Jaw Surgery Orthognathic Surgery

Jaw malformations. Introduction.

 "Jaw malformations” represent all the malformations of the lower jaw (mandible) and the upper jaw (maxillary). They can focus on either the mandible or  the maxillary or the mandible and  the maxillary.

In the presence of a jaw malformation, several rules are observed:

1) No treatment can be offered without a complete assessment in which many specialties participate: Maxillofacial Surgery, Orthodontics and orofacial physiotherapy. Other specialties are sometimes involved: ENT (for the study of breathing and the assessment of the airways), Ophthalmology (in case of oculomotor muscle disorders), Genetics (in case of a potentially transmissible family anomaly), Psychology ... The treatment is almost always multidisciplinary involving Maxillofacial Surgery, Orthodontics and Orofacial Physiotherapy (to rehabilitate swallowing and phonation). Otorhinolaryngology is frequently associated to suppress a respiratory obstruction. Multidisciplinary collaboration is essential and is one of the conditions to obtain a successful treatment and therefore a stable result.

2) There is no emergency to treat jaw malformation. This is a non-vital therapeutic indication; thorough information has to be given to the patient about the origin of the malformation and its mechanism of installation, the various possible treatments (and for each of them the advantages and disadvantages), the overall medical care duration , the operative follow-up and the risks of relapse according to the therapeutic strategy chosen. As with any treatment, a complete quote is given to the patient before the beginning of any treatment.

Anatomy, Lexicon

Two types of bone coexist in the jaws.

• Alveolar bone

The alveolar bone is the bone that surrounds the teeth and holds them on the dental arch. Throughout life, the alveolar bone undergoes remodelling according to the forces or the stresses that it undergoes (action of facial muscles and the tongue, orthodontic forces). During the course of life, its dimensions can thus tend to increase (in case of dental eruption or dental extrusion) or decrease (dental decoupling).

"The alveolar bone is born and dies with the tooth". It forms and develops around dental germs during foetal life and childhood. In case of congenital absence of teeth (dental agenesis) the alveolar bone is not formed; there is a primitive atrophy of the alveolar ridge. During aging and in case of loss of teeth, the alveolar bone will gradually be absorbed; it is a secondary bone atrophy (acquired atrophy).

The tooth is connected to the alveolar bone by the desmodontal ligament. It is therefore a real "articulation" with micro movements (even if they can hardly be observed with the naked eye). The tooth is not welded to the bone, except in case of ankylosis (the cementum which constitutes the dental root and the bone fuse). The alveolar bone is continuous with the basal bone of the maxillary and mandible.

• Basal bone

The basal bone is the architectural base of the jaws (the mandible at the bottom and the maxillary at the top). It remains present throughout one’s life as it is stable, very strong and independent from the teeth and the alveolar bone. In case of complete tooth decay and after a long period of involution of the alveolar bone, only the basal bone remains. This phenomenon affects both the mandible and upper jaw.

The "balanced" architecture of the skeleton of the face and skull and the "normal" occlusion

(Text and diagrams from the work of Professor Jean Delaire.)

In humans, the cephalic extremity composed of the skull and the facial mass rests on the superior end of the vertebral column (cervical spine). The weight of the face and the tractions exerted on it by the viscera of the neck and thorax (respiratory and digestive ducts, blood vessels, etc.) are balanced by the muscles of the posterior and lateral necks.

In humans, at the level of the cephalic extremity (skull-face complex), two "fundamental mechanical devices" can be described and make it possible to understand the craniofacial architecture:

• "The suspension apparatus" of the skull on the upper end of the spine. This device reminds us of a "weighing scale" corresponding to the base of the skull, the beam of which corresponds to the height of the skull.  

• The masticatory apparatus or "masticatory compass"

The lines of the "suspension apparatus" of the skull, "masticatory compass" and "cranio-facial architecture" are very intricate.

In the balanced subject, several of them are common or parallel; in particular the lines symbolizing the position of the upper jaw (maxillary) and of the lower jaw (mandible)

According to the family characteristics and the ethical type; several balanced (and therefore stable) cranio-facial architectures are described: orthofrontal, transfrontal, and cysfrontal.

In the balanced subject, the upper teeth are shifted behind a half-cuspid. The anterior cuspid of the first upper molar is positioned opposite the groove of the first lower molar (Dental Class I).

Main anomalies encountered

Although all abnormalities can be found in varying degrees, schematically we can distinguish:

Skeletal Class III or Class III Syndroms

The upper jaw is set back from the mandible. It may be a lack of development of the maxilla and a normal mandible or a normal maxilla and a too developed mandible. The two abnormalities sometimes combine a lack of development of the upper maxillary and an excess of development of the mandible. A tongue in a low position can often be noticed. A "concave" facial profile is usually observed when a class III dental occlusion is found.

Skeletal Class II or Class II Syndroms

The mandible is set back from the maxilla. It may be a lack of development of the mandible and a normal maxillary or a normal mandible and an abnormally projected forward maxilla. The two abnormalities sometimes combine a lack of development of the mandible and a maxilla positioned too far forward. A "convex" facial profile is usually observed when a class II dental occlusion is found.

