Healing of Pinpoint Exposure of Rat Incisor Pulp under Various Capping Agents

¹ Department of Histology and Embryology, School of Medicine, Warsaw, Poland

Both the drugs applied for pulp-capping and the experimental models used for testing their effectiveness are far from being ideal. In the choice of such a model, attention was directed to the constantly growing incisors of rodents, the pulp of which possesses the ability of permanent production of new dentin layers. This phenomenon may be compared to the production of secondary dentin in caries, with, of course, the necessary reservations as to this analogy. The new theory of bone and dentin formation and modern methods used in preparation of tissues to be transplanted have been taken into consideration when choosing the substances investigated for their usefulness in pulp-capping.

In 151 rats the mandible bone above the foramen mentale was exposed under sodium pentabarbital anesthesia, and then access to the incisor was obtained via the bone. A cavity of 0.5 mm. in diameter was drilled deep enough to leave a thin dentin layer in its floor to make possible wounding of the pulp and gentle obtention of a pinpoint exposure by means of a fine root-canal reamer. After the bleeding had been stopped, pulp-capping was performed.

For pulp-capping the following substances were used: sterilized animal charcoal, temporary cement, calcium hydroxide, "Provipast," "Reogan," zinc oxide-eugenol paste, fresh chips of rat dentin, lyophilized sterilized chips of rat and human dentin, sterilized chips of rat enamel, collagen, chondroitin sulfate, and sodium hyaluronate. In some cases the exposed pulp was left without dressing. To examine the course of pulp healing autoradiographically ³H-glycine was administered to two rats.

In the light of the present experiments rat incisors proved to be a very sensitive experimental test model. This was confirmed both by autoradiographic and classical histologic methods. The use of the experimental model described makes possible a correct assessment of the effectiveness of the substances under investigation on the exposed pulp within 10 days after applying the dressing.

Best results were obtained after capping the exposed pulp with lyophilized sterilized dentin chips. Collagen was also found to be suitable for direct pulp-capping. It seems that the introduction of lyophilization, new methods of sterilization, and storage in sealed ampules might permit a wide use of dentin chips for direct pulp-capping.