REVIEW ARTICLEEtiology and Treatment Modalities of Anterior Open Bite MalocclusionLi-Hsiang Lin1, 2*, Guo-Wei Huang1, Chin-Sung Chen1, 31School of Dentistry, College of Oral Medicine, Taipei Medical University, Taipei, Taiwan2Department of Orthodontics, Wang Fan Medical Center, Taipei, Taiwan3Sihjih Cathay General Hospital, Taipei, Taiwanarti cle i nfoArticle history:Received: Jun 1, 2012Revised: Sep 12, 2012Accepted: Dec 21, 2012KEY WORDS:anterior open bite relapse;dentofacial morphology;orthognathic surgery;overbite depth indicatorThe complexity of anterior open bite is attributed to a combination of skeletal, dental, soft tissue, andhabitualfactors. Multipletreatmentstrategies aimedatdifferent etiologiesofanterior open bite havebeenproposed. However, the tendency towardrelapse after conventional or surgical orthodontictreatment has been indicated.Therefore, anterior open bite is considered one ofthe most challengingdentofacial deformitiestotreat. Theaimof thisarticleistoreviewtheetiologies, dentofacial mor-phology, treatment modalities, retention, and stability of anterior open bite. The etiology of anterior openbitemalocclusions is multifactorial andnumerous theories havebeenproposed, includinggenetic,anatomic and environmental factors. The diagnosis and treatment modalities are variable according tothe etiology. Failure of tongue posture adaptation subsequent to orthodontic and/or surgical treatmentmight betheprimaryreasonfor relapseof anterior openbite. Prolongedretentionwith xedorremovable retainers is advisable and necessary in most cases of open bite treatment. The treatment ofanterior open bite remains a tough challenge to the clinician; careful diagnosis and timely interventionwithpropertreatmentmodalitiesandapplianceselectionwill improvethetreatmentoutcomesandlong-term stability.Copyright 2013, Taipei Medical University. Published by Elsevier Taiwan LLC. All rights reserved.1. IntroductionAnterioropenbiteisdenedasnocontactandvertical overlapbetween the maxillary and mandibular incisors.1,2The incidence ofanterior open bite ranges from1.5% to 11% and varies between racesandwithdental age.3Thecomplexityof anterior openbiteisattributedtoacombinationof skeletal, dental, soft tissue, andhabitual factors.4Multiple treatment strategies aimed at differentetiologies of anterior open bite have been proposed. However, thereis a tendency toward relapse after conventional or surgical ortho-dontic treatment.5,6Therefore, anterior open bite is considered oneof themost challengingdentofacial deformitiestotreat duetodifculties in determining the causes, formulating a diagnosis andthe potential for relapse after treatment.4The aim of this article istoreviewtheetiologies, dentofacial morphology, treatmentmo-dalities, retention, and stability of anterior open bite.2. EtiologyOpen bites are generally classied as either skeletal or dental. Thedental open bite is generally found in the anterior regionwithin thearea of the cuspids and incisors and is associated with normal cra-niofacial pattern, proclined and undererupted anterior teeth, andthumbor nger suckinghabits. Theskeletal openbiteis oftenrelatedto excessive vertical growth of the dento-alveolar complex, espe-cially in the posterior molar region. As anterior open bite is often theresult of a combinationof bothfactors, it makes classicationof openbite as either skeletal or dental difcult. Therefore, it has been sug-gestedthatthemostclinicallyuseful classicationofopenbitesshouldbebasedonetiology. Theetiologyof anterioropenbitemalocclusionsismultifactorialandnumeroustheories, includinggenetic, anatomic, and environmental factors, have been proposed.3. Genetic and anatomic factorsAnanterior openbite is relatedprimarilytothepatients unfavorablegrowthpotential andheredity.7e9Obtainingathoroughfamilyhistorywillhelp theclinician predictapatientsgrowthpattern.Based on cephalometric analyses, the steepness of the mandibularplane is considered the key skeletalnding associated with a skel-etal anterior open bite. An increased gonial angle, a downward and*Corresponding author. Li-Hsiang Lin, School of Dentistry, College of Oral Med-icine, Taipei Medical University, Number 250, Wu-Hsing Street, Taipei 11031,Taiwan.E-mail: L.