6.1 Preoperative management of temporomandibular joint function

As a rule, a bite splint (muscle relaxation and temporomandibular joint [TMJ] positioning splint) is first made after jaw relation determination by means of facebow transfer and cast mounting before surgical planning for malocclusion correction due to the existing dysfunction of the TMJs. It is worn preoperatively loosely fixed in the maxilla to cause the adjustment of the TMJ heads in a functionally centric position. It is the starting point for a correct surgical simulation and model surgery and is worn preoperatively for 4 to 6 weeks, checked several times, and, if necessary, ground in to eliminate false contacts (Fig 6-1).

In the authors’ experience, TMJ complaints and pain occurring at the time of planning surgery should also be addressed by functional diagnostics and, if necessary, by obtaining an MRI. Interventions on the TMJ that may result from this diagnosis, eg, lavage or arthroscopy, should follow promptly. Surgical planning for malocclusion correction should only be addressed if there has been at least 3 months of symptom relief and the masticatory muscles are relaxed. Existing anterior dislocations are not a contraindication for surgical malocclusion correction if they do not cause functional limitations or pain. However, they are risk factors for postoperative TMJ problems and recurrences. Close monitoring is then required.

Malocclusions have undefined occlusal contacts that lead to dysfunctions of the TMJs. This complicates surgical planning, especially for Angle Class II teeth. In particular, the Sunday bite (the habitual mandibular advancement for functional and esthetic compensation of the receding mandible/dental arch) leads to an incorrect initial bite without centric positioning of the condyles for the model surgery. The intermediate osteotomy splint produced in this case then leads to incorrect positioning of the maxilla and mandible in the case of maxillomandibular osteotomies, provided that the maxilla is positioned first, which is thus set too far posteriorly by the distance of the mandibular advancement. Consequently, the mandible is brought into the desired Angle Class I target occlusion, but the entire maxillomandibular complex in the skull is positioned too far posteriorly.

The relaxation splint should be checked and, if necessary, changed several times until the condyles are in a functionally physiologic position and the malocclusion correction can be performed according to plan (Fig 6-2).

In the case of a habitual mandibular advancement with chronic painful hardening of the masseter muscle and restricted mouth opening, the faulty bite measure is only detected by checking with a bite splint, made from the bite measure converted into acrylic. Manual therapy in combination with heat application or administration of muscle relaxants can improve the situation. Afterwards, repeated sensitive manual return of the mandible to the physiologic position of both mandibular heads on the supine patient can then lead to centric bite registration. The existing bite splint can be gradually corrected with Splintline (Lang Dental) and the physiologic condylar position can be checked with DVT/CT. In cases with particularly strong and/or painful tense masticatory muscles or even myogelosis, physiotherapeutic measures with short-term application of a relaxing jig-anterior splint, and in certain cases also botulinum toxin injections or even a short anesthesia with relaxation, may be necessary to adjust the mandible to a physiologic condylar position.

At the beginning of the operation, this relaxation splint is first used after induction of anesthesia to check the physiologic position of the mandibular condyle in relaxation. If the bite of the mandible is correct in the impressions of this splint, the surgical planning can be precisely implemented with the prepared intermediate osteotomy and final occlusion splints. If the bite is not correct and the mandible falls back into a distal position, the maxillomandibular surgical planning can only be implemented if the maxilla is moved anteriorly by the amount of the distally slipped mandible during the operation, starting with the maxilla.

6.2 Surgical planning of single-jaw osteotomies

The sole displacement of the maxilla or mandible for malocclusion correction has become rare. It is rare for a jaw to be positioned perfectly in all three dimensions in the facial skull and for the associated dental arch to be symmetrically shaped and centered in relation to the middle of the face.

Today, single-jaw osteotomies are more of a compromise solution if occlusal corrections are the sole treatment criterion or if advanced age or severe diseases have a limiting effect. Effects on facial esthetics also play only a minor role. Single-jaw osteotomies have only limited effectiveness because the extent of jaw displacement depends on the predetermined position of the other jaw in order to achieve neutral occlusion.

