Open bite: a review of etiology and managementPeter Ngan, DMD Henry W. Fields, DDS, MS, MSD

AbstractDiagnosis and treatment of open bite malocclusion chal-

lenges pediatric dentists who attempt to intercept thismalocclusion at an early age. This article updates clinicianson the causes and cures of anterior open bite based on clini-cal data. Patients with open bite malocclusion can be di-agnosed clinically and cephalometrically, however, diag-nosis should be viewed in the context of the skeletal anddental structure. Accurate classification of this malocclu-sion requires experience and training. Simple open biteduring the exchange of primary to permanent dentitionusually resolves without treatment. Complex open bitesthat extend farther into the premolar and molar regions,and those that do not resolve by the end of the mixed den-tition years may require orthodontic and~or surgical in-tervention. Vertical malocclusion develops as a result ofthe interaction of many different etiologic factors includ-ing thumb and finger sucking, lip and tongue habits, air-way obstruction, and true skeletal growth abnormalities.Treatment for open bite ranges from observation or simplehabit control to complex surgical procedures. Successfulidentification of the etiology improves the chances of treat-ment success. Vertical growth is the last dimension to becompleted, therefore treatment may appear to be success-ful at one point and fail later. Some treatment may be pro-longed, if begun early. Long-term clinical outcomes areneeded to determine treatment effectiveness and cliniciansshould consider the cost-effectiveness of these early initi-ated and protracted plans. (Pediatr Dent 19:91-98, 1997)

buccal segments) our discussion will be restricted toanterior open bite.

Diagnosis of open bites should be viewed first in thecontext of skeletal structures. Sassouni3 classified openbites into skeletal and dental open bites. The latter haveno significant skeletal abnormality. When the skeletalmorphology in the vertical dimension has been classi-fied successfully, it can be determined whether or not

DIAGNOSTIC FLOW CHARTOPEN BITE MALOCCLUSION

UPPER FACIAL ~

MIDDLE FACIAL THIRD

LOWER FACIAL THIRD

Fig 1. This diagnostic flow chart demonstrates thepossibilities and relationships between skeletaland dental relationships in open bitemalocclusion.

O Pen bite was de-fined by Subtehaeyand Sakuda1 as

open vertical dimensionbetween the incisaledges of the maxillary andmandibular anterior teeth,although loss of verticaldental contact can occurbetween the anterior or thebuccal segment. Becausedifferent etiologic factorsare involved when theopen bite occurs in the an-terior, as opposed to the

TABLE. CLINICAL AND CEPHALOMETRIC CHARACTERISTICS OF SKELETAL OPEN BITE

Clinical Characteristics Cephalometric Characteristics1. Excess anterior face height,

particularly in the lower third2. Lip incompetence (resting lip

separation > 4 mm)3. Anterior open bite (but not always,

some incisors supraerupt)

4. Tend to exhibit class II malocclusionand mandibular deficiency

5. Tend to exhibit crowding in the lower arch6. Tend to exhibit a narrow maxilla

and posterior cross bite

1. Steep palatal plane and increasedpercentage lower facial height

2. Excess eruption of the maxillaryposterior teeth

3. Downward and backwardrotation of the mandible

4. Excess eruption of maxillary andmandibular incisors

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a dental open bite accompanies the skeletal relation-ships. Fig 1 shows that there are multiple variants ofthis problem.

Patients can be diagnosed (or classified) clinicallyand/or by cephalometric analysis, as shown in theTable. Proffit characterized patients with skeletal openbite and a large total face height manifested entirely inthe elongation of the lower third of the face as havinglong face syndrome.4 Clinically and cephalometrically,these patients have a disproportionately long lowerfacial third. Lowe et al. ~ determined that although fa-cial proportions are important, vertical facial typescould be separated reliably using simple, linearextraoral measures for males and females. Fields et al.6

demonstrated that increased interlabial gap was statis-tically significant between normal and long face chil-dren and adults with a mean difference from normalof 2x and 5x, respectively. Unfortunately, evidencesuggests that general dentists trained to clinically de-tect vertically disproportionate faces are not reliable atthat task.7 In an effort to dissect this problem of verti-cal facial types more scientifically, Lowe et al.8 appliedquantitative assessments (Fourier and cluster analyses)to vertical and anteroposterior profiles of a great rangeof patients. They found distinct characterization anddiscrimination difficult. This same study suggested thatspecialists can make reliable clinical discriminationsbetween vertical facial types after training. In sum-mary, clinical vertical classification of patients can beaccomplished, but it must be attempted with care andappropriate training.

