Key words: combination of mandibular sagittal split and transverse arch correction, clockwise effect, counterclockwise effect, facial height gain, horizontal and vertical positional changes of the mandibular body, Hunsuck/Epker, mandibular sagittal split with segmental osteotomy and chin correction, oblique ramus osteotomy according to Perthes and Schlössmann, Obwegeser/DalPont, transverse maxillary distraction, transverse mandibular expansion/narrowing, sagittal mandibular split in maxillomandibular osteotomy, mandibular clockwise rotation, mandibular counterclockwise rotation, mandibular expansion, mandibular reduction
Sagittal split osteotomy (SSO) in the mandibular angle region offers the possibility of enlarging or reducing the bony mandible in the horizontal and vertical direction. The primary classical indication for mandibular SSO was the forward or backward displacement of reduced or enlarged mandibles to normalize the dentition; today the main indication is the simultaneous mandibular forward or backward displacement in combination with maxillary displacement to correct the facial bone framework and malocclusion.
In addition to the horizontal and vertical positional shift of the mandibular body, rotations of the mandibular corpus may also be indicated to a lesser extent in the context of SSO. For example, anterior open bites can be corrected by counterclockwise rotation (CCWR) of the mandibular body, and deep bites by clockwise rotation (CWR).
A transverse arch discrepancy can also be an indication for mandibular SSO if the transverse arch correction is so extensive that it must be performed not only in the maxilla but also in the mandible. For example, an unusually wide maxillary arch can be surgically reduced and the narrow mandible widened and made congruent with the maxillary arch by an additional median sagittal mandibular osteotomy with simultaneous sagittal split. In contrast, a wide mandibular arch can be narrowed with simultaneous sagittal mandibular split to achieve transversal congruence with the opposing arch.
In sagittal mandibular splits, additional segmental osteotomies in the sense of interdental osteotomies are also possible, especially in the anterior region, if the interdental distance is sufficient. They serve to normalize the mandibular anterior inclination or to correct the bony alveolar ridge. Anterior mandibular block rotations for simultaneous correction of the anterior protrusion, including chin augmentation and chin wing, can also be accompanied by a sagittal mandibular osteotomy.
Indications for mandibular sagittal split are even more extensive in the context of maxillomandibular osteotomy because the entire maxillomandibular block can be displaced three-dimensionally (see Chapter 6).
Three widely used modifications of mandibular SSO, listed in chronologic order of first description, are described methodologically in this chapter, and the advantages and disadvantages, including complications, explained (Fig 13-1):
13.2 Surgical procedure: Perthes and Schlössmann (P/S) method
Key words: 3D CAD grid plate, angle drill, angle screwdriver, Bad Homburg modification, detachment masseter approach, elastics, mandibular condyle positioning in acetabulum, HSSO, incision guidance, Lexer chisel, local anesthesia, oblique sagittal ramus split, miniplate osteosynthesis, monocortical miniscrew, occlusion protection, Perthes/Schlössmann, piezoelectric cutting technique, ramus osteotomy, subperiosteal preparation, surgical splint, vasoconstriction
Local anesthetic and vasoconstrictor (eg, prilocaine 1% with epinephrine 1:200,000) are given for local bleeding prophylaxis and pain reduction depending on the surgical access and extent of the planned jaw displacement from the anterior ramus via the retromolar region to the vestibule of the molar region.
The incision is made with the scalpel through the skin to the bone ≤ 20 mm at the mid-anterior margin of the ramus (Fig 13-2a).
The subperiosteal preparation of the jawbone surface is performed on the inner side of the ramus cranial to the posterior margin of the ramus. The direction of preparation is based on the protrusion of the lingula of the mandible, which is located caudally, and the mandibular notch cranially. On the outer side of the ramus, the mucoperiosteum is tunneled to the angle of the jaw and the cranial masseter muscle is detached (Fig 13-2b).
In order to pre-cut the osteotomies in grooves, the subperiosteally detached soft tissue is carefully lifted with the ramus or channel retractors. First, gentle grooving is performed down to the cancellous bone layer on the inner side of the ramus above the lingula to the posterior margin with the piezoelectric instrument, then caudal to it on the outer side of the ramus. Both grooves are then connected by an oblique groove osteotomy on the anterior margin of the ramus from cranial inside to caudal outside (Fig 13-2c).
The caudal position of the outer groove varies and determines the size of the bony adaptation surfaces. Today, powerful piezoelectric instruments are used to perform the groove osteotomy, which ablate less bone and minimize the risk of mechanical injury to the inferior alveolar nerve (Fig 13-2d).
The Lexer chisel is then used to carefully perform sagittal splitting of the ramus strictly under the buccal cortical layer. By manual rotation of the chisel, the inner and outer sides of the ramus are expanded and completely separated. Special attention must be paid to the variant course of the nerve (Fig 13-3).
