Introduction

The relationship between dentofacial deformity (DFD) and temporomandibular dysfunction (TMD) is one of the more controversial topics within our area of expertise. DFD is diagnosed objectively, but what constitutes TMD has been contested for decades. This complicates our ability to delineate the association between DFD and TMD. For example, only a subset of TMD patients have pathology involving the mandibular condyle itself (condylar TMD or cTMD) that may result in DFD.

Alloplastic reconstruction of the temporomandibular joint—commonly referred to as total joint replacement (TJR)—involves removing the diseased condyle and/or fossa and replacing both condylar and fossa components with prosthetic materials ( Fig. 1 ). Today, these materials are made of cobalt chromium alloy, titanium alloy, and ultra-high molecular weight polyethylene (UHMWPE). In considering the role of total replacement of the temporomandibular joint (TMJ) in the orthognathic patient, it is helpful to categorize patients into ( A ) primary pathology of the mandibular condyle (condylar TMD or cTMD) or ( B ) primary DFD (Box 1). The primary cTMD patient is described as one whose pathology arises from condylar abnormality. These patients are represented by conditions including idiopathic condylar resorption (ICR), inflammatory arthritides, severe osteoarthritis, end-stage internal derangement, TMJ ankylosis, severe septic TMJ arthritis and primary condylar tumors, such as osteochondroma. It is this primary condylar abnormality which results in secondary dentofacial deformity. In these patients, the mandibular condyle is, by definition, always pathologically involved and requires treatment. In contrast, the primary DFD patient is described as one whose pathology does not arise from a condylar abnormality, although the condyle itself may also be involved. These patients are represented by conditions including craniofacial microsomia (CFM), craniofacial dysostosis, and maxillary or mandibular hypo- or hyperplasia. In these patients, the condyle may or may not require treatment. Lastly, one may consider condylar hyperplasia (including hemimandibular hypertrophy and hemimandibular elongation) as a hybrid of these two primary patient populations.

Zimmer Biomet TJR prosthesis. Shown are the mandibular component fixated to the mandibular ramus and the fossa component fixated to the posterior aspect of the zygomatic arch.

Categorization of patients in the above fashion is helpful when considering treatment of the TMJ. Primary cTMD patients by definition have unstable, potentially unstable, and/or malfunctional condyles either unamenable to traditional orthognathic surgery or prone to adverse post-operative changes following traditional orthognathic surgery. Even in patients with quiescent ICR or arthritic processes, the risk of disease recurrence remains after surgery. In the primary cTMD patient group, presentation is often skeletal Class II with a high mandibular occlusal plane angle whereby surgical correction with advancement and counterclockwise rotation of the maxillomandibular complex further stresses the TMJ lever arm. The primary cTMD patient, in particular, may benefit from TMJ TJR in combination with orthognathic correction of the presenting dentofacial deformity ( Table 1 ).

Management of DFD in patients with TMD – when TJR is not indicated

In addition to controversy regarding the association of DFD and TMD, controversy exists regarding how to manage traditional DFD patients with TMD signs and/or symptoms. A determination should be made as to whether the patient is seeking corrective treatment for the DFD or TMD. The treatment of one will not automatically improve the other.

Many patients presenting with DFD and a history of TMD signs and/or symptoms do not have cTMD. These patients should be considered primary DFD patients with an overlying TMD. The two most common presentations falling into this category are patients presenting with myofascial pain or internal derangement of the disc-condyle complex. Myofascial pain patients often have parafunctional and/or psychosocial etiologies. The associated chronic, persistent, regional pain is in the absence of radiographic signs of TMJ abnormality. This type of patient is not a TMJ surgical candidate, including TJR, and is best treated conservatively by a dedicated orofacial pain team. Internal derangement patients present with various joint signs and symptoms (noises, popping, locking and/or limited range of motion) and demonstrate an abnormal disc-condyle relationship on soft tissue imaging (MRI). Although these patients are rarely TJR candidates, they may benefit from TMJ surgery, including arthrocentesis, operative arthroscopy, and a range of open joint procedures beyond the scope of this chapter. Both TMD patient types—myofascial pain and internal derangement patients—benefit from the management of presenting TMD signs and/or symptoms by methods other than TJR, before any dentofacial deformity correction utilizing traditional orthognathic surgical techniques.

Management of DFD in patients with TMD – Indications for TJR in orthognathic surgery

Compared to the primary DFD patient, the primary cTMD patient presents with dentofacial deformity as a direct result of condylar pathology. The decision on TJR is dependent on the ( 1 ) patient’s growth status and ( 2 ) the pathologic process.

Orthodontic treatment in primary cTMD patients undergoing TJR and orthognathic surgery

The orthodontist is an integral team member managing patients undergoing TJR and orthognathic surgery. The patient may present to the surgeon or the orthodontist. In some cases, patients demonstrate failed treatment, including occlusal equilibration, orthognathic surgery, occlusal splint therapy and orthodontic treatment. One survey found 81% of patients presenting for a consultation had undergone 1 or more treatments that had failed. The correct diagnosis is key to developing a successful treatment plan. Careful attention must be paid to the skeletal discrepancy in all three planes of space. cTMD patients often present with a Class II skeletal base associated with mandibular retrognathia. Not uncommonly, patients may present with bimaxillary sagittal hypoplasia. There is an increased mandibular occlusal plane angle leading to increased lower anterior face height and reduced overbite or anterior open bite. There may also be mandibular asymmetry with chin deviation to the side of the unilaterally affected TMJ and possible maxillary and mandibular occlusal cants. Depending on the rate of change in the unilateral affected TMJ and ensuing occlusal compensation, there may be a unilateral posterior open bite, crossbite and dental centerline discrepancies. Dental compensation needs to be identified in all three planes of space.

Radiographs, photographs and study models aid diagnosis and treatment planning. The lateral cephalogram often demonstrates an increased gonial angle and pronounced antegonial notch, and also confirms the increased mandibular and occlusal planes, decreased posterior face height and Class II skeletal pattern. The lateral cephalogram may also demonstrate a reduced oropharyngeal space ; patients occasionally complain of breathing problems. In growing patients not in immediate need of TJR, sequential standardized photographs and study models provide non-invasive methods of monitoring progression of the disease as it relates to the developing malocclusion. In certain cases, technetium bone scans can confirm absence of active disease.

The orthodontist will work with the surgeon to develop the treatment plan. The surgeon provides information on the desired surgical movements to correct the skeletal problem and the orthodontist will work to provide the correct tooth positioning to facilitate surgical jaw repositioning. Particular attention needs to be given to the anticipated maxillary incisor inclination following counterclockwise rotation of the maxilla. The lower incisors will need to be decompensated in cases of proclination associated with a Class II skeletal pattern, and the dental arches need to be coordinated. In the presence of maxillary and mandibular cants, the lip-incisor relationship will influence the side to be corrected. The surgeon and orthodontist must work together to decide if this is to be corrected surgically or orthodontically. Post-surgical orthodontics will utilize guiding intermaxillary elastics for the patient while detailing of the occlusion is undertaken.

On occasion, patients will need to have the original TJR explanted for reasons such as infection. As an interim measure between removal of the original TJR and implantation of the new TJR, the orthodontist can help with the provision of removable bite planes or guiding elastics attached to removable or fixed appliances.