Investigators disagree on the site of the skeletal dis-turbances associated with long faces. Some investiga-tors9 noted the maxilla was at fault, while others6,1° in-dicated the lower face associated with mandibularmorphology (ramus height or mandibular plane) wasthe location of the disturbance.

Excessive dental eruption is a confusing variable. Ina study by Fields et al., no dental vertical variables wereobserved in adults, but long face children had signifi-cantly more vertical development, except in the max-illary anterior region.6

The study of facial morphology suggests that facialtypes, no matter how they are defined, are a complexentity. The inter-relationships of the regions makecephalometric measures highly correlated because theyoften look at similar morphology from slightly differ-ent perspectives.11 Such correlations should not beviewed as confirming the identification of the sourceof a problem. The inter-relationships are a result of themethod of analysis, not the problem of inquiry. Whenthese correlations are taken into account, it appears thatthe lower face height is at fault in patients with clini-cally disproportionate vertical facial relationships.6

Once the skeletal abnormality is identified, patientscan be classified as dental open bite or nonopen bite.Patients with increased lower face height may or maynot have an anterior dental open bite.1° In all patients,an open bite exists during the exchange of primary in-

92 American Academy of Pediatric Dentistry

cisors to permanent incisors, which is part of normalgrowth and development.

In summary, both normal and long face skeletalmorphology are observed in association with normaland open bite dental occlusion. In other words, theopen bite dental occlusion is not indicative of a specificskeletal relationship.

Prevalence and problems related to open bitesThe prevalence of skeletal long face malocclusion is

unknown, but has been estimated to be 0.6% or1,350,000 U.S. citizens.4 The prevalence of dental openbites in U.S. children is approximately 16% in the blackpopulation and 4% in the white population,12 with theprevalence of simple anterior open bites (involvingmainly the incisors) decreasing until adolescence.~3 Allchildren experience anterior open bites during the tran-sition from the primary to permanent dentitions withlittle disruption in their oral physiology during thisperiod, which can span I to 2 years.

Masticatory14 and speechis problems have been at-tributed to open bites. The inability to incise is the chiefcomplaint often voiced by open bite patients. Otherpatients indicate displeasure with their facial esthetics.16

Many open bites will resolve by gradually closingwithout treatment, and transitional open bites, whichmake up many of the simple open bites, are of littleconsequence. Complex open bites, those that extendfarther distally and those that do not resolve at the endof the mixed dentition years, can be more problematic.

Relationship between temporomandibular jointdysfunction (TMD) and open bite

Several studies have related the morphologic aspectsof malocclusion to mandibular dysfunction in chil-dren.~7-2° Williamson surveyed 304 pre-orthodonticpatients (aged 6-16), and found that 72% of those withpain dysfunction symptoms had either open bite ordeep bite. 17 In a random sample of 402 children,Egermark-Ericksson et a128 found a correlation betweenTMJ clicking and dental wear. They also found thatfunctional malocclusion due to occlusal intereferenceswas more important than morphologic malocclusion inthe etiology of mandibular dysfunction28 In a later lon-gitudinal study on malocclusion in relation to signs andsymptoms of TMD, the authors found that no singleocclusal factor is of major importance in the develop-ment of TMD, but that morphological malocclusionsuch as crossbite and anterior open bite might be apotential risk factor29 In a larger longitudinal studywith 7337 Japanese children, the prevalence of TMDwas found to be 12.2%. In subjects with TMD, 72.9%exhibited some form of malocclusion and 5.4% hadopen bite. Because a large number of subjects withTMD also had malocclusion, the authors recommendedearly treatment to prevent severe TMD.2°

Etiology

According to Dawson,~1 the major causes of an an-terior open bite are forces that result from thumb or

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finger sucking, pacifier use; lip and tongue habits; air-way obstruction; inadequate nasal airway creating theneed for an oral airway; allergies; septum problems andblockage from turbinates; enlarged tonsils and ad-enoids; and skeletal growth abnormalities. This reviewwill demonstrate that one factor is unlikely to be thecausative agent and a multifactoral etiology that mostlikely explains open bite problems. Our discussion canonly be used as information on how to treat the condi-tion when, and if, certain diagnostic and etiologic cri-teria are present.

