[Studies on the strength and the cutting performance of dental canal reamer. (III) Cutting performance and torsional fracture (author's transl)].

Characteristics of cutting torque and fracture strength of pulp canal reamers are important problems as for the severity used at many of dental cutting tools. And it is the most difficult problems that reamers are cutting tools to be used for magnification of root canals. So, this paper makes a report on the measurements of reamer's section and dimension of the under hole, which are required for cutting test, and on the safety of characteristics of dental canal reamers. Diameter of under hole are determined by the relationship of reamer's section. And these results of measurements are compared with the Japanese Industrial Standard values and we discussed the probabilities of the clearance of these dimensions. Cutting torque of reamers are measured with twisting test machine of our making. Concerning the safety of fractures, we apply the theoretical analysis for the fracture to torque of bite tips and estimated the fracture torque of cutting section of reamers. And probablity of twisting fracture of reamers are existed about from one half to one-fifth values for the dental reamers of practical used.