20.1 Indications
Key words: asymmetry, disharmony of lower third of the face, lack of mandibular angle prominence, missing arch width, pointed chin, transgender
Indications for chin wing osteotomy exist within the framework of the functional esthetic facial concept, according to Triaca et al,1 or isolated for the 3D correction of disharmonies of the lower third of the face or the mandible. These disharmonies include vertical hypoplasia of the mandibular body and asymmetries, and can affect the entire mandibular body or only the anterior (chin region, lip insufficiency) or posterior portion (mandibular angle region) in isolation.
Chin wing osteotomy is particularly indicated when the mandible is too narrow, for example with retrogenia (weak jawline), and also when the mandibular angles are not prominent.
In particular, chin wing osteotomy should be considered as an alternative to the frequently used chin correction (genioplasty). Although this improves the facial profile, no augmentation effect can be achieved on the lateral mandibular margins, either vertically or horizontally. Furthermore, osteotomy-related bone steps can develop at the lateral mandibular margin, resulting in a disharmonious overall appearance.
In transgender medicine, the chin wing osteotomy may also be indicated to masculinize a feminine mandible. Likewise, the chin wing can also be used in combination with ostectomy to help feminize the mandible.
20.2 Surgical planning
Key words: 3D mandibular model, DVT, model surgery, photo documentation, Photoshop simulation
The planning of the chin wing osteotomy is based on facial photos (frontal view, frontal smiling view, 45-degree lateral views on both sides, 90-degree lateral views on both sides, and 45 degrees from below), photo retouching (Photoshop, Adobe), and on the DVT (CT if necessary). It is often advisable to print a 3D model of the mandible in advance for better spatial understanding of the osteotomy in the mandible, and to allow estimation of the distances of the osteoeomy lines to the base of the jaw, to the mental nerve, and to the tooth root tips.
The bone structures of the mandibular corpus and the course of the alveolar inferior nerve in the mandibular canal are displayed three-dimensionally on the DVT or CT and allow individual determination of the extent, height, and slope of the mandibular body osteotomy.
The bony displacement distance can be measured in advance in all three dimensions by means of a distance measurement in the DVT and provide an indication of the extent of the displacement distances. The final bony displacement position, especially in the vertical dimension, must be determined intraoperatively, since the soft tissue reacts individually to the displacement.
The entire body of the mandible from the chin up to and including the mandibular angle can be tilted horizontally, vertically, or transversely so that the chin apex and the body of the mandible can be adjusted to normalize a harmonious facial profile (Fig 20-1).
Figs 20-1a to 20-1g Potential displacements of the mandibular corpus with the chin wing method.
Figs 20-1a to 20-1g (a and b) In the absence of mandibular angle prominence and normal anterior mandibular height, the posterior mandibular corpus can be tilted caudally to emphasize the mandibular angle. By advancing the body of the mandible, the chin prominence can also be increased at the same time. (c) If there is mandibular retrognathia with protrusion of the mandibular anterior teeth, the mandibular angle can also be emphasized by advancing and tilting the mandibular corpus; the chin, including the anterior alveolar process, can be enlarged with an additional bone graft. (d and e) In cases of mandibular prognathism with pronounced chin prominence, the body of the mandible can be repositioned by removing bone segments from the chin and the mandibular angle. This method can also be used to feminize a prominent masculine mandible. (f) Mandibular asymmetries can also be compensated by unilateral caudalization of the mandibular margin. (g) An individual design of the body of the mandible is possible by segmenting the displaced bone. In this way, a narrow chin apex can be widened.
20.3 Method
Key words: bone graft, local anesthesia, neurolysis of mental nerve, oblique osteotomy, osteosyntheses, trial fixation
Local anesthetic and vasoconstrictor (eg, prilocaine 1%, with epinephrine 1:200,000) are injected in the mandibular vestibule (approximately 0.5 cm in the buccal mucosa) from region 38 to 48. A step incision is made through the mucosa, followed by transection of the upper mentalis muscle layers, leaving the superior muscle belly of at least 3 mm (Fig 20-2a). Neurolysis of the mental nerve is performed bilaterally into the buccal soft tissue (Fig 20-2b), followed by subperiosteal detachment of the buccal soft tissue from the incision to approximately 2 cm from the chin apex and into the lateral portions to 0.5 to 1.0 cm from the mandibular margin, which is not tangent. The periosteum remains firmly attached to the entire mandibular margin and must be preserved. Then oblique osteotomy follows from buccal above to lingual below, first in the mandibular anterior region and then laterally on both sides under the mental nerve through to the mandibular angle (Figs 20-2c and 20-2d
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