Studies on oral clearance of citric acid and its effect on enamel erosion

Abstract: Citric acid in foods is one of the most important factors causing erosionof enamel. The aims were to study citric acid clearance from the oralcavity, the effect of the clearance on the salivary saturation with respectto hydroxyapatite (OHAp) and the effect of the clearance rate andfrequency of the citric acid challenges on enamel erosion. Salivasamples were collected from each of 12 subjects after a rinse with 2%citric acid. The citric acid concentration in the saliva was analyzedenzymatically and found to decrease rapidly during the first minutes. Thedifference between subjects was highly significant (p<0.001). In thesecond study. The citric acid retention was investigated in 34 subjectsafter sampling from the labial surfaces of the upper and lower incisorsand sublingually after a rinse citric acid. The citric acid concentrationsdiffered significantly between these sites and averaged 32.12+19.5, 11.90+8.60 and 1.52+1.90 mmol/l, respectively. In the third study the degreeof saturation of the saliva with respect to OHAp was calculated after anoral rinse. Large differences between individuals were observed. Thecorrelation between the rate of clearance of citric acid during the firstminute and the degree of salivary saturation with respect to OHAp wassignificant (r=0.82, p<0.01). In order to simulate the oral clearanceprocess, sections of teeth were immersed in an artificial mouth intowhich a remineralizing solution was constantly pumped. Into theartificial mouth 2% citric acid, was injected each other hour or once eachhour for 16 hours a day. The enamel surface was studied withlongitudinal microradiography or a scanning electron microscopy. Theanalysis of variance of the area above the demineralization curve (AAC)showed that the simulated clearance rates had a significant influence onthe mineral loss (p<0.05). A dose-response relationship was foundbetween the half-time for citric acid clearance (t1/2) and the AAC(r=-0.78, p< 0.001). The mean lesion depth at the clearance t1/2 of 26,148, 291 and 684 s was 4.6 + 2.8, 39.9 + 20.4, 57.1 + 26.1, 58 + 14 (SD)µlm, respectively. Distinct difference in the appearance of the enamelsurface was observed after doubling the frequency of the acid attacks.Key words: Citric acid, Saliva, Site specificity, Degree of saturation,In vitro model, Flow rate, Enamel erosion, Clearance rate, Frequency,Microradiography, Scanning microscopy ISBN 91-85910-92-9