[Effect of coronal gingival contour on contact between food bolus and cervical tooth surface during mastication]

At the coronal cervix, the so-called uncleaned area, the path of the food bolus and its rubbing effect are said to be regulated by the coronal and gingival contours. However, it has not been ascertained whether such regulation really exists. So, the force which was generated by a food bolus rubbing on the buccal surface was measured at the height of the cervical third of the lower first molar with a load cell inserted into the denture. The results obtained were as follows: 1. Cervixward forces were observed in the closing phase and cuspward forces, in the opening phase during mastication. The intensity of cervixward forces was stronger than that of the cuspward ones. And the occurrence of the former was more frequent than that of the latter. 2. The intensity and frequency of cervixward forces differed according to the kind of food. 3. Cervixward force under the degree of convexity of 0 mm was stronger in intensity and more frequent than that under the degree of convexity of 0.5 mm. 4. Cervixward force under the marginal gingiva thickness of 1 mm was stronger in intensity and more frequent than that under the marginal gingiva thickness of 2 mm.