Computer-Assisted Surgical Simulation for Concomitant Temporomandibular Joint Custom-Fitted Total Joint Reconstruction and Orthognathic Surgery

Key points

  • Temporomandibular joint conditions and dentofacial deformities commonly coexist.

  • Combined orthognathic and total joint reconstruction cases can be predictably performed in one stage.

  • The application of computer technology for concomitant temporomandibular joint total joint replacement and orthognathic surgery improves the accuracy of treatment outcomes.

  • With the correct diagnosis and treatment plan, combined temporomandibular joint and orthognathic surgical approaches provide complete and comprehensive management of patients with coexisting temporomandibular joint conditions and dentofacial deformities.

Introduction

Patients with temporomandibular joint (TMJ) conditions and coexisting dentofacial deformities can have these conditions corrected with concomitant TMJ and orthognathic surgery (CTOS) in 1 surgical stage or separated into 2 surgical stages. The 2-stage approach requires the patient to undergo 2 separate operations (surgery to correct the TMJ condition and a second operation to perform the orthognathic surgery) and 2 general anesthetics, significantly lengthening the overall treatment time. Performing CTOS in a single operation significantly decreases treatment time and provides better outcomes but requires careful treatment planning and surgical proficiency in the 2 surgical areas. Some TMJ conditions require total joint prostheses for best results. The application of computer technology for TMJ and orthognathic surgical planning and implementation has significantly improved the accuracy and predictability of treatment outcomes.

This article presents the treatment planning and surgical protocol for the application of computer-assisted surgical simulation (CASS) for CTOS cases requiring TMJ reconstruction with patient-fitted total joint prostheses and orthognathic surgery. The CASS protocol decreases the preoperative workup time and increases the accuracy of model preparation and subsequent surgery.

Introduction

Patients with temporomandibular joint (TMJ) conditions and coexisting dentofacial deformities can have these conditions corrected with concomitant TMJ and orthognathic surgery (CTOS) in 1 surgical stage or separated into 2 surgical stages. The 2-stage approach requires the patient to undergo 2 separate operations (surgery to correct the TMJ condition and a second operation to perform the orthognathic surgery) and 2 general anesthetics, significantly lengthening the overall treatment time. Performing CTOS in a single operation significantly decreases treatment time and provides better outcomes but requires careful treatment planning and surgical proficiency in the 2 surgical areas. Some TMJ conditions require total joint prostheses for best results. The application of computer technology for TMJ and orthognathic surgical planning and implementation has significantly improved the accuracy and predictability of treatment outcomes.

This article presents the treatment planning and surgical protocol for the application of computer-assisted surgical simulation (CASS) for CTOS cases requiring TMJ reconstruction with patient-fitted total joint prostheses and orthognathic surgery. The CASS protocol decreases the preoperative workup time and increases the accuracy of model preparation and subsequent surgery.

Indications for concomitant temporomandibular joint and orthognathic surgery

TMJ disorders or conditions and dentofacial deformities commonly coexist. The TMJ condition may be the causative factor of the jaw deformity or develop as a result of the jaw deformity, or the 2 entities may develop independent of each other. The most common TMJ conditions that can adversely affect jaw position, occlusion, and orthognathic surgical outcome stability include (1) articular disc dislocation, (2) adolescent internal condylar resorption, (3) reactive arthritis, (4) condylar hyperplasia, (5) ankylosis, (6) congenital deformation or absence of the TMJ, (7) tumors; (8) connective tissue and autoimmune diseases, (9) trauma, and (10) other end-stage TMJ pathologies. These TMJ conditions can be associated with dentofacial deformities, malocclusion, TMJ pain, headaches, myofascial pain, TMJ and jaw functional impairment, ear symptoms, and sleep apnea. Patients with these conditions may benefit from corrective surgical intervention, including TMJ and orthognathic surgery. Some of the aforementioned TMJ conditions may have the best outcome prognosis using custom-fitted total joint prostheses for TMJ reconstruction.

