**2.4.3 Results**

Fig.13 showed the comparison of the mean half-times of each place, expressed as a standard in the value at LAL. The half-times were lowest in LAL and were highest in UAB. There were significant differences between the LAL and UAB (p<0.01), and between the LAL and UPB (p<0.05).

Table 3 showed the comparison of the mean volume of fluoride retention at 6:30 am. when the subjects had been sleeping. The fluoride concentrations were expressed as a percentage of that of the initial agarose which did not expose to saliva in the mouth. The values in LAL were also lowest, and UAB were highest. There were significant differences between the LAL and UAB (p<0.05) and between the LAL and UPB (p<0.05).

Most studies on fluoride clearance in the mouth have been carried out when the subjects were awake, and there is little information when they were sleeping. Ekstrand et al. (1986) and Featherstone et al.(1986) have suggested that fluoride, even at low concentrations, is necessary in the oral fluids to obtain maximum caries inhibition and have concluded that continuous or frequent elevation of the fluoride concentration in the oral fluids would be advantageous.

upper and lower mouthguards were fixed in the mouth and exposed to saliva for 15, 45 minutes. The agarose was taken out of the holder and put into 2 ml of distilled water mixed with 0.1 ml of the total ion strength adjustment buffer (TISABⅢ, Thermo Orion, IL, USA) for 90 minutes and the fluoride concentration was measured by atomic absorption spectrophotometry (Shimadzu AA-6105, Kyoto, Japan) as described in study 1. The fluoride concentration of the agarose held in the holder of each mouthguard was measured six times, and holders in which the mean concentration of agarose was more than 2 SD from the mean were excluded. To examine the retention of fluoride in the mouth during sleep, the mouthguards were placed before going to bed (0:00 a.m.) and removed at 6:30 a.m. and the fluoride concentration measured by a fluoride electrode (Thermo Fisher Scientific , MA, USA). The subjects, 6adults who were all in good health and whose salivary flow rates exceed 0.3 ml/min were selected. Before the experiment, the subjects were explained the purpose and got their cooperation. In order to determine the effects of site specificity of salivary clearance, the data were analyzed by analysis of variance in randomized blocks and

by Duncan`s New Multiple Range Test.

**2.4.3 Results** 

UPB (p<0.05).

advantageous.

Fig. 12. Mouthguard with agarose holders. (Left: Upper, Right: Lower)

LAL and UAB (p<0.05) and between the LAL and UPB (p<0.05).

Fig.13 showed the comparison of the mean half-times of each place, expressed as a standard in the value at LAL. The half-times were lowest in LAL and were highest in UAB. There were significant differences between the LAL and UAB (p<0.01), and between the LAL and

Table 3 showed the comparison of the mean volume of fluoride retention at 6:30 am. when the subjects had been sleeping. The fluoride concentrations were expressed as a percentage of that of the initial agarose which did not expose to saliva in the mouth. The values in LAL were also lowest, and UAB were highest. There were significant differences between the

Most studies on fluoride clearance in the mouth have been carried out when the subjects were awake, and there is little information when they were sleeping. Ekstrand et al. (1986) and Featherstone et al.(1986) have suggested that fluoride, even at low concentrations, is necessary in the oral fluids to obtain maximum caries inhibition and have concluded that continuous or frequent elevation of the fluoride concentration in the oral fluids would be

Fig. 13. The comparison of the mean half-times of each place, expressed in relation to the value for LAL. (p<0.01: LAL vs. UAB, p<0.05: LAL vs. UPB)


(\*p<0.5: Significantly different from the mean volume of UAB)

Table 3. The mean volume (%) of fluoride retention at 6:30 a.m. when the subject had been sleeping

In this study it was shown that the fluoride concentration in the saliva was kept at high level for a long time during sleeping. In order to prevent dental caries at the buccal surfaces of the upper anterior teeth, it seems to be good to use a fluoride rinse before going to bed.

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

connected to the device via polyethylene tubing.

square root of time, and the half-time was calculated.

**2.5.3 Results** 

from an agarose gel, 1.5 mm in depth

– Measurement of Potassium Chloride in the Agar Using Atomic Absorption Spectrophotometry 67

The device was maintained at 37 °C, and de-ionized water at the same temperature was infused with an infusion pump (Model 2000 IW, Harvard Apparatus Co., USA), the flow rate of which was adjustable over a wide range. The pump activated a 5-mL syringe

For an experiment to be initiated, the flow rate of the pump was set to 1.07 ml/min. As soon as the water filled the tubing and completely covered the gel, a stop watch was started, and the flow rate of the pump was set to the desired value. After a pre-determined time, the pump was stopped, the two halves of the acrylic device were separated, and the agarose gel was removed with a needle and transferred to an appropriate volume of 100-ppm NaCl. The

For each flow rate, the experiment was repeated using five different gels for different durations to enable up to 70% of the KCl to be cleared from the gel. For each flow rate, a control gel that had not been exposed to water was used to determine the initial potassium concentration. The experiment was repeated three times for each flow rate. A least-squares straight line was fitted by computer to the potassium concentration plotted against the

There was a significant difference in the mean clearance half-time for the UAB between unstimulated (51.2 ± 19.3 min) and stimulated (40.1 ± 15.1 min) (P < 0.05) salivary flow rates. A significant difference was also found in the mean half-time for the UPB between unstimulated (19.2 ± 6.9 min) and stimulated (12.1 ± 5.2 min) (P < 0.01) salivary flow rates. The results on the effect of velocity on the clearance half-time are shown in Table 4. With the flow rates set, the film velocity varied from 0.67 to 100 mm/min. The clearance half-times were inversely related to the velocity of fluid flow, and varied from 2.2 min to 58.3 min.

Fluid Velocity of Half-time Flow Rate Fluid flow (min) (ml/min) (mm/min) 6 mm in diam

Table 4. Effect of velocity of fluid flow on the mean half-time ± S.D. for clearance of KCL

Table 5 shows the in vivo clearance half-times for the UAB and the UPB as well as the estimated velocities of flow of the salivary film, as determined from the data in Table 1.

When salivary flow was unstimulated, the velocity of the salivary film of the UAB was estimated as 0.8 mm/min, whereas for the UPB it was estimated as 40.1 mm/min. When

 0.06 100 2.2 ± 1.9 0.005 8.33 8.3 ± 1.2 0.003 5.00 15.1 ± 1.9 0.001 1.66 21.5 ± 2.8 0.0005 0.83 39.4 ± 4.2 0.0004 0.67 58.3 ± 6.1

potassium concentration was determined by atomic absorption spectrophotometry.
