Nonsurgical Management of the Anterior Open Bite: A Review of the Options Richard A. Beane, Jr

The open bite malocclusion has been described as being of 2 types: dental and skeletal. Proper differentiation is essential in determining the appropri- ate corrective measures. Dental open bites are generally more responsive to treatment with orthodontics alone, whereas skeletal open bites often require a combination of orthodontics and orthognathic surgery. Patient selection and treatment principles for nonsurgical open bite treatment are discussed, and a review of various methods of treatment for the skeletal open bite is presented. Posttreatment stability and retention concerns are addressed. (Semin Orthod 1999;5:275-283.) Copyright © 1999 by W.B. Saun- ders Company

T he open bite malocclusion is a c o m m o n clinical entity and has long been recognized

as one of the more difficult problems to treat successfully. Although much attention has been devoted to the open bite problem, there remains controversy as to the factors contr ibut ing to an open bite and, consequently, there is often lack of agreement as to the appropr ia te way to treat this condition. Development of an effective treat- men t plan and p roper m a n a g e m e n t is depen- dent on p roper diagnosis. This requires careful evaluation and a broad knowledge of the various etiologic factors that may cause an open bite.

For many years, clinicians have recognized that the cause of open bite is multifactorial. Etiologic factors can be classified in three broad categories: digit sucking habits, abnormal size and function of the tongue, and a vertical growth pattern, which can be innate or environmenta l in origin. Other causative factors, which are less commonly encountered , are arthritic degenera- tion of the condyles, muscle weakness (for ex- ample, muscular dystrophy), and total nasal obstruction. 1,2

O p e n bites are generally classified as ei ther

From the School of Dentistry, Department of Orthodontics, UNC Chapel Hill, Chapel Hill, NC.

Address correspondence to Richard A. Beane, Jr, DDS, Clinical Professor, Department of Orthodontics, University of North Carolina, School of Dentistr); Chapel Hill, NC 27599-7450.

Copyright © 1999 by W.B. Saunders Company 1073-8746/99/0504-0008510. 00/0

skeletal or dental. The dental open bite is associ- ated with the following characteristics: normal craniofacial pat tern, procl ined incisors, under- e rup ted anter ior teeth, normal or slightly exces- sive molar height, and thumb or fingersucking habits. The open bite is generally found in the anter ior region within the area of the cuspids and incisors. 3 The craniofacial characteristics most consistently associated with the skeletal open bite are 3-9 increased mandibular plane angle, increased gonial angle, long anter ior fa- cial height, increased total facial height, palatal p lane t ipped up anteriorly, and retrognathic mandible.

Some studies have found evidence of short poster ior facial height, 7,s a l though other investi- gators repor ted little or no difference in poste- rior facial height between patients with and without open b i te ) ° The ratio of posterior to anter ior facial height has been found to be less than normal in patients with open bite, and the ratio of uppe r facial height to total facial height is reduced, s,9 Increased flexure of the cranial base (Na-S-Ba) has also been associated with open bite. n

The "long-face" syndrome has been associ- ated with a posteriorly directed growth pat tern of the mandibula r condyle resulting in increased anter ior facial height. The direction of mandibu- lar growth is mainly vertical. The increase in anter ior facial height is apparent ly a result of erupt ion of maxillary and mandibular posterior

Seminars in Orthodontics, Vol 5, No 4 (December), 1999: pp 275-283 275

276 Richard A. Beane, r

teeth and the amount of sutural lowering of the maxilla. 6

Although it is apparent that skeletal factors are important in the cause of open bite, the dentoalveolar processes also have a considerable role in the open bite malocclusion. Richardson 12 suggests open bite might be a result of increased axial inclination of maxillary and mandibular incisors, as well as increased lower facial height. Others have suggested that both the upper and lower incisors have an adaptive function in main- mining an overbite by virtue of a vertical develop- mental potential. 13-15 The actual depth of bite does not appear to be related to facial height. Betzenberger et a115 analyzed skeletal characteris- tics in growing high-angle individuals and found that 80% of the subjects showed a normal over- bite or a deep bite. Only 20% of the sample had an open bite. This is an indication that skeletal pattern alone is not sufficient to identify those patients who present with an open bite or open bite tendency.

