Open bite
An open bite may exist anteriorly or posteriorally in the arch.
Anterior open bite
The incisors do not overlap vertically when the posterior teeth are in occlusion.
Aetiology
Skeletal pattern An increase in lower facial height and high FMPA leads to an increase in the distance between the upper and lower incisors. Where it is not possible for the incisors to erupt sufficiently to compensate for the increased interocclusal distance, an incomplete or anterior open bite results. This is worsened by the downward and backward pattern of mandibular growth, which contributes to the likely additional class II skeletal pattern.
Soft tissues Rarely an open bite is caused by the action of the tongue. The forward positioning of the tongue to achieve an anterior oral seal is usually adaptive in those with increased vertical skeletal proportions, as there is a greater tendency for the lips to be incompetent. A similar swallowing pattern is often observed in children with an anterior open bite caused by a digit-sucking habit. Where a tongue thrust is endogenous / primary (which is rare), there is often a lisp and some proclination of upper and lower incisors.
Habits A persistent digit-sucking habit inhibits eruption of the incisors, often producing an asymmetric anterior open bite. Occasionally a posterior crossbite is produced through unopposed action of the cheek muscles as the tongue is lowered by the presence of the digit during sucking.
Localised failure of alveolar development A localized failure of alveolar development can occur in those with clefts of the lip and palate, but it can also occur where no cause is readily discernible.
Treatment
With the exception of when an anterior open bite is caused by a habit, treatment is complex and is best managed by a specialist.
Treatment in open bite caused by skeletal factors
The open bite may be accepted if it is mild or where the prospect of stability is poor because of adverse skeletal and / or soft tissue factors, notably grossly incompetent lips and / or the suspicion of a primary tongue thrust.
Orthodontic management of anterior open bite The aim is to increase or at least maintain the overbite. Extrusion of molars, which may occur through use of a flat anterior bite plane on an upper removable appliance or cervical-pull headgear, must be avoided. Expansion of the upper arch, which is likely to extrude the palatal cusps and prop open’ the bite, should also be avoided. Assuming that there are no adverse growth or soft tissue factors, growth modification may be possible using high-pull headgear to the upper molars in mild open bite, or by attaching high-pull headgear to a removable or functional appliance with buccal capping where a class II skeletal pattern and a more marked anterior open bite exists. Where an anterior open bite is associated with a gummy smile’, high pull headgear to a full-coverage maxillary splint is indicated. As extrusion of the incisors to close an anterior open bite is unstable, the aim in all cases is to attempt to maintain the vertical position of the maxilla while preventing eruption of the upper posterior teeth. Attempts to intrude the maxilla and modify growth require excellent patient cooperation, with a minimum of 14–16 hours per day wear of the headgear and any other appliance. Following correction of the anterior open bite, fixed appliances are often required, sometimes in conjunction with extractions, to detail the occlusion. Occasionally, camouflage by incisor retraction following relief of crowding can be stable if the lips become competent post-treatment. The contention that extraction of molars may aid overbite increase is unproven. Where the anterior open bite is severe, a combined orthodontic / surgical approach is best when growth is complete.
Treatment in open bite caused by habits Gentle discouragement of a digit-sucking habit in the early mixed dentition often leads to spontaneous correction of an anterior open bite, although it may take up to 3 years for the overbite to be regained. Fitting an upper removable appliance may act as a habit breaker and allow incisor retraction once the habit has ceased.
Treatment of open bite with aberrant soft tissue factors
Where an endogenous tongue thrust is suspected or the lips are grossly incompetent, treatment is best withheld, as relapse of any treatment is guaranteed.
Posterior open bite
Posterior open bite exists where there is no contact between the buccal segment teeth when the remainder of the dentition is in occlusion. It is very rare and the exact aetiology often incompletely understood. Causes include unilateral condylar hyperplasia. Here removal of the condyle is required if growth is excessively active. It is also caused, rarely, when the molar teeth fail to erupt despite apparent bone resorption in advance of the tooth, or eruption is arrested at a certain occlusal level while adjacent teeth maintain contact with the opposing teeth. In both cases, a posterior open bite will result and extraction of the molar is the only treatment option. A lateral open bite is occasionally seen in the buccal segments with submergence or following early loss of primary molars. In the latter situation, lateral tongue spread has been proclaimed as a cause, but it is likely that other factors operate. Any attempt to extrude the teeth into occlusion usually relapses. Lateral open bites usually occur bilaterally as a transient feature during twin block therapy but resolve as the buccal blocks are trimmed and the posterior teeth erupt into occlusion.
