**2.4.2 Materials and methods**

40 mg of NaF and 5 ml distilled water were mixed with 0.15 g agarose which was heated until the agarose dissolved. Aliquots were pipetted into holders (diameter 4 mm, depth 1 mm) and these were bonded onto mouthguards produced from plaster casts of each subject (Fig.12).

The bonding sites were on the labial of maxillary incisors (UAB), the buccal of left maxillary molars (UPB) and the lingual of lower incisors (LAL). When the subjects were awake, the

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

– Measurement of Potassium Chloride in the Agar Using Atomic Absorption Spectrophotometry 65

Fig. 13. The comparison of the mean half-times of each place, expressed in relation to the

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

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.

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)

sleeping

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.

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