Concomitant temporomandibular joint total joint replacement and orthognathic surgery

Treatment planning for concomitant TMJ total joint replacement and orthognathic surgery (C-TJR-OS) cases is based on cephalometric analysis, prediction tracing, clinical evaluation, and dental models, which provide the templates for movements of the upper and lower jaws to establish optimal treatment outcome in relation to function, facial harmony, occlusion, and oropharyngeal airway dimensions. For patients who require total joint prostheses, a medical-grade computed tomographic (CT) scan with 1-mm overlapping cuts is recommended for the maxillofacial region that includes the TMJs, maxilla, and mandible. The surgeon has 2 options for model preparation to aid in the construction of patient-fitted total joint prostheses using the TMJ Concepts System (Ventura, CA). We previously published the traditional protocol technique versus the CASS protocol. The CASS technique is also known as virtual surgical planning . This article presents only the CASS technique.

Protocol for concomitant temporomandibular joint and orthognathic surgery using computer-assisted surgical simulation

For CTOS cases, the orthognathic surgery is planned using CASS technology and moving the maxilla and mandible into their final position in a computer-simulated environment ( Fig. 1 ). Using the computer simulation, the antero-posterior and vertical positions, pitch, yaw, and roll are accurately finalized for the maxilla and mandible based on clinical evaluation, dental models, prediction tracing, and computer-simulation analysis.

Fig. 1
CASS. ( A C ) Simulated preoperative position of the maxilla and mandible. ( D F ) The maxilla and mandible in the simulated intermediate position, with the maxilla in its original position but mandible in its final position with the mandibular surgery performed first for fabrication of the intermediate splint ( red simulated splint ). ( G I ) The final position of maxilla and mandible, after counter-clockwise rotation-advancement of the mandible and segmented maxilla, for the production of a palatal splint.

Using Digital Imaging and Communications in Medicine data, the stereolithic model is produced with the maxilla and mandible in the final position and provided to the surgeon for removal of the condyle and recontouring of the lateral rami and fossae if indicated The stereolithic model is sent to TMJ Concepts for the design, blueprint, and wax-up of the prostheses. Using the Internet, the design is sent to the surgeon for approval. Then, the custom-fitted total joint prostheses are manufactured ( Fig. 2 ). It takes approximately 8 weeks to manufacture the total joint custom-fitted prostheses.

Fig. 2
Stereolithic model fabricated after simulated maxillary and mandibular advancement to the final position. Condylectomy and recontouring of the lateral rami and fossae were performed and prostheses manufactured. The basic design of the TMJ Concepts patient-fitted prosthesis is observed. The black arrow points to the mesh framework on the underside of the custom-fitted titanium shell that secures the polyethylene articulating portion of the fossa component. The yellow arrow points to the mesh on the superior surface of the fossa component that allows osseo-integration with the fossa bone. The red arrow points to the posterior stop of the fossa: a necessary component for mandibular advancement and stability. The green arrow shows the bony defect created from the counter-clockwise rotation of the posterior maxilla. These defects require bone or synthetic bone grafting for stability of the maxilla.

Approximately 2 weeks before surgery, final dental models are produced. If single piece maxillary and mandibular surgery without equilibration is planned, then only one set of models is required. Two sets of maxillary and mandibular models are required if the maxilla or mandible is to be segmented or dental equilibrations are required. One of the maxillary models is segmented if indicated, dental equilibration performed, and segments placed in the best occlusion fit with the mandibular dentition. The maxillary segments are then fixed to each other with glue, wax, or other means that the surgeon prefers. The dental models do not require mounting on an articulator. The 3 or 4 models (2 maxillary and 1 mandibular, or 2 mandibular models if equilibrations are done) are sent to Medical Modeling for scanning and simulation into the computer model. Because the author routinely performs the TMJ reconstruction and mandibular advancement with the TMJ Concepts total joint prosthesis first, the unsegmented maxillary model is simulated into the original maxillary position and the mandible is maintained in the final position. The intermediate splint is constructed (see Fig. 1 E; Fig. 3 A, B ). Then the segmented maxillary model is simulated into the computer model in its final position, with the maxilla and mandible placed into the best occlusal fit, and the palatal splint is fabricated (see Fig. 3 C). The dental models, splints, and images of the computer-simulated surgery are sent to the surgeon for implementation during surgery.

