The shaping effects of three rotary Nickel-Titanium systems in simulated curved canals

Transcription

1 The shaping effects of three rotary Nickel-Titanium systems in simulated curved canals Hamid Kassim, B.D.. (1) Abdul Karim J. Al-Azzawi, B.D.., M.c. (2) ABTRACT Background: The purpose of this study is to compare three rotary endodontic nickel-titanium systems (ProFile, GT and ProTaper) with stainless steel hand K-flexofile in simulated curved canals at different levels, this includes: Incidence of canal aberrations (apical zipping associated with elbow, ledge and perforation), Changes of working length, Preparation time for each system and Breakage and permanent deformation of instruments. Materials and method: Eighty simulated curved canals made of clear polyester resin were used to assess instrumentation. The acrylic blocks were divided into four groups, 20 simulated canals for each group were enlarged from #10 to # 25. In the first three groups all NiTi rotary instruments were set into a permanent rotation with a 16:1 reduction hand piece powered by a torque-limited electric motor set at 300 rpm. All the instruments were used in a crown down manner using a gentle in-and-out (pecking) motion. In the fourth group the simulated canals were instrumented with stainless steel K-flexo-files by using balanced force technique. Each simulated canal was filled with a drawing ink using to increase the color contrast for photographic documentation. Photographs of the unprepared canals were taken by the aid of stereomicroscope and digital camera at magnification of 40 times. When instrumentation of the canals was completed, the canals were injected again with the drawing ink and the image procedure is repeated. Preand postoperative digital photographs of the resin blocks were accomplished using Adobe Photoshop C2 software program. At this stage the amount of resin removed i.e. the difference between the canal configuration before and after instrumentation was determined for both the inner and the outer side of the curvature at five reference points. Assessments were made under the stereomicroscope according to the presence of different types of canal aberrations (apical zip associated with elbow, ledge and perforation). The changes of working length were determined by subtracting the length of master apical file from the original length (16mm). The time taken to prepare each canal was recorded in minutes with the aid of a stop timer. Throughout the study a record was kept of the numbers and sizes of instruments that fractured or became permanently deformed during use. Results: there were significant differences among the groups, even though more zips and ledge were created with K-flexofile followed by ProTaper. NiTi instruments caused a significantly greater loss of working length than K-flexofile; while there was no significant difference among NiTi groups. The shortest mean of preparation time was recorded when ProTaper were used; while the longest time was documented for GT. No permanent deformation occurred with NiTi groups. None of the stainless steel K-flexofile was separated. Conclusion: K-flexofiles created significantly more aberration than NiTi systems. ProTaper caused more morphological changes compared with ProFile and GT systems. mall mean changes in working length occurring with rotary NiTi instruments. The preparation time of ProTaper was faster than with other groups. NiTi instruments may be more susceptible to separation than stainless-steel instruments. Most failures of the hand stainless-steel files were deformations rather than fractures. Fracture rate was approximately 30% for ProTaper, 16.6% for GT and 8.3% for Profiles. Keywords: Canal aberrations, preparation time, working length change, instrument fracture and permanent deformation, ProTaper, GT, ProFile. (J Bagh Coll Dentistry 2012;24(3):1-7). INTRODUCTION The aim of root canal preparation is to clean and shape the root canal while maintaining its special relationship within the root. The desired result is a uniformly tapering canal that results from cutting the canal circumferentially as evenly as possible, maintaining the original canal outline with a definite apical seat which facilitates a hermetic seal at the obturation stage. This is especially difficult in curved canals, where procedural errors such as transportation, zipping, elbow formation, ledging, perforation, stripping perforation, and instrument fracture can occur (1,2). (1) M.c. tudent, department of conservative dentistry college of dentistry, university of Baghdad. (2) Professor, department of conservative dentistry, college of dentistry, university of Baghdad. Restorative Dentistry 1 Various techniques have been used to avoid or minimize these errors, though none has been universally accepted as the answer to the maintenance of root canal curvature. imilarly, modification to instrument tip design, and flute alteration have not provided a solution to the management of the apical section of the curved root canal (1). However, in particular when used in severely curved canals, traditional stainless steel instruments often fail to achieve the tapered root canal shapes needed for adequate cleaning and filling (3). In 1988, nickel titanium was first introduced in endodontics to overcome the limitations of stainless steel IO instruments and make the preparation of curved canals much easier because of its superior elasticity and shape memory effect. During the last 10 years, scientific evidence has clearly shown that rotary Ni-Ti

