Orthognatic surgery

Orthognathic surgery (Greek “orthos” means straight and “gnathos” means jaw) is a single or double jaw surgery which

is performed to reposition the jaws. During orthognathic surgery a correct jaw alignment and

occlusion, as well as, facial harmony is achieved. When the jaws are moved forwards or backwards, up or down, or

rotated, the facial soft tissue in the chin, cheeks, lips and tip of the nose move accordingly.

Previously, both dental and skeletal malocclusions were managed with orthodontic treatment alone. Either braces

were bonded to the teeth or removable orthodontic appliances were made to align the dental arches in order to achieve the

best possible interdental contact, irrespective of the position of the jaws. This method is called “orthodontic camouflage” since it usually improves the chewing function but does not

correct the misalignment of the jaws. In addition, frequently the facial profile worsens after this

type of treatment is completed.

Nowadays, a combined of orthodontic and surgical treatment is available for patients suffering from skeletal malocclusions. In all cases, treatment begins with preoperative orthodontic setup. After the dental arches are aligned, jaw surgery is then

performed so that one or both jaws are fixed in the new correct position. Orthodontic treatment continues for a long as necessary after surgery until all the teeth are brought into

perfect occlusion.

Malocclusion may be classified into two major groups: skeletal and dental.

Skeletal malocclusion is caused by discrepancy in shape, size and/or position of one or both jaws; e.g., if one of the jaws is too large or too small, or if one of them is too large and the other one is too small. For these patients a simple alignment of dental arches provides little help

since their teeth are not in proper occlusion since the jaws don’t match each other.

Skeletal malocclusion is often accompanied by an incorrect facial profile.

Orthodontic treatment alone is insufficient for successfully correcting skeletal malocclusions when the chewing function and the facial aesthetics is also a desired outcome in addition

to occlusion. Surgery, on one or both jaws, is usually performed to correct the position of the jaws, improve the chewing function, enhance the facial features, and reduce

airway related problems.If the jaw interrelation is correct in a patient, the dental

malocclusion may be the result of an incorrect inclination or crowding of the teeth. In these cases orthodontic treatment

alone, usually with the help of braces, is sufficient to achieve a stable correct occlusion.

Most frequent manifestations of skeletal malocclusion

Distal biteOcclusion. Distal bite is often the result of a small lower jaw which causes the lower teeth to fall behind the upper teeth.

Occasionally, the front teeth may be obviously flared

Mesial biteOcclusion. Lower front teeth are in edge-to-edge contact, or,

in front of the upper front teeth. This may result in a large lower jaw, a small upper jaw, or both.

Open biteThe molars are the only teeth that come in contact. When the mouth is closed, no overlap or a gap between the upper and lower front teeth is noticeable. The incorrect position and

shape of the upper jaw, or the divergent growth profile of both jaws, are frequent causes for this malocclusion. This type of

malocclusion is often diagnosed for patients who are mouth-breathers or who had sucked their thumbs for an extended

period of time.

Cross biteOcclusion. The upper molars are inclined or positioned

inward more than the lower molars. Most often occlusion is caused by a narrow upper jaw or the incorrect position of the teeth within the dental arches. In many cases, a cross bite is

associated with mouth breathing.

Scissor biteOcclusion. The upper molars are positioned outward or the

lower molars are positioned inward. When the mouth is closed the molars miss each other and overlap with no

contact. A possible reason for this is a naturally narrow lower dental arch or a hyper-expansion of the upper jaw resulting

from wearing orthodontic appliances in childhood.

Vertical asymmetryFace. The lower jaw angles are found at different heights so that the whole lower third of the face looks twisted. This is accompanied by a vertical cant in the lip line both in repose

and during smiling, as well as, a cant in the teeth line.

Horizontal asymmetryFace. The lower jaw body is longer on one side; so therefore,

the chin obviously moved toward the shorter side. Horizontal asymmetry usually develops when the growth of one side of

the lower jaw is accelerated. The cause for this growth acceleration is unknown.

Gummy smileGummy smile is an aesthetic consequence rather than a

malocclusion. It can be noticed in patients with either ideal or incorrect occlusion, as well as, in patients with upper jaw

vertical excess. When smiling, patients show a fair amount of gums in their upper front teeth which looks unattractive in

most cases.