In principle, these single-jaw osteotomies require, in addition to a maxillary relaxation splint (see Fig 6-1) for preoperative positioning of the mandible, an occlusion splint for positioning the jaw to be corrected, be it the maxilla or the mandible. Even in cases with orthodontically exactly congruent dental arches, a surgical simulation and model surgery should be performed to identify future articulation movements (canine guidance). Occlusal adjustment may be necessary to deepen the intercuspidation or improve articulation and thus counteract recurrence. The model surgery may also lead to the consideration of manufacturing an occlusion splint that initially stabilizes the new occlusion intraoperatively and is removed 2 to 4 weeks postoperatively to continue orthodontic treatment or to grind in articulation movements. In cases of exact congruent orthodontic shaping of both dental arches, the occlusion can also be adjusted intraoperatively without an occlusion splint.

The surgical procedure for maxillary displacement requires more experience than for mandibular displacement, since intraoperative correct adjustment of the maxillomandibular block is complicated by the mobility of both condyles and the initially punctiform, often varying bony contacts of the mobile maxilla to the midface base. Repeated fixations of the maxilla with miniosteosynthesis plates are not uncommon until the planned occlusion with occlusion splint corresponds to the planning. Vertical displacement of the maxilla with autorotation of the mandible without or with malocclusion correction can lead to esthetic improvement of the facial profile and functional lip closure (Fig 6-3).

Surgical mandibular advancements for the correction of mandibular retrognathia are associated with the risk of overlooking an existing Sunday bite (see Fig 6-1). As a rule, these considerations are not necessary for mandibular advancements for the correction of mandibular prognathism with Angle Class III. The covering soft tissue mantle pushes the large mandible back into a functional condylar position permanently and also during bite planning. However, isolated mandibular retraction should only be performed after checking the airway to minimize the risk of subsequent obstructive sleep apnea. Additionally, retraction of the mandible can also lead to an excessive relaxation of the submental soft tissue and a double chin contour, even in young patients.

In single-jaw osteotomies, additional interdental osteotomies in the sense of segment formation in the anterior region of the opposing arch are common; median sagittal osteotomies for widening or narrowing of the mandible may also be indicated in order to achieve transverse congruence with the opposing arch. Anterior mandibular block rotations for simultaneous correction of anterior protrusion and chin augmentation may also be associated with sagittal mandibular displacement.

Instead of using an occlusion splint in a single-jaw osteotomy, it is also methodically possible to prosthetically redesign the occlusion of the maxillary and/or mandibular arch and, after insertion of the tabletops, to surgically adjust one of the two arches exactly to the planned occlusion. In individual cases, an additional rotation of the bony mandible in the sense of a counterclockwise rotation (CCWR) can also be achieved by prosthetic lengthening of the molar crowns, which is otherwise only possible with maxillomandibular osteotomy with CCWR (Fig 6-4).

To harmonize the facial profile and improve the chin prominence, the mandible must be rotated counterclockwise (CCW). The resulting distal open bite in the model surgery is closed with ceramic tabletops to create a new occlusal plane. The crowns are lengthened in the molar region. After preoperative insertion of the onlays, an anterior open bite is created, which is closed by sagittal splitting of the mandible with exact setting of a new occlusion.

Pronounced curves of Spee in the mandible cannot always be compensated orthodontically (Fig 6-5). Surgical correction with lowering of the anterior segment can be an alternative, but in cases with reduced vertical mandibular height it can lead to an undesirable reduction of the anterior facial height. Therefore, it may be advantageous to first fabricate and fit acrylic temporaries or tabletops in the mandibular posterior region as part of the model surgery. Only then is the mandibular cast relocated and the occlusion splint fabricated in the usual manner. The tabletops are inserted preoperatively in the patient’s mandible and then the mandibular pre-displacement is carried out classically with the occlusion splint. The facial height can thus be preserved. Splint removal is performed after 2 to 4 weeks depending on the extent of maxillomandibular correction. After the end of the orthodontic treatment, the prosthetic restoration is made. The facial height can be further increased if necessary (see above and case description Fig 6-4).

6.3 Surgical planning of maxillomandibular osteotomies

The simultaneous shifting of the maxilla and mandible to correct a malocclusion can have a significant effect on facial esthetics. A precondition is the compliance between bony maxillary center and dental midline.

In the vertical direction, a “long face,” in the sense of a vertical extension of the anterior facial height of the maxilla and/or mandible, can undergo maxillomandibular correction, as can a “short face,” often associated with a deep bite or a vertical reduction of the anterior facial height of the maxilla and/or mandible.

