An overview of the surgical correction of dentofacial deformity

Timing of treatment

Most osteotomies in healthy, non-syndromic individuals are planned following cessation of active facial growth,^1,2,3 which is generally accepted to be at approximately 19 years of age in boys and 17 years in girls, although individual variation does occur. The timing of surgical correction also depends upon the type of malocclusion, particularly for Class III skeletal patterns where surgery is deferred until 18–20 years in girls and boys to minimize the likelihood of unfavourable late mandibular growth.³ Assessing a patient after cessation of active growth has the following advantages:¹

Le Fort I osteotomies

Indications

Le Fort I maxillary advancement

This is mainly indicated for the treatment of maxillary hypoplasia (Table 3, Figure 1), most commonly associated with Class III skeletal bases. The magnitude of the advancement is determined by the need to place the upper incisors in the relationship to the rest of the face and the upper lip. This is generally the extent of negative overjet plus the desired positive overjet of 2–3 mm after single jaw surgical correction of the maxilla alone. This corrects the incisal relationship and builds in a small amount of relapse correction (Figure 2 a–h). The Le Fort I procedure can also be used for minor midline (1–2 mm) discrepancies by rotating the maxilla sagittally after the down fracture.¹

Table 3. Indications for maxillary osteotomies.

Type of Osteotomy	Indication
Le Fort I, II and III Maxillary (Mx) advancement	Mx hypoplasia
Mx impaction	Vertical Mx Excess (VME)
Mx differential impaction	Skeletally caused AOB
Mx differential rotation	Mx asymmetry
Mx expansion (SARPE)	Transverse Mx hypoplasia

The extent of maxillary advancement depends upon the following:

The extent of skeletal anterio-posterior discrepancy;

Whether the surgical correction is desired in the maxilla alone or in both the jaws;

The limit of correction that can be obtained surgically;

The likelihood of adverse effects upon nasal morphology.

The scope of stable maxillary Le Fort I advancement remains a contentious issue as the published data has various drawbacks,^4,5,6 such as grouping of samples with different osteotomy procedures (Le Fort I maxillary advancement – with or without a simultaneous mandibular procedure), heterogeneous samples (mixing of cleft and non-cleft osteotomy cases), pooling of data irrespective of direction of maxillary movement following the Le Fort I osteotomy (forward alone, forward and downward or forward with impaction) or type of fixation (intermaxillary fixation ‘IMF’ or rigid internal fixation ‘RIF’).

The range of surgical anteroposterior (AP) advancement of maxilla has been reported from 2–10 mm with a mean movement of 4.9 mm.⁶ Most of the surgical relapse occurred in the first six months of surgery.⁶

A second approach that may be used to address a severe AP discrepancy between the maxilla and mandible is a bimaxillary osteotomy.^4,5 Depending on the severity and nature of the discrepancy, this will involve a combination of maxillary and mandibular advancement or setback. (Figure 3 a–h).

Le Fort I maxillary setback

This can be achieved by removing a triangular wedge of tuberosity sectioned through the third molar region.⁷ The third molar, if present, may have to be removed prior to the tuberositectomy.⁷ However, this procedure is rarely indicated.

Le Fort I maxillary impaction

This is indicated for the correction of excessive gingival display (>3 mm) on smiling,⁸ which is seen with vertical maxillary excess (VME) when the anterior + posterior face height is increased⁷ (Figure 4), and for the surgical correction of anterior open bite (AOB) of skeletal aetiology⁷ (Figure 5). The degree of impaction is determined by the amount of gingival show at rest and on smiling and the upper lip length.⁷ There is no established limit of maximum maxillary impaction, but up to 8 mm of posterior maxillary intrusion has been reported in the literature.^8,9

Maxillary impaction tends to shorten the upper lip length by up to 25%.⁷ Condylar resorption of 9–12% has been reported with Le Fort 1 posterior maxillary impaction and mandibular autorotation.¹⁰

Mandibular autorotation

The concept of mandibular autorotation (MA) with maxillary surgical anterior and/or superior repositioning is based on the perception of neuromuscular adaptation which takes place as a compensatory phenomenon immediately following surgery.^11,12 It is essential to establish the extent of MA as this leads to greater anterior prominence of the mandible in the aforementioned circumstances.¹² Assessment of the incisor position of an autorotated mandible determines if further adjustment of the AP maxillary position is required in order to establish a positive overjet and overbite.¹²

Research to determine the centre of autorotation (CR) of the mandible was controversial two decades ago.¹² The assumed CR is at the centre of the condyle, which is replicated on articulators, mastoid air cells and on lateral cephalograms. Another hypothesis is that autorotation is a combination of translation and rotation of the mandible with no constant centre of rotation in the condyle. Autorotation of the mandible has been reported to cause condylar resorption in 9–12% of cases.¹⁰

SARPE

Bilateral Sagittal Split Osteotomy (BSSO)

This procedure, in combination with an advancement procedure, is the most common technique used to correct a severe Class II skeletal pattern with mandibular retrognathia (Figure 6) and, when coupled with a mandibular setback, is used to correct a moderate to severe Class III skeletal pattern with mandibular prognathism (Figure 7).¹ The extent of anteroposterior mandibular movement depends upon:

The mean surgical threshold for BSSO mandibular setback is 10 mm with no range given.¹⁹ A stable result is more likely after mandibular setback than after mandibular advancement, because the soft tissues are not extensively stretched when the condyles are set correctly in the fossae before rigid fixation.¹⁹ Relapse can be expected if the condyles are not properly located within the fossae at the time of surgery. If stretched, the pterygomasseteric sling reverts to normal function when mandibular mobility resumes, which tends to return the proximal segment to its original position, again resulting in relapse.¹⁹ Moreover, the inter-condylar width tends to decrease after BSSO mandibular setback. This change in axial inclination involves either medial or lateral rotation of condylar axis, however, rigid internal fixation limits this type of relapse.¹⁹ Finally, remaining growth can contribute to relapse. Its effects are more pronounced in males with more anti-clockwise (anterior and downward) growth rotation.²⁰ In contrast, women show more clockwise rotation.²⁰

