fig. 12.7). Characteristically, the anterior open bite produced is asymmetrical (unless the patient sucks two fingers) and it is often associated with a posterior crossbite. Constriction of the upper arch is believed to be caused by cheek pressure and a low tongue position.
After a sucking habit stops the open bite tends to resolve, although this may take several years. During this period the tongue may come forward during swallowing to achieve an anterior seal. In a small proportion of cases where the habit has continued until growth is complete the open bite may persist.
12.2.4. Localized failure of development
This is seen in patients with a cleft of the lip and alveolus (Fig. 12.8), although rarely it may occur for no apparent reason.
12.2.5. Mouth breathing
It has been suggested that the open-mouth posture adopted by individuals who habitually mouthbreathe, either due to nasal obstruction or habit, results in

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overdevelopment of the buccal segment teeth. This leads to an increase in the height of the lower third of the face and consequently a greater incidence of anterior open bite. In support of this it has been shown that patients referred for tonsillectomy and adenoidectomy had significantly increased lower facial heights compared with controls, and that post-operatively the disparity between the two groups diminished. However, the differences demonstrated were small. Other workers have shown that children referred to ear, nose, and throat clinics exhibit the same range of malocclusions as the normal population, and no relationship has been demonstrated between nasal airway resistance and skeletal pattern in normal individuals.
On balance, it would appear that mouthbreathing per se does not play a significant role in the development of anterior open bite in most patients.
12.3. MANAGEMENT OF ANTERIOR OPEN BITE
Notwithstanding the difficulties faced in determining aetiology, treatment of anterior open bite is one of the more challenging aspects of orthodontics. Management of an anterior open bite due purely to a digit-sucking habit can be straightforward, but where the skeletal pattern, growth, and/or soft tissue environment are unfavourable, correction without resort to orthognathic surgery may not be possible.
In the mixed dentition, a digit-sucking habit that has resulted in an anterior open bite should be gently discouraged. If a child is keen to stop, a removable appliance can be fitted to act as a reminder. However, if the child derives support from his habit, forcing him to wear an appliance to discourage it is unlikely to be successful. Although a number of barbaric designs have been described (involving wire projections for example), a simple plate with a long labial bow for anterior retention will usually suffice if a habit-breaker is indicated. After fitting, the acrylic behind the upper incisors should be trimmed to allow any spontaneous alignment. Once the permanent dentition is established, more active steps can be taken, although this can often be combined with treatment for other aspects of the malocclusion.
A period of observation may be helpful in the management of patients with an anterior open bite which is not associated with a digit-sucking habit. In some cases an anterior open bite may reduce spontaneously, possibly because of maturation of the soft tissues and improved lip competence, or favourable growth.

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Skeletal open bites with increased vertical proportions are often associated with a downward and backward rotation of the mandible with growth. Obviously, if growth is unfavourable, it is better to know this before planning treatment rather than experiencing difficulties once treatment is under way.

