Mandibular Subapical Osteotomies

Armamentarium

  • #15 Scalpel blade

  • Appropriate sutures

  • Bite block

  • Chisels (thin spatula and large ones)

  • Curved hemostats

  • Dietrich tissue forceps

  • Electrocautery

  • Frasier suction tip

  • Handpiece, #701, #702, #703 burs

  • Kocher’s forceps

  • Local anesthetic with vasoconstrictor

  • Mallet

  • Metzenbaum scissors

  • Minnesota retractor

  • Needle holder

  • Obwegeser channel retractor

  • Obwegeser retractors (up, down, and ramus)

  • Periosteal elevator

  • Smith spreader

  • Weider retractor

  • Wire cutter

  • Wires (24 and 26 gauge)

History of the Procedure

Surgeries of the alveolar segments were probably the first techniques described to correct occlusal deformities. Kostecka and Wassmund were the pioneers of the technique, and other surgeons, such as Bell and Dann and Kent and Hinds, established details regarding indications and management. Most important, Bell and Levy, Castelli et al, and Hellem and Ostrup studied the blood supply to the osteotomized segment. Epker also pointed out some important details that must be taken into consideration to avoid tooth loss and avascular necrosis, which he considered the most devastating complications.

Hofer and Köle were probably the first to describe the mandibular subapical osteotomy technique. They recommended operating the models before actual surgery to achieve favorable occlusion and to fabricate the surgical splint. Hofer proposed a technique to treat the prognathism with the incision located in the buccal gingiva. Harming the mental nerve was not a concern, and correction of the occlusion was limited to tilt the alveolar segment. On the other hand, Köle positioned the anterior incision in the vestibule so that the mobilized segment remained covered by mucosa and the nerve remained sound. The posterior portion of the incision was placed over the alveolar ridge and along the lingual gingival margin to the retromandibular triangle, with vertical extension provided medianward. According to the author, this extensive incision permitted elongation of the mobilized mucosa, allowing for protrusion, and not merely tilting, of the osteotomized bone.

In 1974 MacIntosh was the first to describe the total mandibular subapical osteotomy. In this description, the author recommended an extraoral approach to perform the vertical bone cut behind the last molar in cases of micrognathia complicated by limited mouth opening. In 1980 Epker and Wolford published a book that presented great improvements on this technique, combining a sagittal osteotomy with the total mandibular subapical osteotomy.

History of the Procedure

Surgeries of the alveolar segments were probably the first techniques described to correct occlusal deformities. Kostecka and Wassmund were the pioneers of the technique, and other surgeons, such as Bell and Dann and Kent and Hinds, established details regarding indications and management. Most important, Bell and Levy, Castelli et al, and Hellem and Ostrup studied the blood supply to the osteotomized segment. Epker also pointed out some important details that must be taken into consideration to avoid tooth loss and avascular necrosis, which he considered the most devastating complications.

Hofer and Köle were probably the first to describe the mandibular subapical osteotomy technique. They recommended operating the models before actual surgery to achieve favorable occlusion and to fabricate the surgical splint. Hofer proposed a technique to treat the prognathism with the incision located in the buccal gingiva. Harming the mental nerve was not a concern, and correction of the occlusion was limited to tilt the alveolar segment. On the other hand, Köle positioned the anterior incision in the vestibule so that the mobilized segment remained covered by mucosa and the nerve remained sound. The posterior portion of the incision was placed over the alveolar ridge and along the lingual gingival margin to the retromandibular triangle, with vertical extension provided medianward. According to the author, this extensive incision permitted elongation of the mobilized mucosa, allowing for protrusion, and not merely tilting, of the osteotomized bone.

In 1974 MacIntosh was the first to describe the total mandibular subapical osteotomy. In this description, the author recommended an extraoral approach to perform the vertical bone cut behind the last molar in cases of micrognathia complicated by limited mouth opening. In 1980 Epker and Wolford published a book that presented great improvements on this technique, combining a sagittal osteotomy with the total mandibular subapical osteotomy.

Indications for the Use of the Procedure

Mandibular subapical osteotomies are not the most common choices to treat patients with dentofacial deformity. However, the anterior subapical osteotomy is a very versatile technique that allows the osteotomized segment to be moved in different directions. It is possible to set the anterior segment backward, forward, upward, and downward, depending on the need. Also, this type of osteotomy may be performed along with a bilateral sagittal split osteotomy (BSSO). According to Bell and Legan and Wolford and Moenning, the mandibular anterior subapical osteotomy may be indicated to (1) level the occlusion, (2) produce anteroposterior changes of the osteotomized segment, (3) correct crowding in the lower anterior arch, (4) correct anterior dentoalveolar asymmetries, (5) alter the axial inclination of the anterior teeth, (6) reduce treatment time, and (7) improve treatment stability.

