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Anterior open bite cases are very challenging to manage due to the high relapse potential associated with this feature of malocclusion. It is helpful if the aetiology is established before embarking on treatment to ensure that the appropriate treatment modalities are carried out. Determining whether the aetiology of an anterior open bite is caused by an ‘endogenous tongue thrust’ is extremely difficult. In particular, differentiating between an adaptive and endogenous tongue thrust can be extremely challenging. The case study presented explores the clinical considerations when diagnosing and treating anterior open bites.
CPD/Clinical Relevance: This report raises the question: is it possible to diagnose an endogenous tongue thrust?
Article
An anterior open bite (AOB) is defined as the lack of vertical overlap of the upper over the lower incisor teeth. The incidence ranges from 1.5% to 11% with variation in age and ethnic origin.1 Patients usually seek treatment for AOB because of the appearance or due to poor function, that is, the inability to bite through food effectively. In the permanent dentition, AOBs are very challenging to treat and manage, as they are known to have a high rate of relapse.2,3,4 Factors attributed to relapse are tongue posture, growth pattern, treatment considerations and surgical instability.5,6,7 It is therefore paramount to establish the aetiology before embarking on treatment to ensure that the appropriate treatment modalities are carried out.
Diagnosis is formulated after considering both clinical and cephalometric factors. AOBs are classified into two maincategories:
Skeletal open bite associated with increased vertical facial proportions;
Dental open bite not associated with a significant skeletal discrepancy.
Clinically, skeletal open bites exhibit excess anterior facial portions, often termed ‘long face syndrome’ and incompetent lips.1 Cephalometric analysis would confirm this with increase of the Frankfort mandibular planes angle (FMPA), lower anterior facial height (LAFH) and interincisal angle.8 Skeletal anterior open bites are genetically predisposed and are caused by unfavourable growth of the mandible, namely a backward rotation.8 The treatment of skeletal open bites is complex and involves a combined surgical and orthodontic approach.9 Dental open bites can be further categorized according to the primary cause, such as soft tissue habits and postures, respiratory and neurological disorders, iatrogenic and pathological conditions.10 A digital-sucking habit is the most common cause of AOB in childre–that can continue in the permanent dentition if it persists beyond the loss of the primary teeth.1 This type of AOB can be corrected successfully with fixed orthodontics and cessation of the habit.10 Many authors believe abnormal tongue function is a prime contributor to dental open bites.11,12,13
In the presence of an AOB, the tongue postures forward to make contact with the anterior teeth in order to provide an anterior oral seal for swallowing: this has become known as a ‘tongue thrust’. Profit et al, however, hypothesize that the cumulative time and pressure from the tongue contacting the teeth is actually insufficient to have an effect on the dento-alveolar structures.1 They feel that it is the rest position of the tongue that actually influences the position of the teeth. The tongue also adjusts to affect speech, often producing a lisp.14 However, speech is not always improved by treatment of the AOB and patients should be made aware of this when managing patients' expectations. If abnormal tongue function is diagnosed as the prime aetiology of the AOB, it then needs to be established whether it is:
Primary (endogenous) tongue thrust; or
Secondary (adaptive) tongue thrust.
Patients with an adaptive tongue thrust develop this abnormal tongue function to ‘compensate’ for the AOB, and therefore this developmental habit that can be altered with correction of the AOB.1,15 Patients with an endogenous tongue thrust, however, are believed to be genetically predisposed to the AOB and maintenance of a fully corrected AOB is extremely unlikely.
Treatment of the AOB is therefore not advocated.10,16,17 Treatment modalities for dental AOB can include fixed appliances, temporary anchorage devices, tongue therapy, tongue surgery, orthognathic surgery and any combination of the above.6,7,11,16,18 Consequently, the diagnosis of the type of tongue thrust is extremely helpful in determining the appropriate treatment modalities, prognosis and, most importantly, for managing the patient'sexpectations.
Here a case is presented that demonstrates the difficulties and pitfalls of establishing the aetiology of an anterior open bite associated with a tongue thrust, and the treatment to correct it.
Case report
A 28-year-old female, HM, presented for an orthodontic consultation with concerns about the appearance of her front teeth. She did not like her smile arc or the gap between her upper and lower front teeth and, additionally, noted difficulties biting through food. She previously used to suck her thumb but had stopped this some years earlier.