-H. Lin Contents lists available at SciVerse ScienceDirectJournal of Experimental and Clinical Medicinej ournal homepage: ht t p: / / www. j ecm- onl i ne. com1878-3317/$e see front matter Copyright 2013, Taipei Medical University. Published by Elsevier Taiwan LLC. All rights reserved.http://dx.doi.org/10.1016/j.jecm.2013.01.004J Exp Clin Med 2013;5(1):1e4backward position of the mandibular ramus, and shortened poste-rior facial height are additive in the production of the high man-dibular plane angle inanopenbite population.10It has beensuggestedthat theoverbitedepthindicator(ODI) indexcanbea good predictor in theprimary dentition ofa skeletalopen bitetendency in the adolescent. The ODI is the arithmetic sum of theangle of the AeB plane to the mandibular plane and the angle of thePalatal planetoFrankfort horizontal plane. Thestudyproduceda normof 74.5

, witha standarddeviationof 6.07

.11Avalue of 68

orless indicates a skeletal open bite tendency.12Another usefulmethod to help predict vertical growth patterns is based Nahoumsdiagnosis on the ratio of upper anterior facial height to lower ante-riorfacialheight(AUFH:ALFH). Ifapatienthasanopenbite anda AUFH:ALFHratio of less than 0.65, then the open bite is consideredskeletal which cannot be corrected by orthodontic treatmentalone.13Anatomic conditions such as tongue size and position arewell knowntoaffect skeletal anddental components.14Macro-glossia has been suggested as a possible cause of open bite.15It hasbeenreported thatin patientswithanterior openbite, there aresignicant correlationsbetweenmandibularplaneangle, ramusheight of the mandible, or anteroposterior dimension of the maxillaand movement of the front part of the dorsal tongue during deglu-tition.16Some anatomic conditions such as enlarged adenoids and/or tonsils, swollennasal turbinates, anddeviatednasal septums mayimpair normal upper respiratory nasal function.17Mouth-breathingas a result of upper airway obstruction may cause anterior open bitebut theirdirect relationshiphasnot beenproven.18Mandibularcondylar resorption has also been identied as an etiologic factor ofanterior open bite. Many local and systemic pathologies or diseasescancausemandibularcondylarresorption. Local factorsincludeosteoarthritis, reactivearthritis, avascular necrosis, infection, andtraumatic injuries. Systemic connective tissue or autoimmune dis-eases that can cause condylar resorption include rheumatoidarthritis, psoriaticarthritis, scleroderma, systemiclupuserythe-matosus, Sjgren syndrome, ankylosing spondylitis, etc.194. Environmental factorsVarious habits such as thumb andnger sucking, forward tongueposture, as well as tongue thrust have been reported as causativefactors.20e23Digit suckingcanleadtoanasymmetrical anterior openbite which is worst on the side that the digit is sucked. Not all digitsuckers develop anterior open bite, the important factors being thedurationand frequency of the habit. Those who suck for more than 6hoursadayoftendevelopsignicant malocclusions. Aforwardtongue posture, where the tongue rests between the incisors, mayobstruct incisor eruption and lead tothe development of an anterioropen bite. This should not be confused with a secondary adaptivetonguethrust, in whichthetonguemovesforwardduringswal-lowing tocontact the lips andformananterior oral seal secondary toan anterior open bite. A diagnostic feature on the lateral cephalo-graphsuggestingforwardtonguepostureis thepresence of a reversecurve of Spee in the lower arch caused by reduced incisor eruption.Neuromuscular deciencies also contribute to the skeletalcharacteristicsofan openbite.24,25Patientswithgeneralizedpa-thology of muscle such as muscular dystrophy maybe more pronetoanincreasedvertical dimensionandanterior openbite.26Areduction in the force of contraction of the muscles of mastication,at rest and during function, may lead to excessive vertical skeletalgrowth and molar overeruption.5. Dentofacial