Most open bite malocclusions show some aspects of both dental and skeletal types. The difficulty lies in distinguishing whether a patient should be classified as a dental or a skeletal open bite. The importance of making such a distinc- tion becomes evident when formulating a treat- ment plan. A dental open bite can be treated with orthodontics alone. The true skeletal open bite patient requires a coordinated or thodontic and orthognathic surgical approach to achieve a stable occlusion, acceptable esthetics, and im- proved function. 16-18 The more severe the skel- etal pattern, the more likely surgery will be required. A plan that includes orthodontics and surgery entails considerable costs. Most patients find these costs prohibitive unless they have adequate insurance coverage that will pay for the bulk of the costs of surgery and hospitalization. Insurance companies have become increasingly restrictive in the procedures they are willing to cover in their policies. Another important consid- eration is that, even if orthognathic surgery is the preferred treatment, many patients refuse to consider jaw surgery. This leaves few options other than to deny treatment or attempt to resolve as much of the malocclusion as possible, finishing with a compromised result.

Several investigators have attempted to pre- cisely identify the criteria that can be evaluated to give the clinicians an accurate indication of

which patients have the best potential for bite closure by orthodontics alone versus the patients who will have a poor prognosis and should be candidates for surgery. Another critical aspect of this process is to attempt to predict which pa- tients with a suspected open bite tendency will "open up" during orthodontic treatment, even if they begin treatment with a positive overbite.

Nahoum 19 emphasized the importance of dis- tinguishing between a purely dental open bite and one involving the form of the jaws. He believed the crucial measurement in the cephalo- metric appraisal was the ratio of upper anterior facial height to lower anterior facial height (UAFH to LAFH). Patients with a dental open bite and a UAFH-LAFH ratio less than 0.650 are considered poor risks for conventional orthodon- tic treatment.

Kim 20 developed an analysis called the over- bite depth indicator (ODI). The value of this analysis is that it purports to identify those patients who have an open bite tendency and identifies open bite patients who have good potential for orthodontic correction. This analy- sis attempts to pinpoint those patients with a poor prognosis for orthodontics-only correction. The ODI analysis is a combined measurement of two facial angles; The A-B plane to the mandibu- lar plane and the palatal plane to the Frankfurt horizontal plane. The normal mean of the ODI is 74.5 °. The lower the ODI figure, the more likely an open bite will be present or a tendency toward it. An ODI of 65 ° or less is an indication of an open bite type. Several studies have found the ODI to be a better diagnostic criterion for the presence of open bite than other commonly used cephalometric measurements o r r a t i o s . 21,22

Treatment Methods

Dental Open Bite

The teeth and alveolar processes adapt to vary- ing relationships of the denture bases; therefore, they have an important role in the vertical position of the dentition and the degree of overbite present. 6,14 This finding is good news for the orthodontist. Orthodontics has little influ- ence on the skeletal framework, but there is a great deal of benefit that can be derived from tooth movement in the correction of open bites, particularly in the nongrowing (adult) patient.

Nonsurgical Management of the Anterior Open Bite 277

Sarver and Weissman 23 proposed some useful guidelines for the nonsurgical treatment of adult patients with open bite who have no potential for growth modification. They discussed clinical re- sults using extraction and retraction for dental open bite correction. It is emphasized that there are a limited number of open bites that are amenable to this type of treatment. Patients who are candidates for this type of therapy should meet the following criteria: (1) proclined or procumbent maxillary or mandibular incisors, (2) little or no gingival display on smile, (3) normal craniofacial pattern, and (4) no more than 2 to 3 mm of upper incisor exposure at rest.

Figure 1 shows the principle underlying the ability to close an anterior open bite by reducing incisor angulation. This treatment approach can be effectively used to treat the dental open bite patient. Treatment mechanics are directed to- ward retracting and elongating the anterior teeth. The following patient illustrates the aforemen- tioned treatment procedures (Fig 2).

Patient P.M. (Fig 2) is an adult woman with a Class I, severe anterior open bite malocclusion. A symmetrical open bite extending from cuspid to cuspid was measured as 8 mm in magnitude. There was no history of a digital habit, but a relatively large tongue with tongue thrust during function was noted. The lower facial height was moderately increased. A severe bimaxillary den- toalveolar prot rus ion was evident, with ex- tremely proclined lower incisors. It was con- cluded that the open bite was primarily a dental, rather than a skeletal, problem.

The treatment plan involved closure of the open bite by extraction of upper and lower first

Figure 1. The "drawbridge effect," which shows in- creased overbite by changing incisor angulation.

