Three-dimensional Virtual Planning of Total Temporomandibular Joint Replacement Using Standardized Prosthesis.

Aim and objectives

The aim of the present study was to evaluate the possibility to perform patient specific treatment planning with the use of standardized total TMJ prosthesis on previously performed treatment with total TMJ replacement and occlusal adjustment due to a severe malocclusion. The objectives were surgical feasibility of virtual planning on standardized TMJ prosthesis measuring virtual possible maximal interface (mm2) between prosthesis and bone, possible maximal number of fixation screws and possibility to centre the mandibular part in the fossa part. The outcome measures were surgical movements to correct a severe malocclusion using standardized TMJ prosthesis.

Survey of the field

A total replacement of the temporomandibular joint (TMJ) has been successfully offered to patients with severe joint disease since more than three decades. In the early years, the surgical technique has been judged as complex and similar to other joint prosthesis the TMJ prosthesis has been burdened with some risk of complications. With emerging technologies, within computer science, biomedical design, and biocompatible materials the treatment option has been possible to use in a wider perspective. Thus, a broader patient spectrum has been possible to rehabilitate with TMJ prosthesis. Today, not only joint-related pathologic conditions are offered joint reconstruction, but also congenital deformities like Hemifacial Microsomia and Dentofacial deformities. Furthermore, the advancement of the treatment quality has enabled patients with severe joint-pathology, like Juvenile Idiopathic Arthrosis with a subsequent severe malocclusion and facial deformity, to have a total rehabilitation with both normalization of the joint function together with improved facial appearance and bite function.

However, in many of these severe cases the corrections of the facial structures simultaneously with a joint replacement provides the surgeon with a complex treatment-planning phase. Frequently, the movements need to be planned and simulated virtually to evaluate both the best positioning of segments and joint components and to manufacture surgical indexes and cutting templates. The invention of patient specific solutions (PSI) have made hardware design based on 3D radiological imaging and soft tissue predictions possible. Patient specific total TMJ prosthesis provided the surgeon with virtual planning, cutting guides, occlusal splints and well-fitted alloplastic TMJ components. However, this came with additional costs and the advantage of customized prosthesis over standardized have been debated. Attempts have been made to retrospectively compare customized with standard prosthesis, but this fare no prospective or RCT have been published. Presently, this lack of prospective comparisons leaves the evaluation with only retrospective and observational comparisons. This results in a risk of bias because of a difference in treatment indication between the compared treatment modalities. Thus, the outcome from a retrospective comparison will be coloured by a selection bias with the indication for treatment as a confounding factor.