Thumb and finger sucking or pacifier useIn younger children, the major cause of anterior

open bite (excluding open bites associated with thetransition from the primary to mixed dentitions) arenon-nutritive sucking habits. By adolescence, environ-mental causes of anterior open bite are less importantthan skeletal factors.

Prolonged thumb-sucking tends to create this mal-occlusion. A surprisingly large percentage (10-15%) children continue to suck a thumb, finger, or other ob-ject well into the elementary school years,la Johnsonand Larson2~ use the term non-nutritive sucking (NNS)to describe habits that involve digits, pacifiers, andother environmental influences. Two theories addressthe possible cause of NNS: Freud’s psychoanalyticaltheory and the learning theory. A combined explana-tion suggests that all developmentally normal childrenpossess an inherent, biologic drive for sucking. Therooting and placing reflexes are merely an expressionof this drive. Furthermore, environmental factors con-tribute to the transfer of this sucking drive to non-nu-tritive sources, such as the thumb or fingers.

A typical thumb-sucker has a malocclusion charac-terized by an asymmetric anterior open bite due to digitposition and a transverse constriction of the maxillaryarch. Adair, et al. evaluated the effects of orthodonticand conventional pacifiers on the primary dentition.23

The results showed a statistical increase in overjet inthe "orthodontic" pacifier group and significantlygreater incidence of open bite in the conventional paci-fier group when these groups were compared. Subse-quent data demonstrate no significant benefits ofnonconventional pacifiers, but a tendency for openbites to close after cessation of the habit,a4

Lip and tongue habits

Dentists and speech therapists often attribute openbite malocclusion to abnormal tongue function. Straubsuggested that tongue thrusting can produce open bitesbut presented no data to substantiate the claim,a5 Jamesand Townsend described different types of tonguethrusting based on the resulting deformities,a6 Tulleya7

classified tongue thrusting as an endogenous habit oras an adaptive behavior based largely on facial mor-phology and swallowing activity.

According to Proffit and Mason, tongue thrust ismore likely to be an adaptation to the open bite, andtherapy aimed at changing the swallowing pattern is

Pediatric Dentistry - 19:2, 1997

not indicated.2s Given the physiology of tooth move-ment, it is unlikely that tongue thrust, but rather rest-ing tongue posture, plays a role in the etiology of openbite. Equilibrium theory suggests that light continuousforces are responsible for tooth movement and posi-tion.29 These forces can be external (digits) or internal(tongue posture or periodontal forces). Abrupt, inter-mittent forces (tongue forces due to swallowing) aremuch less likely to be a causative factor. Proffit andMason’s recommendations,as then, make good clinicalrecommendations even today. They suggest thattherapy for anterior tongue position is not warrantedwith or without malocclusion before adolescence. Fur-ther, tongue therapy is most effective when combinedwith orthodontic treatment. Speech therapy may becombined with orthodontic treatment and possiblymyofunctional therapy in older children.

Airway obstructionPatients with skeletally disproportionately long

faces are often suspected of having an airway obstruc-tion. These patients’ facial appearances were character-ized many years ago as adenoid facies: the cheeks arenarrow, the nostrils are narrow and pinched, the lipsare separated, and often there are exaggerated shadowsbeneath the eyes.1°, 30 This terminology prompted theerroneous notion that the familiar elongated facial pat-tern, with an open mouth and dull expression, wasexclusively related or primarily related to an obstruc-tive adenoid mass or some other respiratory impair-ment. It failed to take into account that the pathologiccondition causing the obstruction could be related todisease or abnormalities of the turbinates, septum, andexternal nasal architecture, or an obstructing adenoidmass that may have resolved by the time an upper air-way assessment is performed.

