The effects produced by 1200 R of x-radiation on growing bone, cartilage and dentine in the mandible have been studied in albino rats.
Foreshortening of the irradiated mandibles was apparent within seven days. There was some indication that the most severe effects resulted when the radiation was administered in a single dose but statistical analysis failed to show any significant differences between the three dose/time patterns used (l x 1200 R, 2 x 600 R and 4 x 300 R ).
The femurs, which were protected during irradiation, were also examined. There were no statistically significant dimensional differences between them, and histologically they were all structurally normal. There was no evidence that irradiation of the pituitary gland had caused any impediment to the growth of bone.
Qualitative changes occurred in the dentine. In the more mature portions of the incisors, the dentine which formed following irradiation was hypomineralized. In the less mature regions, the changes included the formation of a niche, degeneration of odontoblasts, differentiation of adjacent pulpal cells into osteoblasts and the formation of a coarse osteodentine. These changes were marked whether the radiation was administered in one, two or four doses.
In the irradiated mandibular condyles the haemopoietic marrow was replaced by fibrous tissue. Differentiation of osteoblasts was temporarily impeded and as a result ossification close to the cartilage was reduced. Isolated functional chondrocytes were identified in the metaphysis.
The findings of this study are :
(1) 1200 R of x-radiation produces severe dimensional and qualitative changes in the hard tissues of the mandible.
(2) Fractionation of the total dose into 2 x 600 R and 4 X 300 R treatments does not significantly reduce the deleterious effect which the single large dose has on the growing bone, cartilage and dentine.
(3) Inclusion of the pituitary gland within the field does not result in any noticeable changes in the protected bones.
(4) The effects in the mandible result from the direct irradiation of that bone.