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Endo file separation discussion


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Endo file separation discussion

  1. 1. FractureFriday, January 27, 12
  2. 2. TorsionalFriday, January 27, 12
  3. 3. CyclicFriday, January 27, 12
  4. 4. JOE 2009Friday, January 27, 12
  5. 5. Review Article Figure 2. The method described by Pruett et al (14) for describing canal geometry using two parameters: radius of curvature and angle of curvature. (Reprinted with permission [14]). Figure 1. The degree of root canal curvature obtained using the method described by Schneider for determining canal curvature using only one param- eter to define the angle. A has an angle of 43 and B has an agle of 52, even angle of curvature and radius of curvature (Fig. 2). To determine these though both angles measured according to the method of Pruett et al. equaled parameters, a straight line is drawn along the long axis of the coronal 60 degrees. Location of the curve along the canal will also change the straight portion of the canal. A second line is drawn along the long measured angle. (Reprinted with permission [14]). axis of the apical straight portion of the canal. There is a point on each of these lines at which the canal deviates to begin or end the canal curvature. The curved portion of the canal is represented by a circle An ideal model would involve instrumentation of curved canals in with tangents at these two points. The angle of curvature is the number natural teeth. However, in such tests, a tooth can only be used once and of degrees on the arc of the circle between these two points. Angle of the shape of the root canal will change during instrumentation, making curvature can also be defined by the angle formed by perpendicular it impossible to standardize experimental conditions. As a result, several lines drawn from the points of deviation that intersect at the center of devices and methods have been used to investigate in vitro cyclic fatigue the circle. The length of these lines is the radius of the circle and defines fracture resistance of NiTi rotary endodontic instruments. the radius of the canal curvature defined in millimeters. This parameter The aim of this review of the literature was to summarize and represents how abruptly a specific angle of curvature occurs as theFriday, January 27, 12
  6. 6. Review Article a dynamic model without specifying at what distance from the tip of the instrument the point of maximum curvature was located. Stainless steel tubes with an inner diameter of 1.04 mm and a radius of curvature of 6 mm were used by Lopes et al (23). The authors used two different arcs lengths because in the curved canals with the same radius, it is possible that there are arcs (curved segments) with different lengths represented by angles with different degrees. They used an arc of 9.4 mm corre- sponding to an angle of 90 and an arc of 14.1 mm, corresponding to an angle of 135 when using a 6-mm radius of curvature. They used a straight coronal part of 10.6 mm and 5.9 mm, respectively, so that the total length of the curved and straight parts was 20 mm. Bui et al (24)Review Articlethat were constructed by bending used artificial canals a 16-mm gauge stainless steel Monojet blunt needle to a 5-mm radius on curvature and angles of curvature of 30 , 45 , and 60 . The point of maximum curvature was 7 mm from the tip of the instrument. Similar to Pruett et al (14), Kramkowski et al (25) constructed artificial canals by bending stainless steel tubing. Two canals were bent to a 5-mm radius of curvature with angles of curvature of 45 and 60 . The center of the radius in the curved section of the canal was 7 mm from the tip of the file. The artificial canals were inserted into predrilled acrylic blocks for mounting in a fixed jig on the platform of the cyclic fatigue instrument. The jig was placed at the opposite end of the rotary handpiece fixed at a distance so that the files protruded approximately 2 mm out of the end of the tube. Instruments were rotated in the artificial canal with a consistent insertion and withdrawal of 8 mm. Silicone spray (CRC Industries Inc, Warminster, PA) as a lubri- cant and a debris-clearing agent was applied between each file tested. Cylindrical tubes did not sufficiently restrict the instrument shaft, which spring back into its original straight shape, aligning into a trajec- tory of greater radius and reduced angle, as it has been speculated in previous articles that have used this type of methodology (19–21, 