Anterior open-bite has received relatively scanty attention in the literature despite its obvious aesthetic and functional implications. In spite of its worldwide variation, it is a relatively common malocclusion trait. Difficulty in predicting its long-term stability continues to generate interest among orthodontists. This article reviews the relevant literature on the subject particularly its prevalence, common aeteiological factors and their possible contribution to the development of anterior open-bites. Clinical and cephalometric characteristics in the differential diagnosis were also discussed. Treat­ment of anterior open-bites including magnets and surgery were highlighted.

Anterior open-bite is said to exist when there is no incisor contact and vertical overlap of lower incisors by the uppers. Incomplete overbite is a minor variant of anterior open-bite and is present where there is no lower incisor contact with either upper incisor or palate but the incisal overlap still exists. The severity of anterior open-bite may vary from almost edge to edge relationship to a severe handicapping open-bite [Figs. 1,2]. Mizrahi¹ de- scribed anterior open-bite as a vertical discrepancy where upper incisor crowns fail to overlap the incisal third of the lower incisor crowns when the mandible is brought into full occlusion.

Despite the obvious functional and aesthetic problems produced, the subject has received rela- tively minor attention in the dental literature. The long-term stability of anterior open-bite correction is difficult to predict as it continues to generate considerable interest among orthodontists.²"¹⁶ Also of interest is the variation of anterior open- bite among the world's population (Table 1). There seems to be a general tendency towards racial predilection.

Isolated posterior or lateral open-bites are rare and there is seldom any obvious cause. These are, however, attributed to primary failure of alveolar process development.¹⁷¹⁸ Brady¹⁹ and Ireland²⁰ reported cases of familial posterior open- bites in a mother and son, and two sisters, respec- tively. Bosker et al²¹ earlier suggested this condi- tion to be transmitted by an autosomal dominant gene. Mew²², however, suggested that the phe- nomena may be related to tongue between tooth postures.

This paper intends to review the literature on anterior open-bite including its etiology, clinical features and management.

Etiology and Clinical Features

The cause of anterior open-bite is generally multi- factorial and can be attributed to a number of facts. Clinically, anterior open-bite is grouped into two main categories: the dental or acquired open-bites, which do not show any distinguishing craniofacial malformations; and the skeletal open-bite with superimposed craniofacial dysplasia. Both the dental and skeletal open-bites may be classified as simple and complex, respectively, based on the difficulty in their diagnoses and management.²³ From the etiological standpoint, anterior open-bites fall into six groups with specific causes. 


1. Dental open-bite (Habits)

This open-bite is caused by obstruction of eruption of the anterior teeth. Classically, this open-bite is asymmetrical and fits snugly around the offending agent. Many of these cases show spontaneous remissions²⁴, and about 75 to 80% had marked improvement without any form of treatment.²⁵ Since the vast major- ity of these patients are children in the transi- tional dental stage, it is conceivable that the rate of eruption of the anterior teeth will slow down temporarily. These subjects are often referred to as having "transitional or pseudo open-bite".

2. Skeletal open-bite (Hereditary)

This group shows some craniofacial malforma- tion which often varies with maturity.²⁶ Ad- verse functional activities such as mouth breathing may affect the facial architecture and enhance the development of open-bite.²⁷'²⁸ Masticatory muscle functions probably affect mandibular posture and progressively alter the skeletal configuration.^29,30

3. Abnormal tongue function

The cause and effect relationship of abnormal tongue function and open-bite is not clear.¹ This controversy still rages on because little scientific evidence exists to establish the rela- tionship. However, Cooke³¹ reported that young patients possessing anterior open-bite are frequently presented with large tongues. Evi- dence also suggests that in some cases, the aberrant tongue³² and tongue behavior known as "endogenous tongue thrust"³³ are the actual cause of the anterior open-bite. The population of children with such endogenous tongue thrust behavior is small (0.6%) and they often demon- strate lisping with open-bite larger than would be expected with a tongue to lower anterior oral seal and also with excessive muscular activity around the lips during swallowing.³²

4. Neurological disturbances

Neurological disorders contribute to the devel- opment of anterior open-bite. Gershater³⁴ demonstrated a very high incidence (32.3%) of anterior open-bite in his survey of mentally retarded and emotionally disturbed children. This supports other studies where problems in controlling the tongue at rest or in function are encountered.

5. Iatrogenic open-bite

This open-bite is produced by active orthodon- tic treatment obviously represent examples of poor treatment technique or inappropriate treat- ment planning. More common mistakes in this category include the use of anterior bite plane in already reduced overbite and the extrusion of upper molars in high angle cases.

6.     Pathological open-bite

Pathological conditions may also present as anterior open-bite, such as in cleft palate, acromegaly or in bilateral condylar fracture cases. Le Fort II and III fracture cases often present with gagging occlusion, hence anterior open-bite.^35,36

Cephalometric studies on anterior open bite

A review of the literature indicates that there are no consensus on the cephalometric criteria for determining the presence of open-bites. Dung and Smith³⁷ reported that the cephalometric criteria used in their study were not predictive of open-bite tendency.

