article anterior open bite

O R T H O D O N T I C S

Dental Update – June 2003 2 3 5

Abstract: Anterior open bite has multiple aetiologies, but can be broadly described asbeing dental or skeletal in origin. Accurate differentiation is essential in determiningthe appropriate treatment plan: dental open bites may close spontaneously in thegrowing patient and are generally amenable to orthodontic treatment, whereas skeletalopen bites frequently worsen with growth and usually require a combination oforthodontics and orthognathic surgery. The incidence of post-treatment relapse is high,making these malocclusions a challenge to treat successfully.

Dent Update 2003; 30: 235-241

Clinical Relevance: Anterior open bite is frequently seen in general practice, soknowledge of its causes and management is important.


nterior open bite (AOB) is present when there is no incisor contact and

no vertical overlap of the lower incisorsby the uppers.1 The severity varies, froman almost edge-to-edge relationship to asevere handicapping open bite (Figure 1).

The incidence of AOB also variesaccording to age and ethnic group. Inthe UK the reported incidence inchildren is 2–4%,2 falling from the age ofnine to the early teens. This reduction isaccounted for by normal occlusaldevelopment, neural maturation of thechild favouring the cessation of oralhabits, decrease in size of the adenoidsand the establishment of a normal adultswallowing pattern. The incidence thenincreases again during the mid-teens,presumably as a consequence of latevertical growth. The prevalence in

adults is 4%.3 AOB is more common inAfricans and Afro-Caribbeans (5–10%).4,5

AETIOLOGYAnterior open bite can be broadlydivided into two categories:

l Dental open bite – the verticalskeletal pattern is not contributory.

l Skeletal open bite – the open bite isat least partly due to the verticalfacial form.

The causes of AOB can besubdivided into a number of areas.

Digit Sucking HabitsDigit sucking is a common cause ofAOB (Figure 2). The incidence of digitsucking is around 30% at 1 year of age,reducing to 12% at 9 years and 2% by 12years. Most persistent suckers arefemale.6 The influence made by the digitdepends on the age of the patient and

the intensity, frequency and duration ofthe habit. Open bites produced in theprimary dentition are of littleconsequence as they resolvespontaneously once the child gives upthe habit.

The open bite caused by digit suckingis frequently asymmetrical, being greateron the side where the digit is inserted.The thumb or finger effectively acts as abarrier to the incisors erupting, whilstallowing excessive eruption of theposterior teeth. The upper incisors areinvariably proclined whereas the effecton the lower incisors is more variable.Not infrequently there is a crossbite dueto narrowing of the upper arch.

How much the teeth are displacedcorrelates better with the number ofhours per day of sucking than themagnitude of pressure. Children whodigit suck for 6 hours or more each day,particularly those who sleep with a digitbetween the teeth all night, can developa significant malocclusion.7 There issome evidence that, as well as dento-alveolar effects, persistent digit suckingcan have a minor effect on the skeletalpattern, causing tilting of the maxillaryplane in an anti-clockwise direction6 andanterior displacement of the maxilla.8

However, these effects are thought tobe transient, and if the habit ceasesduring growth the underlying growthpattern will be re-established.

Abnormal Tongue FunctionA tongue thrust on swallowing is oftennoted in patients with an AOB. Twotypes of tongue thrust have beendescribed:

The Causes, Diagnosis and Treatmentof Anterior Open Bite

DANIEL BURFORD AND JOE H. NOAR

Daniel Burford, BDS, MSc, MOrth, FDS(Orth)RCS, Senior Specialist Registrar (FTTA), EastmanDental Hospital, London and Kingston Hospital,and Joe H. Noar, BDS, MSc, FDS MOrth RCS,Consultant Orthodontist, Eastman DentalHospital, London and Watford Hospital.

A

2 3 6 Dental Update – June 2003


l primary (endogenous) tonguethrust;

l secondary (adaptive) tongue thrust.

Nearly all tongue thrusting falls intothe second category – the tongue isthrust forward on swallowing as anadaptive response to the presence of ananterior open bite to prevent food/liquid/saliva escaping from the front ofthe mouth.9 Tongue function is alsomodified to aid speech.

