**3. Conclusion**

In clinical dentistry, it is generally accepted that the mandibular front teeth has low caries sensitivity, and the maxillary front teeth has high (e.g. nursing bottle caries) and the caries incidence of the buccal side of teeth in old person is higher than the lingual side. The results of this study have confirmed these clinical situations.

The author has also concluded that the velocity of salivary film is different by each site in the oral cavity and the slow velocity of the salivary film over the different surfaces of the teeth will retard clearance from diffusants of plaque such as acid. This suggests that the pH of each site in the oral cavity is slso different (Watanabe 2008),