26). Because of the inner diameter of the tubes (glass and metal) is greater than that of the instruments, an instrument rotated in the tube will follow a trajectory that is not predictable and without the parameters of radius and angle of curvature and point of maximum curvature that were established when constructing the artificial canals. Furthermore, each instrument, depending on tip size, taper, design, pitch length, and morphologic and geometric features, will follow its own trajectory in tubes that do not sufficiently constrain the shafts of the instruments, especially the smaller ones. If instruments of the same dimensions follow different trajectories in the test apparatus, a direct comparison between instruments of different brands may be difficult to establish and the results obtained may be unreliable and not consistent. Furthermore, it is unclear what Figure 5. A schematic drawing of the three stainless steel pins that con- the predictability of these parameters of radius and angle of curvature strained the instrument into the curvature in the studies by Cheung et al (32–36). and point of maximum curvature obtained by bending a straight metal or glass tube. Another problem with a loose-fitting canal is that the file may ‘‘walk’’ or vibrate in that space, leading to a change in the magni- tude of stress and 4. The inclined planevariations in the results. Figure possibly leading to used in some studies to produce the curvature the beginning of the curvature will gradually move away from the long Ounsiof al (27) have used a custom-designeda sloped steel model A groove et a rotary instrument working against stainless metal block. axis of the shaft. For this reason, the choice of this point may vary greatly, mimickingmachined into the face ofcanal space. Thethe file in place during testing. (Re- a 2-mm-wide artificial the block keeps constant diameter of and the calculated angle may present great variability. Furthermore, it is printed with permission [28]). the cavity that reproduced the curved canal presents the same problems not possible to establish exactly the point of maximum curvature of the tube-like devices in lacking the reproducibility of the actual because the physical and geometric features of the different instruments trajectory followed by different files. curvature as done by Pruett et al (14). They considering the radius of may determine different bending properties, so that the point of In other studies,angles of curvature: 37 , instrument ,was produced study by used four the curvature of a rotary 40.5 , 45 and 48 . In the maximum curvature may lie at different points and at a different distance when worked against aal (30),metal block using a groove machined into the face of Kitchens et sloped a 2-mm-wide groove was from the tip of each file. the face ofathe block to keep the filesteelplace during polished chrome plating to hardened 316 stainless in block with testing (28–31) As mentioned earlier, bending properties of different files may (Fig. 4). The block file in place during testing.resist the operation of keep the had sufficient hardness to Three angles of curvature were determine a different trajectory if the file is not constrained in a precise an instrument. The different angles of Schneider’s method (14): 25 , 28 , and used and measured using curvature used in these studies trajectory. If testing is completed for all different files at a given angle to 33.5 Ray et al to Schneider’s method (15). were determined. according (31) used a highly polished area of a stainless steel ensure consistency, the bending properties of the different files deter- Figure 3. A schematic drawing of curved glass or metal tubes used for fatigue Li et al (28, with used a sloped 15 to the horizontal plane, similar to Li et block 29) an incline of carbon-steel block and calculated mining different angles of curvature, thus biasing the results and the testing of NiTi rotary instruments. only the angle of29). At a maximum flexure, all files produced an angle of 28 al (28, curvature by Schneider’s method (15), without comparisons. determined according to Schneider’s method (15). To limit these problems, Cheung et al (32–36) constrained the Despite the radius of curvature having been recognized as the most instrument into a curvature using three stainless steel pins (Fig. 5). JOE — Volume 35, Number 11, November 2009 important factor influencing cyclic Rotary Instruments 1471 Cyclic Fatigue of fatigue, these studies measured file They used three smooth cylindrical pins of 2-mm diameter fromFriday, January 27, 12 curvature according to Schneider’s method, which takes into consider- a high hardness stainless steel mounted in acrylic shims, which were ation only the angle of curvature and not the more important radius of adjustable in the horizontal direction; the position of the pins deter-
