The aim of the present study was to use an in vitro enamel demineralization model (1) to confirm that whole saliva pretreatment conferred acid resistance to dental enamel and (2) to determine whether this phenomenon was attributable to specific salivary proteins, minerals, lipids, or some combination of these. Crowns of human teeth, each with one exposed window, were prepared in groups of ten. They were each pretreated by immersion individually in 4 ml of either (1) clarified whole saliva for 18, 72, or 168 h, (2) dialyzed saliva (3500 MWCO membrane), (3) the "flow-through" fraction from a DEAE separation of whole saliva (neutral and basic proteins), (4) the "eluted" fraction of a DEAE separation of whole saliva (anionic proteins), or (5) a combination of salivary lipids and the DEAE "flow-through" fraction of whole saliva (neutral and basic proteins). Control groups were group 6 with no pretreatment, group 7 pretreated for 168 h in a borate buffer (5 mmol/l), and group 8 pretreated in a mineral solution containing calcium (0.7 mmol/1) and phosphate (2.6 mmolfI). The crowns were then demineralized for 7 d in vitro (0.1 mol/I acetate, 1 mmol/I Ca and phosphate, pH 5.0) to produce artificial caries-like lesions. Lesions were assessed by cross-sectional microhardness profiles, and mineral loss (AZ, Rim x vol% mineral) calculated. Mineral loss (AZ) values decreased linearly with the square root of time of pretreatment by whole saliva, confirning a time-dependent protective effect of salivary pellicle against demineralization of enamel. Pretreatments (168 h) by whole saliva (group 1), dialyzed saliva (group 2), and lipid/'flow through" proteins (group 5) gave equivalent protection (approximately 55%). However, no protection was provided by DEAE-separated protein fractions (no lipid present) or by the mineral alone. The protection of surface enamel against demineralization appears to be given by a combination of specifically adsorbed salivary lipids and proteins.

In a comparative study of caries-resistant and -susceptible adults, no significant differences were found in the concentrations of lactoperoxidase, thiocyanate, and pre-formed hypothiocyanite in parotid and submandibular saliva, or in hypothiocyanite formed in expectorated saliva over a 60-minute period. The concentrations per se of these components are not critical determinants of caries resistance or susceptibility. Thiocyanate concentration was higher in both unstimulated parotid and submandibular saliva than in the respective stimulated secretions. At comparable flow rates, parotid values were higher than submandibular.

The enzyme formylhydrate dehydrogenase has been found to be present in human serum. A spectrophotometric rate assay is described. Kinetic and other properties of the enzyme are discussed.