First, the bony attachment surfaces are adapted to each other depending on the mandibular displacement direction. In the case of mandibular repositioning, the joint-bearing segment is shortened by placing a narrow bulbous spatula between the joint-bearing and tooth-bearing segments to protect the inferior alveolar nerve before a corresponding cut parallel to the vertical osteotomy is made with the oscillating saw/piezo device to shorten the excess bone of the joint-bearing segment. This bone graft can be used as a bone graft in the usually simultaneous maxillary advancement. In the case of mandibular advancement, no further adjustment of the bony adaptation surfaces is usually necessary.
The target splint is then inserted with maxillomandibular fixation (MMF) via a wire loop (thickness 0.4 mm) on each bracket or 11-mm MMF screws (temporary anchorage devices [TADs]) bilaterally. If the closure of an open bite requires more force, additional screws are placed in the maxillary and mandibular centers for anterior MMF (Fig 13-4).
Depending on the displacement distance, an eight-hole or a more stable 10-hole 3D CAD grid plate with a thickness of 1 mm (Mondeal) is available for osteosynthesis (Fig 13-5a), which is applied directly without prior bending and initially fixed to the joint-bearing segment dorsocranially with a 5-mm screw using an angled screwdriver (Fritzemeier right-angle drilling head, KLS Martin) (Fig 13-5b). After alignment of the plate, the second 5-mm screw is placed dorsocaudally. The joint-bearing segment is guided into the socket without pressure by means of a gauze packer according to Luniatschek before the plate is fixed to the tooth-bearing segment with two 7-mm screws in the upper area of the plate (and thus at a safe distance from the nerve). For further fixation, a 5-mm screw is used mediocaudally, the passive intermaxillary fixation is opened and the undisturbed occlusion setting is checked. Finally, at the craniomedial hole of the plate in the area of the joint-bearing segment (thus at a safe distance from the nerve), a bicortically mounted 9-mm screw is inserted to ensure that sufficient stability is provided despite the small bone attachment surfaces, which are aligned almost parallel to each other (Fig 13-5c). Irrigation of the wound area is performed before single-layer wound closure with absorbable suture material (monocryl 3/0). A 6-mm Redon drain is placed in the suture on both sides, and drained transorally. The MMF screws remain in situ as TADs for loose skeletal elastics to secure the occlusion without a splint. A cooling face mask (Hilotherm) and individual pain pump are suggested.
13.3 Surgical procedure: Obwegeser/DalPont (O/D) and Hunsuck/Epker (H/E) methods
Key words: condyle positioning in acetabulum, elastics, guide elastics, Hunsuck/Epker, incision guidance, Lexer chisel, Lindemann reamers, lingual periosteal detachment, lingula, local anesthesia, miniplate osteosynthesis, MMF, nerve displacement, nerve exposure, Obwegeser/DalPont, pain reduction, piezoelectric osteotomy, pre-cutting sagittal osteotomy, predetermined breaking point, sagittal mandibular split, spacer screw, subperiosteal preparation, surgical splint, vasoconstriction
The O/D and H/E methods differ only slightly in operational procedure, so they are considered together in this section, and comparison made only to the Perthes/Schlössmann (P/S) method (also known as the Bad Homburg modification).
Local anesthetic and vasoconstrictor (eg, prilocaine 1% with epinephrine 1: 200,000) are injected as for P/S from the anterior margin of the ramus over the retromolar region into the vestibule of the molar region.
The incision is made with a 15-gauge scalpel through the mucosa to the bone ≤ 35 mm from the anterior margin of the ramus to vestibular of the molar region.
Subperiosteal preparation is performed on the anterior margin of the ramus and on the inner side of the ramus with exposure of the lingula with nerve entry for both methods. With O/D, the preparation is guided to the posterior margin of the ramus, with H/E only ≤ 3 mm cranially beyond the lingula. In both methods, the oblique line and the buccal margin of the mandible are exposed up to the molar region.
Pre-cutting of the osteotomy begins in O/D after holding off the subperiosteal soft tissue with a narrow ramus or channel retractor on the inner side of the ramus above the lingula to the posterior margin of the ramus. In H/E, the subperiosteal soft tissue is retained only with the raspatory up to the lingula, so that the groove can be formed up to 2 mm cranially and posteriorly. Short and long Lindemann burrs or powerful piezoelectric instruments (eg, Mectron) are used for this purpose. This results in nerve contact at the lingula without further neurolysis in O/D, which is more intensive than in H/E with groove formation only up to the lingula because of the extensive intervention up to the posterior margin of the ramus. In both methods, the groove milling at the anterior margin of the ramus is continued from cranially inward to the oblique line, bends angularly caudally, and meets the mandibular inferior margin vertically in the region of the second molar, whose cortical inferior margin is severed in the sense of a predetermined breaking point (Fig 13-6).
For sagittal splitting, a narrow and a medium-width Lexer chisel are inserted into the groove at the anterior margin of the ramus, if necessary driven in slightly deeper with the hammer and then followed by slow careful spreading of the buccal bone segment against the lingual one (Fig 13-7