2 instruments used in a crown-down fashion produce consistent canal shape, less debris extrusion and stay well centered inside the root canal (4). It is expected from modern engine-driven rotary root canal instruments made of nickel-titanium (Ni-Ti) to allow adequate and acceptable preparation of even severely curved root canals. Procedural errors were reported to be rather infrequent when root canals of extracted teeth were shaped with rotary Ni-Ti instruments (2) The purpose of this study is to compare three rotary endodontic nickel-titanium systems (ProFile, GT and ProTaper) with stainless steel hand K-flexofile in simulated curved canals at different levels, this includes: a) Incidence of canal aberrations (apical zipping associated with elbow, ledge and perforation). b) Changes of working length. c) Preparation time for each system. d) Breakage and permanent deformation of instruments. MATERIAL AND METHOD imulated curved canals made of clear polyester resin were used to assess instrumentation. The diameter and the taper of all simulated canals were equivalent to an IO standard size 10 root canal instrument. The canals were 16 mm long, the straight part being 11 mm and the curved part 5 mm with angle of 40 (5) (Fig.1). Figure 1: Angle and radius of canal curvature Preparation of artificial canals Eighty acrylic blocks were divided into four groups, 20 simulated canals for each group were enlarged from #10 to # 25. The first penetration in the simulated canal was performed with #10 K-file hand instrument to the full working length (16 mm). Patency of the resin blocks was checked with the same size after each sequence. Prior to use, each instrument was coated with glycerin to act as a lubricant and copious irrigation with tap water was performed repeatedly before and after the use of each instrument using disposable syringes and 27 gauge tips. Rotary NiTi instruments In the first three groups all NiTi rotary instruments were set into a permanent rotation with a 16:1 reduction hand piece powered by a torque- limited electric motor set at 300 rpm. And the torque at 1.2 Ncm. All the instruments were used in a crown down manner using a gentle inand-out (pecking) motion until resistance was felt and changed for the next instrument. Manual technique In the fourth group the simulated canals were instrumented with stainless steel K-flexofiles by using balanced force technique described by Roan et al in 1985 (6). Which continue until an apical stop of size 25 was achieved. Then stepping backs the preparation with # 30, # 35 and # 40files and used also in balanced force motion. Assessment of canal preparation Postoperative canal shape Prior to their preparation, each simulated canal was filled with a drawing ink using a 27 gauge needle to increase the color contrast for photographic documentation.' In order to achieve a standardized position of the resin blocks against the lens of the microscope, a holder was constructed from stone for this purpose with a hole in the center in which the resin blocks could be placed and repositioned in exactly the same position. The central hole was covered with a transparent paper on which the five chosen levels were drawn and the artificial canal could be measured easily. Photographs of the unprepared canals were taken by the aid of stereomicroscope and digital camera at magnification of 40 times. One image on screen corresponded to 2 mm of the real canal length. Therefore eight images were needed to assemble the entire canal. Both X and Y coordinates on the microscope's nonius scale were recorded for each image, allowing repositioning and reproduction of the pictures at any given moment (i.e. pre- and postoperative). The images were standardized by securing the camera at a fixed distance from a microscope lens. After that the simulated canals were cleaned using tap water with irrigating syringe. When instrumentation of the canals was completed, the canals were Restorative Dentistry 2

