Validity check of easy-to-use torsion test method for bioceramics

This article examines the validity of a test method to determine the torsion strength of bioceramics under in-vivo-mimicking circumstances. The torsion test setup consisted of upper and lower grip jigs, designed to grip dog bone-type bioceramic specimens, and an opening torque tester for PET bottles. A specimen was set on the torque tester through the lower grip jig at the bottom, and the upper grip jig was then mounted on the top end of the specimen. The upper grip jig was rotated by hand to apply torque until the specimen was fractured by the torsion. The torsion strength was calculated using the maximum torque at fracture and the gage diameter. Five calcium phosphate bioceramics were employed for the torsion test. The torsion strength data obtained by this method agreed closely with data measured using a material testing machine with a convertor from the linear crosshead motion into the rotation. Round-robin tests among four different organizations in Japan revealed that the torsion strength data showed good agreement for each sample immersed for 24 hr under phosphate-buffered solution as in-vivo-mimicking circumstances. These results verified the ability of the easy-to-use torsion method to give appropriate strength data with a simple experimental setup.