Finite Elemental Analysis of the displaced disc in TMJ.

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Internal derangement of the temporomandibular joint(TMJ) means a malposition of the articular disc relative to the condyle and articular eminence. With the development of arthrography and,subsequently ,arthrotomography of the TMJ, it has been established that anterior disc displacement is related to joint clicking and locking. Since then, a lot of researches have been done using arthrographic technique to establish an actual image of disc position and configuration.Disc deformation at the jaw closing position has been described as reversed biconcave, biplanar, or biconvex. Nevertheless, Disc configuration at the maximal jaw opening position has not yet been reported. Now, magnetic resonance imaging(MRI) has easily revealed disc position in the patients with internal derangement of TMJ. But MRI can not reveal disc configuration. The aim of this study was to produce 3-dimensional images of permanent displaced disc of TMJ for study of disc configuration at the jaw opening position. Matria … More ls and methods: 116 simultaneous multisectional arthrotomograms at the maximal jaw opening position were taken from 100 patients with permanent disc displacement of TMJ. A leaden marker for a reference point was put on the film cassette which involved five films. Prior to digitizing, the reference point and the contours of the following structures of each film were traced on transparent paper: external auditorycanal, glenoid fossa, articular eminence, the inferior border of the dye in the upper compartment, the superior border of the dye in the lower compartment, and condyle. Subsequently, the reference point and contours of the joint structures were digitized with the tablet cursor. Three-dimensional reconstruction was performed by the software package COSMOZONE -2S(Nikon Co.). The inferior border of the dye in the upper compartment(blue) and the superiorborder of the dye in the lower compartment(orange) means the upper and lowerborder of disc, respectively. All assessments were performed by the sameobserver. Result:On all of the joints, disc configuration was deformed at the maximal jaw opening position. Four types of disc deformity were discerned:1) folding disc configuration,2) twisted disc configuration , 3) compressed disc configuration, 4) combination disc configuration Discussion: This results may give us a hint about why some reducing disc displacement change in to permanent disc displacement. The use of three-dimensional disc images may improve the diagnostic value of conventional arthrotomogram at no additional risk to the patients and may provide new insights into the complex deformities of disc in the patients with internal derangement of TMJ. Less