Review Article DESIGN FEATURES OF ROTARY INSTRUMENTS IN ENDODONTICS INTRODUCTION ABSTRACT

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1 DESIGN FEATURES OF ROTARY INSTRUMENTS IN ENDODONTICS Review Article ZARNA SANGHVI*, KUNJAL MISTRY** ABSTRACT The last decade has been witness to phenomenal growth in endodontic technology. The introduction of these new technologies has resulted in endodontics becoming easier, faster and most importantly, better. Principal among these is Nickel Titanium (NiTi) rotary instrumentation that results in consistent, predictable, and reproducible shaping. The purpose of this article is to review the design features of different rotary instruments used for pulp space preparation. Individual design features affect the performance of NiTi rotary instruments. Important mechanical features include the variability of taper, rake angle, cross-sectional geometry, tip configuration, design of blades, helical angle and pitch. These design features influence flexibility, cutting efficiency and safety. In this review design features of commonly used NiTi rotary systems are summarized. Key Words: Rotary Instruments, NiTi Files, Taper, Rake Angle, Radial Land. INTRODUCTION The fundamental aim of endodontic treatment is to prevent or cure apical periodontitis. One of the main objectives of root canal preparation is to shape and clean the root canal system effectively whilst maintaining the original configuration without creating any iatrogenic events such as instrument fracture, external transportation, ledge, or perforation. Preparation of the root canal system is recognized as being one of the most important stages in root canal treatment which includes both enlargement and shaping of the complex 1,2 endodontic space together with its disinfection. A variety of instruments and techniques have been developed and described for this critical stage of root canal treatment. Over the last few years, endodontics has undergone a complete revolution with the introduction of the Nickel Titanium alloy for the manufacture of manual instruments initially and then rotary endodontic instruments. The extraordinary characteristics of super-elasticity and strength of the NiTi alloy have made it possible to manufacture rotary instruments with double, triple and quadruplet taper compared to the traditional standard.02 taper of the stainless steel hand manual 4,5,6 instruments. This has made it possible to achieve perfect shaping with the use of very few instruments in a short period of time and without the need for above average skills on the part of the operator. The super-elasticity has furthermore made it possible to carry out extremely conservative shapes, better centered, with less canal transportation and therefore with more respect of the original anatomy. In order to improve working safety, shorten preparation time and create a continuously tapered, conical flare of preparations advanced instrument designs with non-cutting tips, radial lands, different cross-sections, superior resistance to torsional 7,8,9 fracture and varying tapers have been developed. Truly, NiTi rotary instrumentation has been one of the most significant changes in dentistry in the past years. All endodontic companies are trying to produce files that will work more efficiently and safely. Some of the areas though, where file design *READER (DEPT. OF CONSERVATIVE DENTISTRY AND ENDODONTICS ) **READER (DEPT. OF CONSERVATIVE DENTISTRY AND ENDODONTICS *AHMEDABAD DENTAL COLLEGE & HOSPITAL, BHADAJ-RANCHHODPURA ROAD, TA:- KALOL DIST:-GANDHINAGAR. ADDRESS FOR AUTHOR CORROSPONDENCE : DR. ZARNA SANGHVI, PHONE:- ( ) ** DHARAMSINH DESAI UNIVERSITY, FACULTY OF DENTAL SCIENCE, NADIAD. 6

2 continues to differ is in tip and taper design, presence of radial lands, rake angles, helical angles, 11 and pitch. The intention of this article is to compare the various rotary endodontic instruments, based upon clinical performance, as dictated by their design feature. Tip Design A rotary cutting instrument may have a cutting or non-cutting tip. Cutting tips on rotary files make them too aggressive. An advantage of cutting tip is that it has the ability to enter narrow, somewhat calcified canals, but it also has disadvantage, if it accidentally go long (past the end of the tooth), upon retraction of the file, it will generally create an elliptical tear which is very difficult to repair and obturate and it also has the distinct possibility of transportation if the file is held at length for any period of time. Going long with a non-cutting tip will create a concentric circle at the end of the root. These are easily filled with a non-standardized cone. Files such as the Profile and the Greater Taper(GT), along with the new K, Hero 642 and RaCe employ a non-cutting tip. ProTaper System has Shaping files with partially active tips while the finishing files have non-cutting