Fig. 3
( A , B ) Intermediate splint is printed from the CASS model with the mandible in the final position and maxilla in the original position. ( C ) Palatal splint constructed.

The protocol is as follows:

  • 1.

    CT scan of entire mandible, maxilla, and TMJs (1-mm overlapping cuts).

  • 2.

    Processing of Digital Imaging and Communications in Medicine data to create a computer model in CASS environment.

  • 3.

    Correction of dentofacial deformity, including final positioning of the maxilla and mandible, with computer-simulated surgery.

  • 4.

    Stereolithic model constructed with jaws in final position and sent to surgeon for condylectomy and rami and fossae recontouring if indicated.

  • 5.

    Model sent to TMJ Concepts for prostheses design, blueprint, and wax-up.

  • 6.

    Surgeon evaluation and approval using the Internet.

  • 7.

    TMJ prostheses manufactured and sent to hospital for surgical implantation.

  • 8.

    Two weeks before surgery, acquisition of final dental models (2 maxillary, 1 or 2 mandibular models if dental equilibrations are required); one maxillary model is segmented and models equilibrated if indicated to maximize the occlusal fit; models sent to the company performing the CASS planning.

  • 9.

    Models incorporated into computer-simulated surgery for construction of intermediate and final palatal splints.

  • 10.

    Models, splints, and printouts of computer-simulated surgery sent to surgeon.

Although dental model surgery is necessary only if the maxilla requires segmentation or equilibration, the models do not require mounting on an articulator. This process eliminates the time required to mount the models, prepare the model bases for model surgery, reposition the mandible, construct the intermediate occlusal splint, and make the final palatal splint. With CASS technology, the company performing the CASS planning manufactures the splints.

Surgical sequencing for concomitant temporomandibular joint total joint replacement and orthognathic surgery

  • 1.

    Condylectomy

  • 2.

    Coronoidectomy (if mandible significantly advanced or lengthened vertically)

  • 3.

    Detach the masseter and medial pterygoid muscles from ramus

  • 4.

    Modify rami and fossae if indicated from the stereolithic model preparation

  • 5.

    Mobilize mandible

  • 6.

    Maxillomandibular fixation with intermediate surgical splint

  • 7.

    Placement of total joint prostheses

  • 8.

    Bilateral TMJ fat grafts harvested from the abdomen or buttock

  • 9.

    Maxillary osteotomies and mobilization

  • 10.

    Turbinectomies, septoplasty, and others

  • 11.

    Maxillary segmentation and application of the palatal splint if indicated

  • 12.

    Maxillary rigid fixation and bone grafting

  • 13.

    Adjunctive procedures such as genioplasty, rhinoplasty, uvulopalatopharyngoplasty, facial augmentation

A potential risk to patients receiving TMJ total joint prosthesis is infection. The occurrence rate is less than 2% with greater risk for patients on immunosuppressant medications such rheumatoid patients or others with connective tissue/autoimmune diseases. Bacterial or viral contamination of the prosthesis can occur during surgery or develop at a later time from bacterial seeding through a hematologic route or localized bacterial sources. As a result, strict adherence to sterile technique for the procedures performed can help prevent or reduce the chance of infection.

The TMJ Concepts prostheses use design principles and materials that are proven highly successful and are the gold standard in orthopedic joint reconstruction for hip and knee replacements. The prosthesis consists of a fossa component with a commercially pure titanium framework covered with a mesh and an ultra–high-molecular-weight polyethylene functional component fused to the mesh on the bottom side of the framework. The fossa component is attached to the lateral rim of the fossa with four 2-mm-diameter screws. The mandibular component is composed of a titanium alloy shaft with a cobalt-chromium alloy head with the prosthesis secured to the mandibular ramus with 7 to 9 bicortical screws that are 2 mm in diameter. The fossa and mandibular components osseointegrate with the fossa and ramus, respectively.

Surgical procedure

Jan 23, 2017 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Computer-Assisted Surgical Simulation for Concomitant Temporomandibular Joint Custom-Fitted Total Joint Reconstruction and Orthognathic Surgery
Premium Wordpress Themes by UFO Themes