High facial angleHigh angle patients usually have an extremely convex facial profile and a steep occlusal plane. The downward growth of

both jaws results in a small and receding chin, reduced airway, and sleep problems. The reduced airway and chewing

function are the main reasons this type of patients should have orthognathic surgery.

Indications for orthognathic surgery are based on functional and esthetic considerations.

Functional considerations include problems with: Chewing and swallowing

AirwaySpeech

Esthetic considerations are characterized by disorders of the facial harmony including:

ProportionsBalance

Symmetry Esthetic considerations may have a psychological

impact, which is also to be considered.

The primary goals of orthognathic surgery are the improvement of function and esthetics. This usually requires an interdisciplinary

approach with a surgeon and an orthodontist as a core team. Other disciplines such as restorative dentistry, prosthodontics, speech

therapy, and psychology are consulted if appropriate. In any case a patient should be seen and diagnosed by every team member and a complete treatment plan should be established before starting with

individual treatment. When treating a facial deformity patient, several factors may

influence the choice of treatment.

These are: Type and complexity of the individual deformity

Expectations of the patientSocial background and compliance

Socioeconomic environment

For the majority of the affected patients orthognathic surgery is an elective procedure. Rarely are facial bone deformities life

threatening. Different surgical procedures can be used for the correction of a given deformity. In this case the surgeon should explain the pros and cons of each of the surgical alternatives.

Criteria are: Severity and complexity of the deformity

Incidence and severity of potentially associated surgical complications

Stability of the procedureDuration and complexity of orthodontic treatment

Patient and surgeons preferencesIssues with time (growth) and timing (planning)

The key to proper planning is a precise diagnosis. To come to that diagnosis clinical examination, cephalometry, and standardized photography.

Above that 3D-imaging (CT, 3D-reformatted CT, 3D-photography, 3D-models) may be indicated for

complex asymmetric cases. Besides that, the expectations of the patients and the potential risks

of the surgical procedures must be seen as well.

Profile evaluationLooking to the profile the following items are of

importance: antero-posterior position of the maxilla

antero-posterior position of the mandiblenasal size

contours of the cheekslip support/lip competence

size of the mandibular angle (illustrated)facial soft tissues (amount, tension)

Frontal view (en face) evaluationThe following items are of importance:

Facial midlineSymmetry

Muscle activity of the lower lip and chinTooth to lip relationship

Lip lengthFacial contour

Head to body proportion

Documentations of findingsIt is recommended to record the clinical findings on

standardized documentation sheets. Standard digital photography (profile, frontal view, three quarter view, bird's

eye view) are taken and attached to the clinical documentation. Standard photos, especially profile pictures,

are necessary to do a profile outcome prediction.

CephalometryCephalometry is done to evaluate the proportions of the facial

skeleton and to compare an individual patient with norm.

Today programs are developed to perform 3D cephalometrybased on 3D reformatted CT scans.

Model analysisPlaster of Paris models from the maxilla and mandible are taken and

the actual centric occlusion of the patient is recorded. The models are oriented in a semi adjustable articulator after facebow transfer.

The models allow to analyze the: occlusion

shape of the dental archesposition

size and shape of the teethposition of the jaws in relation to the skull base

Model analysisUsually two sets of models are used. One is kept to analyze and

document the preoperative situation. The second set of models is used to perform mock surgery.

Mock surgery and fabrication of splintsBased on the results of the clinical and cephalometric analysis, a

problem list and treatment plan are generated. The mounted models can then be moved into the planned position for correction of the skeletal disorder. Keeping in mind that treatment of facial bone

abnormalities is usually a combined endeavor for both surgeon and orthodontist, this position has to be agreed upon by both parties.

Mock surgery and fabrication of splintsIt is important that all movements become visible in a three dimensional fashion. This

can be achieved using reference lines scribed on the models before performing the movements.

The models are fixed in the new positions with wax or glue.

Mock surgery is performed to mimic the planned surgical procedure. It is also a powerful tool to demonstrate the treatment plan to the patient. Finally the reoriented models after mock surgery are used to fabricate the surgical splints that will be used in the operating room to reposition Mock surgery can also be performed using individual

stereolithographic models. This is indicated for severe and mostly asymmetric deformitiesthe osteotomized segments.

