Conditions of the temporomandibular joint (TMJ) can either cause or result in malocclusion and other dentofacial deformities. Thus, it is often advantageous to simultaneously correct the deformity and address TMJ pathology, as stability of orthognathic surgery depends on a healthy TMJ.
Use of virtual planning has allowed for more efficient and accurate workflow: diagnosis, treatment planning, length of treatment, and outcomes.
Of the many conditions involving the TMJ, the authors’ focus is on excessive growth conditions and resorption of the TMJ and how they should be taken into account when doing orthognathic surgery.
The advent of virtual surgical planning (VSP) in oral and maxillofacial surgery has aided surgeons and patients by reducing preoperative treatment planning and improving accuracy of surgery. It has become a “game changer” for providers and changed the way surgery is practiced, especially for the asymmetric patient. In this article, the authors focus on the use of VSP for cases involving concomitant orthognathic and temporomandibular joint (TMJ) surgery. Although there are a range of conditions affecting the TMJ in which computer-aided treatment planning can be advantageous, the authors focus their discussion on conditions of the TMJ that can cause resorption or malformation, needing operative intervention and correction, specifically (1) excessive growth conditions and (2) TMJ resorption needing alloplastic reconstruction. The craniofacial congenital deformities will be covered in a different chapter. The authors discuss the key considerations for the surgeon during diagnosis, treatment planning, and execution. These considerations are highlighted in the context of patient care.
General principles of virtual surgical planning
The steps and workflow involved in virtually planning orthognathic surgery are well known. If TMJ surgery is planned concomitantly, especially when using a total joint prosthesis system, there are some minor but important differences one must consider. Cone beam computed tomography (CBCT) is first used to help virtually construct the patient’s anatomic model. However, when fabricating a custom TMJ device, a medical grade CT offers better definition that translates into better adaptation of the prosthesis and continues to be the gold standard. Using the individual cuts from the CBCT or CT dataset, segmentation is done to help outline structures from one another, such as separating the maxilla and mandible, outlining soft tissues compared with bony structures, etc. One must consider the head position of the patient and correct it accordingly. This is the first step one should always do because it is critical and a potential source of errors that is often overlooked ( Fig. 1 ).
The authors like to use the patient’s clinical analysis (clinical cant and yaw) and maxillary midline position in conjunction with anatomic three-dimensional (3D) lines to align the head. As an example, in severe skeletal class II patients with breathing difficulties due to an obstructed airway, the tendency is for these patients to roll their head slightly forward and up in order to open the airway. One must account for this and using virtual planning, correct the head position in order to provide a more accurate outcome.
After 3D models have been generated and segmented, the models can be imported into an appropriate software where virtual dental models from an intraoral scanner (usually in an STL format) are merged, allowing the surgeon to then plan any necessary osteotomies. The planning phase is not different with virtual technology. One must account for the position of the maxillary incisor in all 3 planes of space and the degree of occlusal plane rotation and transverse changes based on the clinical and cephalometric analysis. Once the necessary movements have been performed virtually, a 3D model is made and used by the manufacturer to fabricate the custom device. The surgical splints can also be 3D printed ( Fig. 2 ).
If the mandible is moved and an intermediate splint is necessary, it is critical not to print the splints until close to the surgery day to account for any possible tooth movements that may have occurred while waiting for the fabrication of the custom device. It is recommended that a second set of dental models is uploaded and checked against the first model closer to the surgery day, to allow for an accurate fitting of the splint during surgery.
Another advantage of using virtual planning when doing concomitant TMJ Surgery, especially a total joint reconstruction (TJR), is the possibility of planning for any bone remodeling and recontouring before surgery, including the placement of the condylectomy and if indicated, the corresponding coronoidectomy. One can then request custom cutting guides that would aid in the accuracy and later placement of the device during surgery ( Fig. 3 ).
This is not always necessary but very helpful in cases where bone recontouring or removal is planned such as in a large bony ankylosis. Positioning of the screws away from anatomic structures, depicting potential interferences, or perforation in the glenoid fossa are just a few of the advantages of using virtual planning. In the case of condylar hyperplasia (CH), it is possible to virtually plan for the condylectomy, predicting the rotation of the mandible, and plan accordingly.
