Odontoblasts in Equine Hypsodont Teeth-How They Cope with Permanent Occlusal Wear

Horses' hypsodont (high-crowned) teeth face permanent dental wear. This is compensated for by a continuous eruption, which requires a high adaptability of odontoblasts; otherwise, the dental pulp would be exposed. Here, we report on how equine odontoblasts respond to the challenge of maintaining a high production rate of dentin. We analyzed CD90, a marker of odontoblastic differentiation, and nestin, a marker of mature odontoblasts, in equine pulpal tissue via immunofluorescence. For comparison, we examined the hypselodont (ever-growing) incisors and brachydont (short-crowned) molars of rats. Immunofluorescence and Western blot analysis of pulpal tissue revealed a higher content of CD90-positive cells in hypsodont equine teeth than in brachydont and hypselodont rat teeth. The odontoblastic layer of hypsodont teeth was positive for CD90 (marker for differentiating odontoblasts), which was not the case for brachydont and hypselodont rat teeth. Most samples of hypsodont teeth were negative for nestin, whereas in hypselodont and brachydont teeth, odontoblasts were positive for nestin (marker for mature odontoblasts). Our findings suggest that there is a constant replacement of odontoblasts in the equine dentition, enabling a continuous high production rate of dentin. These results contradict the idea of lifelong vital, postmitotic and productive odontoblasts.