17.1 Indications
Key words: airway obstruction, alternative to sagittal mandibular cleavage, convergent distraction vectors in growth, enlargement of the mandibular body during growth, increase of the intercondylar distance, one-sided and two-sided, parallel mandibular distraction in adulthood
A small mandibular body is the classic indication for intraoral horizontal mandibular distraction. It enlarges the mandible and adapts it to the position of the maxilla. The small mandible can be congenital, growth-related, or acquired. It can be unilateral or bilateral, often in combination with severe facial malformations.
Indications for mandibular distraction at growing age are rare and occur predominantly in congenital severe mandibular retentions to improve airway obstruction. Hemifacial microsomia of greater severity is not suitable for distraction if the bone structures of the malformed portion of the jaw are rarified (Pruzansky type II and II). In this case, they also show only insufficient new bone formation in the distraction gap. After distractor removal, the distraction region is then compressed, and growth is further reduced. If stable bone structures of the malformed mandible are present during growth, horizontal mandibular distractors can be screwed onto the posterior buccal surfaces of the mandible and successfully activated (Fig 17-1). They function unidirectionally, can be used unilaterally or bilaterally, but are then convergent to each other anteriorly. Since the two distraction cylinders correspond to the distraction vectors and are convergent to each other anteriorly, an increase in the transverse temporomandibular joint (TMJ) distance also occurs when the mandible is distracted anteriorly. During growing age, the condylar growth that follows compensates for these changes in the joint areas without affecting the joint functions.
Figs 17-1a to 17-1e Method for horizontal mandibular distraction during skeletal growth. (a) Left horizontal mandibular distractor fixed with monocortical miniscrews on the buccal side of the left mandible, with marking of the vertical osteotomy between the two miniplates of the distractor. (b) Peroral activation of the distractor after placing the screwdriver on the anterior end and counterclockwise rotation. (c) New bone formed in the distraction gap, leading to the enlargement of the mandibular corpus. The distraction vector corresponds to the distraction cylinder, which is set parallel to the mandibular tooth row. (d) The mandibular distractor is applied obliquely anterocaudally if a deficit of corpus and ramus is to be compensated in unilateral arch malformations. This distraction vector results in an enlargement of the corpus and ramus, but neglects the formation of a mandibular angle. (e) Depending on the severity of the malformation, an improvement of the distal occlusion can be achieved or even an open bite. (Reproduced from Wangerin et al,1 by permission of Thieme Verlag)
In adults, on the other hand, a small mandibular arch should be enlarged with angled mandibular distractors applied parallel to each other, without changing the intercondylar distance (Fig 17-2). This method has entered orthognathic surgery as an alternative to sagittal splitting in extreme cases of mandibular retrognathia. It is also preferably used for the correction of severe facial malformations, eg, in mandibular microsomia, when the mandibular displacement distance is so pronounced that there are no longer sufficient bony adaptation surfaces for functionally stable fixation in an alternative sagittal mandibular cleft. Alternative indications for sagittal mandibular splitting are also conceivable if the bone structures do not have sufficient stability of the buccal and lingual bone lamellae due to the fracture.
Figs 17-2a to 17-2g Method for parallel horizontal mandibular distraction in adulthood.
Figs 17-2a to 17-2g (a) Horizontal mandibular distractors applied on both sides of the buccal surfaces anteriorly converge towards each other and lead not only to an increase of the TMJ distance but also to an increase of the intercondylar distance with lateral dislocation of the condyles in adulthood. This procedure is tolerable in childhood or early adolescence (see Fig 17-1) because all bony and soft tissue structures of the stomatognathic system are still growing. However, it is contraindicated in adulthood because joint function is severely disrupted and painful late sequelae may result. (b) Parallel angled horizontal distractors maintain the position of both condyles as far as possible and avoid lateral TMJ dislocation. (c) The anterior ends of the distraction cylinders come to rest at tooth level in the mandibular vestibule and are used for activation with the screwdriver. (d and e) At the posterior end of the cylinder, there is a 10-mm lateral angulation. This offset is used for posterior fixation of the distractor to the buccal surface of the ramus. Screw fixation of the distractors is done monocortically by intraoral approach on the buccal mandibular margin and on the outer surface of the ramus. The parallelism of both distractors is achieved with a positioning bracket, which previously holds both distraction cylinders parallel and is mounted on a plastic plate parallel to the occlusal plane. (f and g) With a distraction vector running parallel to the occlusal plane on both sides, mandibular retrognathia for example can be successively corrected in adulthood and a normal occlusion can be set up with function of the mandible. (a, b, d to g, Reproduced from Wangerin et al,1 by permission of Thieme Verlag)
17.2 Method for horizontal mandibular distraction during skeletal growth
Key words: buccal osteotomy groove, check completeness of the osteotomy, distraction cylinder = distraction vector, distraction vector parallel to occlusal plane, incision with scalpel, left and right horizontal mandibular distractor, local anesthesia with vasoconstrictor, parallel alignment of the distractors, temporary attachment of the distractors, transverse osteotomy in the angle of the jaw, trial traction, uni- or bilateral application
Local anesthetic and vasoconstrictor (eg, prilocaine 1% with epinephrine 1:200,000) are injected vestibularly in the molar region up to the jaw angle on both sides.
A buccal incision is made, preferably with the scalpel through the mucosa to the bone surface of the oblique line from the posterior mandibular vestibule to the first molar region. Caution is needed, as incision guides with an electric needle often lead to wound healing problems. The oblique line, anterior margin of the ramus, and buccal bone surface of the mandibular angle are exposed. There is no detachment of the periosteum on the inner side of the ramus in order not to compromise the new periosteal bone formation in the resulting distraction gap. A left (Fig 17-1a) and a right unidirectional intraoral horizontal mandibular distractor (Medicon) with a distraction distance of 20 to 25 mm can be used, unilaterally or bilaterally depending on the indication. The L-shaped osteosynthesis plate is bent posterior to the outer surface of the ramus, and the T-shaped anterior to the buccal outer surface of the mandible. The distraction cylinder corresponds to the distraction vector. It is activated postoperatively with a screwdriver through the mouth opening in a counterclockwise (CCW) direction (Fig 17-1b). Distractors fixed to the mandible on both sides are convergent to each other (see 17.1 Indications). If only a lengthening of the mandibular corpus is desired, the two distraction cylinders are adjusted bilaterally at the same height and parallel to the mandibular occlusal plane (Fig 17-1c). If only a unilateral lengthening of the mandibular corpus is planned, the distraction cylinder is adapted anteriorly to the caudal and posteriorly to the cranial. An open bite is created from a deep bite (Figs 17-2d and 17-2e
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