A Low Concentration of Carbonic Anhydrase Isoenzyme VI in Whole Saliva Is Associated with Caries Prevalence

Carbonic anhydrases maintain pH homeostasis in various tissues of the human body by catalyzing the reversible reaction CO₂ + H₂O <=> HCO₃^– + H⁺. Carbonic anhydrase isoenzyme VI (CA VI) is secreted into human saliva by the serous acinar cells of the parotid and submandibular glands. Although it represents about 3% of the total protein in stimulated parotid saliva, its exact physiological significance in the saliva has not been established. In the present study, saliva samples were collected under strictly controlled conditions from young, healthy men and assayed for CA VI concentrations using a specific time–resolved immunofluorometric assay. Salivary secretion rate, pH, buffering capacity, α–amylase activity levels, lactobacillus and <i>Streptococcus mutans</i> counts were also determined, and the results were correlated with the dental status of the subjects. Salivary CA VI concentration, pH and buffering capacity values correlated negatively with the numbers of decayed, missing and filled teeth (DMFT index). The correlations between salivary CA VI concentration and DMFT index were most significant in subjects with poor oral hygiene. No correlation was found between salivary CA VI concentration and lactobacillus or <i>Streptococcus mutans</i> counts. As predicted, salivary lactobacillus and <i>Streptococcus mutans</i> counts showed a close positive correlation with the DMFT index. In contrast, no significant correlation was seen between salivary secretion rate or amylase activity and the DMFT index. The present results indicate that low salivary CA VI concentrations are associated with increased caries prevalence, particularly in subjects with neglected oral hygiene.