Although being able to predict soft tissue changes based on the movement of the bones is done at every planning session, advances in technology are now more accurately predicting soft tissue changes with osteotomies but still are lacking validation. Perhaps the greatest advantage of virtual planning versus the traditional method for a TJR fabrication in concomitant orthognathic surgery is the accuracy between the model surgery and device/splint fabrication, because it is all done in the same model. In the conventional method, 2 separate model surgeries were needed, thus creating inaccuracies that affected the fitting of the device and ultimately the outcome for the patient ( Fig. 4 ).
Growth disorders of the condyle can lead to a dentofacial deformity due to alteration of occlusion, morphology of the mandible, and its potential effects on the maxilla. They tend to be classified as horizontal, vertical, or mixed. It is important to determine if the condition is ongoing or arrested and at what age it began. In general, CH that affects growing patients will affect the maxilla if left untreated, but CH that presents in adults tends to spare the maxilla, unless there has been compensatory orthodontic or dentoalveolar movements.
As proposed by Wolford and colleagues, one can use a classification system to determine if one or both of the condyles are resulting in the dentofacial deformity and thus guide the surgeon on how to correct the problem. In the authors’ experience most of these patient suffer from a unilateral deformity and asymmetry. When attempting to correct a facial asymmetry caused by unilateral CH, a surgeon mainly considers 3 treatment options: waiting for the overactive condyle to cease growth and treat the deformity later, performing a condylectomy (high or low) to arrest unilateral growth before performing orthognathic surgery (if indicated), or performing concurrent condylectomy and orthognathic surgery. Others such as Nitzan have proposed to use condylectomy only as the sole treatment of CH with good outcomes.
There are several questions that must be answered before treating a patient with CH:
Is it a growing patient? ( Fig. 5 ). The authors prefer to perform a condylectomy-only approach, in the growing patient to try to prevent the need for orthognathic surgery in the future.
Is it active or not? If active, when did it begin? There are numerous ways in which to assess active growth in a patient. One of the more widely accepted methods for assessing if there is an actively growling condyle is through use of single-photon emission computed tomography ( Fig. 6 ).
Has it affected the TMJ only or has the asymmetry occurred in the ramus and body of the mandible? ( Fig. 7 ).
Is it affecting the maxilla? This will guide the need for single versus double jaw surgery.
What is the status of the occlusion? Has the dentoalveolar bone compensated for the asymmetry? ( Fig. 8 ). It is key to plan with the orthodontist for any decompensation to be done first, to achieve maximum symmetry with surgery.
The benefit of using virtual planning is that the surgeon can visualize in 3D all the possible deformities. It is possible to trace angles and lines to approximate the most symmetric correction at the bone level and translate that into the planning with the use of cutting guides and splints ( Figs. 9–11 ).
When deciding to fixate the maxilla and mandible in their new positions, one must also keep in mind the forces on the moving segments brought on by the soft tissue and musculature. For example, in a rotational movement from a mandibular osteotomy, the soft tissue and musculature has the tendency to pull the mandible back toward the side it is rotating away from, whereas the structures are more relaxed on the opposite side. For this reason, some surgeons prefer to overcorrect to help prevent relapse, whereas others may argue that overcorrection can make the gap wider between the osteotomy and the soft tissues.
Not only has computer-aided design and computer-aided manufacturing (CAD-CAM) afforded surgeons the ability to expediently plan cases but the use of technology has also allowed to fabricate custom cutting guides and plates. Before the use of virtual planning, the fabrication of surgical splints was through an inherently flawed process. From ensuring that accurate impressions are obtained initially to the mounting of casts on an articulator using a facebow transfer and verifying that the final movements on the casts reflect what is done during the surgery, there are many potential errors that can be introduced during the traditional planning process depending on the surgeon’s experience. Furthermore, even though CAD-CAM can be used to fabricate very accurate intermediate and final splints, it is still up to the surgeon to execute the plan and secure the osteotomies in their desired position. Although custom guides and plates are not routinely used for every patient, there are cases where it is warranted and the surgeon should use good judgment to determine which are appropriate ( Fig. 12 ).
Lastly, because virtual planning has also afforded us with the ability to preview soft tissue changes from changes in hard tissue structures, surgeons are able to discuss with patients the need for soft tissue reduction or augmentation with custom implants without further workup given that virtual planning was used from the start.
Temporomandibular joint reconstruction
More and more the modern oral and maxillofacial surgeon is considering TJR as an accepted technique that is not “a last resort” but indicated in specific conditions as first-line treatment. There is very good long-term evidence of its success, and when used appropriately, it is one of the most predictable operations that can be offered to a patient. Autogenous alternatives are a possibility and should be discussed with the patients; however, here the authors focus on conditions that can be treated with an alloplastic device.
