**2.3.4 Discussion**

62 Macro to Nano Spectroscopy

there was a high degree of inter-individual variation. No significant left-right differences were identified. The intra-individual right-left differences were significantly less (P< 0.001)

The unstimulated parotid saliva flow rates for left and right sides were 0.02 ± 0.02 and 0.02 ± 0.02 ml/min, respectively and no significant difference was found between results for the two sides. No significant differences in half-time could be detected between comparable left and right regions. Fig.11 shows the half-times for the right and left sides without stimulant. The half-time of the central cylinder was the shortest, followed by the mesial and then the distal cylinders, in that order, for both left and right sides. The half-time values among the 3

Y axis (mm)

**2**

for the 35 subjects. The x indicates the mean position of the duct orifice.

Fig. 11. Half-times when saliva flow was unstimulated

**-8 -6 -4 -2 0 2 4 6 8**

Fig. 10. The location of the parotid duct orifice. The symbols indicate the individual results

Mesial Distal

**4**

**X 8**

**6**

**10**

X axis (mm)

Left side Right side **X** Mean location

than the overall variability among subjects.

cylinders were all significantly different.

The main finding from the second study was that clearance from a site directly opposite the opening of the parotid duct was significantly faster than from sites only one cm either mesially or distally. When salivary flow was unstimulated or stimulated, the clearance halftimes mesial or distal to the duct opening were two or more times longer than those opposite the duct opening.

The present results are in conformity with those of Weatherell et al. (1986) who found that when a fluoride tablet was placed in the buccal vestibule, the fluoride concentration peaked in the fluid adjacent to the tablet but was much lower both mesially and distally. The previous reports and our results suggest that when parotid saliva exits the parotid duct, it primarily flows downwards and then, from the results of Weatherell et al. (1986), probably lingually over the occlusal surface of the teeth, rather than flowing mesially or distally in the buccal sulcus. If it flowed primarily in either of these two directions, one would have expected very little difference between the clearance rates from the mesial or distal agar cylinder and that from the cylinder positioned over the parotid duct opening. Sass and Dawes (1977) also reported that very little parotid saliva appeared to flow mesially when flow was either unstimulated or stimulated by the use of chewing gum.

In conclusion, the degree of individual variation in the location of the parotid duct orifice is great and its exact location will markedly affect oral clearance at different positions on the buccal surfaces of the upper molars.
