| 摘要 |
PROBLEM TO BE SOLVED: To enable a post of canalis radicis dentis to be fixed with the minimum number of rotation and without applying unnecessary load thereto by forming a plurality of spiral thread rides of only at an upper section close to a head of a part to be fixed. SOLUTION: Three thread rides are formed at a fixed part 4, and the respective spiral ridges are arranged so that they are shifted by the angle of about 120 degrees on a circular cross section. It is advantageous that the part without thread ridges becomes about 1/3 of the whole length of the fixed part 4. Accordingly, especially in the region of thin wall canalis radicis dentis, generation of stress caused by abutting of thread groove can be avoided surely. It is also advantageous that two to four spiral thread ridges are formed. |