In the anterior-posterior direction, the esthetics of the facial profile from the tip of the nose to the pogonion can also be improved by maxillomandibular correction.

In the transverse direction, additional surgical measures such as zygomatic bone augmentation, chin correction, and septorhinoplasty can extend the esthetic corrective measures to the entire face.

The contours of the facial soft tissue do not always express the extent of the skeletal malocclusion. For example, mandibular prognathisms may show a normal facial profile if the soft tissue mantle is thin. Mandibular retrognathia may show a nearly normal chin profile if the mentalism muscles have become hypertrophied due to the habit of forced lip closure in the presence of lip closure insufficiency. When the soft tissue mantle is thin, skeletal changes due to maxillomandibular osteotomies are more noticeable than when the soft tissues of the face are voluminous. In these faces, dysgnathia is often hidden and maxillomandibular rearrangements are then also not visible. In such cases, the width of the nasopharyngeal airway must be taken into account in mandibular prognathisms with Angle Class III interlocking, which, planned cephalometrically, tend to require a backward displacement of the mandible. In order to preserve or, if necessary, widen the arches, the malocclusion should be corrected primarily by advancing the maxilla. These aspects should be considered individually in each case in addition to the standardized planning of maxillomandibular malocclusion corrections.

6.3.1 Indications

Simultaneous repositioning of the maxilla and mandible is indicated when a malocclusion cannot be corrected by positional correction of one arch alone because the position of the other arch also does not meet the planning criteria for a harmonious face.

Indications for maxillomandibular osteotomy may also exist if the sagittal or transverse discrepancy between the maxillary and mandibular teeth is so great that correction should be performed half in the maxilla and half in the mandible for stability reasons. Simultaneous displacement of the maxilla and mandible to normalize the face in three dimensions may also be indicated for esthetic and functional reasons, eg lip closure.

Closure of skeletally open bites may also require maxillomandibular surgery if the maxilla is rotated clockwise and the mandible is rotated counterclockwise (with additional segmental osteotomies, if necessary), in order to achieve not only normal dentition but also standard proportions of the maxilla and mandible in the facial skull.

Often, maxillomandibular osteotomy is also indicated with simultaneous clockwise rotation of the entire maxillomandibular block if the posterior-hanging occlusal plane is to be normalized, the maxillary anterior height improved, the maxillary anterior protrusion reduced but, if necessary, the upper lip accentuated by maxillary anterior advancement.

Counterclockwise rotation of the maxillomandibular block may be indicated to correct a “bird face,” to caudalize the occlusal plane posteriorly (increase posterior facial height), and enlarge the mandible, or to emphasize the entire lower third of the face anteriorly.

Similarly, congenital malformations of the face can often only be treated by comprehensive corrections involving maxillomandibular osteotomies in sequential procedures. These malformations include cleft lip and palate, visceral arch syndromes (hemifacial microsomia, Goldenhar syndrome), or facial asymmetries of any degree.

The aim of a maxillomandibular osteotomy is the normalization of all functions of the stomatognathic system including normal occlusion, orthograde position of the skeletal framework including maxilla and mandible and normalization of the facial profile, and creation of esthetic contours of a symmetrical face.

With the performance of a maxillomandibular osteotomy, the maxillofacial surgeon is provided with a tool that changes the function and esthetics of the face so comprehensively that even the authentication of postoperative faces via digital facial recognition is likely to reach its limits.

6.3.2 Surgical planning options for maxillomandibular osteotomies

Maxillomandibular osteotomy requires extensive surgical planning. Photographic documentation is standardized intra- and extraorally (see Chapter 1). It is not only used to record the initial findings, but also serves as a source of information for the surgeon during the surgical procedure, since the head is sterilely covered and only allows a view of the central face. Photos facilitate the control of the center of the face and the vertical adjustment of the maxilla.

Clinical surgical planning is based on the examination of the patient. The key to surgical planning is the maxillary center with adjustment in the vertical, sagittal, and transverse planes. Consideration is given to a harmonious smile line, a gender-specific nasolabial angle, and the adjustment of the facial center (see Chapter 2).

