OBJECTIVETo analyze the influence of four types (class II long elastic, class II short elastic, class III long elastic, class III short elastic) of inter-arch elastics on the stress distribution and displacement of temporomandibular joint (TMJ).

METHODSTo reconstruct a three-dimensional element model of left craniofacial bones with TMJ, maxilla, mandible and dentition with MBT straight wire appliance by CT images, Mimics, Ansys software. The influence of four types elastic on the model was analyzed by simulating the clinical conditions.

RESULTSThe stress distribution and displacement of TMJ under four types of elastics have been acquired. The stress distributed rule of condition 1 and 2 was similar, compression stress centred on the frontal surface of the condyle, while stretching stress centred on the posterior surface. The stress distributed rule of condition 3 and 4 was similar too, the frontal surface of the condyle was most stretching stress, while posterior surface was most compression stress. The displacement of the condyle of condition 1 and 2 was overall forward and downward with a clockwise rotation, the displacement of the condyle of condition 3 and 4 was overall backward and upward with a anticlockwise rotation.

CONCLUSIONClass II long elastic and short elastic, class III long elastic and short elastic, the stress distributed rule was similar, the strength under short elastics was gentle under the same strength value. Overall displacement was downward and forward under class II elastics, the condyloid made a clockwise rotation. Overall displacement was upward and backward under class III elastics, the condyloid made a counterclockwise rotation.