**2.1.5 Discussion**

In this study, we measured the concentration of residual potassium in agarose gel to determine the velocity of salivary flow for the 7 different sites. The reason why potassium chloride was used as the target substance (with an agarose gel used as artificial plaque) is that it is readily soluble in water, harmless, has a low molecular weight enabling it to diffuse easily, is present at a low concentration (around 20 mM) in saliva and can be measured relatively easily. Because the potassium concentration in the agarose gel used in this study was much higher than that in the saliva of the subjects, it was unlikely that the potassium concentration in the saliva affected that in the gel.

The relationship between time and the quantity of potassium diffused from the gel into the saliva was pre-determined in a pilot study. Clearance was evaluated by determining the half-time, the time at which the concentration at time 0 is reduced to half, from the relationship between 3 time points, including time 0, and potassium concentration, as well as by comparing the mean half-time between different sites. Since the correlation between time and the quantity of potassium eluted from the agarose gel was found to decrease in the early and late phases of the test (Lecomte P, Dawes C, 1987), the time to hold the holder in the mouth was determined so that the half-time would be almost at the mid-point of the test. For the measurement of potassium concentration, sodium chloride solution was used as the solvent to avoid errors in measurements due to ionization of potassium.

Estimation of the Velocity of the Salivary Film at the Different Regions in the Mouth

Fig. 7. Spacing arch at 5 years old.

Fig. 8. No spacing arch at 5 years old.

allowed to drip off the lower lip into a weighed container.

– Measurement of Potassium Chloride in the Agar Using Atomic Absorption Spectrophotometry 57

The subjects were 4 boys and 8 girls, 5 years of age, who were all in good health and with complete primary dentitions. Six subjects had primary spaces (located mesial to the maxillary and distal to the mandibular canines) and developmental spaces (present between the remaining teeth) (Fig. 7), and the other 6 subjects had no spaces in their arches (Fig. 8). The mean values of right and left primary spaces and total developmental spaces for 6 subjects who have spacing arch were 1.1 ± 0.4 mm, 1.2 ± 0.4, and 4.2 ± 1.9 mm for the upper dentition and 0.8 ± 0.3 mm, 0.7 ± 0.3, and 3.8 ± 1.4 mm for the lower dentition, respectively.

Seven different sites in the mouth were chosen for measurements. These were the lower anterior lingual (LALi) and buccal (LAB), lower posterior buccal (LPB) and lingual (LPLi), upper posterior lingual (UPLi) and buccal (UPB), and upper anterior buccal (UAB). The flow rate of unstimulated whole saliva was also measured on each occasion for 5 min by being