As described by MacIntosh in 1974, the total subapical osteotomy of the mandible was indicated primarily to treat infantile apertognathia. Other indications pointed out by MacIntosh included treatment of retrognathia due to relapse of a previous ramus surgery and treatment of condylar agenesis/hypogenesis. Currently, the main indication for this technique is to correct a dentoalveolar retrusion in a “normal” mandible. With this technique, it is possible to correct an overjet discrepancy without affecting the position of the pogonion. However, the technique is extremely harmful to the inferior alveolar neurovascular bundle, often leading to dysesthesia and paresthesia. Furthermore, it poses a threat to the blood supply of the osteotomized bone.

Finally, the posterior mandibular subapical osteotomy presents the single indication of repositioning an extruded posterior segment into proper relationship with the remaining occlusion, creating adequate space for esthetic and functional restoration. In the past, this osteotomy had also been indicated to close a dentoalveolar space, in the absence of a molar or premolar tooth, by advancing the mobilized segment. However, with the advance of dental implants, these absences are best treated with implant rehabilitation. Because it is necessary to detach most of the buccal mucosa to expose the bone and because of the tenacious mucosa that lies in the lingual bone in this region, there is a high risk of avascular necrosis. For these reasons, this technique should be mostly avoided.

Limitations and Contraindications

All segmental osteotomies in the maxillary bones share some potential complications, which may be mild, moderate, or severe. As proposed by Epker, mild complications include periodontal defects, pulp necrosis, infection, and delayed union. Moderate complications may include infection, delayed union, and malunion. Severe complications include nonunion and tooth and/or bone loss.

Because the mandible presents a thick cortical bone, the blood supply may be threatened after soft tissue detachment. Therefore, osteotomies that involve small segments of bone, with one or two teeth mobilized, should be discouraged. Also, because the soft tissue pedicle attached to the mobilized segment is the exclusive blood supply, the more it is mobilized or manipulated surgically and the further it is repositioned, the greater the potential for detachment of the pedicle and thus compromise of its vasculature.

The anterior subapical osteotomy is mostly contraindicated when the anterior mandible is short in height. In some cases the apices of the anterior teeth, especially the canines, are close to the inferior border of the mandible, impeding performance of the osteotomy. Even if enough space is available to complete the osteotomy, at least 1 cm of basilar bone should remain to ensure the integrity of the mandible.

Technique: Anterior Subapical Osteotomy

Step 1:

Incision

Before the incision is made, the surgeon should inject a local anesthetic with a vasoconstrictor. This reduces both stimulus to the patient and bleeding during surgery. The incision begins toward the lip and usually extends from canine to canine region, leaving at least 15 mm of mucosa attached to the gingiva. When the mentalis muscle is reached, the muscle is sectioned and the incision is directed to the bone, leaving part of the mentalis muscle attached to the mandible. This permits suturing of the muscle to avoid lip ptosis.

Step 2:

Mucoperiosteal Dissection

Bone is exposed according to how far posteriorly the osteotomy will be extended. Only enough bone to complete the osteotomy is exposed, keeping as much soft tissue attached as possible. This minimizes the risk of avascular complications. In some cases it might be necessary to expose and dissect the neurovascular bundle so that it is best protected. This can be accomplished by detaching the mucoperiosteum from around the mental foramen and making longitudinal incisions on the periosteum surrounding the nerve.

Step 3:

Osteotomy

It is essential to study the patient’s tomograms carefully before performing the osteotomies. The horizontal osteotomy is made at least 5 mm below the teeth apices and should go deep enough to leave just a thin layer of bone in the lingual cortex. Care must be taken not to violate the lingual mucosa. A chisel is then used to finish the osteotomy. These distances can all be measured in the tomogram and then transferred to the surgery. If the vertical osteotomy is performed without tooth extraction, the orthodontist must separate the roots adjacent to the cut before surgery. Like the horizontal osteotomy, the vertical cuts should leave a thin layer of bone in the lingual cortex, and the final separation is achieved with a thin chisel. If the mental foramen is close to the osteotomy cut, it may be necessary to reposition the neurovascular bundle ( Figure 30-1, A ).

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Jun 3, 2016 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Mandibular Subapical Osteotomies
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