[Response of exposed pulp to capping agents in germ-free rat molars].

The response of the dental pulp to calcium hydroxide or zinc oxide and eugenol cement was investigated histopathologically, using the germ-free and conventional rats. The upper first molar pulp was exposed with a p1/2 round bur through the mesial surface of the teeth and covered with the capping agents. The observation period was 1, 2, 4, 7, 10, 14 and 28 days postoperatively. The results obtained were as follows: 1) In the conventional rats, severe inflammation of the pulp was observed as the result of bacterial contamination throughout the observation period. The response of the pulp itself to the capping agents could not be assessed exactly. 2) In the germ-free rat pulp covered with calcium hydroxide, the inflammation was slight and a higher calcified tubular dentin bridge was observed 28 days postoperatively. 3) In the germ-free rat pulp covered with zinc oxide and eugenol cement, the inflammation was moderate and a relatively poorly calcified dentin bridge without the dentinal tubules was observed 28 days postoperatively. 4) In the germ-free rat whose pulp was left open to the oral environment, the response of the pulp was the mildest of all the experimental groups. The calcification of the dentin bridge of this group was slightly higher than that of the pulp capped with zinc oxide and eugenol cement 28 days postoperatively. 5) The presence of the dentin chips weakened the response of the pulp tissue to the agent, but the formation of the dentin bridge was delayed.