Masticatory Stresses in Normal and Modified Occlusion

U SING a simple electrical recording device, Anderson and Picton' showed, during unilateral chewing of various foods, that the teeth on the empty side of the mouth frequently came into contact. Previous experiments by Anderson2 had established values for the loads transmitted by a tooth on which food was being chewed, and the first of the series of experiments to be reported here was designed to enable a comparison to be made between the loads on the chewing and empty sides of the mouth. Such measurements were made with the object of estimating the load distribution over the whole dental arch. If whole-arch contact and even distribution of load were normal features of masticatory behavior, then, from a purely mechanical standpoint, reduction of the loadbearing area to one or two teeth with the same total over-all load should greatly increase the pressure on the supporting tissues of the contacting teeth. Such a situation might occur if teeth were lost or came into premature contact due to misplacement, and could be described as potentially traumatic occlusion. A. concept of this nature would ignore the possibility of some force-regulating mechanism depending on contact or pressure receptors within the supporting tissues of the teeth and jaws. In addition to recording the loads on the chewing and empty sides of the mouth, comparisons were also made between the loads recorded on the normal tooth and those recorded when the strain-gauge unit and occlusal surface of this tooth were raised by approximately 0.5 mm. above the general occlusal level. In a third group of experiments, a comparison was made between the loads on the normal tooth and those recorded with the strain-gauge unit, out of occlusion by 0.5 mm. This series was designed to mimic the loading experience of a tooth out of occlusion. The results of the 3 groups of experiments can be summarized as follows: (1) there is a great similarity between the loads on the chewing and empty sides of the mouth, (2) when the recording oeelusal surface was elevated, the loads taken by the tooth appear in some cases to be increased above the normal, although not to the extent to be expected from a simple physical system, and (3) when the recording surface was lowered, the records were markedly changed both qualitatively and quantitatively.