  7. 7. Figure 12. An example of several instruments that follows the saFriday, January 27, 12
  8. 8. JOURNAL OF ENDODONTICS Printed in U.S.A. Copyright © 2004 by The American Association of Endodontists VOL. 30, NO. 3, MARCH 2004 Effect of a Separated Instrument on Bacterial Penetration of Obturated Root Canals Jeffrey L. Saunders, DDS, Paul D. Eleazer, DDS, MS, Ping Zhang, PhD, DDS, and Susanne Michalek, PhD The aim of this study was to determine the effect a of bacteria in more than 50% of the root canals in their study within separated instrument has on the time required for 19 days and 42 days when using Streptococcus epidermidis and bacterial penetration of obturated root canals. Proteus vulgaris, respectively. Khayat et al. (9) found complete Twenty-six extracted human mandibular premo- bacterial penetration in an average of 28.8 days and 25.4 days for root canals filled using lateral condensation and vertical conden- lars with single canals were used in the study. sation, respectively, when human saliva was introduced into the Group 1 consisted of teeth that contained a sepa- access cavities. No study has been performed investigating the rated size 40 Profile rotary file and were obturated effect of bacterial penetration of root canals with broken files plus with gutta-percha and zinc oxide eugenol sealer to gutta-percha and zinc oxide eugenol (ZOE) sealer. the level of the separated file. Group 2 consisted of Because separation of instruments is a sequela of endodontic teeth that were similarly obturated, but without a treatment, it would be useful to know how such occurrences affect separated file. The negative control canals were the sealing ability of the obturation material. Knowing the answer obturated and had the entire root surface sealed may affect a clinician’s decision whether to attempt separated with nail polish. The positive controls were obtu- instrument retrieval. Through the endodontic literature, it is unclear rated without sealer. Streptococcus sanguis was whether a fluted instrument separated in a root canal would allow placed in the access chamber daily, and penetra- quicker penetration of bacteria than the same length of gutta percha tion was determined when turbidity was noted in and ZOE sealer. The purpose of this investigation was to determine the effect a separated instrument has on the time of bacterial the culture broth. The results showed no signifi- penetration of canals obturated with gutta-percha and ZOE sealer. cant difference between the two experimental groups.Friday, January 27, 12 MATERIALS AND METHODS
  9. 9. experimental group 2. The remaining six teeth were divided into two control groups containing three teeth each. None of these teeth contained a broken file. For experimental group 1, 10 size 40 .04 Profile rotary instru- ments were nicked with a #2 round bur 3 mm from the tip to facilitate file separation at this point. The size 40 Profile rotating at 300 rpm was then introduced with apical pressure into each canal until separation occurred. After instrument separation, each of the 10 teeth in this group was again radiographed to ensure that the separation occurred in the apical third of the canal. After instrumentation, the roots of all 26 teeth were coated with two applications of fingernail polish. The apical 2 mm of the roots were not covered with polish, except for the three teeth in the negative control group, which had their entire root coated. All 26 teeth were then autoclaved. All teeth in the negative control group and experimental group 2 were obturated to the working length with gutta-percha and Roth 811 sealer (Roth International, Chicago, IL) using the lateral con- densation technique. A sterile technique was used for obturation of all teeth. A heated plugger was used to remove coronal gutta-Friday, January 27, 12
