Temporomandibular joint (TMJ) reconstruction with a TMJ Concepts total joint prosthesis (TMJ Concepts, Ventura, USA) requires a precise 3D model of the jaws in centric occlusion. The authors present a virtual procedure for repositioning the lower jaw in centric occlusion to obtain a precise stereolithographic model for TMJ reconstruction using a custom-made total joint prosthesis in a case of TMJ ankylosis and anterior open bite.
Ankylosis of the temporomandibular joint (TMJ) is caused by the presence of a fibrous or bony unit between joint components. Patients with severe internal derangements and cortical irregularities may benefit from a TMJ reconstruction with a total joint prosthesis .
For good long-term prognosis following reconstruction with a custom-made total joint prosthesis, a precise model of the patient’s jaws and joints in centric occlusion is necessary. This is challenging when TMJ ankylosis occurs with an anterior open bite and the clinical outcome depends critically on accurate preoperative planning. The integration of virtual procedures into reconstruction with custom-made implants has enabled increased consideration of individual anatomic parameters .
A 58-year-old woman with a fibrous TMJ ankylosis of the right joint, 2 years after condylar trauma, was referred with an anterior open bite of about 3 mm and severe limitation of mandible movements. Initial treatment included closed reduction and maxillo-mandibular fixation. Computed tomography (CT) showed a severely deformed and displaced right condyle in a ventral position ( Fig. 1 ). The proposed treatment involved resection of the deformed right condyle and reconstruction with a total joint prosthesis.
To obtain an accurate anatomic model using rapid prototyping technology for construction of a custom-made total joint prosthesis, the precise position of the mandible in the best interocclusal relationship to the maxilla had to be determined. Alginate impressions were taken to produce plaster models. Gum slips made from poly-methyl-methacrylate (PMMA) with gutta-percha markers were constructed on plaster models as referencing devices for the maxilla and the mandible.
A cone beam CT (CBCT) scan (scanner: NewTom VGi-MF, Verona, Italy; resolution: 0.30 mm cubic isometric voxel) of the plaster models with the gum slips, which were fitted in the maximum intercuspidation, was performed ( Fig. 2 ). A high resolution CT scan (scanner: SOMATOM Sensation 10, Siemens, Erlangen, Germany) of the patient wearing the gum slips was carried out. Axial slices were reconstructed with 0.75 mm slice width and 0.6 mm increment. The image data were imported to a workstation in Digital Imaging and Communications in Medicine (DICOM) format ( Fig. 2 ).
Preoperative virtual planning was performed on a PC with the VoXim software (IVS Solutions, Chemnitz, Germany). The skull and the maxilla and mandible were segmented; each segment with its markers.
The dataset of the plaster scan was matched with the patient’s dataset employing a point-matching procedure using the gutta-percha markers of the maxilla gum slip with an accuracy of 0.15 mm. The gutta-percha markers of the mandible gum slip set the target position of the mandible. The segmented mandible was moved to its target position by point-matching, using the gutta-percha markers of the mandible ( Fig. 3 ).