The Indirect Effect of X-Ray Irradiation on the Dental Pulp of the Dog

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Abstract
Circulatory disturbances, in-creased formation of collagen around blood vessels (sometimes of radiant structure), fibrous metaplasia of pulp appeared in the roots in teeth where the crowns were exposed to fractionated irradiation (3000 to 19,500 r in 52 to 79 days, generated by 170 kv), but the roots were protected by means of lead shields. Since it was found that the dose received by the root as secondary radiation was very small, only 0.8% of the dose received by the crown, it was suggested that the lesions in the root may depend on the indirect effect of X-rays due to the formation of so-called H substances or leukotoxins in the irradiated pulp of the crown. An unsuccessful attempt was made to produce changes in the crown pulp by means of irradiation of the dentin wall only, while the pulp itself was protected by platinum shields. Since the normal odontoblasts were observed in spite of irradiation by doses of more than 6,900 r., it was assumed that mature odontoblasts belong to some of the most highly radioresistant cells of the body.