**2.3.1 Aim**

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

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

holder, 3 cylinders were placed horizontally at 6-mm intervals (Fig. 9).

period without stimulant.

Fig. 9. Agar holder

holder with their tongue or talking.

**2.3.3 Result** 


10 mm

– Measurement of Potassium Chloride in the Agar Using Atomic Absorption Spectrophotometry 61

the agar holders in position, parotid saliva was collected on 5 separate occasions for a 5-min

Oral clearance was assessed using the same methods of the study 2-1. 1% agar containing 1 mol/l potassium chloride was placed into cylinders (diameter, 4 mm; depth, 1 mm) held by an acrylic holder (width, 30 mm; height, 10 mm; thickness, 2 mm). The open surfaces of the cylinders were initially covered with microscope slides to allow the agar to set. In each agar

30 mm

The cylinders were attached to the teeth using Hydroplastic (TAK, Tokyo) so that the central cylinder would be on the buccal surface of the first molar, at the coordinates of the mean X and Y values obtained in Study 2-4-2-1. After salivary secretion stabilized, which took about 1 minute when parotid flow was measured with a Lashley cannula, the Parafilm was removed to initiate the experiment. On separate occasions, the holder was retained for 5, 10, 20 or 40 min without stimulant. At each time point, the concentration of residual potassium in the agar was measured for calculation of the half- time (the time for half of the potassium chloride to diffuse from the gel), as described by the study 1. Concentrations of potassium were measured by removing the agar cylinders from the holder, soaking each in 300 ml of 100 ppm sodium chloride solution for 90 min, and measuring the levels of eluted potassium by atomic absorption spectroscopy using an ANA-182 spectroscope (Tokyo Koden, Tokyo). The experiment was performed 3 times on both sides of each subject, and mean values were calculated. During the experiment, subjects were asked to refrain from touching the agar

Along the X axis, the location of the left and right parotid duct orifices varied within a range of -7.5 to +6.1 mm (Mean ± S.D.) from the reference point. Mean location (-0.36 ± 3.76) was just mesial to the reference point. Along the Y axis, the orifice was always located on the positive side of the reference point, ranging from +3.8 to +10.4 mm (mean value: 7.21 ± 2.15) (Fig. 10). This suggests that the parotid duct orifice is located above the reference plane near the contact surface between the maxillary first and second molars. Also, ranges of 13 mm in the mesiodistal direction and 6 mm in the perpendicular direction were noted, showing that

2 mm 1 mm

6 mm 4 mm

3 mm
