| PURPOSE To investigate the impairment of Pro Taper Engine-Driven Rotary Ni-Ti Endodontic Instruments in artificial molar root canal models. And provide a refere nee of the safe use of these instruments.METHODS The pure copper with a Brinell hardness value HB58 was chosen as the material of the model.Three different angles of artificial root canals were designed.The fatigue life of Ni-Ti root canal instuments were tested after used in the models and then compared with those of clinical used Ni-Ti instruments in molar root canals. (The curvature angle:15°=a<25°) Six sets(six each)of Pro Taper Ni-Ti instruments(Dentsply, 21mm) were used, five of six sets were prepared in artificial molar root canal models,and the other sets as the blank control group.The stereo microscope was used to check and record each file if there was abrasion or rupture after prepared one canal.RESULTS The safe life of each file in artificial root canals with different angles were:70°S1(344.6±27.3),F3(262.3±14.6)(P>0.05); 64°S1(375.5±9.7) S2 (369.4±23.3) F1 (303.0±9.5) F3 (328.2±28.3) (P>0.05); 60°F1 (306.6±12.4) F3 (300.8±34.2) (P>0.05). The situation in The Ni-Ti Endodontic Instruments with a curvance angle of 64 dgree was most close to the clinical situation.Impairment was appeared when preparing the nineth root canal in Three of five sets of Pro Taper Ni-Ti insruments.Two types of Impairments were observed:The edge damage which was characterized by abrasion on the edge and the thread damage characterized by tightened or loosened spiral.The incidence rate of the edge damage was 16.7%. The thread damage was 26.7%.CONCLUSION The pure copper artificial root canals with an angle of curvature of 64 degrees could be an ideal model for the research of Ni-Ti rotary-instruments in vitro. The number of safe use of ProTaper Ni-Ti instruments is nine, The stere o microscope is recommended to check the instrumets in order to prevent the disr upture when it working. |
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