A report by Linder-Aronson in 197031 renewed in-terest in this complex relationship between respiratorypattern and facial growth and development. The authordemonstrated a statistically significant relationshipbetween obstructing adenoid tissue and certain skeletaland dental patterns. These changes included rotationof the mandible in a clockwise manner so that the man-dible was in a more vertical and backward direction,causing elongation of the lower anterior face height,open bite, and retrognathia. Although statistically sig-nificant, the clinical ramifications were minimal. Inanother study, Hultcrantz examined the incidence ofopen bite in children with tonsillar obstruction andfound a higher proportion of open bites than in chil-dren with unobstructed airways.3a

Harvold showed that total nasal airway obstructioncaused various developmental problems, but an openbite did develop in some animals.33 This was mistak-enly interpreted by many to indicate that mouth breath-ing was the cause of open bites. In reality total nasalobstruction in humans is rare and incompatible withlife in the newborn.

Much of the controversy appears to result from thelack of objective criteria used to assess facial morphol-

American Academy of Pediatric Dentistry 93

ogy and respiratory behaviors. Recent developmentsin evaluation of both facial morphology and respiro-metric variables make it possible to explore this rela-tionship further.

Considerable progress also has been made in quan-tifying the mode of respiration. Previously, investiga-tors used undisclosed, subjective, or unreliable meth-ods to evaluate and label respiration as either nasal,oral, or a combination of these two modes.34-36 Lateralcephalometric radiographs have been used to quanti-tatively evaluate airway size and patency.37 Althoughpositive correlations have been found between airflowand airway measurements from cephalometric radio-graphs,38 the validity of evaluating a three-dimensionalstructure with a two-dimensional radiographic projec-tion is questionable.39

Several investigators used measures of nasal resis-tance to determine airway dynamics.31, 4o, 41 Althoughnasal resistance measurements are valid and reliablewhen used appropriately, this method does have cer-tain limitations.42 Nasal resistance cannot be correlatedwith respiratory mode, the proportional nasal and oralcomponents of breathingo43, ~

A system to measure respiratory behavior objec-tively should provide continuous monitoring of succes-sive respiratory cycles, measure both inspiratory andexpiratory airflow, provide simultaneous measure-ments of oral and nasal airflow, interfere minimallywith normal respiratory behavior, and have a highdegree of reliability and reproducibility. 4s Such meth-ods have been developed.4~8

Warren42 demonstrated a method to assess nasal air-way impairment using a technique to measure a mini-mum nasal cross-sectional area. This method involvedmodifying the theoretical hydraulic principle and as-sumed that the smallest cross-sectional area of a struc-ture can be determined if the differential pressureacross the structure is measured simultaneously withrate of airflow through it. This technique enables clini-cians to estimate the size of the nasal airway’s mini-mum cross-sectional area during breathing and givessome indication of the potential for nasal impaired ornormal respiratory function. Warren et al. 4s also de-scribed an alternative approach for measuring oral andnasal respiration and tested its reliability.

Fields et al. 49 demonstrated that the normal and longface groups had similar tidal volumes and minimumnasal cross-sectional areas, but the long face subjectshad significantly less nasal component of respiration.These results illustrate that groups without significantdifferences in airway impairment can demonstrate sig-nificantly different breathing modes that may be behav-iorally based instead of airway dependent. Posturalchanges may be responsible for the morphologicchanges of the face and may have been establishedearly as an adaptation for previous airway deficiencies.The adaptive posture may have resulted in alteredmuscle forces that can impact dental and skeletal struc-tures. Solow et al. 5° advanced this theory that was noted

by Warren and Spalding.sl

Because of conflicting results, these studies suggestthat one should have a clinically reliable evaluation ofthe airway before intervention, so that any treatmentis directed at a valid etiologic agent.

Skeletal growth abnormalities

In 1931, Hellmans2 suggested that open bite is dueprimarily to skeletal deficiencies. In a study of 43treated and untreated open bite cases, he found thepercentage of successful treatments was equal to thepercentage of self-correcting cases in the untreatedgroup. Using anthropologic measurements, he foundthat subjects with open bite had shorter rami andgreater total facial height. In another study by Schudy,s3

clockwise rotation of the mandible (as viewed from thepatient’s right) was found to be a result of excessivevertical growth as it relates to horizontal growth. Thiskind of growth pattern occurs when vertical growth inthe molar region is greater than growth at the condyle.Genetic and environmental influences that encouragevertical growth in the molar region, which are not com-pensated by growth at the condyle or posterior ramus,will result in anterior open bite.s4 Similarly, forces thatimpede the eruption in the incisal region also result inanterior open bite.

