The purpose of this study was to observe the pathological changes in the exposed pulp in the germ-free Wistar rats compared with those in the conventional rats.
Pulp tissues of the rats were exposed with No. 19 carborundum point or No. 1/2 round bur and the exposures were left unsealed. In order to study the growth of the newly produced calcified tissues, the rats were injected intraperitoneally every 5 days with an aqueous solution of lead disodium ethylene diamine tetraacetate. The animals were sacrificed at 14 and 28 days after the pulp exposure.
The results obtained were as follows:
1. In the pulp tissues of the conventional rats, a high percentage of extensive necrosis and inflammatory cell infiltration was observed and even periapical abscess was recognized frequently. Dentine bridge formation was not seen.
2. In the pulp tissues of the germ-free rats, although odontoblast disturbance, proliferation of fibroblasts and slight infiltration of the inflammatory cells were observed, dentine bridge formation occurred in 30 per cent of the teeth in 14 days and 57 per cent in 28 days after the pulp exposure.
The lead lines by the time-marking method, however, were not clearly seen in the dentine bridge.
3. Pulp tissues exposed with a round bur were more damaged than those exposed with a carborundum point in both the conventional and germ-free rats.
4. There was no apparent difference between the histologic changes of the injured pulp tissues in the 8 to 11-week-old germ-free rats and those in the 29-week-old rats.
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