The surgical simulation created according to cephalometric analysis (see Chapter 3),¹ is used to determine the extent of surgical jaw displacements, measured in millimeters at dental orientation points (see Chapter 4), taking clinical surgical planning into account. For less experienced surgeons, this planning is a check on clinical surgical planning.

The relaxation splint worn preoperatively in the maxilla (relaxation splint loosely fixed to the maxillary arch, see Fig 6-1b) sets the TMJ heads in a functional position. It serves as a centric register and is the basis for the extent of malocclusion, which is revealed in the arbitrarily articulated casts after facebow transfer. In the model operation, the position of the maxilla and mandible is corrected in compliance with all surgical planning criteria so that a standard dentition results (see Chapter 5). There are two possibilities: first correct the maxilla and then the mandible, or vice versa.

In the “maxilla first” model operation, the specified displacement distances are implemented at the dental measuring points in the maxillary midline (see point “is”, Chapter 3) and the two mesiobuccal cusps of the maxillary first molars. In the present case with a displaced maxilla model, the intermediate osteotomy splint was created, containing information on the setting of the dental midline, the setting of the vertical height of the maxilla, and thus the maxillary anterior view (corresponding to the anterior facial height), the posterior facial height, and also the symmetrical setting of the transverse occlusal plane (parallel to the interpupillary line). The asymmetry of the splint on both sides shows the lateral shift of the preoperatively asymmetrically positioned maxilla to the center of the face at the tooth impressions (Figs 6-6a and 6-6b).

Afterwards, the mandibular cast is positioned in planned or neutral dentition and the final occlusion splint is fabricated. Its tooth impressions contain the information of a normal dentition. The marginal holes are used for fixation with wire loops to the brackets (Fig 6-6c).

In most orthognathic surgery centers, “maxilla first” is the routine model surgery. If the maxillomandibular procedure is planned vice versa (“mandible first”), the model surgery is basically performed in the same way, but a second identically socketed maxillary cast is used to produce a surgical splint that contains the impressions of the maxilla in the normal position on the one hand, and those of the already displaced mandible on the other. This is the “vice versa” intermediate osteotomy splint. The final occlusion splint previously created in routine model surgery with the information of a neutral occlusion is the same if the procedure is reversed (see Chapter 5). Detailed considerations on the choice of procedure are presented in Section 6.4.

6.3.3 Maxillomandibular osteotomies with multiple divisions of the maxilla to correct incongruities between bone and teeth or asymmetries of the maxillary arch

The same extensive preparation of the surgical planning takes place as indicated in Section 6.3.1. The relaxation splint is used for muscle relaxation and the physiologic adjustment of both TMJ heads. The tooth impressions of this bite block splint correspond to the centric registration of the previous bite registration (see Fig 6-1d).

Due to the existing incongruence of the bony maxilla and the dental arches, mostly due to a maxillary compression with a standard-sized mandibular arch, a segmentation of the maxillary cast is performed. In rare cases an additional segmentation of the mandibular anterior teeth is necessary. Most frequently, the maxillary segmentation is Y-shaped between lateral incisor and canine on both sides (see Fig 6-8f). Median bisections of the maxillary dental arch (see Chapter 5) occur as well as asymmetrical segmentations. It is important to check on the panoramic radiograph that there is sufficient distance between the tooth roots to avoid tooth root damage due to osteotomies. The segmentation of the maxillary cast serves to adapt the segments to the mandibular arch and the dental midline. Both an extension of the maxillary arch and the opening and closure of an existing gap are possible. Caution is needed in the model operation regarding the interfering cast edges during the dental arch adjustment. The maxillary arch segments are fixed on the corresponding base and then the intermediate osteotomy splint is fabricated. This contains the information about the redesign of the maxillary arch and the sagittal and vertical displacement of the maxilla.

As described above, the final occlusion splint contains on one side the information on the position of the maxillomandibular displaced maxillary components with redesigned maxillary arch, and on the other side that of the mandible displaced into neutral occlusion; the row of holes on the splint margin is used to fix wire loops to the brackets of the maxilla (Fig 6-7a). It is stabilized transversely with a palatal steel bracket to counteract bony recurrence due to palatal scarring and dental recurrence due to tooth tilting.

The sandwich technique removes the need for an intraoperative surgical splint change after Le Fort I osteotomy. The sandwich splint consists of a combination of two splints fixed together (Fig 6-7a

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