3 injected again with the drawing ink and the image procedure is repeated. Pre- and postoperative digital photographs of the resin blocks were stored in a Pentium 4 computer and measurements were accomplished using Adobe Photoshop C2 software program. At this stage, the amount of resin removed, i.e. the difference between the canal configuration before and after instrumentation was determined for both the inner and the outer side of the curvature at five reference points, using a method described by Calberson et al (7). All measurements were made at right angles to the surface of the canal (Fig.-2). Point 1 (O): the canal orifice. Point 2 (HO): the point half-way from the beginning of the curve to the orifice. Point 3 (BC): the point where the canal deviates from the long axis of its coronal portion and is called the beginning of the curvature. Point 4 (AC): the point where the long axes of the coronal and the apical portions of the canal intersect and are called the apex of the curve. Point 5 (EP): the end point of preparation. The time was logged from the beginning of the preparation procedure and included total active instrumentation, instruments changes within the sequence and irrigation. Throughout the study a record was kept of the numbers and sizes of instruments that fractured or became permanently deformed during use by examining the instruments after each use under magnifying lens (10X). REULT Canal aberrations The results concerning the assessment of canal aberrations are summarized in Table-1. Table 1: Incidence of canal aberrations by instruments types. ystem Zip/elbow Ledge Perforation PF GT PT KO Chi-square P-value With respect to the different types of aberration evaluated; there were significant differences among the groups, even though more zips and ledge were created with K- flexofile followed by ProTaper. ProFile created the lowest percentage of elbow; while GT produced the least number of ledges. No perforations were observed during preparation. Figure 2: The five levels of measurement Furthermore, basing on the superimposition of pre-and postoperative images, assessments were made under the stereomicroscope according to the presence of different types of canal aberrations (apical zip associated with elbow, ledge and perforation). These different types of canal aberrations were defined according to the detailed descriptions published by Thompson and Dummer (8). When the preparation was completed, a K- file size 10 was inserted into each canal to the apical stop to prove that working length had been reached. The changes of working length w.ere determined by subtracting the length of master apical file from the original length (16mm). The time taken to prepare each canal was recorded in minutes with the aid of a stop timer. Restorative Dentistry 3 Figure 3: Composite image of the simulated resin canal with apical zip and elbow Changes of working length All canals remained patent following instrumentation; thus, none of the canals became blocked with resin shavings. None of the canals showed overextension of preparation, whereas a loss of working distance was found in

4 several canals. The mean changes of working length that occurred as a result of the preparation of th e canals are given in Table -2. The difference among the four groups was statistically significant as in Table -3. Table 2: Mean changes of working length (mm) and standard deviation with the four different instruments. ystem Mean D± PF GT PT KO Table-3: ANOVA table of change of working length. ystem F-test P-value PF GT PT KO P<0.05 NiTi instruments caused a significantly greater loss of working length than K-flexofile; while there was no significant difference among NiTi groups (Table-4). Table 4: t-test of change of working length (mm) among groups ystem t-test P-value PF&GT N PF&PT N PF&KO GT&PT N GT&KO PT&KO Preparation time The mean time taken to prepare the canals with the different instruments is shown in Table-5. The shortest mean of preparation time was recorded when ProTaper were used (7.304 min.); while the longest time was documented for GT (8.309 min.). Table- 5: Mean and standard deviation of preparation time (min.) ystem Mean D± PF GT PT KO Table -6: ANOVA table of time ystem F-test P-value PF GT PT KO P<0.05 The statistical analysis of the data by ANOVA test showed significant difference among the four groups (Table -6). By tudent t-test (Table-6) a significant difference was found between ProTaper and other groups. The ProFile was significantly quicker than GT; while there was no significant difference with K-fiexofile. Finally there was no significant difference between GT and K-flexofile. Table 7: t-test of time between groups ystem t-test P-value PF&GT PF&PT PF&KO N GT&PT GT&KO N PT&KO Instrument fracture and permanent deformation The number of fractured and permanently deformed instruments that occurred during the study is listed in Table -8. Table 8: Number of fractured and permanently deformed instruments ystem Fracture Deformation PF 2 0 GT 4 0 PT 6 0 KO 0 4 Chi-square P-value Throughout the preparation no permanent deformation occurred with NiTi groups. In term of fracture all happened at the tip region of the files. ix instruments of ProTaper were fractured (two Fl in the fourth use and four F2, two during the fourth manipulation and two throughout the fifth use).two pieces of ProFile were broken (both were taper.04 size 25 in the fifth use) and four files of GT were separated (one taper.04 size 20 during the preparation of the fifth canal and three instruments taper.04 size 25 in the fourth handling). Restorative Dentistry 4