Previously, it was thought that extracting molars in cases with increased vertical skeletal proportions would help to ‘close down the bite’. However, this was not based on scientific evidence.
12.3.1. Approaches to the management of anterior open bite
There are three possible approaches to management.
Acceptance of the anterior open bite
In this case treatment is aimed at relief of any crowding and alignment of the arches. This approach can be considered in the following situations (particularly if the AOB does not present a problem to the patient):
  • mild cases;
  • where the soft tissue environment is not favourable, for example where the lips are markedly incompetent and/or an endogenous tongue thrust is suspected;
  • in more marked malocclusions where the patient is not motivated towards surgery.
Orthodontic correction of the anterior open bite
If growth and the soft tissue environment are favourable, an orthodontic solution to the anterior open bite can be considered. A careful assessment should be carried out, including the anteroposterior and vertical skeletal pattern, the feasibility of the tooth movements required, and post-treatment stability.
Extrusion of the incisors to close an anterior open bite is inadvisable, as the condition will relapse once the appliances are removed. Rather, treatment should aim to try and intrude the molars, or at least control their vertical development. Intrusion of the molars can be attempted with high-pull headgear and/or by using buccal capping on a removable appliance.
In the milder malocclusions the use of high-pull headgear during conventional treatment may suffice. In cases with a more marked anterior open bite associated with a Class II skeletal pattern, a removable appliance or a functional appliance incorporating buccal blocks and high-pull headgear can be used to try to restrain vertical maxillary growth. In order to achieve true growth modification it is necessary to apply an intrusive force to the maxilla for at least 14–16 hours per day during the pubertal growth spurt, continuing until growth is complete. This is only achievable with excellent patient cooperation and favourable growth. The maxillary intrusion splint and the buccal intrusion splint are removable appliances which were developed by Orton and are now widely adopted. The maxillary intrusion splint incorporates acrylic coverage of all the teeth in the upper arch and high-pull headgear (Fig. 12.9). The buccal intrusion splint is similar, except that only the buccal segment teeth are capped. Functional appliances used for Class II maloclusions with increased vertical proportions include the twin-block appliance (Fig. 12.10) and the van Beek appliance (Fig. 12.11). Both incorporate high-pull headgear and buccal capping. In many cases fixed appliances are then used to complete arch alignment, together with extractions if indicated.
Fig. 12.9. A patient wearing a maxillary intrusion splint and high-pull headgear. The face-bow of the headgear slots into tubes embedded in the acrylic of the occlusal capping, which extends to cover all the maxillary teeth.
In cases with bimaxillary crowding and proclination, relief of crowding and alignment of the incisors can result in reduction of an open bite (Fig. 12.12). Stability of this correction is more likely if the lips were incompetent prior to treatment but become competent following retroclination of the incisors.
If it is difficult to ascertain the exact aetiology of an anterior open bite but a primary tongue thrust is suspected, even though these are uncommon, it is wise to err on the side of caution regarding treatment objectives and to warn patients of the possibility of relapse.
Surgery
This option can be considered once growth is complete for severe problems with a skeletal aetiology and/or where dental compensation will not give an aesthetic or stable result. In some patients an anterior open bite is associated with a ‘gummy’ smile which can be difficult to reduce by orthodontics alone necessitating a surgical approach. The assessment and management of such cases is discussed in Chapter 20.
12.3.2. Management of patients with increased vertical skeletal proportions and reduced overbite
The specifics of treatment of patients with increased vertical skeletal proportions will obviously be influenced by the other aspects of their malocclusion (see appropriate chapters), but management requires careful planning to try and prevent an iatrogenic deterioration of the vertical excess. The following points should be borne in mind:
  • Space closure appears to occur more readily in patients with increased vertical skeletal proportions.
  • Avoid extruding the molars as this will result in an increase of the lower facial height. If headgear is required, a direction of pull above the occlusal plane is necessary, i.e. high-pull headgear. Cervical-pull headgear is contraindicated.
  • If overbite reduction is required, this should be achieved by intrusion of the incisors rather than extrusion of the molars. For this reason anterior bite-planes should be avoided.
  • Avoid upper arch expansion. When the upper arch is expanded the upper molars are tilted buccally which results in the palatal cusps being tipped downwards. If arch expansion is required, this is best achieved using a fixed appliance so that buccal root torque can be used to limit tipping downwards of the palatal cusps.
  • Avoid Class II or Class III intermaxillary traction as this may extrude the molars.
12.4. POSTERIOR OPEN BITE
Posterior open bite occurs more rarely than anterior open bite and the aetiology is less well understood. In some cases an increase in the vertical skeletal proportions is a factor, although this is more commonly associated with an anterior open bite which also extends posteriorly. A lateral open bite is occasionally seen in association with early extraction of first permanent molars (Fig. 12.13), possibly occurring as a result of lateral tongue spread.
Posterior open bite is also seen in cases with submergence of buccal segment teeth. Submergence of deciduous molars is discussed in Chapter 3. There are two rare conditions which affect the eruption of the permanent buccal segment teeth:
  • Primary failure of eruption: this condition almost exclusively affects molar teeth and is of unknown aetiology. Although bone resorption above the unerupted tooth proceeds normally, the tooth itself appears to lack any eruptive potential (Fig. 12.14). Extraction is the only treatment alternative. The aetiology is not understood.

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  • Arrest of eruption: this also usually involves molar teeth. Affected teeth appear to erupt normally into occlusion, but then subsequently fail to keep pace with occlusal development. As growth of the rest of the dentition and alveolar processes continues, lack of movement of the affected tooth or teeth results in relative submergence (Fig. 12.15). The aetiology is not understood and again the usual treatment is extraction of the affected tooth or teeth.
More rarely, posterior open bite is seen in association with unilateral condylar hyperplasia, which also results in facial asymmetry. If this problem is suspected, a bone scan will be required. If the scan indicates excessive cell division in the condylar head region, a condylectomy alone, or in combination with surgery to correct the resultant deformity, may be required.
PRINCIPAL SOURCES AND FURTHER READING
Chate, R. A. C. (1994). The burden of proof: a critical review of orthodontic claims made by some general practitioners. American Journal of Orthodontics and Dentofacial Orthopedics, 106, 96–105.
An excellent discussion of the evidence on the postulated and actual effects of mouth breathing upon the dentition, plus much other information. Highly recommended.
Di Biase, D. (1992). The management of open bite. Dental Practice, November, 11–14.
An excellent and very readable account of the aetiology and management of anterior open bite.
Linder-Aronson, S. (1970). Adenoids: their effect on mode of breathing and nasal airflow and their relationship to characteristics of the facial skeleton and dentition. Acta Otolaryngologica (Supplement), 265, 1.
Lopez-Gavito, G., Wallen, T. R., Little, R. M., and Joondeph, D. R. (1985). Anterior open-bite malocclusion: a longitudinal 10-year postretention evaluation of orthodontically treated patients. American Journal of Orthodontics, 87, 175–86.
Mizrahi, E. (1978). A review of anterior open bite. British Journal of Orthodontics, 5, 21–7.
A worthy review.
Oliver, R. G. (1980). Submerged permanent molars: four case reports. British Dental Journal, 160, 128–30.
The cases reported are classified into primary failure of eruption and arrest of eruption. The management of these two conditions is discussed.
Orton, H. S. (1990). Functional appliances in orthodontic treatment. Quintessence Books, London.
A beautifully illustrated and informative book. The maxillary and buccal intrusion splints are described.
Vaden, J. L. (1998). Non-surgical treatment of the patient with vertical discrepancy. American Journal of Orthodontics and Dentofacial Orthopedics, 113, 567–82.
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