Handpieces providing a mechanical movement to the root canal cutting instrument have been available since 1964. Their function was primarily a reciprocating action through 90 and/or a vertical movement, according to the design and make. Because steel files do not have the flexibility necessary for rotary movements in a curved canal without damaging the canal configuration, these instruments were never really acceptable in endodontic practice. A totally new concept in canal preparation came with the development of sonic and ultrasonically activated endodontic handpieces. Much research took place into the mode of action and effectiveness of these machines. It was generally agreed that while the sonic machines were more effective at hard tissue removal, the ultrasonic machines were more effective in irrigation. The piezo-electric machines were found to be more effective than the magnetostrictive. The latter also generated more heat, and irrigation with effective quantities of sodium hypochlorite was found to be difficult. The ultrasonic action causes acoustic microstreaming of the irrigant, intensive circular fluid movement carried right to the tip of the instrument, found to be very effective at canal debridement. This effect is reduced, however, when the file is constrained by the canal wall. The main use of these instruments today is in irrigation and debridement, using a freely oscillating file in a sodium hypochlorite filled canal, after thorough mechanical canal shaping. However, the development of nickel-titanium alloy for endodontic instruments has allowed the concept of an engine driven endodontic instrument to be fully explored. The total flexibility of this alloy, and the use of radial lands on the cutting flutes to keep the instrument centred in the canal, permit controlled cutting of the dentine walls. Most major manufacturers have developed a nickel-titanium rotary system. Lightspeed, Profiles, GT Rotary files, FlexMaster, Quantec system, Hero, K3, Protaper, and no doubt more will appear before this book is even published. It would not be possible to describe each of these fully, but the basic concepts are presented here, with a general description of their use being given in Part 7.
The systems will generally conform to one of three patterns.
The system may have a standard ISO tip size sequence, with the instruments being manufactured with an increased taper, usually either 4% or 6%.
The system may be presented with a single tip size, but with the sequence of file sizes having an increased taper of up to 12%. In order to accommodate this taper in a narrow root canal, the diameter of the instrument is usually limited to 1 mm, giving quite a short functional blade in the greater tapers. Both of these new developments may be combined into one system.
A low-speed, controlled-torque motor is necessary when using these instruments, as illustrated in Figure 12.
The systems will generally conform to one of three patterns.
The system may have a standard ISO tip size sequence, with the instruments being manufactured with an increased taper, usually either 4% or 6%.
The system may be presented with a single tip size, but with the sequence of file sizes having an increased taper of up to 12%. In order to accommodate this taper in a narrow root canal, the diameter of the instrument is usually limited to 1 mm, giving quite a short functional blade in the greater tapers. Both of these new developments may be combined into one system.
A low-speed, controlled-torque motor is necessary when using these instruments, as illustrated in Figure 12.