tips. Taper Taper is another feature of file design and it is particularly important concerning system concepts. There are two ways to shape a canal First, instrumentation of a root canal by using files of the same taper but with varying apical tip diameters. An example for this would be files that all have a consistent taper (.02) but with various tip diameters. A rotary file of constant taper would be the.04 taper Profile that has a constant taper (.04) but has varying apical tip diameters. Secondly, instrumentation of root canal by varying or 12,1 graduating tapers. These files have the constant apical tip size but their taper varies from.04 to.12. The idea behind variable or graduating tapers is that each successive file is only engaging a minimal aspect of the canal wall. Therefore, frictional resistance is reduced and requires less torque to properly run the file. The popular GT Series of files consist of three different instrument sequences, GT20, GT0 and GT40, according to ISO size and employs a varying taper (10%, 8%, 6%, 4%) while the Quantec files use a graduated increase in 14,15 taper. RaCe instruments are available in sizes from ISO with various tapers of 2%, 4%, 6%, 8%, 10% while K files are available in different sequence, each including six files in sizes 15 to 60 with three different tapers (2%, 4% ) along with two orifice openers of 8% and 10% for coronal pre-flaring. The Protaper System features a progressive taper along its shank. One of the benefits of such a design, according to the 16 manufacturer, is reduced torsional loading. Hero 642 system compiles a complete set of 12 files with varying ISO sizes, tapers and length of cutting 17 segments. Flex Master instruments are 2% tapered files used to finish apical area and to blend the apical 18 with the coronal preparations. ISO sizes 20, 25 and 0 instruments have three different tapers (2%, 4% ). ISO sizes 5 to 70 are only available as a 2% taper. Rake Angle Rake angles are also important and affect the cutting efficiency of the instrument. There remains confusion over what constitutes a rake angle and what is the cutting angle. The rake angle is the angle formed by the cutting edge and a cross section taken perpendicular to the long axis of the instrument. The cutting angle, on the other hand, is the angle formed by the cutting edge and a radius when the file is sectioned perpendicular to the cutting edge. Positive rake angles will cut more efficiently than neutral rake angles, which scrap the inside of the canal. Most conventional endodontic files utilize a negative or substantially neutral rake angle. An overly positive rake angle will result in digging and gouging of the dentin. This can lead to separation. 7

3 Profile has negative rake angle. The K, ProTaper, Hero 642, RaCe and Flex Master systems exhibit positive rake angle resulting in their optimum cutting efficiency. Light Speed and GT rotary system have neutral rake angle. Fig.-1: Rake Angles Fig.-2: Negative Rake Angle the instrument. This part of the file is called the radial land. This design feature is critical to the instrument. The less blade support (the amount of metal behind the cutting edge) the less resistant the 19 instrument is to torsional or rotary stresses. It is the combination of a non-cutting tip and radial land that keeps a file centered in the canal. Most rotary files derive their strength from the mass of material in the core. Peripheral strength can also be added to a file by extending the width of the radial land. This feature has been incorporated into the K file. Previously, rotary files either had full radial lands (Profile, GT) or their lands were recessed (Quantec). The K, like the Profile, is a three fluted file with three lands. Superior peripheral strength is achieved in the K by adding more mass behind the cutting blade. The increase in the K 's peripheral mass prevents the propagation of cracks and reduces the chances of separations and deformation from torsional stresses. The K blade relief areas, in addition to reducing frictional resistance also play another role. Many files have no means to control the depth at which the flutes engage the dentin. The harder one pushes apically, the deeper the blades will engage the canal walls. The K peripheral blade relief helps to control the depth of cut. This aids in protecting the file from over-engagement, and separations (breakage). The chance of transporting a root canal with a rotary file that has a non-cutting tip and radial lands is minimal. Radial Land Fig.-: Positive Rake Angle Another critical design feature is the concept of radial lands. A radial land is a surface that projects axially from the central axis, between flutes, as far as the cutting edge. The best way to explain this is blade support. Blade support is defined as the amount of material supporting the cutting blades of Fig.-4: Profile/GT Radial Land Fig.-5: K Radial Land There is an important concept of rotary instrumentation that should be remembered. The concept is not of drilling a hole in a root. Rather, it is one of taking a small hole, planning the inside, 8