5 In the manual technique none of the stainless steel K-flexofile was separated on the other hand four files were permanently deformed (two pieces size 20 and two pieces size 25 during the fourth and fifth use respectively). DICUION Canal aberration From Table-1 it is appear that the preparation with ProFile resulted in a significantly fewer zipping /elbow (n=4) than other tested instruments followed by GT (n=6), ProTaper (n=8) and K-flexofiles (n=10) respectively; While the incidence of ledges was as follow: GT (n=2), ProFile (n=4), ProTaper (n=8) and K- flexofiles (n=8). K-flexofiles created significantly more aberration than NiTi systems. imilar results have been established by most of reports concerned shaping ability of endodontic instruments (3) (9) (10). This highly incidence may be attributed to the inherited rigidity of these instruments. On the other hand ProTaper caused more morphological changes compared with ProFile and GT systems. This result is consistent with investigations of chafer and Vlassis, 2004 a, b (11) ; onntag et al, ). This could be related to two reasons :(a) ProTaper is less flexible than other NiTi instruments due to progressive tapering of this system, (b) convex triangular cross-section design of ProTaper with no radial lands unlike U-shape cross-section of ProFile and GT with three radial lands which plane the canal walls rather than engaged and screwing into them and to cut of dentin evenly along the canal wall (13). The number of morphological changes in the present study was higher when compared with similar studies on NiTi instruments (Hulsmann et al, 2001 (14) ; chafer and Vlassis, 2004 a, b (1I) ). This may be due to the sever curvature degree of artificial canals were used in this study (40 ) compared with other reports (28-35 ). Changes of working length In the present investigation the only statistically significant differences were found between rotary groups and the manual technique, whereas no significant differences were found among NiTi systems (Table-2). This finding is in agreement with observations of other studies whose observed only small mean changes in working length occurring with rotary NiTi instruments (Kum et al, ) ; Thompson and Dummer, 2000 (8) ; chafer Restorative Dentistry 5 and Florek, 2003a 10) ; chafer and Vlassis, 2004a,b (11) ; Paque'et al, ) ; Guelzow et a1,2005 (3) ). A number of reasons have been discussed to explain possible reasons for alteration of the working distance. Thompson and Dummer in 2000 (8) reported that these changes may probably be due to a minor canal straightening during canal enlargement. Other factors may be explain the significant difference of working length between NiTi groups and K-flexofiles, these related to the fact that, NiTi instruments caused early flaring of the coronal portion of the canal due to employment of crown-down technique and greater tapering of these instruments ending with great changes of working distance compared with balance force technique and IO tapering of K- flexofiles. Therefore it is advisable to measure the working length after preparing the coronal part of the canal to avoid alteration of the working distance. Preparation time Although a brushing action had to be used with ProTaper before further advancing the files, the preparation time of this system was substantially faster than with other groups (Table-5). This outcome corroborates the results of previous studies (3) (16) This may be due to the convex triangular cross-sectional design of ProTaper resulting in a very aggressive cutting edges and a positive rake angle which is known to require less energy to cut dentine than blades with a neutral or negative rake angle as present in ProFile and GT. In other word the cutting ability of the active instruments is superior when compared with passive instruments with radial lands (16).Furthermore, the finding that ProTaper took less working time was largely to the fact that the fewer number of instruments used (PT: 5; PR 6; GT: 6 KO: 9). The assumption that instrumentation times with rotary NiTi files were substantially faster than with stainless-steel hand files could not confirmed in the present study which demonstrated that root canal preparation was less time consuming when using K-flexofiles compared with GT, although the number of instruments was larger with K-flexofiles than GT.This outcome disagree with the findings of the most similar reports (chafer and Florek, 2003a (10) ; Guelzow et al, 2005 (3) ). This longer preparation time for GT could be attributed to the operator's influence as well as to the cutting efficacy of the files. Additionally most of the previous investigations employed

