Topographic Analysis of the TMJ Mandibular Fossa using MicroCT Imaging

The morphological characteristics of the Mandibular Fossa, the temporal component of the temporomandibular joint (TMJ), have been described using methods with several limitations. For instance, the inclination of the Mandibular Fossa (MF) towards its anterior eminence has been measured using lateral cephalometric radio‐graphs. This approach not only compromises the real anatomy of the MF by tilting the patient's head to avoid superimposed left and right images. But also classifies a complex three‐dimensional shape using a single two‐dimensional radio‐graphic projection. Furthermore, the overall thickness distribution of articular cartilage coating the MF is unknown. The aim of this study is to generate the first objective method to describe the topology of the MF and its overall articular cartilage distribution. Six bisected heads (4 males and 2 females; age 73: ± 11.76 years) were dissected in order to expose the left and right mandibular fossae and the occipital condyles. The articular cartilage of the MF was preserved while half of the condylar cartilage was removed. The subjects were then stained 48 hours prior being micro CT scanned. The RAW data was reconstructed and the occipital condyle used for the calculation of the threshold values for the segmentation of bone and cartilage. The distance between bone/cartilage and the Frankfort Horizontal plane was calculated. The data generated two topographic images used to locate the deepest point of the MF, the highest point of the anterior eminence and any substantial change in the morphology. Finally, an image of the overall distribution of cartilage thickness was obtained by subtracting the values of bone out of the topographic image of cartilage. The analysis of bone and cartilage showed that the highest point, determined as the point in the corresponding mesh located farther away from the Frankfort plane, is located 100% (n=12) of the times in the anterolateral quadrant of the MF. In contrast, the lowest point is located 100% (n=12) of the times in the posteromedial quadrant. The contour analysis on the bone showed that the anterior eminence has an antero‐posterior groove roughly located at the level of the middle line in 83.34 % of the specimens (n=10). The thickness of the cartilage showed two areas of increased value. One lined parallel to the junction between the fossa and the anterior eminence the other above the before mentioned bony groove. The fact that the internal topography of the MF presents a cross shaped structure may explain the causes of instability among total joint replacement patients and play an important role when studying condyle rotation and anterior translation. The areas of thickening correlate with previous research that has identified the areas where functional bio‐mechanical loads are the strongest. Our results demonstrate the biological response of the articular cartilage to these compressing forces. Both findings can improve the way total joint prosthesis are being manufactured and contribute with the future of TMJ bio‐engineering systems. Support or Funding Information Senescyt (Secretaria Nacional de Educación Superior Ciencia, Tecnología e Innovación)3D Representation of the isosurface of bone (Light Brown) and the articular cartilage (Light Blue) The thickness of the cartilage can be better represented using topographic images.Topographic analysis of the bone structure of the (GF) The colours indicate the difference between distance of the Frankfort plane and the surface of the articular surface of the bone. The deepest point is opposite to the highest elevation. Also there is a grove in the middle of the joint where the Mandibular Condyle moves anteriorly.Difference between bone and articular cartilage. The color map indicates the measurements in a scale from 0 to 256. The resolution of the image is 154 μm.