Rotary Instrumentation Systems Using Nickel Titanium

ProFile System

Introduced in 1994, ProFile instruments have increased tapers compared to conventional hand instruments. The tips of the ProFile Series 29 rotary instruments have a constant proportion of diameter increments, specifically 29%. The cross-section of a ProFile instrument features a U-shape design with radial lands and a parallel central core. Lateral views reveal a 20-degree helix angle, a constant pitch, bullet-shaped noncutting tips, and a neutral or slightly negative rake angle, which facilitates a reaming action. This design effectively transports debris coronally, removing it from the root canals. The preferred speed for these instruments is between 275-325 rpm.

ProFile GT Files

The Greater Taper (GT) file was also introduced in 1994. Similar to the ProFile system, the GT file features a U-shape design. These instruments are available in four tapers: 0.06, 0.08, 0.10, and 0.12. The maximum diameter of the working part coronally is 1 mm, while the apical instrument diameter is 0.2 mm. GT files have a variable pitch and an increasing number of flutes in progression to the tip. The instrument tips are noncutting and rounded.

ProTaper Universal System

The ProTaper system is based on a different concept, comprising six instruments: three shaping files and three finishing files. This set is augmented by two larger finishing files and a set designed for retreatment procedures. In cross-section, ProTaper instruments show a modified K-type file with sharp cutting edges and no radial lands, creating a stable core and sufficient flexibility for the smaller files. The cross-section of finishing files F3, F4, and F5 is slightly relieved for increased flexibility. A key distinction of this system is the varying tapers along the instruments’ long axes. The three shaping files have tapers that increase coronally, while the five finishing files exhibit the reverse pattern.

Shaping files #1 and #2 have tip diameters of 0.185 mm and 0.2 mm, respectively, and 14-mm-long cutting blades. Their diameters at D14 are 1.2 mm and 1.1 mm, respectively. The finishing files (F1-F5) have tip diameters of 0.2, 0.25, 0.3, 0.4, and 0.5 mm, respectively, between D0 and D3, with apical tapers of 0.07, 0.08, 0.09, 0.05, and 0.04, respectively. All finishing files have rounded noncutting tips. The convex triangular cross-section of ProTaper instruments reduces the contact areas between the file and the dentin. To enhance cutting efficiency, the pitch and helix angle are balanced, preventing the instruments from threading into the canal.

ProTaper instruments are recommended to be used within the range of 250 to 300 rpm. Two usage characteristics are recommended for the ProTaper system:

Preparation of a glide path.
The use of a more lateral “brushing” working stroke. This stroke allows clinicians to direct larger files coronally away from danger zones and counteract any "threading-in" effect.

RaCe, Bio Race

Manufactured since 1999 by FKG, RaCe stands for reamer with alternating cutting edges. This design aims to reduce the tendency of the file to thread into the root canal. Cross-sections are triangular or square for 0.02 instruments with sizes #15 and #20 tips. The surface quality of RaCe instruments is achieved through electropolishing. The tips are round and noncutting.

Twisted File

In 2008, the first fluted NiTi file was introduced, manufactured by plastic deformation, a process similar to the twisting process used to produce stainless steel K-files. This is accomplished through a thermal process that allows twisting during a phase transformation into the “R-phase” of nickel-titanium. The instrument is available only with size #25 tip sizes, in tapers from 0.04 up to 0.12. This production process enhances physical properties.

Wave One Single File Reciprocating System

This system is a single-use, single-file system to shape the root canal. Typically, the technique requires one hand file followed by one single Wave One file to shape the canal completely using reciprocation motion. The file is made with M-wire technology, which improves strength and resistance to cyclic fatigue about four times that of traditional rotary NiTi files. The system includes:

The Wave One small file: used in narrow canals, with a tip ISO of 20 and a continuous taper of 6%.
The Wave One primary file: used in the majority of canals, with a tip ISO of 25 and an apical taper of 8% that reduces towards the coronal end.
The Wave One large file: used in wide canals, with a tip ISO of 40 and an apical taper of 8% that reduces towards the coronal end.

The instruments are designed to work with a reverse cutting action. All instruments have a modified convex triangular cross-section at the tip end and a convex triangular cross-section at the coronal end. This design improves instrument flexibility. The variable pitch flutes along the length of the instrument enhance safety.

ProTaper Next

This system comprises 5 files: X1, X2, X3, X4, and X5. These files correspond to sizes 20/04, 25/06, 30/07, 40/06, and 50/06, respectively. The X1 and X2 have a variable tapered design, whereas X3-X5 files have a fixed taper from D1-D3, then a decreasing percentage tapered design over the rest of their active portions. This system has a rectangular cross-section that is off-centered, allowing two points of contact with the dentin wall, leaving the rest of the space free for storing debris, which will be removed by the file's swaggering motion.