  10. 10. fillings. Swanson and Madison (4) also found a significant vari- ability when they examined the penetration of a dye through obturated root canals. The large range of time for penetration of the experimental groups can possibly be attributed to variable root canal anatomy, shape of canal preparation, and sealer type. The presence of 3 mm of separated instrument did not speed up or slow down penetration of bacteria when compared with the normally obturated experimental group. This result implies that the separated file did not compromise obturation of the root canal space. This fact is surprising, because root canal anatomy is quite variable and is not perfectly round like the separated instrument. Also, the separated instrument has flutes, so it would be unlikely to completely obturate the root canal space by itself. With sealer extruded into the flutes, the separated file may become the equiv- alent of any other obturation material. The results of this study indicate that the separated instrument itself does not play a large role in the sealing ability of theFriday, January 27, 12
  11. 11. Friday, January 27, 12
  12. 12. 2 Studies included: Crump/Natkin 1970 - Spili et al 2005 199 cases Incidence of separation: Stainless Steel: 0.5-7.4 % Niti: 0.4-3.7% Does retention of a separated instrument, compared w/ no retained instrument - result in a poorer clinical outcome?Friday, January 27, 12
  13. 13. Assessment: 1 year is the earliest possible foully time to determine whterh the lesion has healed Influence of a preoperative RL 80.7% of lesions healed when a periapical lesion was present 92.4% remanning healthy when no lesion was presentFriday, January 27, 12
  14. 14. Important finding - studies w/ no controls only used the presence of a preoperative periapical lesion to act as the main prognostic factor for successful mgmt. of these casesFriday, January 27, 12
  15. 15. Highest proportion of instrument fragments occurs in the apical third Removal should be weighed against modest benefitFriday, January 27, 12
  16. 16. A dozen ways to prevent nickel-titanium rotary instrument fracture Peter M. Di Fiore, DDS, MS D uring the past 15 years, nickel-titanium (NiTi) rotary instruments have become a part of the ABSTRACT ✷ J A D A ✷  standard armamen- Background and Overview. With the N CON tarium in endodontics. They are IO increased use of nickel-titanium (NiTi) rotary instru- T used extensively by generalists and T A ments for root canal preparation in endodontics, N I U C specialists to facilitate the cleaning A ING EDU 4 instrument fracture has become more prevalent. RT and shaping of root canals,1 and it Extensive research has been conducted on the physical ICLE appears that with the increased properties and mechanical characteristics of NiTi rotary instruments, as application of these instruments in well as the factors that can contribute to instrument failure. NiTi rotary contemporary endodontic practice, instruments are subjected to torque and are susceptible to cyclic fatigue, fractures have become more which are the main causes of instrument fracture. However, with an prevalent.2,3 understanding of how these instruments function in preparing root Fractured instruments are a defi- canals and by applying ways to reduce torque-generated metal fatigue, nite hindrance to the goals of clinicians can use the instruments safely in clinical practice. cleaning, shaping and filling root Results. The author presents 12 measures that clinicians can take to canals,4,5 and they may adversely prevent NiTi rotary instrument fracture and discusses them in detail. affect the outcome of endodontic Clinical Implications. NiTi rotary instrument fracture complicates treatment.2,6-8 Techniques for the progress, and compromises the prognosis of endodontic treatment. removing fractured instrument However, when clinicians take appropriate measures, rotary instrument fragments from root canals have fractures can be prevented. been described in the dental litera- Key Words. Nickel-titanium; rotary; instrument; fracture; prevention. ture.9,10 However, removal of frag- JADA 2007;138(2):196-201. ments may be impossible or imprac- tical, especially when they are small and located in the apical portion of narrow curved root canals or when Dr. Di Fiore is an associate professor of endodontics and the director, Predoctoral Endodontics, New repeated attempts at removal could York University, College of Dentistry, Department of Endodontics, 345 E. 24th St., New York, N.Y. result in excessive enlargement of 10010. Address reprint requests to Dr. Di Fiore. 196 JADA, Vol. 138 February 2007 Copyright ©2007 American Dental Association. All rights reserved.Friday, January 27, 12
  17. 17. File CharacteristicsFriday, January 27, 12