Figure 2. Pretreatment occlusion of open bite pa- tient, P.M. Lateral views showing class I occlusion (A and C). Front view of severe anterior open bite.

bicuspid teeth, followed by retraction and elonga- tion of the anterior teeth. The patient was informed there was some chance the open bite might not be corrected by orthodontics alone. Orthognathic surgery was discussed as an alterna- tive in the event the orthodontic treatment was not successful. Alignment, retraction, and space closure were accomplished, and the bite gradu- ally closed, resulting in a normal overbite and

278 Richard A. Beane, Jr

overjet. Retention consisted of removable upper and lower retainers. The bite has remained closed for more than 5 years (Figs 3 and 4).

The limiting factor in this type of treatment is the relationship of the upper incisors to the upper lip. If elongation of the upper incisors produces excessive show of incisors and gingival tissue when smiling, the clinical result will be unacceptable (Fig 5).

Figure 4. Superimposition of pre- and posttreatment tracings illustrating significant dental changes result- ing in closure of the open bite. Solid lines indicate initial (33 yrs, 7 mos), and broken lines indicate retention (37 yrs, 1 mo).

Skeletal Open Bite

There are also a number of r ecommended tech- niques for orthodontic treatment of the patient with skeletal open bite. Most of these procedures are designed to intrude posterior teeth or at least prevent molar eruption or extrusion in an at- tempt to reduce or control anterior facial height. The most common methods involved highpull headgear, lingual arches, and posterior bite- blocks to control molar extrusion. The following are treatment principles that have been pro- posed for the patient with skeletal open bite3: prevent extrusion of upper posterior teeth; pre- vent eruption of the lower molars; maintain or

Figure 3. Posttreatment occlusion of P.M. Lateral views after treatment (A and C). Front view showing corrected open bite (B).

Figure 5. Posttreatment photograph shows excellent relationship of the upper incisors to the upper lip.

Nonsurgical Management of the Anterior Open Bite 279

create a curve of Spee; avoid both Class II and Class III elastics as both encourage poster ior extrusion; anter ior vertical elastics are usually not indicated because the incisors are often already overerupted to compensate for excessive anter ior facial height; and if extractions are indicated, the more posterior the better.

When indicated (caries, gross p remature con- tact, and so on), extraction of molars can be very effective in reducing facial height. The presence of usable third molars is an impor tan t consider- ation. Forward m ovem en t of the terminal molars allows the mandible to hinge upward and for- ward. It has been postulated that 1 m m of intrusive vertical m ovem en t of the molars results in approximately 3 m m of bite closure by man- dibular counterclockwise rotation. 24

Trea tment of the pat ient with skeletal open bite requires that the clinician observe sound t rea tment principles. A procedure that would p romote an increase in facial height or extrusion of posterior teeth must be avoided. Leveling the arches is usually not appropriate , and the mainte- nance or creation of a curve of Spee is desirable. Banding of second molars should be avoided because they tend to ext rude when engaged on the arch wire. If second molars are banded, they should be banded or bonded with the molar tubes in the occlusal third of the clinical crown, or the arch wire should be s tepped gingivally to avoid extrusion of the terminal molar on the appliance. 25

Implants

When the objective is to increase the overbite, as in skeletal open bite correction, it would be ideal to close the bite by intruding poster ior teeth. An intrusive force on the molars can only occur when an extrusive force is placed elsewhere. 26 Undesirable movements of anchorage units, such as extrusion, can cause downward and backward rotation of the mandible, resulting in poo r t rea tment outcomes. Implants offer a possibility of achieving a source of stationary anchorage in skeletal open bite cases. Osseointegrated im- plants have been successfully used with intrusion mechanics in open bite malocclusions to prevent extrusion of poster ior teeth .27

In addition to single-tooth implants, a skeletal anchorage system using a t i tanium miniplate temporari ly implanted in the maxilla or man-

dible has been repor ted to provide a source of immobile anchorage. Ti tanium miniplates im- planted in the buccal cortical bone in the apical regions of the first and second molars have been shown to produce as much as 3 to 5 m m of molar intrusion. Counterclockwise rotation of the occlu- sal plane is achieved. There is evidence that the skeletal anchorage system may be an effective adjunctive biomechanical procedure for correc- tion of skeletal open bite malocclusion without many of the usually unfavorable side effects. 28

