歯科用リーマの強度と切削性能に関する研究．(II)．歯髄管リーマのねじり強度と先端径（筆者訳）．

[Studies on the strength and the cutting performance of dental canal reamer. (II). Torsional strength and tip diameter of dental canal reamers (author's transl)].

抄録

歯科領域における歯根の切削治療において，歯髄管リーマの強度は重要な問題である．リーマーはねじり運動により切削工具として使用されており，リーマーの破折は特に咬合先端部のせん断応力により生じる．そこで本稿では，リーマーのせん断強さ（ねじり強さ，ねじり剛性）について検討した．そして，切削・ねじり試験用のねじり装置を製作し，原料および歯髄管リーマのねじり強度を試験した。リーマの形状は日本工業規格(JIS)で扱われ、これらの特性はリーマの直径寸法で再調整される。リーマのせん断強さは120〜140kg/mm2であり、テーパ付きストレートバーの強さはリーマの約2倍の40kg/mm2である（リーマ番号1、2を除く）。これらのリーマの強度とねじれ角の値のばらつきを調べ、これらの特性のばらつきの範囲を示した。また，ねじれ角が破折特性に及ぼす影響を臨床治療上考慮し，破折の安全性を検討した．

Strength of pulp canal reamers are important problems for cutting treatments of the root of tooth at the dental regions. Reamers have been used as cutting tools by the twisting movements, and then, fracture of reamers are especially caused by the shearing stress at the bite tips. So, this paper treated the shear strength of dental canal reamers, which are torsional strength and twisting rigidity of these cutting instruments. And we made the torsional apparatus for cutting and twisting tests, and tested the torsional strength of raw materials and pulp canal reamers. Type of reamer's configuration are treated by Japanese industrial standard (JIS) and these properties are readjusted with dimensions of diameter of reamers. Shear strength of reamers are 120 approximately 140 kg/mm2 and strength of straight bar with taper are about two times of that of reamers which are about 40 kg/mm2 (except reamer's number 1, 2). Scattering of value of strength and torsional angle of these reamers are examined and showed the range of scattering of these properties. Effectiveness of torsional angle on the fracture properties are considered on the clinical treatments and treated the safety of fracture of these reamers.