Key words: chin correction, chin wing, combination with sagittal mandibular osteotomy, deep bite, incorrect position of alveolar ridge and partial dental arch, lack of congruence of alveolar ridge and dental arch size, Le Fort I osteotomy, normalization of Spee curve, past bite, segmental osteotomy prerequisite for orthodontic therapy
An indication for segmental osteotomy exists in the case of pronounced malposition of a part of the alveolar ridge with the affected group of teeth, if orthodontic treatment alone is not effective.
Segment osteotomies may be indicated:
to make orthodontic treatment possible
as an adjuvant anterior segment osteotomy to correct re- or protrusion of the incisor segment, eg during a Le Fort I osteotomy, a chin or chin-wing correction, or a sagittal mandibular shift
as a follow-up correction if the postoperative orthodontic treatment does not lead to the planned widening, eg crossbite adjustment after a multi-part Le Fort I osteotomy.
The most common indications for segmental osteotomy occur in the maxillary and mandibular anterior regions for reduction of an elongated segment, and rarely for augmentation to reduce a skeletal open bite with an inverted curve of Spee. Segmental tilting to correct pathologic inclination can also be accomplished to a lesser degree with segmental osteotomy. Alternatively, stepwise distraction has become accepted for larger displacement distances of the segment (see Chapter 21).
In the mandibular posterior region, an unusual constellation is required to indicate a segment osteotomy, since the nerve course in the mandible, the strong cortical bone structures, and the unclear lingual access make surgical measures considerably more difficult. Nevertheless, subapical segment osteotomies are conceivable there to correct a lingual tilt of the segment. A group of teeth that is ankylosed during tooth eruption and is in infraocclusion can hardly be successfully elevated and brought into occlusion by subapical segment osteotomy.
The indication for segmental osteotomy alone has become rare since the entire dental arch is routinely successfully shaped orthodontically with fixed appliances. A prerequisite for successful orthodontic shaping of a dental arch is congruence between the size of the alveolar ridge and the dental arch. If this is not the case, segmental osteotomy is still indicated.
28.2 Orthodontic planning
Key words: DVT, LCR, model surgery, occlusion splint, panoramic view, periodontal splint, segment fixation: microplates and screws, segment shift in all directions, set up for planning, titanium trauma splint
A prerequisite for segmental osteotomy is agreement with the orthodontist (treating beforehand or subsequently) and the model setup for the teeth to be surgically adjusted.
For interdental osteotomy, sufficient interdental bone volume (> 3 mm) must be evident on a panoramic radiograph. In cases of doubt, a DVT of the surgical region is more informative, as the interradicular distances can be assessed in three dimensions. In the anterior region, a lateral cephalometric radiograph can be used. This can be the basis for cephalometric planning of the segment tilt in order to correct protrusion or retrusion of the anterior teeth.
Model surgery on arbitrarily articulated models serves to specify the planned occlusion and provides important additional information for surgery, eg in the case of segment formation within a dental arch. In this case, the converging or diverging alignment of the interdental transalveolar osteotomies can be particularly important for segment relocation. Horizontal osteotomies in the alveolar process can also be simulated. They can be performed horizontally or obliquely depending on the planned segment tilt to correct protrusion or retrusion. Segment displacements apically are performed by removing a bicortical horizontal block, and those crestally by filling the gap with local bone graft.
All segmental movements are limited because the vestibular incision limits access to the segment even after tissue undermining. If the interdental area is widened more than 2 mm during segment relocation and the papillae under tension threaten to no longer cover the bone gap, exposed bone should be covered with vestibular mucosa advancement flaps and bony deficits filled with cancellous bone grafts.
Auxiliary devices for segment fixation are required in the bony and/or dental region. Monocortical microplates and the corresponding screws with a diameter of 1.2 mm are mainly used in the bony area. Dental interocclusal splints are used to fix the new tooth positions. These can be removed to improve oral hygiene as soon as the wound has healed, and replaced with fixed orthodontic treatment appliances. UV light-cured periodontal splints (eg, Ribbond) can also be applied to stabilize the teeth, or a titanium trauma splint (TTS) can be used. Wire arch plastic splints are also still used today in different variations for dental fixation.
28.3 Surgical method
Key words: 5-mm safety distance to tooth roots, bone grafts for bone gap filling, intubation anesthesia or analgosedation with local anesthesia, mentalis muscle severance, mentalis muscle sutures, piezo techniques preferred for osteotomy, preservation of vitality of the gingiva pedicled alveolar ridge segment, relief by loosening the lingual lateral gingiva, segment displacement and microosteosyntheses
The most common segment osteotomy, the central and lateral incisors (region 32 to 42) in the mandibular anterior region, is described as an example (Fig 28-1