Crossbite
A crossbite is a buccolingual malrelationship of the upper and lower teeth. It can be anterior or posterior, unilateral or bilateral and may be associated with a mandibular displacement on closing. That is, an occlusal contact deflects the mandible laterally or anteriorly to allow maximum interdigitation. With a lateral displacement there is often a centre-line shift. By convention, the lower teeth are described relative to the upper so where the lower teeth occlude buccal to their opponents a buccal crossbite exists. Conversely, where the lower teeth occlude lingual to the palatal cusps of the upper teeth, a lingual (scissors) crossbite exists. problems in susceptible individuals. In addition, a traumatic displacing anterior occlusion may deflect a lower incisor labially and compromise periodontal support.
Treatment of anterior crossbite
Where one or two incisors are in crossbite there is usually a mandibular displacement, and correction early in the mixed dentition is advisable provided adequate overbite exists to maintain correction. Space must be present in the arch (or can be created by extraction) to allow alignment of the tooth. If the tooth inclination is amenable to tipping, an upper removable appliance with buccal capping to free the occlusion and a Z-spring for proclination may be used. Anterior retention must be good to resist the displacing force caused by the action of the spring. Alternatively, an appliance with a screw section, clasping the teeth to be moved, overcomes this problem. Where insufficient overbite is likely to exist post-treatment, or the incisor is bodily displaced, treatment is better carried out with a fixed appliance in the permanent dentition. Treatment of anterior crossbite involving two or more incisors is considered in
Aetiology
Skeletal factors A mismatch in the widths of the dental arches or an anteroposterior skeletal discrepancy may produce a crossbite of a complete arch segment – a lingual crossbite commonly found in class II – while a buccal and/or anterior crossbite is often associated with a class III malocclusion. Growth restriction of the maxilla following cleft repair or of the mandible secondary to condylar trauma can lead also to buccal segment crossbite.
Soft tissue factors
With a digit-sucking habit, the tongue is lowered and the cheeks contraction during sucking is unopposed. This displaces the upper posterior teeth palatally and often creates a crossbite.
Crowding
Where the arch is inherently crowded, the upper lateral incisor may be displaced palatally and the upper second or third molar pushed into a scissors bite.
Local causes
Retention of a primary tooth or early loss of a primary second molar in a crowded arch can lead to the permanent successor erupting in crossbite.
Treatment
It is important to realise that where a crossbite is associated with a mandibular displacement, there is a functional indication for its correction, as displacing occlusal contacts may predispose to temporomandibular joint.
Treatment of unilateral buccal crossbite
An upper removable appliance incorporating a T-spring or screw section may often be considered for correcting a crossbite on a premolar or molar, respectively (Figs 1 and 2). However, where reciprocal movement of opposing teeth is needed, fixed attachments should be placed and cross-elastics used to achieve the desired movement. Where a single tooth is mildly displaced from the arch, relief of crowding may be necessary to aid crossbite correction. In those with more marked tooth displacement, extraction rather than orthodontic alignment may be a better option.
Fig. 1 Correction of crossbite on a premolar – upper removable appliance to move 4 I buccally. T spring (0.5 mm stainless steel wire) to 4 : Adams’ clasps 6 I 4 6; buccal capping, with acrylic relieved over 41.
Fig. 2 Correction of crossbite on a molar – upper removable appliance to move I 6 buccally. Screw section to move I 6 buccally; Adams clasps 6 4 I 4 6; buccal capping.
Where a unilateral buccal segment crossbite is associated with a mandibular displacement, this usually results from a mild mismatch in widths of the dental bases, often as a result of narrowing of the upper arch caused by digit sucking. Upper arch expansion using an upper removable appliance with rnidline expansion screw and buccal capping to disengage the occlusion, or by a quadhelix appliance, may be used for correction provided the teeth are not tilted buccally already. The quadhelix consists of a 1 mm stainless steel wire with four coils in the shape of a ‘W’; it is attached to bands cemented to a molar tooth on each side of the arch. Alternatively, a preformed appliance may be slotted into welded attachments on the palatal aspect of the molar bands. Differential slow arch expansion anteriorly and / or posteriorly may be achieved following customary activation of 1.5 and 2 cm, respectively.
