| 摘要 |
PCT No. PCT/JP97/01551 Sec. 371 Date Nov. 12, 1998 Sec. 102(e) Date Nov. 12, 1998 PCT Filed May 8, 1997 PCT Pub. No. WO97/42854 PCT Pub. Date Nov. 20, 1997A tooth brush comprises a plurality of tufts each of which comprises a plurality of bristles embedded respectively in bored holes which are vertically and laterally formed in a head portion of the toothbrush. The tufts each comprises first and second bristles, such that in each of the tufts, the total of the first and second bristles is 50% or more, in number. The first bristles are tapered bristles having a factorial coefficient n=0.29 to 0.51 in the equation (I) r(x)=a{(L-x)/L}n. The distal ends of the second bristles are located in a lower position than the distal ends of the first bristles, vertical intervals between the bored holes are from 1.2 mm to 3.0 mm, and lateral intervals are from 0.75 mm to 1.5 mm. In formula (I), r(x): sectional radius, x: length from base of each bristle, L: length to distal end from base of each bristle, a: sectional radius in case x=O[=r(O)], n: factorial coefficient.
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