Some of the most common causes that may benefit from TJR are disorders that cause resorption or malformation of the TMJ:
Connective tissue/autoimmune disease (ie, juvenile idiopathic arthritis, Sjogren syndrome, rheumatoid arthritis, systemic lupus erythematosus, etc.)
Reconstruction of the TMJ using an alloplastic device provides several advantages:
Physical therapy may be started almost immediately when compared with allografts. The ability for patients to return to function quickly after surgery allows for faster rehabilitation, which is essential in joint disease that has compromised muscle function over an extended period of time.
Decreased morbidity and length of surgery because there is no need for a donor site and therefore, no morbidity associated with it. Thus, operating time, length of stay, and cost (despite cost of custom-made prosthesis) are decreased.
Construction of the prosthesis: because these alloplastic devices are constructed in a manner to reflect the anatomy that it is replacing, they can lead to quicker return to function, even in situations in which the architecture is severely distorted (ie, complete ankylosis or destruction of glenoid fossa).
Today these devices have shown more than 30 years of stability and very little wear. Its rejection rate is less than 1%, and infections should not occur in more than 1% to 2% of the cases. Possibly their biggest disadvantage is the cost of fabrication; however, this should also decrease with time. As with the patients with CH, the timing of the occurrence, the compensation of the contralateral side, and the maxillary position are key during planning ( Fig. 13 ).
VSP has aided maxillofacial surgeons when performing total joint replacement, particularly in the positioning of the mandible before prosthesis fabrication. Before the widespread use of VSP, the protocol for movement of the mandible to a different location than that preoperatively had opportunities for errors that could be propagated throughout the treatment planning process and could lead to a less than ideal result. For example, after a stereolithic model had been fabricated from a CT scan, the surgeon used the cephalometric tracing to place the mandible in its future location based on the planned movements to correct the position in all 3 planes of space. The same process had to be repeated manually in a mounted articulator in order to fabricate the splints that would guide the procedure. The differences in surgical experience and dexterity could lead to errors during this process ( Fig. 14 ).
Using VSP for concomitant TJR and orthognathic surgery can be done in a more expedited and accurate manner. The final position of the maxillomandibular complex can be determined using information obtained from the clinical analyses, models, and cephalometric measurements. After the final position of the maxilla and mandible has been digitally determined, a stereolithic model is created in order to fabricate the prosthesis. The cutting guides, aids for surgery, and splints used to position the mandible against the uncut maxilla before placement of the custom device are printed based on the VSP.
We advocate the use of a custom-made TMJ implant (ie, TMJ concepts) for all cases where a dentofacial deformity needs to be corrected. The virtual STL model is sent to the manufacturer, who can electronically send the proposed prosthesis design to the surgeon once it has been waxed up and wait for approval by the treating provider. Custom devices have a better bony adaptation, allow for significant larger movements and asymmetry corrections by correcting yaw and cant, are easier to place, and in the case of TMJ concepts, provide a titanium mesh in the fossa component that allows for osseointegration ( Fig. 15 ).
Although there are different options in which to sequence TMJ replacement surgery in conjunction with orthognathic surgery, we advocate doing the mandible first as described by Perez and Ellis; the typical sequence we use involves the following steps:
Preparing the TMJ (condylectomy, coronoydectomy, and mobilization), unilaterally or bilaterally depending on the case.
Changing to a new set of instruments and doing the contralateral mandibular osteotomy if needed (unilateral replacement cases only).
Placing the patient in intermediate position with a prefabricated intermediate splint for mandible first.
Securing the artificial joint in place, using the clean set of instruments; closing the TMJ incisions.
Securing the mandibular osteotomy with rigid fixation in unilateral cases only, checking intermediate occlusion.
Maxillary repositioning as previously described.
The position of the condyle within the TMJ is altered when doing TMJ surgery. Doing the TMJ surgery first before the mandible allows one to take into account the new position of the condyle before maxillary and mandibular repositioning. The surgeon may also choose to do the maxillary osteotomy before operating on the TMJ and mandible, but this is less favorable due to having to maintain separate sterile fields and 2 sets of instruments, it is also very difficult in cases where the condyle is severely ankylosed or completely absent. If this is the preferred sequence chosen by the surgeon, we advocate the use of custom cutting guides and prefabricated plates to start with the maxilla so that the condylar and mandibular preoperative position becomes irrelevant for the intermediate stage and thus increasing accuracy.