A METHOD FOR MEASURING THE STRUCTURAL-PROPERTIES OF THE RAT MANDIBLE

The rat mandible has been used to study fractures, ridge augmentation, bone defects, and the effects of cryosurgery, all of which affect the structural properties of the mandible. The only previously described mechanical test of the rat mandible used three-point bending with a pi ece of foam placed between the lingual surface of the mandible and the support. The accuracy and reproducibility of this test were not deter mined. Two different, three-point bending tests for characterizing the structural properties of the rat mandible have now been evaluated. Ac rylic specimens representing three different-sized mandibles were test ed in three-point bending with either potted ends or foam interposed b etween the specimen and the outer load points. Flexural stiffness and failure load were compared against data from a conventional three-poin t bending test. In addition; five paired halves of 90- and 210-day-old rat mandibles were tested either with interposed foam or with potted ends and the mean coefficients of variation of the stiffness and failu re loads were determined. Failure loads of the acrylic specimens with the potted and foam methods were significantly higher (50 and 10%, res pectively; p < 0.05) than with the conventional method. The stiffness of the acrylic specimens with the potted and foam methods was signific antly different (75% higher and 21% lower, respectively; p < 0.05) tha n with the conventional test. In addition, there was no difference bet ween the coefficient of variation in stiffness (26 + 11%) or failure l oad (10 + 4%) measured with the foam test and the comparable values (1 6 + 11%) and (18 + 13%) in the potted test. Thus it appears that the f oam test more accurately reflects the stiffness and failure load of th e acrylic specimens than the potted test. Although there was no differ ence in the coefficients of variation in the potted and foam tests, th e technical difficulties associated with potting indicate that the foa m test is a better method for testing the structural properties of the rat mandible. The objective of this experiment was to establish a met hod for accurately measuring the structural properties of the rat mand ible and for detecting differences in structural properties between di fferent treatment groups.