In vivo bone strain in the mandible of Galago crassicaudatus

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Abstract
Single element foil strain gages were bonded to mandibular cortical bone in 8 specimens of G. crassicaudatus. The gage was bonded below the Pm4 [4th premolar] or M2 [2nd molar] adjacent to the lower border of the mandible. The bonded strain gage was connected to form 1 arm of a Wheatstone bridge. Following recovery from the general anesthetic, the restrained animal bit either a piece of wood, a food object or a bite force transducer. During these biting episodes, mandibular bone strain deformed the strain gage and the resulting change in electrical resistance of the gage caused voltage changes across the Wheatstone bridge. These changes, directly proportional to the amount of bone strain along the gage site, were recorded by a strip chart recorder. Bone strain was measured on both the working and balancing sides of the jaws. Maximum values of bone strain and bite force were 435 microstrain (compression) and 8.2 kg, respectively. During bending of the mandible, the correlation between bone strain (tension or compression) and bite force ranged from -0.893 (tension) to 0.997 (compression). Only a small percentage of the Galago bite force is apparently due to balancing side muscle force during isometric unilateral molar biting. The Galago mandible is bent in a predictable manner during biting. The amount of apparent mandibular bone strain is dependent on the magnitude of the bite force and the position of the bite point.