rogress has also been made with the inner tooth structure - the dentin and pulp. Decay that destroys the tough enamel covering of the tooth can also progress into the deeper dentin layer and even into the pulp. The dental pulp is the innermost structure of the tooth, consisting of connective tissue, nerves, and blood vessels. The overlying dentin is produced by specialized cells, called odontoblasts, which reside in the pulp. The dentin itself is a mixture of matrix proteins and mineral, harder than bone, but not as hard as enamel.

When pulp becomes infected, traditional treatments involove removal of all infected or damaged tissues followed by filling the root canal and replacing the dentin and enamel with synthetic materials. Approximately 15 million patients in the U.S. require root canal therapy each year. Two approaches are being pursued to regenerate the tooth's internal structures. Direct application of TGF-beta family proteins (BMP-2, -7, TGF-beta 1) onto exposed healthy pulp has stimulated dentin formation in animal studies. A potentially more versatile approach has been used in vitro to grow pulp-like tissue in a three-dimensional scaffolding material. A combination of cultured human pulp cells (fibroblasts) grown in a polyglycolic acid (PGA) matrix produced new tissue histologically resembling pulp.

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