Objective: Studying the physiological function of proximal contacts between teeth from the biomechanical point of view to get a better understanding of the stress distribution of crown under mastication forces. Methods: The subject used in this experiment was an adult cranium specimen including both maxillae and mandible with intact dentition, normal overjet, overbite, occlusion and compact contact relationship between teeth. A piece of 1X1 resistance stain foil was cemented on each of the crowns after processing of the specimen. Vertical load of 20kg was applied between the upper and lower dentitions under central occlusion and stress values of the crowns were measured by YJD-17 resistance strain gage. Three groups were involved in the study: intact dentition group (ID); dentition with missing first molars (DMM) and dentition with missing right mandibular first molar, lateral incisor and central incisor (DMMI). Results: The stress value (Gpa) of the ID group were as follows£ºsecond molars, 3.4641£» second bicuspids, 0.5132; cuspids, 1.0264; and all the others were zero. Those of the DMM group were£ºsecond molars, 5.003; second bicuspids, 1.4113; and the rest were the same as the ID group. For the DMMI group: the second molars, 5.2603; the second bicuspids, 1.6679; the cuspids, 3.2075; the first bicuspid, 0. Conclusions: Good proximal contact relations preserved in intact dentition can quickly distribute the force subjected to it thus the stress of the crowns can be very small even zero. The last tooth in a dentition sustained higher stress than any other teeth in the same dentition due to its lacking of distal adjacent tooth. Also those of the cuspids locating at the coner of the dentition is considerably higher. In partially edentulous dentition, the stress of those adjacent to the edentulous area increased under the same loading condition.

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