Mandibular sagittal split osteotomy

13.1 Indications

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):

Figs 13-1a to 13-1d Size and location of bony adaptation surfaces in commonly used methods of sagittal splitting of the mandible for correction of mandibular malocclusion. (Solid lines indicate the osteotomy, dashed lines show indirectly on the other ramus side the osteotomies, and dotted lines indicate the passive fracture produced by chisel stretching.) (Modified from Radlanski and Wesker,1 with permission)

Figs 13-1a and 13-1b (a) High oblique ramus osteotomy according to Perthes2,3 and Schlössmann with small bony adaptation surfaces, but almost parallel to each other. (b) The buccal osteotomy can be moved further caudally to increase the bony adaptation surface if more extensive displacements of the mandible are required. The region of the high ramus osteotomy is distant from the third molars. (Modified from Radlanski and Wesker,1 with permission)

Fig 13-1c and 13-1d (c) Sagittal osteotomy according to Obwegeser3 and DalPont4 with large preparation effort to create large sagittal bony adaptation surfaces to allow comprehensive movements of the corpus mandibulae in all directions. Since the bony adaptation surfaces converge towards each other anteriorly, the buccal articulating bone lamella usually has to be individually shaped, shortened, or fractured depending on the displacement distance to allow functionally stable osteosynthesis. (d) The sagittal osteotomy according to Hunsuck6 and Epker7 with a lower surgical preparation depth allows a comprehensive 3D displacement of the mandibular corpus in all directions, and additional rotations of the mandible, which is useful in maxillomandibular osteotomies and for the correction of asymmetries. The bony adaptation surfaces are almost parallel to one another, so that after functionally stable osteosyntheses, restrictions of the TMJ function are rarely to be expected. The method is universally applicable. (Modified from Radlanski and Wesker,1 with permission)

  • high oblique sagittal split osteotomy (HSSO) according to Perthes2,3 and Schlössmann (P/S) (1922)

  • mandibular sagittal split according to Obwegeser4 and DalPont5(O/D) (1955/1958)

  • Hunsuck6/Epker7 (H/E) (1968/1977) methodology.

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).

Figs 13-2a to 13-2d Intraoperative image sequence of a high oblique ramus osteotomy according to Perthes/Schlössmann method. Incision retromolar vertically on the middle of the anterior margin of the ramus, distant from the third molar region, subperiosteal release of the soft tissue buccally and lingually, pre-cutting of the osteotomy on the inner side cranial to the lingula up to the posterior margin of the ramus, parallel to this approx. 1 to 1.5 cm lower follows the transection of the cortical outer side of the ramus up to the posterior margin. The oblique osteotomy on the anterior margin of the ramus connects the sagittal osteotomies.

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).

Fig 13-3 Surgical view of the Perthes/Schlössmann method from dorsal with lingual osteotomy cranial to the nerve entry into the mandible. Originally, an extraoral approach was made. (Modified from Wangerin et al,8 with permission)

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).

Fig 13-4 In lingual orthodontic treatment technique or Invisalign (Align Technology) therapy, MMF screws or TADs can be screwed into the alveolar processes interdentally or cranially of the tooth roots to achieve temporary MMF or to provide stable retention anchors for additional large wire loops.

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.

Fig 13-5a to 13-5c Under MMF, routine buccal placement of the eight-hole grid plate without prebending, in case of larger mandibular displacements also the more stable 10-hole grid plate, screw fixation according to the scheme of point 1-6. with the angled screwdriver (Fritzemeier right-angle drilling head, KLS Martin).

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).

Figs 13-6a to 13-6l Intraoperative sequences of two sagittal osteotomies according to Hunsuck/Epker method for mandibular advancement.

Figs 13-6a to 13-6g Pre-cutting of the osteotomy of the right mandible is performed with the Lindemann burr or piezoelectrically on the ramus inner side cranial to the posterior side of the lingula (a), of which the bony prominence is visible (b, arrow), continues caudally across the anterior margin of the ramus (c and d) toward the oblique line, is continued buccally parallel to the molars, and then runs caudally at a 90-degree angle to the mandibular inferior margin (e). (f and g) Its cortical layer is completely severed in the sense of a predetermined breaking point. Only the cortical layer is cut until the bleeding cancellous bone layer is visible in depth. Then the two bone lamellae are mobilized in opposite directions with two Lexer chisels and then slowly expanded until the nerve canal or the nerve itself is visible. It should come to rest medially or be moved medially before the sagittal mandibular split is finally completed by further chisel insertion.

Figs 13-6h to 13-6l Intraoperative sequence of a sagittal osteotomy according to Hunsuck/Epker with neurolysis and displacement of the left alveolar inferior nerve. If the mandibular canal with its infusory alveolar nerve is located in the lateral joint-bearing part of the mandible in the course of the expansion, the canal is preferably opened piezoelectrically, and the nerve is exposed and then re-embedded medially in the course of the mandibular displacement.

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

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Jan 19, 2024 | Posted by in Orthodontics | Comments Off on Mandibular sagittal split osteotomy

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