The Effect of X-Ray Irradiation on the Teeth and Supporting Structures of the Mouse

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Abstract
Young mice of strain C57 black and Swiss were exposed to dosages of 5000, 3000 and 1500 r of X-radiation in the area between the external auditory meatus and the lower border of the mandible. A contact type X-ray machine was used under the following constant conditions: K.V. 50, M.A. 2, T.S.D. 20 mm. with 0 filter. The quality of radiation is relatively soft, hence the intensity diminishes greatly with the depth of the tissue. This means that the side of the animal farthest from the radiation source receives a relatively small dose. Following irradiation the mice which survived were sacrificed at varying time intervals (5 days to 6 mos.). Littermate controls were also sacrificed to coincide with these time intervals. All heads were decalcified, embedded in paraffin, sectioned serially in either a frontal or sagittal plane and stained with hematoxylin and eosin. Those animals which were irradiated (5000 r) over a small area at the apex of the incisor tooth exhibited developmental abnormalities such as spiked, malformed, or hypoplastic incisors, or failure of the incisors to erupt. With dosages of 5000 r the cells in the ameloblastic layer may appear as low cuboidal or squamous type cells and there is a cessation of histodifferentiation of new ameloblasts. Fifteen hundred to 3000 r produced less marked changes. Dosages of 1500 to 5000 r severely damage the odonto- blastic layer. Surviving odontoblasts resemble osteoblasts in function and form an irregular amorphous acidophilic staining substance (osteodentine). Odontoblasts are more radiosensitive than ameloblasts. There is a retardation or cessation of root formation following exposure to 1500 to 5000 r, while develop-ment of the coronal dentine is only slightly altered. The late post-irradiation changes include atrophy and fibrosis of the pulp and ankylosis of the roots to the alveolar bone.
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