Fabrication of splints Splints are made of acrylic and used in orthognathic surgery to intraoperatively position a mobile osteotomized jaw against the

other stable jaw before an internal fixation procedure is performed. In case of two-jaw surgery two splints need to be fabricated. The first one is used after osteotomy of the first jaw as an intermediate splint, the other one after the second jaw has been osteotomized as a final splint. Usually the two splints are colour coded to avoid confusion

Profile predictionPlanning is based on the clinical examination, evaluation of pictures and cephalometry. In order to visualize profile changes, X-Rays and pictures can be superimposed in commercially available planning

software. If the bone is moved the soft tissues will follow (not in a 1:1 ratio) and a virtual image of the surgical result is created. The virtual images may be used to discuss treatment outcomes and alternatives

with the patient. These pictures show the predicted soft tissue changes following

mandibular advancement.

3D-Virtual planningA cone beam or fan CT-scan is obtained and a virtual 3D-

model of the patients skull is generated. The mandible is segmented (defined) in preparation for

performing the virtual osteotomies

3D-Virtual planning3D Virtual osteotomy planning

The planned osteotomies (Le Fort I and BSSO in this case) are defined using the osteotomy wizard in the software.

The virtual model can be manipulated in 3 dimensions to ensure that

the osteotomy lines are accurately represented.

Transoral approach to the mandibular angle Principles

Extended vestibular incisionsA transoral approach is used for the majority of angle and ramus osteotomies.

The standard approach is a vestibular incision approximately 5 mm away from the attached gingiva, which is extended posteriorly along the anterior border of the

ascending ramus.For vertical ramus osteotomies some surgeons prefer transcutaneous approaches.

Exposure For adequate exposure of the ascending ramus the soft tissues have to be elevated from

the bone in a subperiosteal plane. The lateral aspect of the mandible is exposed from the lower border to almost the sigmoid notch. On the medial aspect of the mandible only

the area above the mandibular foramen is exposed to avoid damage to the inferior alveolar nerve.

Approach to the Le Fort I level of the midfacePreparation

The patient is positioned on the operating table supine with the head in a head holder.

For corrective bone surgery, the whole face including the lower part of the forehead and eye brows, the auricles and the superior part of the neck need to be visible, and not covered with drapes. The nasal anaesthetic tube is covered with sterile adhesive tape and the cranium covered with two sterile drapes as illustrated. The eyes are protected with a bland eye ointment and the lips are

lubricated. Anaesthesia

To achieve a good hemostatic effect, local anaesthesia with a vasoconstrictor is injected into the labio-buccal sulcus from the midline to the maxillary

tuberosities and pterygomaxillary areas. Hypotensive anaesthesia is routinely employed during all but the final stages

of the surgery maintaining the systolic blood pressure around 80 mmHg

Incision Pearl: Using the electrocautery, two vertical reference dots are made in the labial frenum

area of the maxillary midline to ensure that the incision is replaced accurately during suturing.

For a Le Fort I osteotomy or SARPE the incision starts 5 mm anterior and 5 mm superior to the opening of the parotid duct and proceeds forwards and slightly downwards in the labio-buccal sulcus crossing the labial frenulum in the midline and proceeds upwards in

the same manner on the contralateral side. For supra-apical osteotomies preserving the nasal floor, the incision is made at the same level (upper sulcus approach), but with a length appropriate for the surgical procedure

and not circumferential.

Subperiosteal dissectionsSharp periosteal elevators are used to strip the soft tissues in the subperiosteal plane to expose the anterior maxillary wall, pyriform rims and nasal apertures, and zygomatico-

maxillary buttresses.The periosteal dissection is performed in a systematic fashion.

Transoral approach to the chinPrinciples

Vestibular incisionsThe transoral approach is the usual access for chin

osteotomies.The approach can be extended posteriorly (dashed line) in case a chin osteotomy is combined with an angle or ramus

procedure.

Intraoral incision Mucosal incision

Unless contraindicated, infiltrate the area with a local anesthetic containing a vasoconstrictor.

Make an incision through the mucosa in the vestibule. Between the canines the incision is made 10–15 mm away from the attached

gingiva in a curvilinear fashion. Posterior to the canine the incision is only 5 mm away from the attached gingiva, staying superior to the

mental nerve.

