Effect of occlusion on mechanical stress of the TMJ

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To determine whether the changes of occlusion due to the loss of the posterior teeth cause functional overloading of the teeth and the temporomandibular joints, which has been implicated in periodontal diseases and temporomandibular disorders, we investigated the influences of SDA (shortened dental arch) on occlusal and joint loads. Bite forces and masticatory muscles' electromyograms were recorded in five dentate subjects who clenched maximally on intra-oral appliances creating symmetrical SDAs experimentally. Muscular forces estimated from the recorded electromyograms were fed into a finite element jaw model calculating bite forces and joint loads. Comparison between the measured and the calculated bite forces assured that the joint loads were representative. The bite force on each tooth increased with missing molar occlusions while joint loads decreased. The bite force per root surface area was always greatest on the most posterior tooth, and these values were most constant. The findings provide no evidence suggesting that SDA causes overloading of the joints and the teeth