An in vitro investigation into the cutting action of ultrasonic radicular access preparation instruments

The aim of this study was to investigate the dentine cutting action of a CT 4 and SJ4 radicular preparation inserts (Excellence in Endodontics/Analytic Technology, Orange, CA, USA) used in a Piezon Master 400 ultrasonic handpi ece (Electro Medical Systems SA, Nyon, Switzerland). Calibration of the ult rasonic inserts was carried out at minimum, medium and maximum power settin gs using light microscopic measurement of the tip displacement amplitudes ( X120 mag). Polished dentine samples were instrumented, at monitored loads, at the three chosen power settings, to produce uniform dentine cuts. The re sultant dentine debris was collected for SEM analysis, and comparison with that produced by rotary instruments. The depth of dentine cut was measured at X30 magnification. Fracture of the SJ4 insert was noted at medium power setting. Results revealed a significant increase in both displacement ampli tude and depth of dentine cut with power setting (ANOVA P<0.001). Dentine c hip size increased with power, and differed in structure and appearance fro m those produced by rotary instruments. In conclusion, ultrasonic cutting i s influenced significantly by power setting, and dentine chip formation is fundamentally different to rotary instrumentation.