While the dental or acquired open-bites do not show any distinguishing cephalometric features from the normal dentofacial characteristics, skele- tal open-bites, however, show a number of cephalometric characteristics. This include in- creased lower anterior facial height and compara- tively short posterior facial height.³⁸"⁴² Others are steep mandibular plane,^38,40,41,43 large gonial an- gle,³⁸"⁴¹ as well as increased maxillary posterior dentoalveolar height.^38,41 However, Nahoun et al⁴⁴ showed that the dento alveolar height is normal except for the mandibular molar which is signifi- cantly reduced. Sassouni and Nanda³⁸ and Na- houn⁴⁵ reported that the angle between the sella- nasion plane and the palatal plane was significantly reduced in their sample while Frost and associ- ates,⁴⁰ Subtenly and Sakuda⁴¹, Enunlu⁴² and Lowe⁴⁵ showed no significant difference in this angle, which suggested that open-bite deformity arises inferior to the palatal plane. Another area of agreement among the many investigators who stud- ied skeletal open-bite is the statistically significant increase in the angle between the sella-nasion plane and the occlusal plane.^38404146

Most cephalometric studies comparing control samples to subjects with skeletal open-bite exhib- ited no significant difference in the anterior cranial base as measured from sella to nasion^40,41,44 in the cranial base angle (N-S-Ba) or in the angle be- tween the Frankfort horizontal plane and the S-N plane^38,40. However, Subtenly and Sakuda⁴¹ did report that the distance between sella and basion was less in their open-bite sample, indicating a shortened posterior cranial base. These findings seem to indicate that the cranial base is not greatly affected in skeletal open-bite cases.
 

Clinical assessment should include accurate medi- cal and dental history in addition to cephalometric and study model analyses if one is to differentiate between various types of anterior open-bite. Treat- ment planning must be based on the assessment and evaluation of every individual case which may be unique. Some cases may undergo spontaneous im- provement without any treatment.

A variety of treatment philosophies and appli- ance techniques have been used in the correction of anterior open-bite. These can be categorized into simple treatment which are within the scope of a dental practitioner's clinical responsibility while complex treatment may, however, be beyond this scope and such a case would benefit from a special- ist advice.

Simple orthodontic treatment

The treatment of non-skeletal open-bite in which the child indulges in some form of non-nutritive sucking should include adequate effort to dissuade him from this habit, although most clinicians tend to agree that intervention is not usually indicated until about the age of 5 years when the permanent dentition starts to erupt. Prof fit and Fields⁴⁷ suggested a system whereby a small tangible re- ward is provided daily for not engaging in the habit. Other method of interrupting such a habit, especially during sleep and other recreation, is by placing a cotton glove on the hand or a band-aid on the thumb or finger. Fixed habit breaking devices for control of digit sucking and anterior tongue thrusting are also used by a number of general dental practitioners and pedodontists. One of such appliances is the use of quadhelix (0.038") which facilitates expansion of the constricted maxillary arch as well as discourages the habit. Quadhelix appliance often causes buccal tipping and extrusion of lingual cusps of molars resulting in further increase of open-bite in the anterior region. This side effect is minimized by actively tipping the bands on the appliance lingually to counteract this undesirable effect. Removable appliances could be useful but are not usually recommended because of its non-compliance.⁴⁷ Force should not be used to break the habit because of psychologic problems.⁴⁸ The use of dummy sucking, which is more socially acceptable, has proved to be a better alternative. Larsson⁴⁹ demonstrated that children who sucked dummies stopped using them by the age of six years and showed no tendency to suck digits, whereas the group that sucked digits continued with the habit in significant number according to age-groups that are socially unacceptable and or- thodontically harmful.

Complex orthodontic treatment

Removable maxillary intrusion splints which carry posterior bite blocks are very useful in closing anterior open-bite. Functional appliance with bite blocks, such as Clark's twin block (CTB) and Bionator, have also proved valuable in the vertical control of molars.⁵⁰ Both techniques carry extrao- ral tube for the use of headgear. The effects of the passive acrylic posterior bite blocks on the skeletal and dento-alveolar structures in comparison with the control subjects have been studied in previous human clinical studies.^47,51 Recently, Iscan et al⁵² described the use of spring-loaded posterior bite- block in the correction of anterior open-bite. This appliance comprises upper and lower posterior bite blocks held together by helical springs which acts by intruding the buccal segments with consequently forward and upward mandibular autorotations. These methods are quite effective in growing indi- viduals. The use of other functional appliances, like Frankel IV, open-bite bionators, kinators, in the correction of anterior open-bites have also been mentioned by some authors.^47,53,54

The principle of the anterior open-bite or- thodontic treatment includes vertical control of molars and incisors and tipping movement of the incisors. High pull headgear is quite useful in vertical control of the molars. Careful use of Class II intermaxillary elastics should be employed in open-bite tendencies. A millimeter of molar extru- sion will open the bite even when accompanied by a millimeter of incisor extrusion in Class II elastics since the molar is closer to the condylar hinge axis. A multiloop Edgewise archwire technique has been used to extrude the anterior teeth while exerting distal uprighting forces on the posterior teeth.⁵⁵ This technique has previously been described and was based on the characteristic features of anterior open-bite.⁵⁶ Treatment plan should also include the extraction of terminal molars and distal tipping of the dentition. Information has not been available on the stability of this method. Full-time use of vertical box elastics is recommended. More re- cently, the use of reverse curve nickel-titanium archwire, instead of multiloop wires, had worked well.⁵⁷ The use of transpalatal bar, 0.04" thick or half round wire (5-6 mm) kept away from the soft tissues of the palate, allows the tongue to exert a depressive action on the molars, reducing anterior open-bite.