  18. 18. size, taper and cutting flute depths are important factors that affect the torsional and bending prop- erties of rotary instruments. 15-19 Size. A comparative study of the fatigue resis- tance of NiTi rotary instruments of different sizes and flute designs revealed that large instruments were highly susceptible to fatigue failure.15 Research has demonstrated C A Las P R instru- I C E C L I N I that an A C T ment’s cross-sectional diameter increases, it becomes less resistant to cyclic fatigue.18 Afterd performing dynamic stress tests on various NiTi Copyright ©2007as rotary instruments, investigators found that American De ware an instrument’s size and taper increase, the re torque generated during rotation increases andhap. the fracture time decreases.12,13 sures Taper. In cyclic fatigue-to-fracture tests of dif-e risk Friday, January 27, 12 ferent NiTi rotary instruments, researchers found
  19. 19. torque generated during rotation increases and the fracture time decreases.12,13 Taper. In cyclic fatigue-to-fracture tests of dif- ferent NiTi rotary instruments, researchers found that 0.06 taper instruments had less resistance to fracture than did 0.04 taper instruments.19 Shen and colleagues compared the types of failures 20 that occurred with NiTi rotary instruments of various geometric designs and reported that a very high percentage (21 percent) of the instru- ments that fractured had progressively larger tapers and a much lower percentage (7 percent) had consistently even tapers. They also noted that failures for progres-taper and sively tapered instruments tendedflute depths to be fractures, whereas for evenlyFriday, January 27, 12
  20. 20. after they have been used for one clinical case. drills.34,35 efficientl CANAL CURVATURE ASSESSMENT funnel th CANAL CURVATURE ASSESSMENT The fracture potential of an instrument rotating entrance in a curved canal becomes greater as the angle of root cana curvature increases and the radius of curvature binding, decreases.11,13,14 Zelada and colleagues30 and fore, pra Martin and colleagues31 reported that during the introduc preparation of root canals in extracted molar canal. teeth, all instrument fractures occurred in severely curved canals with angles of curvature MANUA greater than 30 degrees. A careful preoperative Hand ins radiographic examination with fine hand instru- sageway ments in the canals will reveal the presence and progress acuity of root canal curvatures. Therefore, when have dem curvatures are present, the operator should be mentatio wary of the possibility of a fracture and proceed ments, u cautiously during root canal preparation. instrume incidenc ACCESS PREPARATION preparat In the internal configuration of an adequate leagues36Friday, January 27, 12
  21. 21. tapered instruments failed rapidly with little rotation. Cutting flute depth. Instruments with deep cut- ting flutes and progressively larger variable tapers have rapidly changing cross-sectional diameters along the entire length of their shafts. These instruments develop high torque levels that make them more prone to metal fatigue and fracture. However, instruments that have shallow cutting flutes, evenly tapered shafts and consis- tently shaped cross-sectional areas are more resistant to fracture. This is because the torsional and bending stresses that develop during use are distributed uniformly along these instruments’ entire length. 19-21 Therefore, practitioners should be completely familiar with the mechanical fea-Friday, January 27, 12
  22. 22. their surfaces. It is important for clinicians to 16,22,23 realize that these pre-existing conditions asso- ciated with the Instrument Use process may con- manufacturing tribute to the propagation of instrument fractures during use.24,25 Cyclic fatigue and torsional testing procedures that measured rotation time and torque level at fracture have demonstrated that used rotary instruments are significantly more susceptible to fracture than are new ones.26,27 These findings are further supported by SEM observations of used instruments that revealed signs of deterioration, including surface cracks that can progress to fractures with further use.22-25,28 Sotokawa29 found that by applying a systematic Practitioner schedule for the disposal of enlarge rooFriday, January 27, 12
  23. 23. ACCESS PREPARATIONFriday, January 27, 12
  24. 24. CANAL ORIFICE ENLARGEMENTFriday, January 27, 12
  25. 25. canal. MANUAL INSTRUMENTATION MANUAL INSTRUMENTATION Hand instruments can create a smooth, open pas- sageway for rotary instruments to follow as they progress to the apical terminus. Three studies have demonstrated that manual root canal instru- mentation with fine stainless steel hand instru- ments, used in a step-back manner before rotary instruments were used, significantly reduced the incidence of rotary instrument fracture during the preparation of curved canals.36-38 Roland and col- leagues and Patino and colleagues used fine 36 37 hand instruments to enlarge curved root canals inFriday, January 27, 12