Proffit10 suggested that the restingposition of the tongue has much greaterinfluence on tooth position than any

tongue thrust, as the duration of anythrusting activity would be too shortto have a significant effect. When thetongue is naturally kept in a forwardposition, overlying the lower incisors,then a reverse curve of Spee is presentin the lower arch (Figure 3), which isparticularly apparent on a lateralcephalogram. This is often a warningsign that closure of the AOB isunlikely to be stable owing to theadverse soft tissue pattern. Tonguereduction is sometimes considered inthese cases, especially if it isabnormally large (macroglossia).

Endogenous tongue thrust is oftenassociated with excessive circumoralcontraction on swallowing. Treatmentfor AOB in a patient with anendogenous tongue thrust should notbe carried out, as relapse will almostcertainly occur.

Skeletal FactorsOpen bites that develop due toexcessive vertical growth are termed‘skeletal open bites’ (Figure 4). Theseare usually more severe in nature thandental open bites, often with only theterminal molars in contact. There is asignificant increase in the loweranterior facial height (LAFH) and theremay be vertical maxillary excess, whichis a feature of ‘long face syndrome’.The Frankfort Mandibular PlanesAngle (FMPA) is usually increased. Incontrast to open bites caused purelyby habit, in which there is impedanceof incisor eruption by the digit, in trueskeletal open bite incisor eruption maybe increased in relation to theunderlying basal bone, although it still

fails to compensate for the excessivevertical development of the jaws.

Dung and Smith11 reported that, in250 patients who exhibited traditionalcephalometric indicators of anexcessive vertical dimension, such asan increased FMPA or LAFH, only13% had actual anterior open bites.They concluded that, in growingpatients, an open bite tendency is inlarge part synonymous with abackward rotation to mandibulargrowth. Hence, attention to thestructural features as identified byBjork12 may be more useful thanconventional cephalometric analysesin predicting how patients will growand how they will respond toorthodontic treatment.

Bjork12 identified seven structuralsigns related to significantly abnormalmandibular growth rotations:

l inclination of the condylar head;l curvature of the mandibular canal;l shape of the lower border of the

mandible;l inclination of the symphysis;l interincisal angle;l interpremolar or intermolar angle;l lower anterior face height.

A patient with a posterior growthrotation tending to give rise to a

Figure 1. (a) Mild dental anterior open bite. (b) Severe skeletal anterior open bite.

Figure 2. Severe anterior open bite due to avidthumbsucking. Note the asymmetric appearance,the open bite being greater on the side thethumb is sucked.

Figure 3. Anterior open bite due to aberranttongue function and posture. Note thecharacteristic reverse curve of Spee in the lowerarch.

Figure 4. Lateral cephalogram of a patient witha skeletal open bite.

a b



skeletal AOB may have some or all ofthe following signs (Figure 5):

l backward inclination of condylarhead;

l a straight mandibular canal;l an antegonial notch;l a receding chin;l a reduced interincisal angle;l a reduced intermolar angle;l an increased lower anterior face

height.

Neurological DisturbancesNeurological disturbances that affectthe oral or facial musculature maygive rise to AOB. Gershater13 reportedan incidence of 32.3% in patients withlearning disabilities.

Muscular DystrophyThe decrease in tonic muscle activitythat occurs in muscular dystrophyallows the mandible to rotatedownwards away from the rest of thefacial skeleton, resulting in increasedanterior facial height, a posterior growthrotation of the mandible, excessiveeruption of the posterior teeth,narrowing of the maxillary arch and AOBthat worsens with growth7 (Figure 6).

Iatrogenic Open BitePoor mechanics during fixed-appliancetreatment may cause extrusion of themolar teeth or ‘hanging’ palatal cusps,which open the bite. Failing to preventovereruption of second molars whenbiteplanes or functional appliances areused may also give rise to an AOB.

Pathological Open BiteLocalized AOB may be associated withcleft lip and palate, acromegaly ortrauma to the facial skeleton, such ascondylar fractures or Le Fort fracturesof the maxilla (Figure 7).

INDICATIONS FORTREATMENTPatients seek treatment mainly onaesthetic grounds. However, there maybe functional problems such asdifficulty incising food and problemswith speech, such as a lisp. Althoughclosure of an AOB may help witheating, there is little evidence to showthat it helps with speech,14 andcertainly this should not be promisedto the patient.

