However, the development of nickel-titanium alloys has revolutionised automated root canal preparation. The remarkable ability of these alloys to alter their crystalline state gives instruments manufactured from nickel-titanium profound flexibility. Mechanised instruments can withstand the distortions caused by repeated rotation in curved canals without causing preparation errors. Most of these instruments have design features such as radial lands (Fig. 4) to keep the instrument centred in the canal, and a non-cutting tip to guide the instrument down the canal. New designs are constantly appearing, (Fig. 5) and the clinician should ensure that considerable experience with whichever system is chosen has been obtained on extracted teeth, before the instruments are introduced into clinical patient treatment.
A controlled high-torque, low-speed motor is required for efficient use of the instruments. Most manufacturers of endodontic instruments produce such a motor, and their complexity may vary from that illustrated in Part 5, Figure 12, to that shown here in Figure 6. It must be emphasized that these nickel-titanium instruments do have a limited life, and will fracture in time after a large number of rotations. Slow (150 250 rpm) rotation does not impede their efficiency but extends their life. However, it is recommended that the instruments should be discarded after a certain number of cases as described by the
Fig. 5 One modern system of nickel-titanium rotary instruments the System GT.
Fig. 6 A state-of-the-art endodontic motor, being a rechargeable slow-speed, high-torque handpiece encompassing an apex locator and associated facilities.
manufacturer, and more frequently if an instrument has been used to negotiate difficult curved canals. The files should also be removed from the canal and cleaned frequently. Although debris is moved coronally it tends to compact in the file flutes, and if these become occluded the instrument will fracture. The separated part will engage in the root canal and may prove extremely difficult to remove.
A controlled high-torque, low-speed motor is required for efficient use of the instruments. Most manufacturers of endodontic instruments produce such a motor, and their complexity may vary from that illustrated in Part 5, Figure 12, to that shown here in Figure 6. It must be emphasized that these nickel-titanium instruments do have a limited life, and will fracture in time after a large number of rotations. Slow (150 250 rpm) rotation does not impede their efficiency but extends their life. However, it is recommended that the instruments should be discarded after a certain number of cases as described by the
Fig. 5 One modern system of nickel-titanium rotary instruments the System GT.
Fig. 6 A state-of-the-art endodontic motor, being a rechargeable slow-speed, high-torque handpiece encompassing an apex locator and associated facilities.
manufacturer, and more frequently if an instrument has been used to negotiate difficult curved canals. The files should also be removed from the canal and cleaned frequently. Although debris is moved coronally it tends to compact in the file flutes, and if these become occluded the instrument will fracture. The separated part will engage in the root canal and may prove extremely difficult to remove.