In summary, vertical malocclusion develops as aresult of the interaction of many etiologic factors. Inyoung children, digit habits and pacifiers are the mostcommon etiologic agents. In the mixed dentition years,other than the normal transitional open bite, some openbites are probably attributable to lingering habits, whileothers are clearly skeletal in nature. In the adolescentand the adult, it is difficult to assign singular causation.The influence of the tongue, lip, and airway on the de-velopment of malocclusion remaIns to be substantiated.Variations in growth intensity, the function of the softtissues and the jaw musculature, and the individualdentoalveolar development influence the evolution ofopen bite problems.

Cures (treatment considerations)To state that there are cures for open bite malocclu-

sion is misleading. To indicate that some approachesare more rational than others is fair. Unfortunately, thelong-term clinical outcomes are not well documented.The discussion presents some data and some clinicalimpression. The treatment for open bite problemsranges from observation or simple habit control pro-cedures to complex surgical procedures. This is com-plicated by the fact that vertical growth is the last di-mension to be completed,ss This means that sometimesa simple treatment will prevail, while at other times,may appear to be successful at one point only to faillater. It also implies that some treatments may be ex-tremely long, if begun early. The cost-effectiveness ofthese protracted plans must be questioned.

Treatment techniques can be categorized as habit,appliance, or surgical. Simple techniques are those in

94 American Academy of Pediatric Dentistry Pediatric Dentistry - 19:2, 1997

which the etiologic factor is removed and the bite closesby the normal eruptive process, or closure is enhancedusing orthodontic appliances. More difficult proce-dures are those in which intrusion (either active or rela-tive intrusion achieved by inhibiting eruption of theposterior teeth) is attempted with orthodontic appli-ances. In some cases, orthognathic surgery is the lastand only resort. Often treatment approaches are com-bined when the etiology is unclear.

Habit therapyIn young children engaged in NNS, treatment con-

sists of controlling the habit, which alone may be suf-ficient to allow the teeth to erupt to a normal position.Johnson and Larson22 suggest that therapy should be-gin when the benefit to the patient outweighs the risks(dental, emotional, and psychologic) of habit discon-tinuation. Treatment may involve habit awareness,time out, contract of reward or punishment, positivereinforcement, and sensory attenuation procedures(procedures designed to interrupt the sensory feedbackfrom NNS such as orthodontic appliances, chemical

Fig 2a. A 5-year-old boy presented with anterior openbite and constricted maxilla due to NNS habit.

2b. Expansion appliance with tongue crib to correct NNShabit. A Hyrax™ rapid maxillary expansion appliancewas chosen rather than a simpler W-arch or quadhelixdue to the ability of this rigid appliance to prevent acompulsive thumb sucker from imbedding the appliancein palatal tissues.

aversion, and hand wraps). A habit device can be in-corporated into the maxillary expansion appliance tocorrect both the transverse (maxillary constriction) andvertical problems (Fig 2). Because patient complianceand cooperation are essential in eliminating NNS hab-its, a child must want to terminate the habit before in-tervention begins.

Early or interceptive treatment of anterior open bitewith cribs or retraining exercises aimed at tongue con-trol remains a controversial issue. Worms et al.,13 in astudy examining 1408 Navajo children ranging from 7to 21 years for occlusal discrepancies, found spontane-ous correction of 80% of the anterior or simple openbites. Appliances such as tongue cribs have been usedto treat anterior open bites by redirecting an anteriorlypositioned tongue. Erverdi et al.56 studied the effect ofcrib therapy to treat anterior open bite. The most sig-nificant findings were the eruption of the mandibularand maxillary incisors and intrusion of the mandibu-lar first molars, which decreased lower face height.These findings were considered to result from the pos-terior tongue posture. Myofunctional therapy periodi-cally resurfaces as a treatment method. At this time, noscientific evidence supports myofunctional therapy aseffective in correcting open bites.25

Appliance therapyAppliance therapy usually has one of several goals:

to impede dental eruption and thereby control verticaldevelopment, to reduce or redirect vertical skeletalgrowth with intraoral or extraoral forces, or to extrudeanterior teeth. Bite blocks often are used as a compo-nent of orthodontic appliances to intrude or controleruption of the posterior teeth. Bite blocks made of wireor plastic fit between the maxillary and mandibularteeth at a slightly increased vertical dimension. Thestretched muscles theoretically place an intrusive forceon the posterior teeth, which in turn helps control erup-tion. With limited eruption, skeletal growth is directedmore anteriorly and less vertically.

