a) Mandibular Sagittal Split Osteotomy
The back of the lower jaw is split bilaterally under general anaesthetic in the region of the wisdom teeth, which are generally removed in a separate operation at least 6 months prior to corrective surgery.
The procedure is carried out in about 1.5 hours and permits the lower jaw to be advanced or pushed back with adequate bone contact for healing.
The bone is fixed in its new position by screws which are inserted through tiny external skin incisions which are located at the angle of the jaw. These heal with minimal external scarring.
Whilst day case treatment is practiced in the USA, it is common practice in the UK to spend one night as an in-patient.
Some adjustment to the position of the dental occlusion (bite) is not uncommon following surgery. This is achieved by joining the upper and lower jaws together with elastic band traction for a week or two.
Facial swelling is variable and is controlled with intravenous steroid injections over the first 24 hours. Patients require a liquidised diet if the jaws are held together with elastics – or soft diet for the first two weeks, after which time more solid food can be introduced.
Specific Complications:
Sensory Nerves
The sensory nerve to the lower lip (inferior dental nerve) runs in the lower jaw in the region of the osteotomy bone cuts. Immediately following the surgery all patients should expect numbness of the lower lip, which improves over a period of months. A degree of permanent altered sensation remains in about 30% of patients and affects one or both sides of the lower lip. This may range from complete numbness as experienced with a dental injection to mild tingling. Male patients may not feel if they cut themselves whilst shaving. The majority of patients, who experience permanent altered sensation to the lower lip, find that it is of little significance, and have no regrets about surgery. Reports of psychological problems and or depression related to sexual activity and altered/reduced pleasure from kissing in particular have been reported but are rare. Similarly the condition of painful numbness (dysthesia) has been reported but is rare. Repair of an injured inferior dental nerve is possible but technically difficult. Such a repair is not guaranteed to restore normal sensation.
The sensory nerve to the tongue lies close to the osteotomy cuts in the soft tissue and is retracted away from the operation site. Altered sensation associated with this traction is rare and usually temporary.
Motor Nerves
Motor nerves are nerve that make muscles contract. Injury to the facial nerve supplying movement for the lower lip has been reported as a result of insertion of screws through the small external skin incisions. This may produce some weakness of the lower lip – more noticeable on smiling and may be permanent. This is a very rare complication.
Relapse
Long term complications include relapse, which may occur if the jaw is advanced or if the jaw is retracted. The cause is controversial. It is thought to be related to continued growth in some patients – seen when the jaw is pushed back, and muscle pull – when the jaw is advanced large distances to accentuate a small chin. It is therefore important to carry out such operations when growth has ceased. Muscles inserted into the chin may be divided in the floor of mouth in cases of large jaw advancement – circa 1cm (myotomy). The majority of cases of relapse are noticed by slight changes in the dental occlusion only noticed by the clinician. It is very rare for relapse to adversely affect the cosmetic improvement achieved.
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