ROOT-CANAL INSTRUMENTS FOR MANUAL USE - CUTTING EFFICIENCY AND INSTRUMENTATION OF CURVED CANALS

The cutting efficiency of different endodontic hand instruments and th e effects of instrumentation on curved canal shape were investigated u nder standardized experimental conditions using an automatic testing d evice. Cutting efficiency in rotary motion was assessed by determinati on of the maximum penetration depth of the instruments into a cylindri cal canal in a special resin block (size 25 and size 35 instruments), Changes in canal shape were determined by instrumentation of standardi zed canals (42 degrees curvature) incrementally from size 15 to size 3 5. Except in the case of one instrument, size 35, in both sizes tested flexible instruments reached significantly (P < 0.05) greater maximum penetration depths than conventional reamers or K-files, Changes in t he canal shape differed significantly between the different instrument s in 13 of the 14 measuring points, Drastic undesirable changes in the canal shape (e.g. straightening or zip and elbow) occurred after inst rumentation with reamers and K-files, but these changes were less noti ceable after instrumentation with flexible instruments with convention al tips, After instrumentation with flexible instruments with modified tips there, were few undesirable changes in shape. The conclusion cou ld be drawn that flexible instruments, especially those with modified tips, were clearly superior to conventional reamers and K-files with r egard to cutting efficiency and instrumentation of curved canals.