Two types of Class II are observed:

• Class II Division 1 with protruded superior incisors. The lower lip that wraps under the upper incisors is responsible for their excessive forward inclination with overjet of the upper incisors.
  
• Class II Division 2 with retroclined incisors (with two retroclined central incisors and two lateral incisors overlapping the centrals). These patients often have strong muscle tone of the lips. In adults, abrasion of the occlusal margin and the anterior surface of the lower incisors are frequently observed.
  

Open-bites

We talk about open-bites when there is a gap between the upper teeth and the lower teeth. The open-bite is most often located in front of the incisors and canines due to an interposition of the tip of the tongue at rest and in function (phonation, swallowing). Most of the time, there is no contact of the lips at rest that is to say, a lack of opposition to the push of the tongue. This muscular imbalance between the tongue inside and the lips outside is referred to as the "centrifugal imbalance".

When the interposition is lateral or posterior, we can observe a lateral or posterior open bite. Open-bites occur with both Class II and Class III. Open-bites are characterized by a high rate of relapse, should there be no orofacial physiotherapy combined with surgery and orthodontics.

Anterior vertical excess

The face is abnormally vertically long (face and profile).

• It may be an anterior vertical excess associated with a Class II. There is usually an excess of vertical development of the upper jaw (gummy smile), a short mandible in its horizontal portion, a chin abnormally vertically developed and with a back position. An anterior open bite frequently complements the chart (Hyperdivergent Class II Pattern).
  

• • It may be a vertical excess associated with a Class III. In this type of abnormality, an abnormally open mandibular angle, a tongue in the lower position and an abnormally developed chin (Hyperdivergent Class III Pattern) are frequently observed. An anterior open-bite can complete the picture.
  

Asymmetries

Facial asymmetries can be of variable importance and are frequently observed in association with Class II or Class III. Numerous causes can be observed: growth abnormalities, abnormal position of the tongue, fractures of the consolidated jaws in a wrong position, tumors, tissue diseases (dysplasia). Most of the time, several mechanisms mingle to achieve this very complex type of malformation. For example, when the asymmetry has been known since childhood, an abnormality of the ongoing development of growth can be quoted. It can also be the consequence of an abnormal position of the tongue such as a unilateral lingual interposition. These two mechanisms are often associated.

In the presence of asymmetry, thorough knowledge of the installation mechanism is essential to propose a surgical treatment that takes into account the origin of the malformation and that acts where it resides.

In the presence of asymmetry, it is rarely possible to obtain a perfect aesthetic result despite the quality of treatments and the surgical symmetry of the skeleton. Soft tissue (skin, muscle, fat) frequently included in the malformative process reduces the effects of surgical treatment on the skeleton. This phenomenon, well known to surgeons, is called "soft tissue memory".

Therapeutic tools

Presurgical orthodontic treatment

Orthodontics is intended to allow the maxillofacial surgeon to obtain stable and balanced occlusion in the operating room without premature contact (without interference). Stable occlusion without interference improves good bone healing. Orthodontics is usually performed before surgery (Pre-surgical orthodontic treatment).

The most frequently orthodontic movements performed by the orthodontist are:

1. Alignment, leveling and coordination of teeth (dental arches). The goal is to prepare a satisfactory occlusion of the teeth at the time of surgery.

2. Decompensation of alveolar processes. It consists in cancelling or reducing the compensations previously endured by the alveolar bone. These compensations may be spontaneous (natural) or induced (due to the existence of orthodontic treatment in the antecedents). In practice, preoperative orthodontic alveolar decompensation consists in removing the compensations on the alveolar bone before the intervention so that the surgical treatment on the bone bases may be as effective as possible (in particular with regard to the aesthetic result and the architectural balance of the skeleton). It is not uncommon to note a worsening of the malocclusion during this initial phase of orthodontic treatment. The patient has been informed.

Nowadays, we sometimes propose a shortening of the preoperative orthodontic phase (“Surgery First”). In the presence of certain malformations and in particular in case of major Class II malocclusions, several recent scientific studies consider that surgery performed first or early facilitates and shortens the orthodontic phase. This attitude cannot be generalized and remains a minority.

Presurgical Orthophony or Presurgical Orofacial Physiotherapy

The whole oro-facial muscle structure participates in the direction of skeletal growth and tooth orientation (modelling action of muscles and function on the alveolar skeleton). In a word, the tongue inside the oral cavity and the lips on the outside are essential players in the growth direction of the alveolar bone and the tooth orientation.

Any abnormality of resting muscle forces: position and volume of the tongue, abnormal muscle tone (muscular hypo or hypertonia) and function (phonation, swallowing, etc.) is likely to cause a dentofacial malformation. It is the same for any harmful attitude: thumb sucking, tongue thrusting, interposition of an object between the dental arches (pen, cuddly toy, security blanket etc.)