Dellinger57 describes the use of the Active Vertical

2c. Correction of NNS habit, normalization of maxillaryarch width and improvement in anterior open bite after 3months of appliance therapy.

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CorrectorTM (AVC), which is a removable or fixed ap-pliance that intrudes the posterior teeth in both themaxilla and mandible by reciprocal forces. This appli-ance reportedly corrects open bites by actually reduc-ing anterior facial height. Haydar and Enacar58 used aFrankelTM appliance (FR4) to correct open bites, andshowed that it did decrease the open bite significantly,but produced mainly a dentoalveolar rather than skel-etal result. Aragao’s function regulators9 was shown tonormalize open bite.

Magnets also have been incorporated into biteblocks to exert an intrusive force on the molars with aresult of decreasing the open bite. 6° Kuster andIngervall compared the use of spring-loaded bite blockswith bite blocks with repelling magnets. Their resultsshowed an average improvement in open bite of 1.3mm in the spring-loaded group and 3.0 mm in themagnet group. There was a tendency toward relapse,but they felt this might be counteracted by a long phaseof active retention.61 Iscan compared spring-loaded biteblocks with passive bite blocks and found no signifi-cant difference between the two.62 Continuous forceappears from clinical reports to be able to intrude pos-terior teeth. This control is required until verticalgrowth is completed. Maintaining correction is themost difficult task.

In correcting skeletal open bite problems, intraoralappliances, such as activators, bionators, FrankelTM

regulators (most with the inclusion of posterior biteblocks), have been used to control vertical maxillarygrowth of the mixed dentition. Weinbach and Smith63

showed that a bionator can be used to treat open biteproblems, especially if accompanied by a class II mo-lar relationship.

Another appliance approach uses extraoral devicesto impede the vertical skeletal and dental growth pat-tern, such as a high-pull headgear. The biggest prob-lem with the headgear is that it is almost impossible toobtain a pure vertical force. Wieslander suggests thatfor the headgear to obtain a skeletal effect, it must beworn 12-14 hr/day with a force of 10-16 oz (400-450g) per side.~4 Schudy advocated a high-pull headgearalong with a mandibular splint covering the secondmolars and anterior vertical elastics to treat open bitesPearson suggests controlling the vertical force by us-ing intrusive forces on the mandibular posterior bylight mandibular headgears, which he states can behelpful in reducing lower molar height increases andgaining control of the occlusal plane angle.66, 67

When patients have increased vertical developmentand a class II malocclusion, the potential exists to useheadgear in combination with a functional applianceincorporating posterior bite blocks.6a, 69 Ngan demon-strated that open bite complicated by a class II verticalgrowth pattern can be treated during the mixed denti-tion with favorable results by using a combination ofan activator and high-pull headgear.7° Dermaut71 stud-ied the effect of headgear activator of Van Beek andfound that the use of combined activator and headgear

96 American Academy of Pediatric Dentistry

controlled the increase in lower anterior face height.This combined approach of functional appliance andheadgear provides some skeletal and dental control.

Another appliance aimed at controlling the verticalgrowth that may cause an open bite is the chin cup.Pearson reported that the use of a vertical-pull chin cupcould result in a decrease in mandibular plane angleand an increase in posterior facial height comparedwith the growth of untreated individuals with a result-ant decrease in open bite tendencies.72 However thechin cup generally has poor compliance rates.

Straight wire appliances and leveling the arches mayspontaneously correct mild open bites.73 This has someefficacy if the upper arch has a curve of Spee and thelower does not. Injudicious leveling of the lower archusually opens the bite and is contraindicated. Someopen bites can be treated by stepping the arch wires toclose the bite combined with use of vertical elastics.Viazis published a case report using rectangular NiTiwires and elastics to close an anterior open bite. 74 Caremust be taken not to erupt the teeth extensively whenthe patient has increased facial height. Excessive andunesthetic dentoalveolar height can result from thisapproach if smiling reveals extensive gingival display.