Treatment of bilateral buccal crossbite
A bilateral buccal crossbite is seldom associated with functional problems. Generally, as its existence indicates an underlying symmetrical transverse skeletal discrepancy, it is best accepted unless correction is planned as part of overall treatment, when rapid expansion of the midpalatal suture should be attempted only by a specialist. This is achieved by turning a midline screw, connected to bands cemented on first premolar and molar teeth, twice daily for 2 weeks. Expansion of the suture must be carried out no later than in early teenage years but dental relapse of 50% promoted by cheek pressure, is common.
Treatment of lingual crossbite
Crowding may displace a single tooth into lingual crossbite. Once the crowding is relieved, the crossbite may be corrected, often by palatal movement of the upper unit using a buccally approaching spring on a removable appliance, provided the occlusion is disengaged. Where a complete unilateral lingual crossbite is associated with a mandibular displacement, lower arch expansion and upper arch contraction with either removable or fixed appliances can produce a stable result provided a good buccal intercuspation is achieved. Surgical correction may be indicated to correct a complete bilateral lingual crossbite or unilateral lingual crossbite with no displacement.
Adult and surgical-orthodontic treatment
Learning objectives
You should
• be aware of special considerations in undertaking orthodontic treatment in adults
• know the indications for surgical–orthodontic treatment
• understand how surgical–orthodontic treatment is planned and executed
• be aware of common orthognathic surgical procedures.
Adult orthodontics
Orthodontic treatment in adults is the most rapidly expanding area of contemporary orthodontic practice because of an increased availability of services, greater acceptability of appliances and increasing awareness of the potential of orthodontic tooth movement.
Special consideration in adults
There are a number of factors that are specific for orthodontic procedures in adults.
• Adults are generally highly motivated orthodontic patients, able to specify their concerns, but they tend to have higher expectations of the final result than younger patients.
• The dentition may be compromised because of periodontal disease, tooth loss or extensive restorative treatment. Careful pre-treatment assessment is required and all systemic and dental disease must be controlled before orthodontic treatment starts. Occasionally existing bridgework may need to be removed to allow tooth movement to proceed. Often, input from a variety of disciplines (restorative, periodontal, prosthodontic, orthodontic and surgical) are necessary to achieve the best result, and integrated treatment planning must be coordinated in a logical sequence.
• There is also a greater likelihood of systemic illness impacting on the treatment plan in adults.
• There is a lack of growth, so skeletal discrepancies (other than mild) are best dealt with by orthodontics in combination with surgery rather than by camouflage.
• Where camouflage is considered, overbite reduction by intrusion of the incisors rather than by extrusion of the molars is necessary.
• Anchorage planning is often more demanding than in the younger patient because of previous tooth loss and the possibility of reduced bony support of the remaining teeth. Headgear is not a realistic treatment option.
• Because of reduced cell population and often reduced vascularity of the alveolar bone, the initial response to orthodontic forces is slow; however, once tooth movement starts it tends to progress as efficiently as in adolescents.
• Some pain is common for 3–4 days following appliance adjustment, and light forces should be applied initially in all cases and throughout treatment where periodontal support is compromised.
• Retention may be lengthy or permanent.
• Aesthetic brackets may be required to improve the appearance of the appliance.
Adjunctive or comprehensive orthodontic treatment in the adult
Adjunctive treatment
Adjunctive treatment involves carrying out tooth movement to correct one aspect of the occlusion to improve dental health or function, although the final occlusal result may not be necessarily ideal or class I. Treatment duration is usually about 6 months and typically is integrated with periodontal or advanced restorative procedures.
Uprighting of teeth that have tilted into an extraction space prior to bridgework, extrusion of teeth with a subgingival fracture margin to allow placement of a coronal restoration on sound root surface, and anterior alignment to facilitate the best appearance of restorative work are examples of some adjunctive treatments.
Comprehensive treatment
The aim of comprehensive treatment is to achieve the optimal aesthetic and functional occlusal result. Where the skeletal discrepancy is mild, camouflage by dentoalveolar movement is possible using fixed appliances.
The principles of treatment planning and practical treatment follow similar lines to those adopted for class I, class II division 1 and division 2 and class III malocclusions but overbite reduction must be achieved by intrusion rather than by extrusion. In those with a more marked skeletal discrepancy, a combined orthodontic and surgical approach is required to ensure that the best facial and occlusal results are achieved.
Where significant periodontal breakdown has occurred, comprehensive treatment may still be possible provided disease is controlled and a regular maintenance scheme operates throughout orthodontic treatment.
Because of the reduced periodontal ligament area, forces should be as light as possible, and anchorage planning is critical. Fixed appliances using a sectional arch approach are often indicated, and permanent retention with a bonded retainer is usual.