The widely accepted limit of BSSO mandibular advancement is 10 mm²¹ (Figure 8). The risk of horizontal surgical relapse increases when the mandible is advanced beyond 7mm.²¹ The mandibular plane angle also has an influence on the horizontal and vertical relapse. High angle cases tend to relapse in the horizontal plane, whereas low angle cases have a tendency for vertical relapse.²¹ There is no gender predilection to surgical relapse although it is more frequently seen in female patients that have undergone BSSO mandibular advancement procedures. This is thought to be due to a greater proportion of females than males seeking surgical correction of their Class II profiles.²¹

Other factors that contribute to relapse include the experience of the surgeon and patient-related factors such as growth and compliance with post-surgical orthodontics during the healing process. Figure 8 demonstrates an example of a BSSO with mandibular advancement for the correction of mandibular retrognathia associated with an increased overjet.

Condylar resorption associated with BSSO mandibular advancement has been reported, where one study has suggested an incidence of 10%.¹⁰ The risk increases with the extent of mandibular advancement, the use of IMF, an increased mandibular plane angle and a low facial height ratio.¹⁰

The most common complication of BSSO mandibular procedures is neurosensory disturbance (NSD).^22,23 Whether this iatrogenic effect occurs along the mandibular canal or at the mental foramen, the symptoms are usually varying degrees of anaesthesia or paraesthesia (numbness) to the lower lip and chin.^22,23 There is a large variation in the reported incidence of iatrogenic NSD with reports of 80–100%, although this tends to be temporary rather than permanent.²³ Ow and Cheung²² reported, in a prospective randomized clinical trial, that all 23 patients in the test group experienced NSD during the six-week post-operative period when assessed subjectively (using a questionnaire based on visual analogue scale) and objectively (with light touch, 2-point discrimination and pain detection threshold). The prevalence of long lasting NSD 1 year after surgery is found in 8–10% of the cases.²³ This large range of NSD incidence exists due to the lack of standard methods of neurosensory evaluation and differences in follow-up periods.^22,23 However, long-term satisfaction rates in the patients undergoing orthognathic surgery are high (87–100%) despite these reports of NSD.²³

Genioplasty

A genioplasty may be used to correct abnormal chin prominence.²¹ It may be undertaken in combination with other surgical procedures or in isolation. If part of an orthognathic treatment plan, the genioplasty may be completed at the same time as the other osteotomies or postponed by six months and undertaken separately.²⁴ This delay permits resolution of the facial swelling and facilitates reassessment of the facial profile following the primary surgery.

An abnormal chin prominence can present as:^24,25

The horizontal osteotomy must run 4–5 mm below the apices of the canines and 3 mm below the mentalis nerve.²⁴ An isolated genioplasty is effective for managing mild anterio-posterior mandibular deficiency of <5 mm.²⁵

The chin can be moved in all three planes of space using various procedures:^24,25

A pressure dressing is applied to the chin for the support of the soft tissues, lower lip and elimination of empty spaces to reduce swelling and achieve definition of labiomental fold.²⁴

Distraction osteogenesis

Distraction Osteogenesis (DO) is a bone-lengthening process by gradual mechanical separation of iatrogenically separated bony fragments. This procedure is indicated for the correction of extremely severe maxillary and mandibular deficiencies when >10 mm advancements are necessary, but which are likely to be unstable using conventional surgical procedures.²⁴

Distraction osteogenesis may be used in the surgical correction of craniofacial anomalies, such as hemifacial microsomia, severe bilateral mandibular deficiency, maxillary deficiency associated cleft lip and palate, bimaxillary facial deficiency associated with Crouzon syndrome, midfacial hypoplasia and transpalatal deficiency^26,27 and maxillary or mandibular vertical alveolar ridge deficiencies following failed graft procedures.²⁸ There is lack of evidence regarding protocols for DO, maximum augmentation distance and long-term success or relapse rate.^26,27,28

The distraction phase of treatment is the period in which traction is applied to the transport bone fragment and the formation of new immature woven and parallel-fibred bone commences.²⁴ The rate of distraction on average is 1 mm/day.^26,28 The distractor is usually activated by 1 mm at the time of placement followed by a latent period which is 7 ± 2 days between surgical placement of a distractor and commencement of distraction.^26,28 The rhythm of distraction ranges between 1–4 times/day.²⁸ The average distraction achieved in mandible and midface are 16–17 mm and 14 mm, respectively,²⁷ whereas that for alveolar distraction osteogenesis was 6.8 ± 2.5 mm (range 3–15 mm).²⁸ Some overcorrection is undertaken to compensate for probable relapse (3 mm).²⁷

The distraction device is left in situ after the active distraction period for 6–12 weeks to allow the consolidation phase to occur.^26,27,28 This is the period during which maturation and corticalization of the callus occurs.²⁸ Complications associated with DO are soft tissue dehiscence, transient paraesthesia, inferior dental and facial nerve injuries, haematoma, deviation of direction of distractor, fracture or instability of the distractor, fibrous non-union and poor quality new-bone formation and relapse.^26,27,28

Summary

This article was written as a brief summary of orthognathic surgical procedures, incorporating some of the relevant literature and aimed at general dental practitioners, to raise awareness of the more common types of treatments available for the correction of severe dentofacial deformities. A comprehensive guide and literature review is outside the scope of this article.