Arat and Iseri compared fixed appliance treatmentwith functional treatment to correct open bite. Duringfixed appliance therapy, marked increases in the maxil-lary and mandibular posterior dentoalveolar heightwere observed, and the mandible rotated backwards. Onthe other hand, with functional appliances, forward andupward rotation of the mandible was noted with thecenter of rotation at the premolars.75 These data vividlyemphasize an important point. If functional appliancesare used for phase I therapy and are followed by phaseII fixed appliances, all the gains from phase I can be lostin phase II. Incorporating removable bite blocks withfixed appliance therapy has shown some clinical successif continued into retention and the nongrowing years.

In summary, any of the mixed dentition approachesmust take several factors into account. First, facialgrowth can make these efforts unsuccessful in the longrun. Fixed appliance therapy with its extrusive biome-chanics, must not reverse gains previously made. Com-binations of techniques may be essential even duringthe finishing and retentive phases. For that reason, itmay be best to tackle only mild or moderate problemsor those in patients who are near the end of growth, andnot severe open bite problems. Second, any treatmentaimed at controlling eruption in one arch must guardagainst compensatory eruption in the opposing arch.

Surgical managementOne method of surgical correction is to extract

second and/or third molars if they are the onlysource of centric contacts.21 Glossectomies have beenused to correct open bite problems associated withabnormal tongue habits. Their effectiveness in clos-ing anterior or posterior open bite problems has notbeen substantiated.4

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Surgical procedures to improve the patency of theairway must be undertaken with caution. Document-ing the amount and location of the obstruction is a pre-requisite. In many cases, a more conservative medicalapproach may serve the same purpose when the ob-struction is related to allergies. This is especially impor-tant because it is recognized that a reduction in tonsilarand adenoid tissue occurs near adolescence, and otherchildren appear to "outgrow" certain allergies.

Severe skeletal open bites in patients who are notgrowing are often treated by combined orthodontic-surgical approach. Superior repositioning of the max-illa, via total or segmental maxillary osteotomies, isindicated in skeletal open bite patients with excess ver-tical maxillary growth. Maxillary impaction allows for-ward and upward rotation of the mandible, thereforedecreasing the lower face height and eliminating ante-rior open bite. 4 This upward and forward autorotationoften makes mandibular reduction or reduction genio-plasty necessary as well. Superior repositioning of themaxilla is one of the most stable orthognathic surgicalprocedures. In a study of 61 patients who had a LeFortI downfracture with the maxilla moved superiorly atleast 2 mm, only three patients (5%) had significantrelapse; 95% were vertically stable, y6 These excess prob-lems are best approached when growth is nearly com-pleted so that residual growth does not obviate thecorrection. Such procedures can be completed earlierin females than males.

SummaryThe problem of open bite is multifactorial. Diagno-

sis should be viewed in the context of the skeletal struc-ture and the dental structure. Anterior open bite accom-

panied by a normal lower face height can be treatedsuccessfully using appliance therapy if the etiology canbe identified as a habit or obvious environmental in-fluence. The influence of tongue, lip and airway on thedevelopment of this malocclusion remains to be sub-stantiated. Reliable and valid otolaryngology consul-tation should be obtained if nasal airway obstructionis suspected.

Open bite problems of skeletal nature require ortho-pedic intervention. Severe skeletal open bite innongrowing patients usually requires treatment withorthodontic-surgical procedures. The treatment of openbite remains a challenge to the clinician, and careful di-agnosis and timely intervention will improve the suc-cess of treating this malocclusion.

A portion of the section on "Airway Obstruction" was excerptedfrom Fields et al.: "Relationship between vertical dentofacial mor-phology and respiration in adolescents". Am J Orthod DentofacOrthop 99:147:154, 1991.

Dr. Ngan is a professor and chair of the Department of Orthodon-tics, West Virginia University School of Dentistry. Dr. Fields is aprofessor and dean of the Department of Orthodontics at The OhioState University College of Dentistry.

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