Surgical-orthodontic treatment
Surgical-orthodontic treatment involves correction of dentofacial deformity through a combined surgical and orthodontic approach. In contemporary practice, surgery to correct a jaw deformity (orthognathic surgery) is rarely undertaken independent of concurrent orthodontic treatment, as the final result is likely to be compromised otherwise.
Timing of treatment
Treatment is usually deferred until growth is essentially completed, which is generally in late teens in males and slightly earlier in females. This delay is most important where growth is excessive, particularly in class III cases, as it safeguards against relapse brought about by further growth. Where the temporomandibular joint is ankylosed or the dentofacial deformity is causing severe psychological distress, earlier intervention can be undertaken.
Indications
Surgical-orthodontic treatment is indicated where the problem cannot be dealt with satisfactorily by orthodontics alone. This includes moderate-to-severe anteroposterior, vertical and lateral skeletal discrepancies as well as craniofacial anomalies, including cleft lip and palate.
Planning surgical-orthodontic treatment
A team approach is required, involving the orthodontist and oral and maxillofacial surgeons. Input from a plastic surgeon, restorative specialist, speech therapist or a clinical psychologist may be required.
First, the patient’s complaint must be ascertained. This may relate to their dental and / or facial appearance, masticatory function, speech or a combination of these. Occasionally a patient may be overly concerned about some relatively minor skeletal or dental anomaly, which is blamed for lack of success in some aspect of life. In these instances, there is often a deep-rooted psychological problem and referral to an appropriate counselor may be indicated. A detailed medical and dental history together with a thorough examination must then be performed, including an analysis of facial form in full face and profile. The height and width proportions of the face, interalar distance, nasolabial angle, upper incisor exposure, relation of the upper dental midline to the other facial midlines, and the location of any cranial, maxillary, nasal, mandibular or chin deformities should be noted. Temporomandibular joint signs or symptoms must be documented.
Facial and dental photographs, panoramic and lateral cephalometric films and dental casts should be obtained. A postero-anterior cephalometric film is indicated if facial asymmetry is apparent.
Record analysis and planning
The patient’s cephalometric film should be traced or digitised and then a ‘standard skull template is superimposed to indicate sites of discrepancy. These templates, however, are composites for males and females. Planning can involve enlargement of the photographicnegative profile to match 1:1 with the cephalometric film and then cutting and pasting’ to simulate the desired surgical changes.
A simpler method is via a computer program that allows movements to be planned and visually displayed on a screen before printing. Newer video-imaging techniques allow superimposition of the patient’s profile on the cephalometric tracing and the video image is adjusted in line with changes in the tracing.
Surgical movement may also be simulated on a duplicate set of dental casts. Where a maxillary procedure is planned, however, the casts should be mounted on a semi-adjustable articulator.
The final plan should be explained to the patient, ensuring that they are aware of the likely final changes to the facial appearance. As presurgical decompensation usually worsens facial appearance, this should be explained also. It may, on occasion, be helpful for a prospective patient to have an opportunity to discuss the process with another individual where a successful outcome has been achieved.
Orthodontic management
Presurgical orthodontics and at surgery
Presurgical orthodontics allows the jaws to be positioned in their desired location without interference from tooth positions. This phase of treatment should rarely take longer than 1 year. It aims to align and coordinate the arches or arch segments as well as to establish the vertical and anteroposterior position of the incisors. Usually, this involves placing the incisors at a normal inclination to their respective bases, decompensating for any existing dentoalveolar compensation (nature’s attempt to camouflage a skeletal discrepancy).
The full extent of the skeletal problem is thus revealed so maximum surgical correction can then be achieved. Intermaxillary traction for class III or II cases is often used to aid decompensation. Depending on the crowding and space requirements, extractions may be necessary to allow the tooth movements required.
Consideration should also be given to removal of impacted third molars at this stage. In some cases, it is not possible or advisable to decompensate fully for the incisor position because of anatomical constraints, for example a narrow symphysis or thin labial gingival tissue in a class III malocclusion. Marked gingival recession is likely in the latter if the lower incisors are proclined. Space must be created interdentally to allow access for surgical cuts when a segmental procedure is planned. Some tooth movements (e.g. levelling of a curve of Spee in patients with a short face) are managed in a more expeditious manner postsurgically while other movements (e.g. correction of a bilateral skeletal crossbite of the upper arch) can be managed simultaneously with Le Fort I correction for other skeletal problems at the time of surgery.
