Salivary clearance of citric acid after an oral rinse

Objectives: Citric acid clearance from the oral cavity may be an important factor in the erosion of dental enamel. The aim of the present study was to investigate the clearance pattern of citric acid in normal subjects. Methods: After determination of the unstimulated salivary flow rate and the residual volume of saliva after normal swallowing, 12 subjects rinsed with 95.2 mmol l−1 citric acid for 5 s. At 1, 2, 5, 10 and 15 min after the rinse a small saliva sample was collected and the concentration of citric acid was determined enzymatically. For each subject three separate experiments on different occasions were performed with a citric acid solution of pH 2.1 and one experiment with a solution of pH 4.5. Results: The salivary citric acid concentration declined biphasically: rapidly during the first 2 min, then more slowly. The elimination rate over the first minute was on average 87.7 mmol l−1 min−1 at pH 2.1 compared with 85.0 mmol l−1 min−1 at pH 4.5. The difference between individuals estimated from the areas under the clearance curve was strongly significant (P < 0.001). No significant relation was found neither between salivary flow rate and clearance, nor between residual volume after swallowing and clearance. Conclusion: The clearance pattern of citric acid is an individual property.