PERFORMANCE OF ENGINE-DRIVEN ROTARY ENDODONTIC INSTRUMENTS WITH A SUPERIMPOSED BENDING DEFLECTION .5. GATES GLIDDEN AND PEESO DRILLS

A laboratory study was performed on Gates Glidden and Peeso drills to determine the incidence of shaft fracture when a bending deflection wa s superimposed on the rotating drills. Samples of sizes #1 to #6 stain less steel Gates Glidden drills, sizes #1 to #6 stainless steel and ca rbon steel-type P Peeso drills, and sizes #009 to #023 carbon steel-ty pe B-1 Peeso drills from each of two manufacturers were evaluated with a unique apparatus that applied a 2-mm bending deflection while rotat ing the instruments. The apparatus did not restrict movement of the bu r head during rotation. The test drills were rotated at 2500, 4000, an d 7000 revolutions per minute, and the number of revolutions at failur e was recorded. Scanning electron microscopic observations established that the stainless steel Gates Glidden and Peeso drills failed by duc tile fracture, whereas the carbon steel Peeso drills failed by brittle fracture. Instrument fracture was always near the handpiece shank wit h this test, and the length of the fractured drills was measured from the working tip. It is recommended that this additional test be adopte d to determine fatigue properties of engine-driven rotary endodontic i nstruments in establishing international performance standards.