4 and making it larger. The concept of radial lands is reassuring in rotary endodontics. However, ProTaper, Hero 642, Endo Sequence and RaCe do not have radial lands. Helical Angle The helical angle is the angle that the cutting edge makes with the long axis of the file. As a rotary file works in a canal, the dentinal debris needs to be removed quickly and effectively. Files with a constant helical flute angle allow debris to accumulate, particularly in the coronal part of the file. Additionally, files that maintain the same helical angle along the entire working length will be more susceptible to the effect of screwing in forces. By varying the flute angles, debris will be removed in a more efficient manner and the file will be less likely to screw into the canal. In the K, the helical angle increases from the tip to the handle. The result of this design is more successful channeling that allows for superior debris removal. The RaCe file is unique and utilizes an alternating helical design that reduces rotational torque by using spiraled and non spiraled portions along the working length. This design feature also reduces the 20 tendency of the file to get sucked into the canal. Pitch Pitch is the number of spirals or threads per unit length. Screws historically have had a constant pitch. The result of a constant pitch and constant helical angles is a pulling down or sucking down into the canal. This is particularly significant in rotary instrumentation when using files with a constant taper. K file has been designed with constant tapers, but with variable pitch and helical angles. The result is a dramatic reduction in the sense of being sucked down into the canal. Profile has a constant pitch throughout its cutting shank. The GT has variable helical angles and a variable pitch. Their variable pitched flutes provide a reamer like efficiency at the shank and K-file strength at the 21 tip. ProTaper has continuously changing pitch and helical angle which reduces the screwing effect. RaCe features one set of cutting edges that alternates with a second set, pitched at a different angle. Consequently, there are two different cutting edges on one file. The cutting shank employs an alternating spiral design. Naturally, this results in 22 variable helical angles along with a variable pitch. Fig.-6: Variable Helical Angle Fig.-7: Various Degrees of Helical Angle 9

5 Table 1- Design Features of Current Rotary NiTi file Systems Instrument system Cross-sectional Design Tip Design Taper Rotation speed(rpm) Other Features Profile (Dentsply Maillefer) Triple U shape with radial lands. Neutral rake angle planes dentin walls o 20 Helix Angle and constant pitch GT Files (Dentsply Maillefer) Triple-U shape with radial lands Fixed Taper 4%,6%, 8%,10% & 12% Files have a short cutting portion. Variable pitch Light Speed Instruments (Lightspeed, San Antonio TX) Triple-U shape with radial lands Specific instrument sequence produces a tapered shape Thin flexible non-cutting shaft and short cutting head ProTaper (Dentsply Maillefer) Convex triangular sharp cutting edge, No radial land.f, F4, F5 have U flutes for increased flexibility Variable taper along the length of each instrument Pitch and helical angle b a l a n c e d t o p r e v e n t instruments screwing into canals HERO 642 (Micromega) Triangular shape with positive rake angle for cutting efficiency. No radial land Variable pitch. File have short cutting portion (12-16mm) K (Sybron Endo) Positive rake angle for cutting efficiency, three radial lands and peripheral blade relief for reduced friction Variable pitch and variable core diameter Flex Master (VDW Munich Germany) Convex triangular shape with sharp cutting edge and no radial land Intro file has 11% taper Individual helical angle for each instrument size to reduce screw in effect. RaCe (FKG Switzerland) Triangular shape (except RaCe 15/0.02 and 20/0.02 which have a square shape), two alternating cutting edges, no radial lands 6%,8% and 10% Alternating cutting edge along the file length due to alternating twisted and untwisted segments to reduce screw-in effect. Qauntec SC, LX (Sybron Endo) S-Shape design with double helical flute, positive rake angle and two wide radial lands Cutting (SC) (LX) Fixed Taper 2%,%, 4%,5%,6%,8%,10% and 12% Flutes space progressively becomes larger distal to cutting blade. CONCLUSION The choice of a specific rotary system for daily use requires consideration of the combined evaluation of all described parameters. The question arises that what is the best design and which is the superior file. It really depends upon the working condition like position of tooth in the arch, number of