Other specialties can be used to ensure a complete and stable treatment. This is particularly the case for Otorhinolaryngology which corrects an abnormality of air ducts before maxillofacial surgery. Any obstacle to nasal breathing must be lifted before engaging in jaw surgery. This is particularly the case for hypertrophic adenoids and tonsils. Hypertrophic adenoids and tonsils are responsible for mouth breathing which keeps the tongue in a low position. The hyperdeveloped mandible and the atrophic maxillary shape a concave profile (classic prognathism).

Surgery

Osteotomies. The term osteotomy refers to the surgical procedure of severing the malformed and / or poorly positioned bone infrastructure for repositioning to a more appropriate architectural balance. Osteotomies used to be performed using rotary instruments (surgical burs) or alternative instruments (bone saws). Nowadays, osteotomies are most often performed using ultrasonic devices which are less traumatic to tissues. There are many types of osteotomies.

Total osteotomies.

The surgeon releases the entire skeletal piece from the rest of the maxillofacial fundus. He makes a complete interruption of continuity of the mandible or maxillary from the rest of the skeleton of the face.

• The Lefort 1 osteotomy

The Lefort 1 osteotomy moves the entire maxilla (basal bone, alveolar bone and teeth) in the 3 dimensions of space.

Lefort 1 osteotomy can also be performed in two fragments or three fragments to allow transverse expansion of the maxilla when it is too narrow or when malformation (or malposition) of the maxilla is asymmetrical.

• Bilateral Sagital Split Osteotomy (BSSO) It allows to move the entire mandibular arch (basal bone, alveolar bone and teeth) in three dimensions of space.
• The Genioplasty It moves the chin in all three dimensions of space.

Segmental Osteotomies. The surgeon releases a segment (a fragment) of the skeleton. Segmental osteotomies are aimed at the skeleton of the chin and the alveolar skeleton. There is no interruption of continuity of the "base" bone of the maxilla or the mandible.

• The Anterior Mandibular Segmental Osteotomy and the Posterior Mandibular Segmental Osteotomy

They can move the alveolar bone and anterior teeth (incisors and canines) of the mandible or maxillary in all desired directions. This type of osteotomy removes alveolar compensations and is often accompanied by the extraction of two premolars.

• The Posterior maxillary segmental Osteotomy It can be unilateral or bilateral. It moves the alveolar bone and maxillary posterior teeth (premolar and molar) in all desired directions.
  

Combined Osteotomies. They allow to act simultaneously on all the anatomical elements of the face. In practice, all combinations of osteotomies are possible depending on the abnormality observed.

Bimaxillary osteotomies. These are the most common combined osteotomies. We can distinguish:

• Bimaxillary Osteotomy with Genioplasty

It combines a Lefort 1 Osteotomy, a Bilateral Sagital Split Osteotomy (BSSO) and a Genioplasty.

• Bimaxillary Osteotomy without Genioplasty

It combines only a Lefort 1 Osteotomy and Bilateral Sagital Split Osteotomy (BSSO).

Osteotomies of the middle section of the face (Lefort II and Lefort III Osteotomies)

They allow to act in the middle section of the face. They are more rarely performed as they address the rarer malformations that extend to the orbit. The approach is always aesthetic, mixed per-conjunctival and per-oral. The associations Lefort III - Lefort I dictated by dental occlusion are possible.

Guided Surgery or Computer Guided Surgery with Custom Made Guides and Miniplates).

Guided surgery consists of simulating the surgical procedure using specialized software and then ensuring the control of surgical execution in the operating room using cutting and pre-drilling guides, while custom-made mini-plates stabilize bone fragments according to the simulation. Guided surgery is mainly indicated:

• When looking for a precise positioning of the bony parts in relation to the base of the skull (search for an architectural balance according to Jean Delaire)

• In the presence of a complex malformation.

This is a new technique that is particularly effective but which results in a more thorough preoperative radiographic assessment and a higher financial cost.

The therapeutic sequence: When to operate?

• Apart from the special cases of facial clefts (alveolar clefts) or cases of major malformative syndroms in cranio-maxillofacial surgery that require specific protocols, jaw malformations are most often performed when growth is complete.

• Jaw surgery is performed in most cases when occlusal preparation is complete (see preoperative orthodontic paragraph).

• For students and high school students, it is better to plan surgical interventions in late June-early July, after the end-of-year exams. July is reserved for convalescence and August to relax before back to school / university.

• Postoperative orthodontics

It aims to correct the last imperfections of the dental articulate after surgery. It is very often necessary to place a "restraint" on the teeth to maintain the quality of the occlusal result obtained by orthodontics and surgery. A thin steel wire or invisible Kevlar is placed on the posterior surface of the teeth.

• Postoperative speech therapy

When a muscular dysfunction was observed during the initial assessment (swallowing or phonation disorder) and to reduce the harmful action of the tongue on the orientation of the teeth and the alveolar bone (risk of recurrence), it is necessary to continue speech therapy or orofacial physiotherapy postoperatively. The active participation of the patient is paramount.