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To the Editor.—
In citing the work of Dr Ruben Eisenstein and associates in a MEDICAL NEWS article (232:14, 1975), it was stated that the small protease inhibitors that decrease the growth of immature fibroblasts and endothelial cells "may be extracellular, since they are also present in dentin, which is an acellular tissue." This statement is perhaps misleading because dentin, although not containing the bodies of cells, is very rich in the long cytoplasmic processes of the odontoblasts whose bodies are located in the subjacent pulp of the tooth. Thus, the presence of protease inhibitors in dentin does not necessarily mean that they are located extracellularly. They might have arisen in the odontoblasts and entered the dentin within their processes (Tomes fibers).Even experimental modification of dentin would not necessarily indicate an extracellular location of these protease inhibitors. Finding them in endodontically treated ("root canal") teeth would merely suggest that
Lorber M. Dentin: Not a Pure Extracellular Tissue. JAMA. 1975;233(10):1049. doi:10.1001/jama.1975.03260100019010