  26. 26. canal instrumentation so that when the torque on an instrument, rotating at a AND TORQUE IRRIGA ROTATIONAL SPEED constant speed, reaches a preset level, the motor automatically Irrigati CONTROL and allows the reverses its rotational direction plishin file to be withdrawn before it locks and fractures SEM st in the root canal.39 Gabel and colleagues40 investi- have de gated the influence of rotational speed on the ated du failure of NiTi rotary instruments for the prepa- root can ration of root canals in extracted molar teeth and remova found that instrument distortion and fracture ethylen were four times more likely to occur at higher is a com rotational speeds (333 rotations per minute) than prepara at lower rotational speeds (167 rpm). Gambarini41 canal c found that instruments used in low-torque motors ical ove ( 1 Newton per centimeter) were more resistant stresse to fracture than those used in high-torque motors fore, du ( 3 N/cm). Therefore, practitioners should use should electric motors set at low rotational speeds and gate ca low torque levels during root canal preparation. ROTAR CROWN-DOWN TECHNIQUE The maFriday, January 27, 12
  27. 27. CROWN-DOWN TECHNIQUeFriday, January 27, 12
  28. 28. IRRIGATION AND LUBRICATIONFriday, January 27, 12
  29. 29. related failures during root canal preparation in ro E extracted teeth. The operator’s ability to sense OPERATOR PROFICIENCY and resist these binding and locking tendencies is A a skill that can be obtained only with experience. N Yared and colleagues, 39,52,53 in several extensive m investigations, showed that preclinical training in 19 the use of NiTi rotary instruments for the prepa- ce ration of root canals in extracted molar teeth was E crucial for avoiding instrument fracture. There- fil fore, inexperienced operators should engage in preclinical training exercises as learning experi- au ences before using these instruments on patients, te then proceed carefully in clinical practice as they in 20 gain experience. ni SUMMARY AND CONCLUSION in There are several measures that practitioners canFriday, January 27, 12 26
  30. 30. rs fore, during root canal preparation, practitioners should lubricate instruments generously and irri- gate canals copiously. ROTARY INSTRUMENT MANIPULATION ROTARY INSTRUMENT MANIPULATION The manner in which NiTi rotary files are manip-s ulated for preparing root canals is extremely important. It has been shown that a cyclic axial motion applied to rotary instruments during oper-f ation was significant in preventing premature fracture.51 Also, a pecking or pumping motion, which lowers apical forces during root canalIn preparation, has been advocated by researchers as an important way to prevent instrumentd binding and torque-generated cyclic fatigue.12-14p- Li and colleagues14 tested the cyclic fatigue of NiTi rotary instruments under static ande- dynamic pecking motion conditions and found Friday, January 27, 12
  31. 31. techniqu then proceed carefully in clinical practice as they instrume 2003;29( gain experience. 11. Pru nickel-tit SUMMARY AND CONCLUSION 12. Sat instrume There are several measures that practitioners can 26(3):156 13. Ha take to prevent NiTi rotary instrument fracture and cycli during root canal preparation: instrume 14. Li U davoid subjecting NiTi rotary instruments to endodon excessive stress; tests. J E 15. Ch duse instruments that are less prone to fracture; Buono V dfollow an instrument use protocol; endodon 16. Ku dassess root canal curvatures radiographically titanium and instrument them carefully; 17. Xu and bend densure that the endodontic access preparation instrume is adequate; 18. Ull loads in dopen orifices before negotiating canals; 2005;31( denlarge root canals with fine hand 19. Yao rotary ni instruments; 55-7.Friday, January 27, 12
  32. 32. g dset rotational speed and torque at low levels; duse the crown-down technique;n dirrigate and lubricate root canals during preparation; dmanipulate rotary instruments with a pecking or pumping motion; dif inexperienced, engage in preclinical training in the use of rotary instruments. Instrument fracture is a serious iatrogenic mishap that can complicate and compromise endodontic treatment. It therefore is imperative that clinicians using these instruments in prac- Friday, January 27, 12