Multiloop Edgewise Arch Wire Technique

The mult i loop edgewise arch wire (MEAW) has been advocated as a resource to treat cases of severe open bite without the benefi t of surgical intervention. This technique uses a combinat ion of mul t i looped .016 × .022 stainless steel arch wires and heavy anter ior elastics to achieve molar intrusion and simultaneous incisor extrusion, resulting in closure of anter ior open bites. 29-31 The t rea tment effects of the MEAW technique have been evaluated to compare the structural changes between an open-bite group and un- t reated individuals without open biteP ° This appliance produces an increase in the uppe r and lower anter ior dentoalveolar heights. No signifi- cant change has been noted in the uppe r poste- rior dentoalveolar height. The lower poster ior dentoalveolar height is significantly decreased. Measurements indicate distal movemen t of the entire dentition. The interincisal angle also in- creases significantly. The MEAW technique mini- mally affected the skeletal pattern. O p e n bites are corrected by altering the occlusal plane and distally upr ight ing the poster ior teeth. This therapy not only prevents extrusion of posterior teeth but actually intrudes them, especially the lower poster ior teeth. The t rea tment changes with the MEAW technique occurred mainly in the dentoalveolar region and showed a great similarity to the natural dentoalveolar compensa- tory mechanism. The extrusion of anter ior teeth evidenced by the MEAW appliance indicates limited usefulness for patients who have ad- equate or excessive dentoalveolar height before t reatment .

Passive Posterior Biteblocks

Passive acrylic poster ior biteblocks are func- tional appliances that invade the interocclusal

280 Richard A. Beane, Jr

space 3 to 4 m m beyond the rest position. This t rea tment approach is claimed to be effective by inhibiting the increase in height of the buccal dentoalveolar processes, thus prevent ing down and back rotat ion of the mandible. It is most effective before cessation of growth of thej aws.32,33 There are two modifications of the passive bite- blocks that have been used to treat skeletal open bites: removable spring-loaded biteblocks and repelling magnets. Cemented magnets have been, on average, twice as effective as the removable spring-loaded appliance (3.0omm improvemen t in overbite v 1.3-mm). 33 The improvemen t was believed to be caused by mandibular anter ior rotation attr ibuted to molar intrusion and in- creased anter ior eruption. This finding is consis- tent with similar results repor ted by others in the literature, especially when the biteblocks are used in conjunction with a highpull headgear. 34

Functional Appliances

Functional appliances have been used to treat open bites on the theory that the open bite malocclusion was caused not only by a skeletal discrepancy, but also involved faulty postural activity of the orofacial musculature. 35 Some consider the functional regulator appliance (FR4) to be mainly effective in changing dentoalveolar structures but produces no significant skeletal changes. 36 In studies compar ing patients with skeletal open bite with untreated controls with skeletal open bites, the open bites were de- creased significantly in the t rea tment group because of vertical e rupt ion of uppe r and lower incisors and retraction of maxillary incisors. Other studies have shown that the usual down- ward and backward rotat ion of the mandible in patients with skeletal open bite can be changed by FR4 therapy, and that skeletal open bites can be successfully corrected through upward and forward mandibular rotation. 37

A retrospective study by Weinback and Smith 3s evaluated the clinical effectiveness of open bite bionators/activators. Most patients showed a small decrease in facial height, with a mean decrease of 1.3 m m in the open bite. The appliance appears to restrict e rupt ion of maxil- lary molars with little effect on lower molar eruption. Longer functional appliance use re- sults in greater changes. Thei r findings suggest

headgear has no significant effect on changes dur ing treatment. Study of the cephalometr ic radiographs indicated clinicians do not use the open bite bionator for severe open bites; rather, the appliance is used for Class II patients in whom posterior erupt ion would be undesirable, ei ther because of a slight anter ior open bite or a divergent skeletal pattern. It can be concluded that the open bite b ionator could be a useful appliance in treating growing patients.

Active Vertical Corrector

The active vertical corrector (AVC) is a fixed or removable appliance that purpor ts to intrude poster ior teeth in the maxilla and mandible by reciprocal forces. It is a version of the present day biteblock therapy. The appliance uses the repel- ling force of somar ium cobalt magnets, embed- ded in acrylic, to intrude the posterior teeth. The effect is to produce autorotat ion of the mandible and closure of open bites. The repel- ling magnetic forces are considered superior to the static biteblock appliance. 39

Patients are requested to wear the appliance as much as possible. Maximum wear will give op t imum results, but it is claimed that 12 hours per day will give acceptable results. Depending on the severity of the p rob lem and amoun t of wear, open bites have been closed in a mat ter of a few months. Although the appliance has been used successfully by both children and adults, growing children exper ience more rapid results than the adult patient. This appliance is a less invasive alternative to surgical correct ion of the skeletal open bite; however, the thickness of the appliance (which requires 7 m m of interocclusal opening) and the requ i rement to wear it most of the day present a significant challenge for most patients.

