Proliferation of Cell Types in Rat Incisors Responding to Injury

BACKGROUND:

Recently, the focus of tooth regeneration studies have been on molecules involved in cell fate determination, cell adhesion, cell-cell communication, and cytoskeletal organization. However, little is known about which cell phenotypes are involved in the tooth regeneration process.

Rats have the remarkable ability to regenerate their incisors one week following injury. By understanding the cells involved in this process, we can gain new information on tooth growth that could be potentially used clinically for human teeth.

OBJECTIVES:

To provide an increased understanding of tooth regeneration in the rodent tooth. Researching new information on the roles of different cell types during rapid tooth reparation following injury will potentially provide us with new approaches to tooth repair.

METHODS:

Rats were injected with a cell division marker, BrdU, intraperitoneally at t=0. Right maxillary incisors of rats were injured, and left uninjured incisors were controls. Teeth were injured at different time points after injection of BrdU (t=0, t=3, t=6, t=12, t=18, t=21 hours). Pulps were dissected out, frozen, and sectioned. Immunohistochemistry was performed against several potential populations of dividing cells (CD 31,34,44, and 45) and slides were visualized using confocal microscopy.

RESULTS:

There were significant increases in dividing cells expressing rPH (a commonly used fibroblast marker) 3-6 hours following tooth injury, which continued to divide up to 21 hours post injury.

Surprizingly, there was no significant increase in BrdU labeled rpH cells in any portion of the pulp.

Preliminary results indicate that the BrdU positive cells following injury have minimal colocalization with CD 31, 34, 44, or 45.

CONCLUSIONS:

Following rat incisor injury, there are significant increases in cell division in rat pulp. Contrast to what was previously thought, this increase in cell division was not found to be in fibroblast cells. We suggest this cell type to be a progenitor cell.