morphologyMany analyses comparing control samples to subjects with skeletalopenbitehaveshownnosignicant differenceintheanteriorcranial base as measured from sella to nasion, in the cranial baseangle (NeSeBa).27Richardson also suggested that there is no sig-nicant difference in the cranial base as measured either from sellato nasion or from sella to basion.28However,Subtelny suggestedthat the distance between sella and basion is less in their open bitesamples.9Thereisagreementamongthemanyinvestigatorswhohavestudied skeletal open bite that the mandibular plane angle is con-sistently larger in skeletal open bite patients than in controls. Thehigh mandibular plane angle is found in open bite patients due toa signicantly shorter mandibular ramus and an opening rotationofthemadibularramus.28,29Anincreasedgonialangle, adown-ward and backward position of the mandibular ramus, and short-ened posterior facial height are additive in the production of thehigh mandibular plane angle in an open bite population.10Whenthe total gonial angle (TGA) is divided by the line NeGo into twoparts, the upper part is termed the upper gonial angle (UGA) andthe lower part is the lower gonial angle (LGA). According to Siriwatand Jarabak, the UGA reects the amount of the horizontal vector ofthe facial growth, and the LGA reects that of the vertical vector.30Theanteriortotal facial height(ATFH)isgreaterthanthatinanormal population, andtheposteriorfacial height (PFH), thedistancebetweensellaandgonion, isusuallyshorterinanterioropenbitepatients thaninnormal individuals.9,29,31,32Insomeprevious studies, the ALFH has been considered abnormally largerthanusual, while the AUFHremainednormal, whichentailedsmaller ratios of PFH:ATFH and AUFH:ALFH in anterior open bitepatients.13,29,32An increase inposterior maxillary dento-alveolar height iscommonlymentionedinopenbitecases,9,29, andthat anover-eruption of the mandibular molar teeth causes an opening rotationof the mandible is also mentioned.27However, no signicant dif-ferences inposterior maxillarydento-alveolar height andover-eruption of the mandibular molar between open bite and normalsamples have been noted.9,326. Treatment modalitiesTreatment of anterior open bite is a great challenge in orthodontics,and several approaches have been addressed. Following treatment,patients can benet from improved ability to incise and chew food,improved esthetics, and improved speech. However, it must be keptin mindthattreatmentstrategies shouldalways address theeti-ology of the malocclusion.It is common for children to have anger or thumb habit andtheyshouldbeencouragedbytheirparentstostoptheirhabitbefore the age of 6 years for creating a favorable environment fortheeruptionof permanentteeth. Therefore, itisimportantthathabits are terminated before commencing orthodontic treatment. Ifinitial attempts are unsuccessful, an intra-oral appliance with loopsthat acts as a mechanical obstruction and reminder may be given.Tonguethrustingcanalsoadverselyaffecttheteethandmouth.Tongue cribs have been used to modify tongue behavior and wereeffectiveinclosingopenbitewhenwornfor aminimumof 1year.33,34Myofunctional therapy is also useful in muscle retrainingbyusingaseriesof tongueexercisestocorrect thedeleteriousrestingandfunctional posture.35Masticationexercises incon-junctionwith concentrated vertical control seemed to reduceaberrant vertical growthpatternsinpatients, particularlythosesuffering from neuromuscular deciencies.36Patients wereinstructed to clench on a soft bite wafer (GAC International, Bohe-mia, NY) for1minute, vetimesaday. Each1-minutesessionincluded 5 seconds of isometric clenching (80% of maximum), fol-lowed by 5 seconds of rest. This cycle was repeated six times, fora total of 1 minute.36L.