COMPLICATIONS
Surgery to the mandible
As orthognathic surgery began on the lower jaw it is perhaps not surprising that a variety of procedures have been described and many of them modified as time has passed. There are several basic principles that should be observed in all orthognathic procedures.
● The results of surgery should be anatomically and functionally stable and acceptable.
● The surgical procedure should carry no undue risk in terms of morbidity and mortality.
● The procedure should be predictable in nature and not subject to relapse.
● The end result should be likely to fulfil the realistic expectations of the patient.
Fig. 12.12 The use of the ‘Dentofacial planner’—computerized software which enables predictive projections for various surgical and orthodontic options.
Planning for orthognathic surgery
● Full history
● Clinical examination
● Radiographs and photographs
● Study models
● Detailed analysis
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● Any side effects (particularly long-term ones) should be fully explained and acceptable to the patient.
Surgery of the mandible can be applied to any point on the ramus, body or the dentoalveolar seg-ment, although ramus surgery is the most common.
The two classical operations—the sagittal split oste-otomy (SSO) and the vertical subsigmoid (VSS)—
have been adapted and modified in various ways from those originally described.
Sagittal split surgery—where the ramus and poste-rior part of the mandible are sectioned between the buccal and lingual surfaces—can be used to treat both the severe class 2 and class 3 malocclusion, whereas the VSS is used only to correct relatively mild prognathism. The sagittal split is performed via an intraoral approach (Figs 12.13, 12.14). The lingual tissues are retracted posteriorly and retained using one of the special retractors developed for this purpose. Buccally, the periosteum is retracted to the lower border of the mandible in the second molar region. The lingual bone cut is made horizontally, through the cortical plate, above the level of the lingula; in the past it was extended to the posterior margin of the ramus but this degree of extension is not necessary and may contribute towards relapse. The sagittal cut is made as lateral as is practicable on the external oblique ridge and extended as far forwards as necessary to ensure adequate contact of the split surfaces after repositioning. Finally the buccal cut is made vertically to the lower border. Bone cuts can be undertaken with burs but reciprocating and
oscillating saws are more efficient and less likely to cause soft-tissue damage. Once the cuts have been completed the mandible is carefully split using ultra-fine osteotomes. The inferior dental nerve should be identified (usually towards the buccal aspect) during this process and gently dissected away from its canal.
On completion of both sides the jaw can be repositioned using an acrylic wafer to locate the mandibular teeth accurately into the maxillary arch.
The mandible is then stabilized with intermaxillary fixation and plates and/or screws are used to stabilize the fragments in their new position.
The other common mandibular osteotomy (the VSS) can be approached intraorally or extraorally. A carefully performed VSS carries little risk of damage to the inferior dental nerve because the bone cuts are made distal to the lingula, unlike the SSO, which frequently results in neuropraxia (and occasionally neurotmesis), causing profound anaesthesia in the distribution of the nerve distal to the point of trauma.
Other mandibular osteotomies using different cuts have been described but are beyond the scope of this book. Surgery of the dentoalveolus alone was popular for a short time in the 1970s and 1980s but its use has diminished considerably because ‘den-toalveolar’ surgery was often undertaken to correct an anomaly in the opposing jaw (or of apparently abnormal tooth position) and did not, therefore, really address the underlying problem in the basal bone adequately.
Fig. 12.13 A sagittal split osteotomy being performed intraorally.
The cuts can be made with a bur or a reciprocating or oscillating saw.
Fig. 12.14 Forward-sliding sagittal split osteotomy. Fixation with miniplates improves stability, and reduces morbidity and the risk of relapse.
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Surgery to the maxilla
When orthognathic surgery was first developed, sur-gical procedures on the maxilla were very limited, usually being restricted to anterior dentoalveolar procedures. The first attempts at total maxillary osteotomies at the Le Fort I level (see Fig. 13.2) were carried out through small multiple vertical incisions because of concern for the vascularity of the maxilla and the presumed risk of total exfoliation of the osteotomized segment. In reality this has not proved problematic and the Le Fort I osteotomy is now a common operation. Higher-level osteotomies at Le Fort II or III level can also be carried out using bicoronal fl aps for access. The latter are only necessary for complex cases such as Crouzon’s and Apert’s syndromes (where intracranial surgery may also be necessary), and most simple orthognathic surgery on the maxilla can be carried out via a Le Fort I osteotomy. As with the mandible, surgery restricted to the alveolus has lost its popularity and anterior segmental osteotomies (such as the Wassmund and Wunderer procedures) are becoming uncommon.
The Le Fort I osteotomy is a versatile procedure, which can be performed at different levels above the apices of the teeth, entering the nasal cavity at the base or higher up on the lateral wall. The only limiting structure of note is the infraorbital nerve, which must be avoided. Posteriorly, care must be taken in separating the pterygoid plates from the posterior wall of the maxilla because any improper use of the chisel may damage the maxillary artery, the consequence of which may be profuse bleeding.
Rarely, it is necessary to transfuse a patient because of excessive blood loss, although the likelihood of this can be minimized by careful surgical technique, local anaesthetic with vasoconstrictor and general anaesthesia with induced hypotension.
The actual technique involves a horizontal incision from molar to molar regions. The height of the incision can be varied but there is some evidence that there is less relapse when the incision is made well above the level of the apices. Anteriorly, the fl oor of the nose, the septum and lateral walls all need to be exposed carefully so as not to tear the nasal mucoperiosteum. The buccal bone cuts are normally made with a bur or reciprocating saw, whilst the septum, the lateral nasal walls and the pterygoid plates are detached with specifically
designed chisels and osteotomes (Fig. 12.15). After mobilizing the fractured bones, as in mandibular osteotomies, an acrylic wafer between the upper and lower teeth should be used with intermaxillary fixation to establish the new position of the jaw.
Care must be taken to avoid unwanted rotational movements before stabilizing the maxilla in its new position with titanium miniplates. Maxillary osteotomies with at least four miniplates in situ are relatively stable and intermaxillary fixation can be replaced with elastic fixation postoperatively. Any cyanosis of the buccal tissues should rapidly resolve at this stage, before the wounds are closed with interrupted or continuous sutures.
Fig. 12.15 A selection of special chisels and osteotomes designed for use in orthognathic surgery. Many more designs exist, each with a special function.
The basic osteotomy procedures
● Osteotomies are controlled fractures
● Surgery should only be undertaken if it offers a realistic chance of fulfilling expectations
● Procedures should be stable with minimal relapse expected
● Sagittal split operations are the most common mandibular osteotomies and Le Fort I osteotomies the most common in the maxilla
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