**2.2.4 Discussion**

58 Macro to Nano Spectroscopy

The rate of potassium chloride clearance from the gels into a large volume (1 liter) of 100 ppm NaCl fluid at 37℃ stirred by a magnetic stirrer was determined for the estimation of

The mean half-times for in vitro clearance into the large volume of stirred 100 ppm NaCl at

The half-times in the mouth varied with location as shown in Table 1. The half-times of all sites for the spacing arch and of the LALi site for the no-spacing arch were reduced (p<0.05)

Statistical analyses werw carried out between UAB site and the other sites in each group: \*p<0.05,

When the saliva flow rate was stimulated (Table 2), the shortest halftimes occurred in the LALi site and the longest in the UAB site. The clearance from the LAB site in the spacing

Table 1. Half-times (mean ± SD) and salivary flow rates when salivary flow was

arch showed almost the same value as those from the LALi sites in both groups.

Halftimes(mean±SD)and salivary flow rates when salivary flow was stimulated

LALi LAB UAB

Halftime,min 4.0±0.3\*\* 4.5±0.8\*\* 11.3±4.5 Flow rate,ml/min 3.4±1.5 4.1±2.1 3.4±1.7

Halftime,min 4.0±0.2\*\* 9.4±2.8\* 15.4±4.2 Flow rate,ml/min 3.7±1.2 3.9±1.7 4.8±1.7

Halftime in large volume at 37°C=3.9 ± 0.5min.Statistical analyses were carried out detween

Table 2. Halftimes (mean ± SD) and salivary flow rates when salivary flow was stimulated

as compared with the values when the flow rate was unstimulated.

Mean unstimulated salivary flow rates were 0.47±0.2 ml/min.

Location

UAB site and the other sites in each group :\*p<0.05 \*\*p<0.01

the half-time.

**2.2.3 Result** 

37°C was 3.9 ± 0.5 min.

\*\*p<0.01, \*\*\*p<0.001.

Spacing arch(n=6)

No-Spacing arch(n=6)

unstimulated

The present study showed that the rate of clearance of substances from agarose gels into saliva varies markedly in different regions of the primary dentition. The location closest to the submandibular and sublingual ducts (LALi) showed the lowest half-time, whereas the UAB site had a clearance half-time 6.5 times longer than that for clearance into a large volume in vitro. As the opening of the parotid duct is situated on the rearward of the upper second primary molar in the children's mouth, there was a relatively long half-time in the UPB site. Since the mean salivary film thickness in 5-year-old children has been estimated to have almost the same value (0.06-0.09 mm) (Watanabe and Dawes, 1990) as in adults (Collins and Dawes, 1987), these results suggest that the velocity of the salivary film varies in different regions.

The relative order of the half-times at the different sites in the no-spacing arches was identical with that found in a study on adult subjects when saliva flow was unstimulated. Although in the spacing arch, the LAB site had a shorter clearance half-time than the UPB site. These results may be due to the fact that in the spacing arches, the tongue pushes out a portion of saliva from the lingual to the buccal side during swallowing, and this is in accordance with clinical findings that these sites are not susceptible to caries. The ideal arch in the primary dentition has spacing between the teeth (Pinkham et al, 1988), but Foster and Hamilton (1969) reported that only 33% had spacing between all the incisors in the upper and lower arches and that only 12% had spacing between all teeth in both arches in 100 British children aged 30-36 months.

Although it is known that nursing bottle caries depends on the feeding pattern in infancy, the present results suggest that the upper anterior buccal site in a no-spacing arch will be the most cariogenic site in a child's mouth because it has the lowest rate of salivary clearance.