The Index of Orthodontic TreatmentNeed (IOTN) is commonly used in thehospital service, and may in the futurebe used in the General Dental Services,to determine the needs of patients fororthodontic treatment. Only patientswith an AOB greater than 4 mm fall intothe ‘need’ treatment category (IOTN 4).An AOB less than 4 mm would beborderline or be considered not to be inneed of treatment, unless some otheraspect of the malocclusion tookprecedence.

METHODS OF TREATMENTTreatment is dependent on the age ofthe patient, his/her concerns andexpectations, and the aetiology of themalocclusion. Mizrahi15 described fourmodalities of treatment:

l myofunctional therapy;l orthodontic mechanotherapy

(using fixed or removableappliances);

l surgical therapy;l combination of two or more of the

above.

It is important to determine whichform of treatment is the most suitablefor each individual case.

Dealing with Sucking HabitsIn the deciduous dentition, unlessthere is evidence of trauma, the AOB ismost probably due to a habit such asdummy or digit sucking. Nointervention is indicated apart fromencouraging the child to stop the habit.As the patient gets older (andproviding the habit stops) a significantproportion of cases improvespontaneously,16 usually during thechangeover from the mixed to thepermanent dentition.14 However,normalization of the overbite can takebetween 3 and 5 years.17

A child who is still sucking his/her

Figure 5. Bjork’s features illustrating a posteriormandibular growth rotation. 1: Backwardinclination of condylar head; 2: straightmandibular canal; 3: antegonial notch; 4:receding chin; 5: reduced interincisal angle; 6:reduced intermolar angle; 7: increased loweranterior face height.

Figure 6. Patient with muscular dystrophy.

Figure 7. Anterior open bite caused by acondylar fracture.



thumb as the upper permanent incisorserupt (7.5–9 years) should be activelydiscouraged from doing so. Initiallythis should take the form of advice,possibly in conjunction with an aidememoire such as a plaster on theassociated finger, a glove or foul-tasting nail polish. Alternatively, asmall tangible reward can be offered ona daily basis for not engaging in thehabit. If this is ineffective but the childwants to stop the habit, a deterrentappliance can be used. The appliance iseither a removable or a fixed appliancewhich prevents sucking of the digit,and must be retained in place for aminimum of 6 months after sucking hasapparently ceased, to ensure the habithas truly stopped (Figure 8). The fixedvariety is more assured of success.Sometimes a quadhelix appliance isused, which not only discourages thehabit, but has the additional advantageof being able to expand the upper arch.This may be necessary in avidthumbsuckers, as excessive cheekpressure produced during suckingcauses constriction of the upper arch.

These methods are likely to producegood spontaneous resolution of theAOB in a pre-teen patient, but in anolder patient the proclined upper labialsegment is held forwards by mesialmovement of the buccal segments, andthe AOB may be maintained by the softtissue pattern and/or failure of furtheralveolar development anteriorly. This issupported by Larsson, who reportedthat, when the sucking habit isprolonged beyond the pubertal growthspurt, the open bite will not usuallycorrect spontaneously.18 In this casefurther orthodontic treatment may beindicated (see below). However, it is

essential that any digit habit is stoppedfirst, otherwise not only will thetreatment be unsuccessful, but there isalso a risk of root resorption of theupper incisors due to the competingforces to which they will be subjected.A protocol for management of suckinghabits is shown in Table 1.

Use of a tongue guard has beenadvocated as a means of treating anAOB in a patient with a tongue thrust:19

this frequently allows spontaneouscorrection of the AOB, providing it isnot skeletal in nature. Stability dependson the thrust being adaptive rather thanendogenous. Proffit and Mason20

suggest limiting use of tongue guards topatients who have reached puberty, asup to 80% of children who have atongue thrust and AOB at 8 years showimprovement without therapy by age 12.

Prevention of HabitsIn a study by Larsson21 the majority of

children who sucked dummies stoppedusing them by the age of 6 years andshowed no tendency to suck digits,whereas the group that sucked digitscontinued with the habit in significantnumbers, resulting in malocclusions inthe permanent dentition. Hence dummysucking has been advocated inpreference to digit sucking.22

‘Orthodontic’ dummies are now available;these flatten on use, thus preventingundesirable effects on the deciduousocclusion. The child, however, does notalways accept such dummies.

