History of Endodontic Instruments
The first endodontic file was crafted in the mid 1800s by Edward Maynard by notching round wires at first from watch springs and then from piano wires, into files that were capable of removing pulp and debris from teeth. K-files, which are, to these days, the most commonly used stainless steel hand files in endodontics, were developed by the Kerr company in 1915. Stainless steel hand file techniques, including the step-back, the anti-curvature, the step-down and the balanced force techniques have all been promoted in order to fulfill the instrumentation objectives proposed by Schilder. In 1960 a novel nickel-titanium alloy was developed by William Bueller in Silver Springs, Maryland at the United States Naval Ordinance Laboratory (that is why we often refer to NITINOL where NOL stands for Naval Ordnance Laboratory).
FIRST GENERATION The first rotary NiTi instrument was designed by Dr. John McSpadden with a 0,02 taper and was placed on the market in 1992, changing how dental practitioners envisioned instrumentation. File breakage issues were substantial at that time. In 1994, Dr. Johnson introduced the PROFILE line, 0.04 and 0.06 tapered instrument series and the “ORIFICE SHAPERS.” Their cross-sectional shape resulted from the machining of three U-shaped grooves around a tapered NiTi wire, with and unground space remaining between the grooves, providing the so-called “radial land” area. Other rotary file lines, such as LightSpeed (Senia and Wildey), Quantec (McSpadden) and Greater Taper files (GT Rotary System by Dr. Buchanan) were developed soon afterwards. All of the first-generation NiTi rotary files featured passive cutting radial lands and constant tapers over their working parts, and, most of all, required a considerable number of files to achieve preparation objectives.
SECOND GENERATION The next generation of NiTi rotary files came to market by the end of the 90s. These instruments differed from the previous generation in their cutting edges (and the absence of radial lands). This generation aimed to reducing the number of instruments needed to achieve the preparation goals. To this generation belong ENDOSEQUENCE (Brasseler USA), BIORACE (FKG Dentaire), PROTAPER (Dentsply Tulsa), K3 (Sybron Endo), M-TWO (Sweden & Martina), FLEXMASTER (Dentsply), HERO 642 (Micro-Mega®, Besançon, France).
THIRD GENERATION The development of new manufacturing technologies made it possible to optimize the microstructure of NiTi alloys, thus giving birth to 3rd generation instruments. Special heat treatment provides files with a more resistant, both to stress and fatigue, alloy; the instruments that underwent this type of processing include HYFLEX CM (HyFlex; Coltene Whaledent, Cuyahoga Falls, OH), K3XF (SybronEndo, Orange, CA), PROFILE GT SERIES X (GTX; Dentsply Tulsa Dental Specialties, Tulsa, OK), PROFILE VORTEX (Vortex) and VORTEX BLUE (Dentsply Tulsa), TYPHOON™ Infinite Flex NiTi (TYP CM; Clinician’s Choice Dental Products, New Milford, CT), and TWISTED FILES (TFs; SybronEndo).
FOURTH GENERATION Better performance reached in reciprocation technology gave birth to this new generation of reciprocating files. The 4th generation comprises instruments used with a motion different from rotary or those crafted for as “single file techniques”, meaning used as the only tool to perform the whole shaping phase. Single-file shaping techniques were launched both by WAVEONE (Dentsply Tulsa Dental Specialties and Dentsply Maillefer) and RECIPROC (VDW) in 2011. The self-adjusting file (SAF; ReDent-Nova, Raanana, Israel) was designed as a thin-walled, hollow cylinder made out of a delicate NiTi grid, featured with an abrasive surface: the SAF system provides a new mode of operation as it uses a simultaneous irrigation, allowed by the void cylinder.
FIFTH GENERATION The fifth generation of shaping files exploits a wave motion along the active part of the files: this is allowed by an off-set design that conveys mechanical rotation into wave motion. Brands that produce variations of this technology are REVO-S,ONE SHAPE® (Micro-Mega®, Besançon, France), and PROTAPER NEXT (PTN; Dentsply Tulsa Dental Specialties/Dentsply Maillefer).