Key words: anterior tooth grinding, anterior tooth protrusion, dental arch length deficit, narrow apical mandibular clasp, narrowing tongue space, premolar extraction, speech sound formation disorder, transverse dental arch discrepancy of both dental arches, transverse discrepancy of both alveolar ridges
Transverse mandibular distraction is indicated when there is an arch length deficit with an excessively narrow apical base. A common symptom is anterior tooth crowding or anterior tooth protrusion. The tongue space may also be narrowed as a result. A functional symptom may be an articulation disorder.
If anterior crowding is resolved by premolar extraction in the course of early orthodontic treatment, the constricted lingual space will remain. Alternatively, transverse mandibular distraction and the associated enlargement of the bony (apical) base can help resolve the anterior protrusion and/or avoid premolar or an alternative anterior extraction. From a functional point of view, transverse maxillary distraction can also help to avoid an excessively steep anterior guidance angle in cases of masticatory problems. Sometimes a gap opening in the anterior or posterior region to improve posterior intercuspation or to flatten the anterior guidance angle can be made possible by transverse mandibular distraction, and it should therefore be included in differential therapeutic considerations.
In contrast, augmentation of the mandibular bone by transverse mandibular distraction can fully preserve the dental arch, expand the lingual space, and harmonize arch length with alveolar ridge size.
Transverse mandibular distraction indications can be assessed clinically, using a model set-up, or radiographically with an anterior cephalometric image. A narrow mandible with a dental arch length deficit may also require transverse maxillary distraction to bring about congruency of both dental arches. Conversely, a transverse deficit of the maxilla may also require transverse mandibular distraction in addition to transverse maxillary distraction to harmonize and coordinate the dental arches. The transverse expansion of both jaws enlarges the entire tongue space and can contribute to the normalization of the tongue function.
The schematic procedure for transverse mandibular distraction is shown in Fig 16-1.
16.2 Surgery planning
Key words: choice of distractor (bony or dental fixation), model analysis, space requirements, transverse mandibular distraction with a narrow mandibular arch
The transverse space required to form a standard compliant mandibular arch with physiologic anterior protrusion corresponds to the transverse distraction distance. This is determined using orthodontic model analysis. Both the width of the antagonistic maxillary arch and the esthetic effect on the lower third of the face should be taken into account. Transverse mandibular distraction is particularly suitable in cases with narrow mandibular bodies that become more prominent. Beside the findings of the panoramic radiograph, an additional anterior cephalometric radiograph can be performed to realize the the transverse width of the mandible and the extent of distraction (see Chapter 3). The choice of distractor depends on the initial clinical situation. If interincisal osteotomies can be performed vertically in the middle of the mandible without traumatizing the tooth roots, the preference is for a stable distractor that can be fixed to the bone (eg, a transverse mandibular distractor from Medicon), which tolerates the normal functions of the mandible despite interruption of the continuity of the mandible and the occurrence of strong shear forces. If impacted teeth are present in the anterior mandible, lingually positioned distractors with dental fixation are preferred.
16.3 Preparation for surgical procedure
Key words: lingual buccal retainer, transverse bone-supported mandibular distractor, thermoforming rail
Transverse mandibular distraction is usually performed by the pretreatment orthodontist. This involves fixation of the mandibular central six teeth (31 to 43) close to the osteotomy with lingual retainers (Fig 16-2) or, in the case of particularly pronounced crowding with a weak periodontium and even greater risk of anterior tooth loss, with additional buccal retainers. A deep-drawing splint can also be inserted to protect the teeth during the procedure. The transverse bone-supported mandibular distractor (Medicon) is positioned below or up to the level of the gingival margin of the mandibular anterior teeth, depending on the depth of the vestibule. However, the transverse distraction cylinder should not be in direct contact with the gingiva so that the distractor, osteosynthesis plate penetration points, and periodontal region can be cleaned, and the vestibule remains unrestricted despite occasional mentalis muscles hyperfunction. Acute periodontitis should be treated in advance. In rare cases without fixed gingiva in the vestibule, a gingival graft may be required before surgery.
16.4 Operative method
Key words: bending the osteosynthesis plates, detachment of mentalis musculature, local anesthesia and vasoconstriction, low test traction without tearing the alveolar ridge mucosa, marking the vertical median osteotomy, median complete osteotomy of the mandible, mobilization of the two mandibular halves, positioning the distractor, reduction of the lower half and fixation of the distractor, removal of the distractor, trial fixation of the distractor
Transverse mandibular distraction begins with injection of local anesthetic and vasoconstrictor (eg, prilocaine 1% with epinephrine 1: 200,000) in the mandibular vestibule of the mandibular first premolar to first premolar (region 34 to 44), followed by horizontal mucosal incision electrically or manually with the scalpel in the mandibular anterior vestibule between the mucogingival border and the attachment of the mentalis muscles in the same region (Fig 16-3a). Free preparation of the alveolar process with detachment of the mentalis muscles (Fig 16-3b) is performed, as far as necessary to attach the distractor. If necessary the mentalis nerve is exposed on both sides. The median vertical osteotomy line is marked, then the osteosynthesis plates of the transverse mandibular distractor pre-bent and adjusted. The distractor is positioned horizontally, followed by trial fixation with one screw on each side of the median osteotomy line. This controls the opposing bite in occlusion, since in the presence of a deep bite with elongation of the anterior teeth a disturbing contact of the maxillary anterior teeth to the horizontal fixed distraction cylinder may occur. All screw holes are predrilled, and the distractor is temporarily fixed with screws (Fig 16-3c