Clinical assessment showed the patient to have a mild skeletal Class III base, high FMPA, convex facial profile, average smile line, incompetent lips and no significant facial asymmetry (Figure 1).
Figure 1. (a, b) Pre-operative extra-oral views.
Intra-oral examination showed the patient to have a full complement of teeth excluding wisdom teeth, Class III incisor classification on a mild Class III skeletal base, with no increase in vertical proportions. She had mild upper and lower anterior spacing, Class I molars and canines on both sides and an AOB of 8 mm (Figure 2). The upper centreline was 1 mm to the left and the overjet was 2 mm. On swallowing, she had a tongue to lip swallow but, during her consultation, there was no excessive tongue protrusion noted. The OPT showed the wisdom teeth to be absent, but otherwise she had a sound unrestored permanent dentition (Figure 3). IOTN DH = 4E, AC = 9.
The cephalometric analysis confirmed a mild skeletal Class III (ANB = 0.6) skeletal pattern with no increased vertical element (MMPA = 29, LFH = 69.5, UFH = 47.1) (Figure 4).
Figure 4. (a, b) Cephalometric view.
Owing to the skeletal pattern and previous thumb-sucking habit, a provisional diagnosis of dental open bite caused by thumb-sucking and perpetuated by tongue protrusion was made. It was impossible to know whether this tongue thrust was adaptive or endogenous.
The patient was referred to secondary care for a second opinion and possible treatment. The patient attended the hospital consultation with her mother, and it was observed at this appointment that HM's mother also had a very similar AOB. This observation, together with HM's clinical findings, led to a diagnosis of ‘endogenous tongue thrust’ by the hospital team. The patient was advised that any treatment carried out would be unstable and, therefore, to accept the AOB.
HM returned from secondary care still very keen for an attempt at treatment, even with the knowledge that the relapse potential of her AOB was very high. She was aware that a private treatment option was now the only possible method of correcting her malocclusion. A detailed discussion followed, in which it was decided to attempt to close the AOB, but with the knowledge that this may prove impossible and that the risk of relapse would be high. The fact that the patient used to suck her thumb meant that there was a possibility that her tongue thrust was, in fact, adaptive and not endogenous. The patient consented to the following treatment plan:
Transpalatal arch with a tongue guardextension;
Upper and lower pre-adjusted edgewise ‘Radiance’ fixed appliances (MBT prescription);
Upper and lower fixed retainers;
Upper and lower vacuum-formed retainers with anterior buttons so that an anterior ‘box’ elastic may be worn at night.
Treatment progressed as prescribed and she tolerated the tongue guard well (Figure 5). The anterior open bite was closed in approximately 6 months with a combination of the tongue guard and 0.019 x 0.025-inch stainless steel archwire with bite-closing curves. A consequence of these treatment mechanics was the opening up of posterior open bites (Figure 6). The use of posterior intermaxillary elastics enabled the posterior open bites to be closed while maintaining a positive overbite. The guard had to be adjusted to a lower position approximately 8 months into treatment due to the force of the tongue permanently altering the position of the tongue guard. It was also noted clinically that there had been some intrusion of the upper first molars due to the change in relationship between the bands and the gingival tissues. The patient was debonded 15 months after the start of treatment.
Figure 5. (a–c) Treatment progression: 2 months into treatment.Figure 6. (a–c) Treatment progression: 6 months into treatment.
Retention involved modified vacuum-formed retainers, so that the patient could apply anterior intermaxillary elastics (Figure 7). HM was advised to wear her retainers full-time for 2 days and then evenings and at night thereafter. Fixed retention was also placed which comprised anterior upper (2-2) and lower (3-3) Flextech wire. The patient was reviewed at 3 months (Figure 8), 6 months, 1 year and 2 years (Figure 9). Although the patient was advised to wear her anterior elastics every night, she admitted that, after 3 months, she stopped wearing them, although her compliance with thevacuum-formed retainers was excellent.
Figure 7. (a–d) Retainers.Figure 8. (a–c) Three months after debond.Figure 9. (a–c) Two years after debond.
Discussion
An adaptive tongue thrust, which should perhaps more accurately be referred to as ‘adaptive tongue swallow’ is the soft tissues' means of obtaining an oral seal for swallowing, when the usual lip-to-lip anterior oral seal is unattainable. This is often seen when an anterior open bite ispresent.
