Microscopic Observations on Living Dental Pulp II. The Effect of Thermal Irritants on the Circulation of the Pulp in the Lower Rat Incisor

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Abstract
In this paper, microscopic observation on the influence of thermal irritants on the circulation of the lower incisor pulp in the living rat are described. Notice was taken of the vascular reactions in the pulp, unexposed and exposed. To induce thermal irritation, the temperature of the Ringer-gelatine solution used to keep the pulp moist was altered for a certain length of time. As to the irritation caused by cold it was noted that when the temperature of the perfusing solution decreased from 37° to 31° C or even lower the speed of the blood flow was slowing down. Return to the original 37° C restored the circulation to normal. In some cases hyperemia occurred. In cases frozen with carbon dioxide or ethyl chloride the changes were irreversible and resulted in thrombosis. The irritation caused by heat (39°–42° C) led to a clearly perceptible increase in the rapidly of the blood flow. Rapid staining of the pulp tissue developed 42° – 44° C in vitally stained cases. Stases and thromboses leading to arrest of the circulation appreared in the exposed pulp at 46° – 50° C and in the unexposed pulp at 46° – 60° C, the duration of the thermal irritation being 30 seconds. When the temperature rise lasted for 2 minutes the changes leading to arrest of circulation developed in the unexposed pulp at 46° C.