Diffusion of Niacin through Extracted Human Teeth and Its Effect on Bacterial Penetration into Dentin

¹ U.S. Naval Dental School, National Naval Medical Center, Bethesda, Maryland

A standard bioassay technique was used to determine whether niacin could diffuse through extracted human teeth in quantities sufficient to support bacterial growth. Niacin diffused through drilled teeth at a constant rate, ranging from 0.04 to 0.28 µg/ day. This rate was two to nine times greater than through the undrilled teeth, which exhibited a constant rate, ranging from 0.01 to 0.05 µg/day. Organisms penetrated the dentinal tubules when the crowns of teeth were covered with a niacin-deficient medium, and the growth of L. arabinosus depended on the diffusion of niacin from the pulp side of the teeth. After 12 weeks, dentinal changes similar to those in natural caries were observed. No penetration of organisms was detected when the crowns of teeth were covered with a complete medium. After 12 weeks, dentinal changes did not resemble natural caries.