Dynamics of Repair in the Pulp

¹ Institutes of Physiology and Dentistry, University of Turku, Turku, Finland, and Institute of Dentistry, University of Helsinki, Helsinki, Finland

Three experimental series were carried out in rats to observe the reactions in the dental pulp during a 1-month period after pulp exposure or diathermy, or both, in the mandibular incisor or in the maxillary first molar.

In the first series, the pulp of the incisor was exposed at the level of the second molar by using a round bur, diameter 0.6 mm. Thermal irritation was produced by applying surgical diathermy to the exposed pulp. The exposed pulp was then covered with sterile bone wax. The mandibles were removed after varying periods, and serial sections were prepared. The stained sections initially showed hemorrhages in the trauma region and heavy cellular infiltration around the site of perforation and in the incisal part of the pulp. There was widespread formation of denticles containing osteodentin or predentin, or both, and dentin. These deposits had a diameter of 1,800 to 2,000 µ after 14 days.

In the second series, the circulation in the dental pulp was observed in vivo. Trauma was produced as in the first series and in additional pulps by applying surgical diathermy to exposed dentin. The most widespread damage was complete thrombosis incisally from the site of exposure. The pulp remained vital apically from the trauma site. The vascular reactions were restricted to a few thrombosed vessels when only diathermy was used. Mineralized deposits and secondary dentin were regularly found in the dental pulp within 1 week after traumatization.

The third series was carried out in the first maxillary molar. These experiments were made in young rats (30 to 40 days old) in which the apex remained open and in older rats (2 months old or more) in which root formation was completed. In both groups, cavities were prepared in the mesial fissure and the dentin exposed to diathermy at 40 ma. for 2 to 3 seconds. The cavities were sealed with ZnO-eugenol. The teeth were sectioned and examined histologically. Necrosis of the dental pulp occurred, especially in the group where the apex formation was completed. The cellular and vascular reactions in the other group diminished near the end of the observation period.

It is concluded that repair in the dental pulp was greatly promoted by unrestricted metabolism during uncompleted root formation.