The equine periodontium as a continuously remodeling system: morphometrical analysis of cell proliferation

The hypsodont equine cheek tooth erupts continuously throughout life. Tooth eruption is inevitably associated with a remodeling of the periodontium. One major process of remodeling in the PDL is cell proliferation. The aim of this study was to detect cell proliferation at different sites of the equine PDL in order to examine the dynamics of the periodontal cell population.

Specimens from nine warm-blood horses were taken-- containing the PDL interposed between the cementum and the alveolar bone--at three designated levels: subgingival, middle, and apical. Cell proliferation was detected immunohistochemically by use of anti-Ki-67 in combination with an elaborate morphometrical procedure using an image-analysis program. Three zones of the PDL were distinguished in each specimen: a zone next to the dental cementum, a central zone, and a zone next to the alveolar bone. The PDL was divided into three levels and three zones, resulting in nine defined regions of interest.

The proliferation index was high at the apical level and in the zone next to the alveolar bone. The opposite was true of cell density, which was high at the subgingival level and in a zone next to the dental cementum.

Evaluation and statistical analysis of the parameters proliferation index and cell density in distinct, biologically appropriate sites of the equine PDL suggest the presence of dynamic processes like cell migration by which the cells of the PDL move from an area next to the alveolar bone towards the dental cementum, and in an apico-occlusal direction. Furthermore, our study confirms the close relationship between cell proliferation, cell migration, and eruption.