Differentiation of new odontoblasts and dentine bridge formation in rat molar teeth after tooth grinding

Abstract

The cusp tips of the molar teeth of the right side of the jaws of 58 male Sprague-Dawley rats were ground producing an area of damage in the pulp horn which corresponded to the area below the cut dentinal tubules. The rats were sacrificed at various time intervals after tooth grinding, the jaws with the teeth were fixed, decalcified and sectioned serially at 5 μ and stained with haematoxylin and eosin, Mallory's, Masson's and pa-S stains. The sequence of pulpal reactions such as displacement of odontoblastic nuclei, inflammatory responses and healing were found to correspond well with previous reports. Spindle-shaped cells believed to be new odontoblasts appeared in increasing numbers after 24 hr. Formation of a dentine bridge began below the area of necrosis at 48 hr with the appearance of separate Mallory positive areas which later apparently fused with the dentine projecting from the side walls. The first complete dentine bridge was found at 4 days after tooth grinding. The bridges became thicker and more regular later. At 8 days well-defined tubules could be seen. Sixteen rats were injected with tritiated thymidine ( 3H-TdR) at various time intervals after tooth grinding. At each time interval except one, two rats were sacrificed 1 hr after 3H-TdR injection. One rat at each time interval was allowed to live for 3 days after 3H-TdR injection. The jaws with the teeth were fixed, decalcified and sectioned serially at 5 μ. Autoradiographs were made from sections in the areas of pulpal damage and from sections of control teeth. The autoradiographs from the rats sacrificed 1 hour after 3H-TdR injection showed an increase in mitotic activity at 24 hr, 48 hr, and 4 days with the greatest increase at 48 hr. The rats injected with 3H-TdR at 24 and 48 hr after tooth grinding and sacrificed 3 days later, showed labelled cells among the new odontoblasts. It is postulated that the new odontoblasts responsible for dentine bridge formation and new dentine were derived from undifferentiated pulpal cells. The remaining original odontoblasts did not proliferate in the ground teeth or in the control teeth. Labelled cells which did not migrate to the odontoblastic layer might have been newly differentiated fibroblasts or other new cells taking part in the repair of the pulpal tissue.