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In orthodontic treatment, extraction of premolars is needed to achieve the proper treatment goals. However, it remains unknown how occlusion without the first premolars affects human jaw biomechanics during function. This study aimed to simulate the effect of premolar-loss on dynamic interaction between muscle force, occlusal and temporomandibular joint (TMJ) loads during biting by means of a dynamic modeling of the human jaw. The TMJ load related to the slight rotatory jaw displacement during biting. The 8.5% heavier TMJ load was determined for the model without the premolars as compared to that for normal model. The greater load derived from the relative anterior location of the posterior teeth in the premolar extraction model. Reduction of anterior temporalis muscle activation prevented the 8.5% increase in the joint loading. It can be concluded that the model allows us to document analytically the effect of changes in a key occlusal variable (premolar-loss) on the biomechanics of the human jaw.