Surgical flap dissectionIncise the mobile mucosal layer lateral to the vestibular fold. Dissect a mucosal flap to

expose the surface of the mentalis muscle. The branches of the mental nerve are located laterally just underneath the mucosal flap and must be avoided.

Mentalis muscle dissectionThe mentalis muscle is divided near the alveolar bone ridge thus creating a stepwise

incision. Later, during wound closure the mentalis muscle needs to be properly reattached to avoid a drooping chin.

Osteotomy site exposureA mucoperiosteal flap is elevated to expose the chin down to the level of the lower border of the mandible. Great care must be taken to avoid stripping of the lingual

periosteum. Lingual soft tissue attachment to the bone is needed to preserve blood supply. Both mental nerves are identified laterally; the subperiosteal dissection is

continued underneath the nerves if needed

Wound closure After thoroughly irrigating the wound and checking for hemostasis the incision is closed. Anteriorly, the mentalis muscle is reapproximated with sutures to prevent drooping of the chin. The mucosa is closed with interrupted or running sutures.

An elastic pressure dressing on the chin region helps support the soft tissues and prevent hematoma formation.

The LeFort I osteotomy is designed to separate the tooth bearing maxillary component from the superior part of the maxilla. The segment always

contains the bony palate.The mobilized segment can be moved in every direction. The procedure is a

very versatile tool to correct maxillary deformities.

Horizontal osteotomies The horizontal osteotomy is usually made at the level of the nasal floor at a safe distance

(~5 mm) from the apices of the teethPosterior and vertical osteotomies

A curved pterygoid chisel is placed with the curvature pointing medially and inferiorly between the tuberosity and the pterygoid plates.

A mallet is used to drive the osteotome medially to complete the pterygomaxillarydysjunction. The position of the tip of the osteotome can be checked with a palpating

finger. Separation of the nasal septum from the palate

The nasal septum has to be separated from the palate with either an osteotome or septum scissors.

Special "guarded" osteotomes are used for this purpose to protect the nasal mucosa. Separation of the lateral nasal walls

The lateral nasal wall is then separated using a nasal osteotome or saw. Special "guarded" osteotomes are used for this purpose to protect the nasal mucosa.

Pitfall: This osteotomy should end anteriorly to the greater palatine vessels and nerve to prevent bleeding.

DownfractureThe maxilla is downfractured anteriorly, with the help of a bone hook or manually.

The downfracture maneuver allows for a complete visualization of the osteotomy lines. Remaining bony bridges at the posterior aspect of the maxilla can be transected under

direct vision. To minimize bleeding when trimming bone close to the posterior maxilla, meticulous soft tissue protection should be employed.

The downfracture technique allows good access to the nasal septum for septalcorrections when indicated.

It may be useful to use Tessier mobilizers (see illustration) or curved osteotomes which are inserted behind the maxilla on each side in order to pull the maxilla forwards. Rowe

disimpaction forceps can also be used for this purpose

Internal fixation Internal fixation is performed with four miniplates, usually L- or reversed L-shaped,

along the pyriform aperture and the zygomaticomaxillary buttress. Care must be taken to passively adapt the plates to the bone surfaces. The screws in the

mobilized maxillary segment must avoid the tooth roots. After osteosynthesis, the need for bone grafts (eg. by rotational movements) should be

evaluated and if required, they should be placed at this time.

A mandibular body ostectomy is an osteotomy with a segmental resection of a defined section of the mandibular body.

The inferior alveolar nerve typically crosses the osteotomy sites and the bony piece which has to be resected. In order to avoid damage to that nerve it is recommended to

free and mobilize it from the inferior alveolar canal before the osteotomies and the resections are performed.

This osteotomy can only be used to shorten the mandibular body.

Correction of Common Dentofacial Deformities

Correcting an Open Bite: Some of the bone in the upper tooth-bearing portion of the jaw is removed. The upper jaw is then secured in position with plates and s crews.

Correcting a Protruding Lower Jaw: The bone in the rear portion of the jaw is separated

from the front portion and modified so that the tooth -bearing portion of the lower jaw can be

moved back for proper

Correcting a Receding Lower Jaw or "Weak Chin": The bone in the lower portion of the jaw is separated from its base and modified. The tooth -bearing portion of the lower jaw and a portion of the chin are repositioned forward.