Recently, removable and fixed appliances with acrylic bite blocks incorporating magnets to intrude the molars have been used to correct anterior open-bite [Figs. 3a-d]. Dellinger reported that the rate of tooth movement with removable bite block system containing repelling Samarium cobalt magnets (active vertical corrector) was greater than conventional approach. Kuster and Inger- vall⁵⁹ reported the advantages of fixed magnetic bite blocks. However, Woods and Nanda,^60,61 in their studies on the growing and non-growing primates saw little difference between the results of these "active" and "passive" bite block appli- ances without magnets and questioned whether the intrusion effects are due to the magnets incorpo- rated in the appliance systems or is it due solely to the increased vertical dimension caused by the acrylic blocks. In a related study, Noar et al⁶² found no sufficient evidence from a laboratory study to support the fact that magnets in bite blocks significantly improve its performance in buccal intrusion. Recent study⁶³ has shown that the thickness and orientation of magnets on the bite blocks may have serious implication on the force produced between them.

Orthognathic surgery continues to play an important role in the treatment of anterior open bite. In cases where anterior facial height is to be reduced surgically (skeletal open-bite), most of the orthodontic tooth movement is accomplished prior to surgery. Maximizing the presurgical orthodon- tics lead to minimal postsurgical mechanics. Avoidance of intrusive mechanics in the buccal region, e.g. high pull headgear, and concurrent avoidance of any extrusive mechanics in the ante- rior region will also facilitate maximum surgical correction and reduced relapse of the open-bite.⁶⁴ This is usually followed by one-piece Le Fort I osteotomy with more impaction of posterior maxil- lary segment. An alternative surgical approach is presurgical segmental leveling in the upper arch followed by Le Fort I osteotomy with a three-part maxillary surgery. Autorotation of the mandible helps close down the open-bite. In some cases, bimaxillary procedure may be necessary. Segmen- tal surgeries, such as Schuchardt procedure with impaction of buccal segments and Kole mandibular procedure, often show disappointed results with frequent tendency towards relapse.⁵³ Bell and Dann,⁶⁵ however, reported a measure of stability in the correction of open-bite using anterior segmental surgical procedures. This stability is probably di- rectly related to the non-involvement of the muscles of mastication in the biomechanics of the surgical change. Anterior segmental osteotomies have lim- ited use in gross skeletal open-bite cases and/or cases of gross antero-posterior malrelationship. In addition to the various surgical procedures described in the literature, many clinicians have also advo- cated a partial glossectomy⁶⁶ in the management of open-bite cases. However, in recent times, partial glossectomy appears to have fallen out of favor in the management of such cases,⁶⁷ possibly because of many reports on disturbance to sensation, speech difficulties and the doubtful efficacy of glossectomy in improving the progress or preventing the relapse of the open-bite correction.⁶⁸

Many studies have indicated that if open-bite correc- tion is not stable, it was because the tongue contin- ues to be postured anteriorly which causes the bite to reopen.⁶⁹"⁷² Incomplete cessation of digit sucking habits, following treatment, often results in the relapse of anterior open-bite due to continued exces- sive vertical growth and eruption of posterior teeth.⁴⁷ Controlling the eruption of upper molar until late adolescence is the key to retention in anterior open-bite cases.⁴⁷ High pull headgear to upper molars in addition to conventional removable retainers prevent relapse of open-bite. Removable appliances with bite blocks, such as open-bite acti- vator worn at night in addition to daytime wear of removable appliance retainer over a long retention period, has also proved valuable in the prevention of relapse of anterior open-bite.⁴⁷ Long-term prog- nosis of anterior open-bite is somewhat unpre- dictable. Lopez-Gavito et al assessed 41 patients all of whom had had an anterior open-bite of at least 3mm. Ten years after treatment, only 35% of patients had an overbite of at least 3mm. No reliable predictor of post-treatment relapse was found.
 

There is a general variation in anterior open- bite among the world's population with great ten- dency towards racial predilection. Basically, two main clinical groups exist. Acquired or dental groups are generally the result of a specific insult or trauma. Developmental or skeletal open-bites are usually much more complex in nature. A detailed understanding of its etiology and develop- mental processes is, thus, essential for their man- agement. The relapse of anterior open-bite could be minimized with appropriate retention regimen. On a long-term basis, no reliable predictors of post-treatment relapse could yet be found.