Year : 2016 | Volume
: 28 | Issue : 2 | Page : 90--91
Revolutionary development of endodontic instruments and its implications
Department of Conservative Dentistry, School of Dentistry, Pusan National University, Busan, Korea
Department of Conservative Dentistry, School of Dentistry, Pusan National University, Geumo-ro 20, Mulgeum, Yangsan, Gyeongnam, 50612
|How to cite this article:|
Kim HC. Revolutionary development of endodontic instruments and its implications.Endodontology 2016;28:90-91
|How to cite this URL:|
Kim HC. Revolutionary development of endodontic instruments and its implications. Endodontology [serial online] 2016 [cited 2021 Dec 7 ];28:90-91
Available from: https://www.endodontologyonweb.org/text.asp?2016/28/2/90/195419
After adoption of the nickel-titanium (NiTi) alloy to the endodontic instrument, there have been numerous trials to make better instruments having superior properties and safety. Especially, by using the NiTi files in a motor-driven way, the clinical efficiency has been much more enhanced.
After introducing the NiTi instruments in 1988, the files were developed in various shapes of cross sections while having similarly tapered shaft as 4% and 6% (fixed taper). In this first generation, the files were made of conventional NiTi alloy without any special treatment. They were introduced mainly with the advantages of better cutting efficiency and better flexibility to follow the curved root canal with reduced transportation.
In the second generation, the manufacturers tried to give asymmetric cross sections and inconsistencies to their designs such as progressive changing taper, reverse taper, round shaft without taper, alternative pitch length, and off-centered cross section. By applying these kinds of variation, the instruments have given the better efficiency for canal shaping. Progressive changing taper gave the instrument system multi-tapered shaft which facilitated crown-down approach during shaping procedure with reduced number of instruments. The round wire shaft without cutting flutes made the system with extensively high flexibility without screw-in forces. Alternative pitch design was also applied to reduce the screw-in forces of the active instruments. Off-centered cross section made the file with snake movement or swaggering movement during rotation, and the files have reduced screw-in forces by reduced contact points with the canal wall and increased debris removal spaces alongside the shaft flute.
Various kinds of heat treatment technique made the conventional NiTi alloy with better mechanical properties for instruments of the third-generation group. The R-phase was introduced in the market with the Twisted File (Sybron Endo, USA) for the first time and M-wire was also introduced with the better fatigue resistances not only in a flexional condition but also in a torsional condition. Further enhancement was achieved with the CM-wire that attempted to increase the centering ratio and minimize the reaction force for reducing transportation and risk of dentinal defect. Gold-wire or Blue-wire was also incorporated to make brand-new instruments with advanced mechanical properties. They also have similar properties of CM-wire but slightly harder than CM-wire. Electrical Discharge Machining (Spark erosion technique) was introduced recently as a new manufacturing method with the HyFlex EDM (Coltene, Switzerland). The manufacturers of all these new instruments have claimed that their products have a higher performance to shape the root canals and their instruments have higher fatigue fracture resistances. The recently introduced instruments should be studied further for their mechanical properties as well as clinical performances.
The next generation is characterized with their special movements of kinematics such as reciprocating and oscillation motion. Due to the increased lifetime of the instrument and simple (single file) instrumentation procedure, reciprocating systems have been also popular. The reciprocating motion instead of continuous rotation motion was proved to have better kinematics to increase the fatigue resistances and torsional resistances by the periodic change of their rotational direction. Although the clockwise movement of noncutting direction may increase the potential risk of debris extrusion to the apical area, it has not been proved yet sufficiently. Some literatures also reported that the reciprocating system might have higher potential risk to produce dentinal defects or apical crack. Meanwhile, some other researchers reported that the heat-treated instruments of the third generation may reduce such dentinal defects and the reciprocating motion is not the main factor of the mechanical failure.
The revolutionary instrument, self-adjusting file (SAF, ReDent Nova, Israel), has a kind of oscillation motion of 0.4 mm in a high speed (4000/min). Because of its hollow design without actual cross section, SAF could change the shape inside the root canal. It means that the file has extremely lower reaction force to the dentinal wall. Therefore, SAF is highly effective to preserve the original natural canal shape.
Some instrument systems have their characteristics from two to three generations simultaneously. Through the third and fourth generation instruments, minimal invasive instrumentation concept is adapting to the root canal system. Not only the SAF but also majorities of the heat-treated instruments are trying to preserve the natural root canal shape and the canal curvatures. Most recently, XP-endo Shaper and XP-endo Finisher (FKG Dentaire, Switzerland), TRUshape (Dentsply Sirona), and GentleWave system (Sonendo, CA, USA) using broad-spectrum acoustic energy are quite specific and revolutionary to the conventional instrument systems. These instruments and their shaping concept may help preserve the natural canal shape but remain with rough canal wall which is potentially infected and difficult to seal using gutta-percha.
It is definitely clear that the currently introduced revolutionary instruments are useful in reducing a mechanical failure of the endodontic treatment but, on the other hand, may increase the risk of biological failure by the remaining infected dentin. Therefore, clinicians may need to focus further on the chemical preparation to minimize the biological failure. Sonic activation and/or ultra-sonic adjunctive devices for chemical preparation would be utmost clinically important. “Revolutionary development and its usage should be under the rationale of endodontics.”