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 oral cavity, the effect of the clearance on the salivary saturation with respect to hydroxyapatite (OHAp) and the effect of the clearance rate and frequency of the citric acid challenges on enamel erosion. Saliva samples were collected from each of 12 subjects after a rinse with 2% citric acid. The citric acid concentration in the saliva was analyzed enzymatically and found to decrease rapidly during the first minutes. The difference between subjects was highly significant (p<0.001).
In the second study, the citric acid retention was investigated in 34 subjects after sampling from the labial surfaces of the upper and lower incisors and sublingually after a rinse citric acid. The citric acid concentrations differed 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 degree of saturation of the saliva with respect to OHAp was calculated after an oral rinse. Large differences between individuals were observed. The correlation between the rate of clearance of citric acid during the first minute and the degree of salivary saturation with respect to OHAp was significant (r=0.82, p<0.01). In order to simulate the oral clearance process, sections of teeth were immersed in an artificial mouth into which a remineralizing solution was constantly pumped into the artificial mouth. 2% citric acid, was injected each other hour or once each hour for 16 hours a day.
The enamel surface was studied with longitudinal microradiography or a scanning electron microscopy. The analysis of variance of the area above the demineralization curve (AAC) showed that the simulated clearance rates had a significant influence on the mineral loss (p<0.05). A dose-response relationship was found between 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 enamel surface was observed after doubling the frequency of the acid attacks.