roots and root canals, size of pulp space, degree and level of curvatures of root canal. If you want a file that cuts quickly, then a file such as the ProTaper or RaCe may fulfill your needs. However, with a fast file, you must understand the limitations and potential complications. The progressive nature of the taper does seem to put the file at greater risk for separation, if there is any deviation from the recommended technique. Additionally, the lack of radial lands must be fully appreciated. If efficiency with safety is more of an issue, perhaps the K should be your choice. The K combines a noncutting tip, along with a positive rake angle with variable pitch, and radial lands. If you prefer to instrument your canals through a series of varying tapers, then a system such as the GT or Quantec may satisfy your needs. One thing we can say with confidence is that before you choose a rotary file, you must try it. Extracted teeth are of a big help in this case. Understanding the fundamentals of file design and combining that with your pre-clinical 10

6 trial will facilitate making the correct choice in rotary files. Keep in mind, that as you become more experienced your expectations of rotary files will change. Eventually, you will realize there is a place in the endodontic armamentarium for many of these file designs. The ultimate goal is to be able to confidently offer patient a root canal procedure, which will hold up long term and be of equal or greater longevity than that of an implant. REFERENCES 1. Ruddle CJ. Cleaning and shaping the root canal system. In: Cohen S, th Burns RC, 9 eds. Pathways of the Pulp. St Louis: Mosby, Hulsmann M, Peters OA, Dummer MH. Mechanical preparations of root canals: shaping goals, techniques and means. Endo Topics 2005;10: Parashos P, Messer HH. The diffusion of innovation in dentistry: a review using rotary nickel-titanium technology as an example. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2006;10: Lam TV, Lewis DJ, Atkins DR, et al. Changes in root canal morphology in simulated curved canals over-instrumented with a variety of stainless steel and nickel titanium files. Aust Dent J 1999;44: Spangberg L. The wonderful world of rotary root canal preparation. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;92: Bergmans L, Van Cleynenbreugel J, Beullens M, Wevers M, Van Meerbeek B, Lambrechts P. Progressive versus constant tapered shaft design using NiTi rotary instruments. Int Endod J 200;6: Thompson SA. An overview of nickel-titanium alloys used in dentistry. Int Endod J 2000;: Koch K, Brave D. Real World Endo: Design Features of Rotary Files and How They Affect Clinical Performance. Oral Health / February 2002 pg Vaudt J., Bitter K, Kielbassa AM. Evaluation of rotary root canal instruments in vitro: A review. ENDO 2007;1: Gerald N. Glickman D.D.S., M.S. and Kenneth A.Koch, DMD. 21st Century Endodontics. Journal of the American Dental Association June 2000; 11: Guelzow A, Stammo, Martus P, Kielvassa AM. Comparative study of six rotary Nickel titanium systems and hand instrumentations for root canal preparation. Int Endod J 2005;8: Hulsmann M, Schade M, Schafer's F. A comparative study of root canal preparation using Profile 0.04 and Light Speed NiTi instruments. Int Endod J 2001;4: Bergmans L, Van CJ, Beullens M, Wevers M, Van MB, Lambrechts P. Progressive versus constant tapered shaft design using NiTi rotary instruments. Int Endod J 200;6: Griffiths IT, Chassot AL, Nascimento MF, Bryant ST, Dummer PM. Canal shapes produced sequentially during instrumentation with Quantec SC rotary nickel-titanium instruments: a study in simulated canals. Int Endod J 2001;4: Griffiths IT, Bryant ST, Dummer PM. Canal shapes produced sequentially during instrumentation with Quantec LX rotary nickel-titanium instruments: a study in simulated canals. Int Endod J 2000;: Paque F, Musch U, Huslmann M. Comparison of root canal preparation using RaCe and ProTaper rotary NiTi instruments. Int Endod J 2005;8: Hulsmann M, Gressmann G, Schafer's F. A comparative study of root canal preparation using Flex Master and HERO 642 rotary NiTi instruments. Int Endod J 200;6: Hulsmann M, Gressmann G, Sch afers F. A comparative study of root canal preparation using FlexMaster and HERO 642 rotary Ni-Ti instruments. Int Endod J 200;6: Schafer E, Tepel J. Relationship between design features of endodontic instruments and their properties. Part III. Resistance to bending and fracture. J Endod 2001;27: Diemer F, Calas P. Effect of pitch length on the behavior of rotary triple helix root canal instruments. J Endod 2004;0: Park H. A comparison of Greater Taper files, Profiles and stainless steel files to shape curved root canals. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;91: Young GR, Parashos P, Messer HH. The principles of techniques for cleaning root canals. Australian dental Journal Supplement 2007; 52: