18.1 Indications
Key words: condyle resorption, facial asymmetry, microsomia, shortened mandibular ramus, shortening posterior face height
Ramus distraction is indicated when the ascending mandibular branch is shortened. Clinically, the lack of mandibular angle prominence is noticeable. Unilaterally, the shortened ramus leads to facial asymmetry and bilaterally to severe mandibular retrognathia. When looking at the closed dentition, the posterior teeth disappear cranially. “Black corridors” are formed. Retrognathia is cephalometrically accompanied by a posterior inclination of the mandibular margin, a shortening of the posterior facial height, and a posterior elevation of the occlusal plane. Cephalometrically, the NSL-ML and NSL-NL angles are increased.
Congenital microsomia, traumatic shortening of the condyle, or condylar resorption can occur unilaterally or bilaterally and can also be an indication for ramus distraction. However, they can only be performed promisingly after skeletal growth has been completed. Because a ramus distraction results in a laterally open bite on the distracted side of the jaw, this must inevitably be closed in a second operation 1 year later. Since there is often still a malocclusion in the sagittal or transversal direction, a maxillomandibular osteotomy has become the standard final correction. In cases of pronounced severity, jaw angle prominence can often only be achieved if the posterior facial height is used for further vertical lengthening of the ramus by means of a sagittal mandibular cleft in the second operation and, if necessary, an interposition of bone blocks in the tuberosity region is performed to stabilize the counterclockwise rotation (CCWR) in the case of a simultaneous Le Fort I osteotomy.
18.2 Description and activation of the ramus distractor
Key words: 15- to 20-mm distraction possible, cardan drive, intraoral, mobile activation pin, positioning aid for parallelization, unidirectional
A unidirectional left and a right distractor (Medicon) (Figs 18-1a and 18-1b) are available in two different lengths, each of which can be activated CCW up to 15 mm or in the long version up to 20 mm using the enclosed Allen screwdriver. The distraction mechanism and the cardan drive are located inside a closed distraction cylinder, which also determines the distraction direction. The activation pin, which is mobile by means of a joint, allows uncomplicated positioning and movement of approximately 30 degrees in the vestibule. A positioning aid that can be screwed onto the distraction cylinder supports the finding of the planned distractor position and the parallelization of both distractors to each other and the device fixation by screws (Fig 18-1c).
Figs 18-1a to 18-1e (a) The ramus distractor (left distractor shown) (Medicon) is a unidirectional distractor that can be applied orally and is available for clinical use. It is fixed as far caudally as possible on the mandibular rim because sufficient bone substance is available there for distraction osteoneogenesis. The red line marks the preferred rounded osteotomy, which integrates the bony jaw angle into the corpus segment for esthetic improvement of the mandibular angle. (b) The articulated activation pin lies tensionless and mobile in the mandibular vestibule and is activated counterclockwise with an key tool. It can be pinched off at the end of the distraction to avoid infections in the distraction gap during the retention period. The distraction cylinder corresponds to the distraction vector. In the schematic representation, not only is there an extension of the shortened malformed ramus with adaptation to the opposite side, but also an emphasis of the jaw angle. (c) The positioning aid (red), which is screwed to the distraction cylinder, is used for laterally identical and parallel positioning of both distractors. It can also be used as a holding element for temporary distractor fixation. (d) The planning of the distraction vector in the lateral cephalometric image is essential for the success of the treatment. The contour of the habitual mandibular position is traced and the center of rotation of the condyle is marked as a point (red). This tracing of the mandible is copied and moved to the target position of a normocclusion. This also shifts the marked center of rotation of the condyle (from red to green). The linear connection of these two points results in the distraction vector (blue). The direction of the distractor cylinder is positioned parallel to the vector on the ramus. The L-shaped osteosynthesis plate at the caudal distractor end is positioned as caudally as possible at the level of the mandibular rim. (e) In facial syndromes with a hypoplastic mandible or if space is limited for other reasons, the fabrication of a stereolithography model for surgical planning is advantageous, eg, in order to position the distraction cylinder below the zygomatic arch in a space-saving manner.
18.3 Surgical method
Key words: bending of the osteosynthesis plates, complete osteotomy of the jaw angle, distractor removal, final distractor fixation, intraoral cut, intraoral positioning of the distractor, local anesthesia/vasoconstriction, marking the osteotomy, temporary parallel distractor fixation, trial traction
Injection of local anesthetic and vasoconstrictor (eg, prilocaine 1% with epinephrine 1:200,000) is performed vestibularly in the molar region to retromolar to the mandibular angle on both sides.
A buccal incision is made in the posterior mandibular vestibule parallel to the mandibular alveolar process up to the premolar region, preferably with the scalpel through the mucosa to the bone surface. This exposes the oblique line, and the anterior margin of the ramus including the buccal surface of the mandibular angle and ramus. The ramus distractor matching the prepared mandibular side is positioned by the positioning aid in the depth of the outer side of the ramus with its distraction cylinder in front, which corresponds to the distraction vector. It is important that the L-shaped osteosynthesis plate of the distractor is positioned as deep as possible on the buccal lower margin of the mandible and the T-shaped osteosynthesis plate on the oblique line or the buccal ramus anterior margin. The osteosynthesis plates of the device are then bent to the individual bone surfaces by multiple placement and removal.
In syndrome cases with ramus dysmorphia of greater severity, it may be necessary to plan the surgical procedure individually after making a stereolithography model and to position the distraction cylinder below the zygomatic arch due to insufficient space (Figs 18-1d).
In the case of bilateral ramus distraction, positioning aids (Fig 18-1e), which are fixed at an angle of 90 degrees on the distraction cylinders, can be used to determine more precisely the direction of distraction already planned preoperatively on the lateral cephalometric radiograph (see Fig 18-1d
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