**2.2.2 Materials and methods**

The determination of the rate of potassium chloride clearance was done by the same methods as in study 1. A 1-mol/L solution of potassium chloride was mixed with sufficient agarose (Electrophoresis Purity Reagent; BioRad Laboratories, Richmond, CA) to give a 1.0% solution which was heated until the agarose dissolved. The acrylic chambers(Fig. 3) to hold the gel were rectangular (16 mm in length, 8 mm wide, and 1.5 mm thick) with a cylindrical central depression (6 mm diameter and 1.5 mm depth). The potassium concentration in agarose was analyzed by absorption spectrophotometry.

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.

Fig. 7. Spacing arch at 5 years old.

56 Macro to Nano Spectroscopy

Nursing bottle caries (Fig.6) is a specific form of rampant decay on the buccal surface of the upper anterior primary teeth. Some etiological factors, such as the types of microorganisms, tooth structure, and diet, have been reported, but there is little information about the

Very little research has been carried out on the salivary flow rate or salivary clearance in children. Although the average thickness of the salivary film covering teeth and oral mucosa in children is essentially identical with values reported for adults, marked differences were found between children and adults for such parameters as unstimulated and stimulated whole-salivary flow rates, the volume of saliva in the mouth before and after swallowing,

The aim of this study was to evaluate the rates of salivary clearance at different locations in the mouths of children and the effect of the spaces in the primary dentitions to determine whether prolonged clearance would occur in sites particularly susceptible to nursing bottle caries.

The determination of the rate of potassium chloride clearance was done by the same methods as in study 1. A 1-mol/L solution of potassium chloride was mixed with sufficient agarose (Electrophoresis Purity Reagent; BioRad Laboratories, Richmond, CA) to give a 1.0% solution which was heated until the agarose dissolved. The acrylic chambers(Fig. 3) to hold the gel were rectangular (16 mm in length, 8 mm wide, and 1.5 mm thick) with a cylindrical central depression (6 mm diameter and 1.5 mm depth). The potassium

concentration in agarose was analyzed by absorption spectrophotometry.

**2.2 Salivary clearance in children with complete primary dentitions** 

**2.2.1 Aim** 

influence of the salivary flow rate.

Fig. 6. Nursing bottle caries

and the surface area of the mouth.

**2.2.2 Materials and methods** 

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

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

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

**2.2.4 Discussion** 

in different regions.

**2.3.1 Aim** 

British children aged 30-36 months.

– Measurement of Potassium Chloride in the Agar Using Atomic Absorption Spectrophotometry 59

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

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

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.

The rate of oral clearance was shown to vary markedly at different locations in the mouth. Oral clearance is slower for teeth in the maxilla than for those in the mandible and slower for the buccal surfaces of the teeth than for the lingual. Oral clearance on the labial surface of the upper anterior region is the slowest, while that for the lingual surface of the lower anterior region is the fastest. The lingual surface of the lower anterior region is near the openings of the ducts of the submandibular and sublingual glands, which probably accounts for the fastest rate of oral clearance being there. The effect of unstimulated parotid saliva on clearance around the maxillary first molar is not very striking, perhaps because the volume ratio of parotid saliva to total saliva is only about 15% at rest for each side. However, with stimulation, the proportion of parotid saliva increases, increasing clearance over the maxillary first molar, which is closest to the parotid duct. Few studies have examined positional relationships between the parotid duct orifice and the maxillary molars or individual differences in this positional relationship (Suzuki et al. 2009). The present study sought to ascertain the location of the parotid duct orifice in relation to the maxillary molars and whether oral clearance at locations 1 cm mesial and distal to the duct opening

**2.3 Influence of the location of the parotid duct orifice on oral clearance** 

would be as rapid as that directly opposite the opening of the duct.

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 half-time.

#### **2.2.3 Result**

The mean half-times for in vitro clearance into the large volume of stirred 100 ppm NaCl at 37°C was 3.9 ± 0.5 min.

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


Statistical analyses werw carried out between UAB site and the other sites in each group: \*p<0.05, \*\*p<0.01, \*\*\*p<0.001.

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

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

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 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


Halftime in large volume at 37°C=3.9 ± 0.5min.Statistical analyses were carried out detween UAB site and the other sites in each group :\*p<0.05 \*\*p<0.01

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