Self-Adjusting File (SAF)

The self-adjusting file (SAF) represents a novel approach in file design and operation. The file is a hollow device, designed as a cylinder of thin-walled, delicate NiTi lattice with a lightly abrasive surface. An initial glidepath is established with a #20 K-file to allow the insertion of the SAF file. The file is compressed from its 1.5 mm diameter into dimensions equivalent to those of a #25 K-file. The handpiece generates in-and-out vibrations with 5000 vibrations per minute and 0.4 mm amplitude. The compressed file adapts itself to the root canal walls, applying a uniform cutting action, gradually removing a uniform dentin layer from the canal walls. Continuous flow of irrigant removes the tissue debris and the dentin powder generated by the file.

Endo-eze Reciprocating Files

The Giromatic handpiece, a rotary instrument in use since 1969, delivers 3000 quarter-turn reciprocating movements per minute. Rasps and barbed broaches are most often used in Giromatic handpieces, but K-type and H-type instruments can also be used. The endo-eze file system (Ultradent) is a recent addition for Giromatic handpieces. The set has four instruments designed to clean the middle third of the canal. The sizes and tapers are 0.10 #0.025 taper, 0.13 #0.35 taper, 0.13 #0.45 taper, and 0.13 #0.06 taper. The use of stainless steel hand instruments is suggested for the apical third of the canal.

Sonic and Ultrasonic Instruments

A distinct approach to root canal instrumentation involves files or ultrasonic tips (of varying shapes and sizes) activated by electromagnetic ultrasonic energy. Piezoelectric ultrasonic units are also available for this purpose, activating an oscillating sinusoidal wave in the file with a frequency of approximately 30 kHz. Two primary types of units are available: ultrasonic and sonic. Ultrasonic devices, operating at 25 to 30 kHz, include the magnetostrictive (Cavi-endo) and the piezoelectric (Enac). Sonic devices operate at 2 to 3 kHz (Sonic Air MM 1500). Ultrasonic devices use regular instrument types (e.g., K-files), whereas sonic devices use specialized instruments known as Rispi-Sonic, Shaper-Sonic, Trio-Sonic, or Heli-Sonic files.

Piezoelectric units offer advantages over magnetostrictive systems, such as generating less heat, eliminating the need for cooling the electric handpiece. The magnetostrictive system generates considerable heat, requiring a special cooling system in addition to the irrigation system for the root canal. The file in an ultrasonic device vibrates in a sinus wave-like fashion. A standing wave has areas with maximal displacement (antinodes) and areas with no displacement (nodes). The tip of the instrument exhibits an antinode. Files must be used for short durations, remain passive within the canal, and the power must be carefully controlled. Ultrasonic devices have proven very efficient for irrigating root canal systems. During free ultrasonic vibration in a fluid, two significant physical effects are observed: cavitation and acoustic streaming. Cavitation is the implosion caused by alternating positive and negative pressure during oscillation in a fluid. Acoustic streaming creates small, intense, circular fluid movement around the instruments.

Generations of NiTi Rotary Instruments

From the 1990s to the present, NiTi rotary instruments have undergone transformative changes in their construction and physical characteristics. The design, shape, and number of instruments used in each group have been significantly modified. The aim of these modifications is to develop a NiTi rotary instrument that effectively cuts and removes dentine while resisting fracture, even in challenging narrow, curved root canals. Another objective is to simplify the cleaning and shaping stage, reduce the number of instruments used, and preserve the original shape of the prepared root canal.

First Generation

Introduced in the mid-1990s, first-generation NiTi rotary files are characterized by passive cutting radial lands along with fixed 0.04–0.06 tapers over the full working length. Important instruments in this category include LightSpeed Endodontics (1992), Profile-Dentsply (1993), Quantec-SybronEndo (1996), and GT system-Dentsply (1998). Research indicates that first-generation rotary instruments create smooth root canal walls, centered in the middle, with low procedural errors. The main limitation was the requirement of numerous files to achieve these outcomes, leading to increased complexity.

Advantages: Optimum flexibility (ability to follow canal curvature), high cutting efficiency, reduced working time, and lower incidence of postoperative pain.
Disadvantages: Increased costs (single-use), possibility of instrument fracture, poor cleaning in flattened root canals.

Second Generation

Introduced in 2001, these instruments featured active cutting edges for greater cutting efficiency, reducing the number of instruments needed. Notable systems include ProTaper UniversalDentsply, K3-SybronEndo, Mtwo-VDW, Hero Shaper-Micro-Mega, I Race, and I Race PlusFKG Dentaire. Studies have confirmed their efficiency in fast preparation and preserving canal shape in curved and calcified cases. However, some researchers reported canal transportation and a tendency for breakage.

Advantages: High resistance to cyclic and torsional fatigue, lower fracture index, greater cutting efficiency, shorter working time, lower incidence of postoperative pain.
Disadvantages: Increased costs (single-use), possibility of fracture (lower incidence than first generation).

The NiTi Alloy Phase R was also utilized in the manufacture of Oscillating (Asymmetric) Systems, usually called Reciprocants, Oscillating Systems (Reciprocants) TF Adaptive (2013) (SybronEndo Kerr Group).

Third Generation

From late 2007, manufacturers began applying heating and cooling technologies to NiTi alloys to improve instrument safety, particularly in curved root canals. These processes enhance the metallurgic properties of the NiTi alloy, reducing cyclic fatigue and the risk of instrument separation. M-wire and R-phase technologies, along with electrical discharge methods, create instruments with high memory shapes and low separation risk. Notable files include K3 XF Files SybronEndo, Profile GTX Series–Dentsply, controlled memory (CM) Files (HyFlex CM)– Coltene, and Vortex Blue (Dentsply Tulsa). Flex files (NeoEndo) files have been predisposed to gold thermal treatment which increases their cutting efficiency along with cyclic fatigue resistance.

Advantages: High resistance to cyclic and torsional fatigue, lower fracture index (when used more than once), greater cutting efficiency, greater flexibility (15% more flexible than first generation), less working time, greater patient comfort, lower incidence of post-operative pain.
Disadvantages: Higher costs (single-use), possibility of fracture (lower incidence than previous generation).

Fourth Generation

Reciprocation, a repetitive back-and-forth motion, was introduced by Blanc in the late 1950s. Reciprocating NiTi rotary instruments have movements with nearly equal clockwise and counterclockwise rotation degrees. This reciprocation theory led to the development of the fourth generation of NiTi rotary instruments. The use of a single-file technique was another success derived from this philosophy, achieving thorough cleaning and shaping goals. Studies have shown that Wave One and One Shape single-file systems efficiently reduce bacterial numbers in the root canal while preserving the original shape. Featured instruments of the fourth generation include Wave One-Dentsply, self-adjusting file (SAF)-ReDent Nova, and Reciproc-VDW.

Advantages: Indicated for root canals with severe anatomical complexity, high resistance to cyclic fatigue, lower fracture index (300% more resistant), greater cutting efficiency, greater flexibility (80% more flexible than conventional instruments), offers less working time, Lower incidence of postoperative pain, greater patient comfort.
Disadvantages: Contraindicated for wide or relatively wide and straight ducts.

Fifth Generation

Improvements in canal shaping efficiency were achieved by offsetting the center of rotation, producing a mechanical wave of motion along the full length of the NiTi file. This enhances cutting and debris removal compared to centered mass rotating instruments. The offset design also reduces taper lock or the screwing effect, preventing instrument separation. Important files of the fifth generation include HyFlex/electrical discharge machining (EDM)-Coltene, Revo-S-Micro-Mega, One Shape Micro-Mega, and ProTaper Next-Dentsply.The Revo-S and the One Shape systems both offer proper root canal shaping through continuous clockwise rotation.

Advantages: 80% more flexible than conventional rotary systems, 150% more resistant to cyclic fatigue compared to the Universal Protaper System, shorter working time.

New Generation System (NiTi Blue)

These systems feature NiTi Alloy with Blue Treatment, such as NiTi Vortex BlueTM instruments (Dentsply/Sirona-United States), manufactured with Nitinol 508 and consisting of a blue titanium oxide layer. This harder surface layer compensates for the loss of hardness compared to Profile Vortex M-Wire. Vortex Blue and shape memory technologies use special thermal processes to control the transition of extreme temperatures, making the instruments highly flexible.

Advantages: Indicated for root canals with severe anatomical complexity, follows natural curvature of the root canal due to its great flexibility, greater resistance to cyclic fatigue (65% higher than M-Wire® NiTi and 99% higher than first generation NiTi), greater resistance to torsion, offers a lower working time, a reduced memory effect so it can be pre-curved slightly and not return to its original position with less resistance of the instrument when introduced into the root canal. instruments have improved material properties within creases fatigue resistance and flexibility compared to Profile Vortex (M-Wire) instruments. However, both NiTi Blue and M-wire alloy show better fatigue resistance compared to conventional nickel titanium alloy. Torsion resistance is also affected by the cross-sectional design, the metal mass and the properties of the alloy.