-H. Lin et al. 2Tongue size and position affect skeletal and dental components,and macroglossia has been suggested as a possible cause of openbiteandmandibularprognathism.15BernardandSimard-Savoiehaveperformedamedial glossectomyonamonkeywithopenbite and the postsurgical observationof 52 months indicateda steady increase of over bite.37Hence, reduction of tongue mass bypartialglossectomyisaneffectivetreatmentforcorrectingopenbite with macroglossia.15Because the direct relationship between anterior open bite andmouth-breathing as a result of chronic respiratory obstruction hasnot been proven, prolonged mouth breathing may not necessarilybe the main etiological factor for malocclusion.18Therefore, diag-nosisofupperairwayobstructionshouldbemadeby anappro-priate team of specialists and the decision for surgical interventionsuch as adenoidectomy or tonsillectomy is not recommended in thepreventionof malocclusion and shouldbe donefor medicalpur-poses only.Thetreatmentofskeletal openbitesvariesbetweengrowingand adult patients. Treatment modalities in growing patients withskeletal open bites are geared towards vertical growth mod-ication. In adult patients, the options are more limited, and ofteninvolve an orthognathic surgery. The overall goal oftreatment ingrowing patients aims to reduce or redirect vertical skeletal growthwithintra-oral orextra-oral forces. Several methodshavebeenproposed for controlling vertical growth. The vertical holdingappliance (VHA) is a modied transpalatal arch that has an acrylicpad. TheVHAusestonguepressuretoreducethevertical den-toalveolar development of maxillary permanent rst molars.38Posterior bite blocks impede posterior teeth eruption and studieshave suggested that posterior bite blocks modify the vertical skel-etal pattern effectively.39They can be made of wire or plastic totbetween the maxillary and mandibular teeth, or they can be spring-loaded,40ortted with magnets.41In correcting skeletal open biteproblems, functional appliances, such as activators, bionators, andFrnkel regulators (most with the inclusion of posterior biteblocks), have been used to control vertical maxillary growth of themixeddentition.42Abionator canbe usedtotreat openbiteproblems, especiallyifaccompaniedby aclassIImolarrelation-ship.43Frnkel IVregulator was introduced and evaluated byFrnkel amongpatientswithahyperdivergent skeletal pattern.Frnkel believed that changes of the vertical components may haveresulted fromlip-seal training, with the function regulator acting asanexercisedeviceandleadingtopostural balancebetweentheforward and backward rotating muscles.44Another applianceapproachusesextra-oral devices, suchashigh-pull headgear, toimpede the vertical skeletal and dental growth pattern. Schudy andBrandthaveadvocatedahigh-pull headgearalongwithaman-dibular splint coveringthesecondmolarsandanterior verticalelastics to treat open bites.45Nganet aldemonstrated that openbite complicated by a class II vertical growth pattern can be treatedduring the mixed dentition with favorable results by using a com-bination of an activator and high-pull headgear.46The vertical chincup, together withxed appliances, has also been used to manageanterior open bite in growing patients by controlling the verticalgrowth. Inasinglecasereport, Pearsonreportedthattheuseofa vertical-pullchincupcouldresultinadecreaseinmandibularplane angle and an increase in posterior facial height.47Some mild cases of open bite can be corrected byxed appli-ances that only allowdental movements in a camouage method oftreatment. However, theskeletal proleandcharacteristics arekept unchanged. Various extractionmodalities havebeensug-gestedtocorrect anterioropenbite, whichaimtoextrudetheanterior segment by the draw-bridge effect of reducing the incli-nation of both upper and lower incisors to increase over bite andmove the posterior teeth anteriorly by the wedge effect, ora combinationof the two. These extractionstrategies includeextractingthesecondmolars, rstmolars, secondpremolars, orrst premolars.48Extrusionof theupper andlower incisors isanothercommonorthodonticmodalityforanterioropenbitebyusing vertical elastics, extrusion arches,49or a multiloop edgewisearchwire (MEAW) appliance.50However, correction of the maloc-clusion by extrusion of the upper incisors may result in an excessivedisplayoftheincisorsandgingivaltissues, especiallyin patientswith anteriorvertical maxillary