CUTTING EFFICIENCY LOSS OF ROOT-CANAL INSTRUMENTS DUE TO BULK PLASTIC-DEFORMATION, SURFACE DAMAGE, AND WEAR

Cutting efficiency loss of #15 H-type and K-type files was studied as a function of bulk plastic deformation and cutting edge wear. Instrume ntation was done by purely extractive filing, without any significant torsional and/or bending strain. Cutting efficiency variations were as sessed by means of cutting force measurement, while absolute cutting e fficiency was obtained through three-dimensional scanning stylus profi lometry. Bulk plastic deformation-induced flute modifications may lowe r the cutting efficiency of H-type files by approximately 50%. For thi s instrument special care is required in tip and flute machining to av oid in vivo breakage. On the contrary, within the normal life-span of an instrument of approximately 100 strokes cutting edge wear is seen t o be negligible. The existence of such wear is ''inferred'' indirectly from a 10% drop in extraction efficiency.