When presurgical orthodontics is nearing completion, impressions should be taken to check arch coordination. Providing this is satisfactory, rigid rectangular stabilising archwires with ball hooks, to allow for intermaxillary fixation, should be placed. Final presurgical records, including a cephalometric film, are taken. An interocclusal acrylic wafer, made from casts positioned to simulate the desired occlusal result, is recommended routinely to ensure accuracy of the postsurgical result. At surgery, the interocclusal wafer is used to locate the jaws or jaw segments accurately; these are then usually fixed semi-rigidly in position by either miniplates in the maxilla or lag screws in the mandible. Intermaxillary fixation may also be required.
Surgical procedures
Surgery may be carried out on the maxilla, mandible or on both jaws depending on the nature and severity of the skeletal problem.
Maxilla
Le Fort I osteotomy The Le Fort I osteotomy is the most common maxillary orthognathic procedure. Access is usually provided by an incision in the buccal sulcus from left to right first molar areas, or by vertical incisions and tunnelling of the mucosa in those for whom the adequacy of the palatal blood supply may be in doubt. The maxilla is sectioned above the apices of the teeth so that it can be downfractured from its anterior wall, tuberosities, lateral nasal walls and nasal septum but remain pedicled on the palate. Superior, inferior or forward movement of the maxilla is then possible; posterior repositioning is not realistic.
Le Fort II osteotomy With the Le Fort II procedure, the incisions pass through the bridge of the nose and lower border of the orbit, allowing the correction of marked maxillary retrognathism and nasal retrusion.
Le Fort III osteotomy Via a bicoronal flap, the whole mid-face including the zygomas is separated from the cranium. This is most frequently employed in correction of rare craniofacial anomalies (e.g. Crouzon’s syndrome where the coronal and orbital sutures fuse early, leading to cessation of forward maxillary growth).
Segmental procedures The Wassmund osteotomy involves separating the premaxilla by vertical cuts distal to the canines; the cuts are then extended horizontally across the palate. It was popular for overjet correction in the presence of premaxillary prominence but is now rarely used. Lack of interdental space for surgical cuts and damage to the adjacent teeth are potential problems with this procedure.
Mandible
Sagittal split osteotomy A sagittal split osteotomy is the most frequently undertaken mandibular procedure. The inner and outer parts of the ramus are split through a cut made horizontally above the lingula and obliquely across the retromolar area. These cuts are extended vertically through the buccal cortical plate to the inferior aspect of the mandible. The tooth-bearing part can then be moved forwards or backwards or rotated slightly, but inferior alveolar nerve damage is a common complication.
Vertical subsigmoid osteotomy The mandible is sectioned via an extra-or intraoral incision by a vertical cut through the sigmoid notch, passing behind the lingula, to the mandibular angle. This procedure is used for correction of mandibular prognathism.
Body osteotomy Surgical cuts are made in the mandibular body, ideally where a space exists. Otherwise space is created orthodontically or by removal of teeth. This operation is valuable in those with marked mandibular prognathism and asymmetry.
Subapical osteotomies Subapical osteotomies are confined to patients in whom the dentoalveolar segment(s) alone need to be moved. They are usually confined to the anterior segment, allowing it to be repositioned inferiorly or superiorly, but may involve the complete arch if necessary. Vitality of the teeth may be compromised.
Genioplasty Using a horizontal sliding osteotomy and muscle pedicle, with/without bone removal or bone grafting, the chin can be repositioned in a variety of locations, often producing dramatic profile changes. In some cases it may be used alone as a masking procedure.
Postsurgical orthodontics
Once adequate bone healing and a satisfactory range of mandibular movement has been achieved, the wafer is removed and light round archwires placed to allow occlusal settling. Light elastic traction is used to guide the teeth into the desired position and ensure that good interdigitation is achieved so the appliances can be removed within 6 months of surgery. This is followed by a retention regimen that usually follows standard fixed appliance therapy. Surgical follow-up should be for a minimum of 2 years.
Stability and relapse
In general, stability is enhanced and relapse minimized when
• surgical and orthodontic plans are correct and realistic, well-integrated and executed competently
• surgical movement is modest – no greater than 5-6 mm vertically or anteroposteriorly in the maxilla or 8 mm in the mandible – does not place the soft tissues under tension and the condyles are not distracted at surgery
• abberant soft tissue factors are absent, e.g. tongue thrust or previous surgical scarring, as may occur in repaired cleft palate
• patient is compliant with all aspects of treatment, particularly postsurgical wear of elastic traction
• fixation is adequate.