excess. Thus, caremustbetakennot to erupt the teeth extensively when the patient has increasedfacial height. Molar intrusion for correction of anterior open biteswas challenging to orthodontists before the development of skel-etal anchorage. Skeletal anchorage, includingdental implants51,surgical miniplates,52and miniscrew or microscrew implants,53,54are now growing in popularity due to their ability to provide ab-solute anchorage. The intrusion of molars with skeletal anchorageproduces counterclockwise rotation of the mandible and decreaseof the overbite.Orthognathic surgery is often indicated for many non-growingpatients, particularly for esthetic needs, considerable open bite, orskeletal problemsinmultipleplanesof space.4Thesurgical ap-proaches include maxilla55,56or mandible surgeries,57,58surgery onboth maxilla and mandible,59,60anterior maxillary and mandibularsurgeries,61,62and mandibular surgeries combined with temporaryanchorage devices (TADs).63Superior repositioning of the maxilla,through total or segmental maxillary osteotomies, is indicated inskeletal open bite patients with excess vertical maxillary growth.Maxillary impaction allows auto-rotation ofthe mandible,there-fore decreasing the lower face height and eliminating anterior openbite. Closing rotation of the mandible using rigidxation is a viablesurgical option for the correction of anterior open bite in instancesin which maxillary osteotomies are not indicated to improve facialesthetics. However, closingrotationof themandiblewithonlymandibular surgery has been shown to be highly unstable becauseit lengthens theramus andstretches themuscles of thepter-ygomandibular sling.64Therefore, a two-jawsurgery involvingsuperior repositioning of the maxilla with a Le Fort I osteotomy isrecommended to obtain more stable and predictable results for thesurgical correctionof skeletal openbite.60Mandibularsurgeriescombined with TADs resolves the high level of surgical invasion andthe possibility of alar aring caused by superior repositioning of themaxilla.637. Retention and stabilityThe importance of retention is to enhance stability,especially byeliminating the cause of the open bite. Studies of long-term resultsof openbiteorthodontictreatment byLopez-Gavitoet al5andsurgically treated cases by Denison et al6indicate that the relapserate can range from 35% to 42.9%. Relapse after anterior open bitetreatment has been attributed to tongue posture, growth patterns,treatmentparameters, andsurgicalfragmentinstability, possiblydue to increased facial height and extrusion of maxillary molars.4Surgical procedures, xation type, and maxillary transverserelapse can be associated with open bite relapse.65With regard tothe surgical procedures, greater over bite stability can be achievedwithmaxillarysurgical repositioningonly, or withbimaxillarysurgery, whereas mandibular surgeryonlyproduces less stableresults.65Failureoftonguepostureadaptationsubsequenttoor-thodontic and/or surgical treatment might be the primary reasonforrelapseofanterioropenbite. Therelativeincreaseintonguevolume in the oral cavity would also cause a relapse of the man-dibular position after the mandibular setback, resulting ina decrease in overjet and over bite.63Myofunctional therapy andplacement of a tongue cribmayimprovestabilityinpatients,Etiology and treatment modalities of anterior open bite 3especially with an anterior tongue rest posture.66Cliniciansattempt to maintain the corrected open bite for growing patients byapplyingavertical chincuporhigh-pull headgeartotheuppermolars inconjunctionwithastandardremovableretainer. Re-tainers with occlusal coverage to prevent further molar extrusions,and wearing conventional retainers in the daytime, combined withwearingafunctional appliancewithbiteblocks (anopenbiteactivator or a bionator) at night time can also be used. Some cli-nicians evensuggestedthat prolongedretentionwith xedorremovableretainersisadvisableandnecessaryinmostcasesofopen bite treatment.65References1. Proft WR, Fields HW, Sarver DM. 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