Barbre and Sinclair 4° studied 25 patients with open bite, with a mean pre t rea tment age of 10 years 8 months, using the AVC. The AVC was cemented to the teeth and worn 24 hours per day. Average t rea tment t ime was 7.7 months, and mean overbite decrease was 3.2 mm. Changes were achieved by maxillary and mandibular mo- lar intrusion combined with a significant amoun t of uppe r incisor retraction and eruption. Al- though the AVC seems to restrict normal erup- tion of the molars as its principal effect, these

Nonsurgical Management of the Anterior Open Bite 98 1

investigators observed that a significant contribu- tion to the closure of the open bite comes f rom changes in the angulation and erupt ion of the uppe r incisors.

Vertical Pull Chineup

Another appliance that might be considered is the vertical pull chincup. Pearson 41 evaluated 79 patients with excessive vertical d imension and backward growth rotation tendencies. He used the vertical pull chincup in addition to fixed appliances. Patients were g rouped according to level of cooperat ion with chincup wear. The chincup was effective in reducing the mandibu- lar plane angle and facial height dur ing treat- ment. As would be expected, excellent coopera- tors showed significantly less molar extrusion than did poor cooperators, and extraction treat- men t p roduced more molar extrusion than non- extraction treatment. He concluded that vertical pull chincup therapy can be a useful t rea tment p r o c e d u r e in some backward-ro ta t ing pa- tients.41. 42

Glossectomy

An abnormally large tongue, or macroglossia, has often been cited as a causative factor in anter ior open bite, dentoalveolar protrusion, or spacing. In patients with open bite when the tongue is of normal size but is engaged in abnormal function, the prob lem is usually caused by an adaptat ion of the tongue to the anter ior open bite. Closure of the open bite results in the tongue adapt ing to the new envi ronment and subsequent elimination of the tongue thrust. However, if the tongue is disproportionally large for the oral cavity, then the best approach may be to reduce the size of the tongue with tongue reduction surgery (partial glossectomy).4~45 Glos- sectomy is much more c o m m o n in Europe than in the United States or Japan. The reason for this discrepancy is unknown, but it has been pro- posed that many surgeons in the Uni ted States and Japan believe the tongue will adapt to a new functional position after open bite correction, making tongue reduct ion surgery unnecessary. 46 However, in cases of true macroglossia, this procedure may be warranted to improve the prognosis and stability of open bite t reatment.

Retention

Considering all the various t rea tment methods to correct the anter ior open bite, including surgery, a c o m m o n concern of all is re tent ion of the treated result. Stability is a particular con- cern with this type of patient. Can the tongue adapt to the new oral envi ronment created by or thodont ic correction? Studies of long-term results of open bite or thodont ic t rea tment by Lopez-Gavito et al5 and surgically treated cases by Denison et al47 indicate that the relapse rate can range f rom 35% to 42.9%. The data f rom the study of Denison et a147 suggested the relapse was caused by dentoalveolar changes, not skeletal changes. This is an indication of the impor tance of maintaining the dental correct ion by empha- sizing retainer wear. It is especially impor tan t to prevent labial flaring of the incisors. Placing retainers with occlusal coverage may be helpful in prevent ing fur ther molar eruption, especially in patients with remaining growth.

The first r equ i rement to enhance stability is to eliminate the cause of the open bite. I f tongue posture and aber ran t function can cause an open bite, it is possible they may have a signifi- cant role in the pos t t rea tment relapse observed in patients with open bite. P lacement of a tongue crib may improve stability in patients with pre- t rea tment open bites. In selected cases in which tongue posture or funct ion is an apparen t factor, some fo rm of crib therapy dur ing or after treat- m e n t may offer promise to enhance stability. 4s,49 Prolonged retent ion with fixed or removable retainers is advisable and necessary in most cases of open bite t reatment.

The findings repor ted by Lopez-Gavito et al5 and Denison et a147 indicate a ra ther high rate of relapse in patients treated for an open bite. Whereas these numbers may appear discourag- ing, it should be noted that the relapse rate includes some patients who exper ienced a reduc- t ion of pos t t r ea tment overbite but did not progress to an open bite. Although correct ion of an open bite cannot always be perfectly main- tained, there are many patients who will derive considerable benefi t f rom t rea tment with only or thodont ic appliances. P ruden t selection of patients and adherence to sound or thodont ic principles can produce very acceptable and, at times, outstanding t rea tment results.

282 Richard A. Beane, Jr

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