Myofunctional Appliances

Posterior Biteblocks

Passive posterior biteblocks arefunctional appliances that are used toopen the bite 3–4 mm beyond the restposition. In growing patients thisinhibits the increase in height of thebuccal dento-alveolar processes, thuspreventing a downwards and backwardsrotation of the mandible;23 it also allowsdifferential eruption to occur as thelabial segments can erupt unhindered,hence closing the AOB. Modificationshave included spring loading thebiteblocks and use of repelling magnetsembedded in the acrylic of thebiteblocks.24 Highpull headgear to thebiteblocks may increase their efficiency.

Figure 8. Fixed thumb dissuader.

Primary dentitionl No treatment indicated.l If dummy-related advise use of

‘orthodontic dummy’.l Reassure parents that AOB should

resolve when habit stops.

Early mixed dentitionl Advise patient to give up habit.l Use simple aides memoire or daily rewards.

Late mixed dentitionl Consider deterrent appliance if advice

has not worked.l May need orthodontic expansion of

upper arch.

Permanent dentitionl Spontaneous resolution of AOB unlikely.l Refer for specialist opinion.

Table 1. Management protocol for digit-suckinghabits.

Figure 9. A patient with a Class II division 1malocclusion and AOB tendency, beingtreated with a Twin Block myofunctionalappliance with EOT tubes for highpullheadgear.

a b



Where the AOB is associated with aClass II skeletal pattern, a Twin Blockappliance with highpull headgear canbe used to correct the anteroposteriordiscrepancy whilst controlling thevertical dimension (Figure 9).

Functional Regulator Appliance (FR-4)

These are thought to be effective wherethe open bite is at least partly due tofaulty postural activity of the orofacialmusculature. The FR-4 works byallowing vertical eruption of upper andlower incisors and retraction of themaxillary incisors, and some authorshave reported a change in mandibularrotation from a downward andbackward direction to upwards andforwards.25

Fixed AppliancesAnterior open bites can be closedusing fixed appliances and verticalintermaxillary elastics to extrude theanterior teeth. This may be combinedwith a transpalatal arch (TPA) andhighpull headgear to limit verticaldevelopment of the maxillary molarteeth. The TPA functions to preventbuccal rolling of the first molars, whichcould cause the bite to be proppedopen on their palatal cusps. Use ofanterior elastics may be successful inpatients in whom a digit-sucking habit

has artificially inhibited eruption, but isunlikely to work if the aetiology isprimarily skeletal. In this situation theincisors have frequently eruptedfurther than normal as part of naturalcompensation, and further extrusionwould be aesthetically inappropriateand highly prone to relapse. Distalmovement of teeth using headgear iscontraindicated, as this will tend toworsen any AOB. Similarly, Class II orClass III elastics should not be used asthey cause molar extrusion.

Where anterior open bites areassociated with proclined incisors,such as some bimaxillary proclinationcases and Class II/I malocclusions,retraction of the incisors results in anextrusive movement, as the crown isrotated around the centre of rotation ofthe tooth.26 This reduces/eliminates theopen bite (Figure 10). Stability dependson the tongue adapting to a newfunctional position after treatment.

Molar extractions have beenperformed in an attempt to reduce themagnitude of the open bite by forwardmandibular rotation. However,Nahoum27 suggested that, althoughthis may close the anterior open bite,the physiological rest position of themandible would not change, thusleaving total face height unaltered.Mizrahi15 suggested limitingextractions to the posterior region ofthe arch where crowding was present.Richardson and Richardson28 reportedthat the extraction of four secondpermanent molars caused an increasein the overbite compared with acontrol group; they attributed this to aslight distal movement of thedentition, with retroclination ofincisors and increase in the interincisalangle.

Kim29 reported on the use of amultiloop edgewise archwire togetherwith heavy anterior elastics to achievemolar intrusion and simultaneousincisor extrusion to close anterior openbites. The posterior teeth are distallyuprighted using this technique.Although this method has provedsuccessful, excellent compliance withelastic wear is essential and long-termstability has yet to be determined.