A lip-to-lip anterior oral seal may not be possible due to multiple factors. These include:19
Short lips;
A retrognathic mandible;
An increased anterior lower facial height;
Prominent upper incisors.
In patients with an adaptive tongue swallow, it is hypothesized that, if a lip-to-lip oral seal can be achieved and maintained with repositioning the teeth of the anterior labial segment, then the patient can be successfully treated with orthodontic therapy alone. In theory, the patient's tongue will adapt and function of the tongue during swallowing will bechanged.
An endogenous tongue thrust or ‘atypical’ swallowing is when an oral anterior seal is produced by forcible contact of the tongue to the palatal surfaces of the upper and lower incisors. This can exhibit the following characteristics:19
Proclination of upper and lower labial segments, often with spacing;
In reality, the features seen in patients with adaptive or endogenous tongue thrust are interchangeable and not mutually exclusive. The difficulty for the clinician, therefore, lies in the initial diagnosis. The literature may point to a diagnosis of an endogenous tongue thrust, but the clinician will not be convinced until the AOB is corrected and they can see whether the tongue is able to adapt to the new tooth/lip position. If the retention protocol is followed, but the features related to an endogenous tongue thrust return, then it is likely that an endogenous tongue thrust exists and vice versa.
It has been postulated in the literature that this tongue activity cannot change or adapt with repositioning of the upper and lower anterior teeth, therefore, relapse is inevitable following orthodontic treatment.1,10 This is based on expert opinion and longitudinal observational studies post-orthodontic treatment. There is insufficient high-quality scientific evidence either to confirm or disprove the concept.
In HM's case, however, she appears to contradict this theory, as she had all the features of endogenous tongue thrust and yet her AOB was successfully treated with orthodontic therapy only, and the correction was maintained 24 months post-treatment (Figures 9 and 10). It should be remembered that one case does not prove anything, but merely allows discussion, hopefully leading towards future, well conducted research to give more evidence to the debate.
This case report highlights the difficulties in confidently diagnosing AOB due to endogenous tongue thrust. Analysing all aspects of the patient's dental and skeletal features, in addition to family and social histories, and collating this information to aid diagnosis and treatment planning is extremely important.
There is a high rate of relapse of AOB, which ranges from 20% to 38%.20 Research has been carried out to try to predict the stability of AOB but remains inconclusive.18,19,20 It was found that pre-treatment cephalometric variables and changes during treatment had no effect on stability post-treatment and neither did the effect of extractions or non-extraction.20 Consequently, various retention regimens have been advocated in order to prevent relapse, but with no strong evidence to promote one particular regimen. Different retainers, such as occipital headgear, functional appliances with posterior thick bite plane or palatal cribs and fixed retainers, have been prescribed with varying results.21,22 Adjunctive tongue treatment has also been suggested, aiming at re-educating tongue position, such as tongue exercise therapy, palatal spurs/cribs attached to fixed or removable appliances, tongue elevators and even tongue surgery.11,12,22
Consequently, the uncertainty with treating AOB cases reinforces the importance of gaining fully informed consent. This is ever more important, in the current era, in which dental ligation is continually rising along with patients' expectations and demands to obtain the perfect smile.23 Huang concluded that there are insufficient well designed studies available to improve our knowledge and understanding of AOB.24 The majority of studies are centred on post-treatment stability. A recent systematic review by Greenlee et al,25 looking at surgical versus non-surgical treatment with follow-up of no less than 12 months, found both modalities had a success rate of more than 75%, but the evidence was insufficient to determine the therapeutic effectiveness and long-term stability of either.
Conclusion
In this case report, HM obtained correction of her AOB with 15 months of fixed appliance therapy with a modified TPA, followed by retention with the aid of elastics for 6 months. A positive overbite and overjet of 2 mm was obtained and this was maintained 24 months post-treatment. The successful treatment of this patient, and prolonged retention, indicates that not jumping to the diagnosis of an ‘untreatable endogenous tongue thrust’ is important. It also highlights the difficulties and challenges orthodontists face when diagnosing the aetiology of AOB. There is a need for well-designed studies to improve our knowledge and understanding of treatment for anterior open bites.
