The role of pulp and saliva in caries susceptibility and resistance was evaluated using a combination of endodontic treatment and desalivation. Evidence was presented that the pulp plays a major role in caries susceptibility. It is suggested that pulpal function is modified by hormonal factor(s) originating from salivary glands. In the rat, saliva appears to play a minor role in resistance to caries.

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A parotid hormone (PH-A beta) has been isolated and purified from porcine parotid glands. The biological effect of the hormone is the stimulation of a dentinal fluid transport (DFT) in molar teeth of rats. The method for purifying the PH-A beta includes: extraction at pH 7 and 5, ultrafiltration through Amicon membranes, ion exchange chromatography on carboxymethyl cellulose, gel filtration on Sephadex G-50, and preparative electrophoresis in polyacrylamide gel. The PH-A beta is characterized as a glycoprotein having a molecular weight of 8100 and containing 2% hexose. The amino acid composition suggests a molecule rich in glycine (46%) and proline (27.7%). Alanine, glutamic acid, arginine, serine, aspartic acid, leucine, and lysine account for the remaining 26% of the residues. The isoelectric point is pH 7.50. The partial N-terminal amino acid sequence was determined to be: NH2-Ala-Pro-Pro-Gly-Ala-Arg-Pro-Pro-Pro-Gly-Pro-Pro-Pro-Pro-Pro-Pro-(Glu)-(Pro)-?-(Pro)-(Pro)-Arg-(Pro)-(Pro)-(Pro)-Gly-(Gly)-(Gly). A 5.5 X 10(7)-fold increase in DFT activity has been achieved relative to the crude gland extract. As little as 9.7 pg PH-A beta are effective in stimulating DFT. The significance of the PH-A beta appears to be the maintenance of a functional DFT within teeth to allow the avascular dental tissues to meet their high metabolic requirements.