Frequencies of Occurrence of Accessory Tubercles and Other Traits in the Lower Deciduous Second Molar.

概要

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The frequencies of occurrence of anomalous traits or tubercles on the lower second deciduous molar were investigated with the use of moire contourgraphy. A molar with negligible attrition was fixed in the tricuspal position where the position of the protoconid, metaconid and hypoconid were in a horizontal plane. A moire photograph in the pitch of 0.2 mm was thus obtained and examined. The frequency of occurrence of a tubercle was counted in three grades according to its contour patterns. The traits and their sex-pooled frequencies were as follows (n=45): (1) Mesial Accessory Tubercle, 17.8%;(2) Metaconid Mesial Accessory Tubercle, 8.9%;(3) Metaconid Distal Accessory Tubercle, 57.8%; (4) Distal Trigonid Crest, 17.8%;(5) Deflecting Wrinkle, 46.7%;(6) Sixth Cusp, 35.5%; (7) Entoconid Mesial Accessory Ridge, 0%; (8) Protostylid, 73.3%. The incidences of the traits were compared with those in the permanent first molars previously studied. The traits nos. 2, 3, 4 and 8 were significantly more frequent in the deciduous molars than in the permanent ones when tested by χ2 test. On the other hand, the frequencies of trait nos. 1, 5, 6 and 7 were not significantly different between both molars. Three of four traits showing significant difference located around the metaconid, which indicated the high morphological variability of the metaconid in the deciduous lower second molar.
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