Extra-Oral Traction

Vertical Pull Chincup

Vertical pull chincup therapy has beenused to limit excessive vertical growth.Pearson30 reported on 20 growingpatients with backward rotationaltendencies treated by the extraction offour first premolars, chincup therapyand fixed appliances. He showed thatchincup therapy was effective inreducing the angle between themaxillary and mandibular planes and atclosing all anterior open bites.Mandibular autorotation was attributedto reduction in the ‘wedging’ effect bypremolar extraction, retardation oferuption of posterior teeth andredirection of condylar growth.However, chincup therapy generallyhas poor compliance rates and there issome concern that it may causecondylar damage.

Highpull Headgear

Highpull headgear applied to themaxillary molar teeth and worn for 14hours per day has been used to inhibiteruption of the posterior teeth andhence limit vertical growth. Headgearcan be applied directly to the uppermolar bands of a fixed appliance or usedin conjunction with a functionalappliance or an upper removableappliance such as a maxillary intrusionsplint. This form of treatment is basedon the assumption that over-development of the posterior maxilla isresponsible for the deformity.31

Orthognathic Surgery

A combination of fixed-applianceorthodontics and orthognathic surgerymay be required to treat skeletal openbites. Treatment should not becommenced until growth has ceased, asfurther growth is very likely to beunfavourable. Presurgical orthodonticsis aimed at individual arch alignmentand arch co-ordination. An obviousstep in the occlusal plane should notbe levelled but maintained usingsegmental mechanics. Surgery may besegmental or involve the whole jaw.Frequently bimaxillary surgery isrequired.

Figure 10. Retraction of proclined upper incisorsresults in an extrusive movement as the crown isrotated around the centre of rotation of the tooth.The distance between the parallel lines indicatesthe increase in overbite.



STABILITYPrediction of the response to treatmentand the stability of the outcome isgenerally unreliable.14 Relapse rates aftertreatment of AOB are high. As a rule,the more the skeletal elementscontribute to the aetiology of themalocclusion the poorer the prognosisfor orthodontic treatment alone.15 Lopez-Gavito et al.32 reported that, followingorthodontic treatment, more than one-third of patients demonstrated a returnof their AOB, and neither the extent ofthe pretreatment open bite or mandibularplane angle nor any other singleparameter of dentofacial form was areliable predictor of post-treatmentstability.

Relapse of AOB has been attributedto:

l unfavourable growth (a posteriormandibular growth rotation);

l soft-tissue factors such as anunfavourable tongue posture;

l resumption of a digit-sucking habit;l inappropriate orthodontic tooth

movement, such as extrusion ofincisors where their eruption hadnot been previously impeded; and

l surgery that has increased theposterior face height – as wouldoccur if the AOB is closed using amandibular procedure only.

Retention has been directed towardsintrusion, or at least prevention oferuption, of maxillary posterior teeth,33

using either headgear attached to anupper removable retainer or a retainerwith passive posterior biteblocks.However, this should ideally becontinued until the patient ceasesgrowing, although compliance isobviously an issue.

CONCLUSIONAnterior open bite has multipleaetiologies and accurate diagnosis is thekey to determining the best managementstrategy for the individual patient. Manyopen bites will resolve spontaneouslybefore the age of 12 due to ceasing ofdigit habits and maturation in theswallowing pattern. Older patients with

an AOB should have the high risk ofrelapse of treatment explained and,where there are no other anomalies to becorrected, thought should be given toaccepting the malocclusion, particularlyif the open bite is small and there are nofunctional problems.

Any associated digit habit should beceased before active orthodontictreatment is commenced. Treatmentoptions include attempting to redirectgrowth using myofunctional appliances,use of conventional fixed applianceswith highpull headgear and/or verticalanterior elastics, and a joint orthodontic/surgical approach for skeletal openbites. Long-term retention isrecommended.

ACKNOWLEDGEMENTS

We would like to thank the following people forproviding illustrations for this article: MrsElizabeth Horrocks, Consultant Orthodontist,Eastman Dental Hospital (Figures 2 and 3), MissHelen Tippett, Senior Specialist Registrar,Eastman Dental Hospital (Figures 6 and 8).

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