Developmental abnormalities of the face, palate, jaws and teeth

Treacher Collins’ syndrome (Fig. 37.14)

Treacher Collins’ syndrome or mandibular facial dysostosis has a variable presentation. The cardinal features are of an anti-mongoloid palpable fissure with a coloboma or groove in the outer portion of the lower lids with deficiency of the eyelashes. There is generally hypoplasia of the midface and zygomatic bones, and occasionally of the mandible. There may be malformation of the external ear unilaterally or bilaterally. Macrostomia and facial clefts may accompany this condition.

Crouzon’s disease (Fig. 37.15)

This is also known as craniofacial dysostosis and may occur together with syndactyly. This is a genetic disease characterised by protruberant frontal bones, a hypoplastic maxilla with relative mandibular prognathism. The hypoplasia may be so severe that the globes of the eye are protruberant to a degree that corneal ulceration and loss of sight can occur. There may well be a hyperteliorism and divergent strabismus. Most patients have a normal cerebral function.

Pierre Robin’s syndrome

This condition is characterised by micrognathia (small lower jaw) and glossoptosis. There is almost always a cleft palate. The overall impression is of bird faces. It does not appear to be an inherited syndrome and it has been thought that extreme flexion of the neck during foetal life may contribute to the disorder: the tongue is thrust upwards between the palatal shelves which fail to fuse so causing the cleft palate to develop. Recent work on gene function suggests that defi­ciencies one of the transformation growth factors (TGFB3) is responsible. Respiratory obstruction due to poor control of the tongue and difficulties with suckling require careful neonatal management.

Hemifacial microsomia (first arch syndrome Fig. 37.16)

In this condition tissues which seem to have been derived from the first branchial arch are deficient. A better under­standing of the embryology, and experimental work by Poswillo, have indicated that there may be haemorrhage from the stapedial artery around the sixth week of intrauterine devel­opment. Tissues that were in development at that time are damaged by the haemorrhage and the subsequent reorganisation so that tissues are smaller or fail to develop completely. The expression is variable but there is always hypoplasia or absence of the mandibular condyle and part of the ramus of the mandible. The masticatory muscles are deficient, and the external, middle and inner ear may fail to develop. Thus, there is the appearance of hypoplasia or the affected side of the face and head with the pinna absent and the external auditory meatus rudimentary or absent. Skin tags over the side of the face beneath the ear are common. The child is almost always deaf in the affected ear. As the growth centre at the mandibular condyle is deficient, the deformity progresses throughout early life and particularly at puberty. The patient requires expert craniofacial surgery that is delayed as long as possible but is generally carried out at the age of 8 years. Further surgery is usually required postpuberty.

Maxillomandibular disproportion

Angle, an American orthodontist, put the occlusion of the teeth into three classes:

class I — normal relationship of the lower to the upper teeth in the molar area;

class II — the lower molar teeth are placed posterior to the normal position;

class III — the posterior molar teeth are placed anterior to the normal position.

This classification has been extended to include the facial skeleton such that:

skeletal II — small mandible is placed posterior to the normal position in relation to the maxilla;

skeletal III — mandible is placed anterior to the norms position relative to the maxilla.

It is a helpful description of a facial skeletal deformity, but it only describes the mandible in relation to the maxilla which itself may be hyperplastic or hypoplastic. Thus, the. ‘Hapsburg jaw’ which described the familial features of the royal houses of Europe in the nineteenth century describes large lower jaw, a hyperplastic mandible, which is frequently associated with a hypoplastic maxilla which accentuates the deformity in the mandible.

The most common deformity of the facial skeleton in the Caucasian is the hypoplastic mandible — skeletal class II -which gives the impression of a hyperplastic maxilla as the upper teeth are very prominent. A hyperplastic maxilla alone is very unusual. Bimaxillary protrusion is a racial characteris­tic of the African races. Occasionally the mandible may grow large and asymmetric owing to hyperplasia of the mandibular condylar neck. Rarely, a hemimandible may be hypoplastic.

Orthognathic surgery

Orthognathic surgery is the term given to the correction of deformities of the teeth and jaws. It should always be under­taken in close co-operation with consultant orthodontists and consultant oral and maxillofacial surgeons. Correction of maxillomandibular disproportion is frequently directed towards changing the position of both the maxilla and the mandible, usually at the end of the growth period. It is essential that there should be a team approach, with treatment planning usually commencing at the age of 12—13 years. Treatment of the syndromes, some of which are described above, may require much earlier treatment (see below). The orthodontist prepares the dental arches for their new position preoperatively, and continues postoperatively with the ultimate goal of a perfect dental occlusion within 6 months of the surgery.

The orthognathic surgery is generally carried out through incisions within the mouth avoiding skin incisions where possible. The upper and lower jaws are mobilised individually and fixed by means of small stainless steel or titanium plates and fixed by means of stainless steel or titanium miniplates. Splinting of the upper and lower teeth by various means is undertaken intraoperatively to achieve an accurate and planned occlusion. Usually it is possible to leave the mandible free for the mouth to be opened at the dangerous times in the first 24 hours postoperatively. An example of maxillomandibular disproportion may be seen in Fig. 37.17, with the effect of bimaxillary surgery in Fig. 37.18.

Craniofacial surgery

Craniofacial surgery is undertaken in a few designated centres in the UK where the team of an orthodontist and a maxillofacial surgeon is augmented to include a craniofacial surgeon (usually with plastic surgery training), neurosurgeons and ear, nose and throat (ENT) surgeons. The whole team includes dedicated nursing staff, both in the ward and in the operating theatre, speech therapists and audiologists. The principles of treatment are to correct deformities from the cranium downwards. Thus, in Crouzon’s disease (see above) the craniofacial surgeon with the neurosurgeon will correct the cranial deformity in the first 2—3 years of life, and will return to deal with the midface by the age of 6 or 7 years, often in co-operation with the maxillofacial surgeon. Final correction will be to the mid and lower face with the patient in their mid-teens where they may be treated much like a more straightforward orthognathic case. The surgical principles involve dividing the various bones of the face and skull, inserting bone grafts where appropriate, and maintaining the position of the bones by miniplates or microplates made of stainless steel or titanium. The surgery to the cranium as far forward as the nose and lateral border of the orbits may be carried out through a coronal incision, pulling the scalp downwards and forwards over the face. For access to particular areas, incisions are made through the skin around the orbits at sites where the scarring is barely noticeable.

New developments in osteogenic distraction in the early growth period in the severe abnormalities may greatly change and reduce the major surgery that is currently undertaken on patients with facial deformity.