6 reaming motion with hand files unlike the present research that exercised balanced force technique which is recommended for the preparation of curved canals as it resulted in better configuration and less time consuming (6). Fracture and permanent deformation everal earlier studies indicating that NiTi instruments may be more susceptible to separation than stainless-steel instruments. This is because of their flexibility, there is a loss of tactile sensation as compared with the more rigid stainless-steel files, also when used NiTi instruments in a mechanical rotary motion to prepare narrow curved canals, the tips can bind and not move in the narrow portion of the canal, whilst the shaft and the coronal part of the file are still active according to the direction of the force exerted by the operator. Under these circumstances unpredictable separation might occur. This is in contrast to what has been observed with hand instruments which tend to unwind before a fracture occurs. o, most failures of the hand stainless-steel files were deformations rather than fractures (17). The given data of Table-8 shown that a total of 4 out of 36 instruments of K- flexofiles permanently deformed and this may reflect their rather inflexible nature a factor which may well explain their relatively high percentage of failure (11.12 %). Related to the total number of instruments used a fracture rate was approximately 30% for ProTaper (6 out of 20 files), 16.6% for GT (4 out of 24 files) and 8.3% for Profiles (2 out of 24 files). Possible explanations for the results noted with the ProTaper might be related to: (a) excessive taper of this system.the taper for finishing files used to prepare the apical portion of the canals in the ProTaper were.07and,08 respectively; while the taper of the ProFile and GT was.04. According to a study by Haikel et at in 1999 (18), taper was found to be a significant factor in determining fracture probability for files, (b) convex triangular cross-section of ProTaper which results in a more massive core, this may reduce the flexibility of the instruments when compared to U-shaped cross-sections of ProFile and GT systems. The degree of influence of the individual geometric characteristics of the instruments, however, remains speculative (12). The highly percentage of fracture of F2 files of ProTaper is in agreement with other study which has been shown that, F2 possess lower resistance to fracture because of cyclic fatigue than the other instruments in the ProTaper series. It is known that instruments with low taper have lower resistance to torsional stress, whereas those with greater size and taper are more subjected to fracture because of cyclic fatigue (5) (19). It is worth emphasizing that all fractured files were occurred when used for the fourth or fifth canal no fractures occurred when instruments were used to enlarge three canals only. This observation is in accordance with previous reports (Thompson and Dummer, 2000 (8) ; chafer and Florek, 2003 a (10) chafer and Vlassis, 2004 a,b (12) ; Paque" et al, 2005 (16) ). With regard to the incidence of file breakage, the amount of fracture in this study was higher than that reported by others (Bryant and Dummer, 1999 (20) ; Yancy et al, 2001 (21) ) and was most likely due to differences in the methodology. This study used curvatures much larger than that of the other studies, thus higher breakage would be expected due to increased stresses. In addition the above mentioned investigations used human extracted teeth; while plastic blocks were used in the present study.the simulated canals may have been a main cause of incidence of failure. - Obviously the instruments tend to attach to the plastic and pull into the canal, which leads to a higher failure rate than is seen when extracted teeth are used. The generated heat may sometimes soften the resin material so that cutting blades may bind and consequently break (22) During this study no NiTi file was deformed.this is in contrary with most of similar investigation which resulted in a high deformation percentage of NiTi instruments (Ehab et al, 2005 (23) ; Ugur et al, 2007 (24) ). This is may be due to the difference in the procedures that has been depended. In the research the magnifying lens (10X) has been used to examine the files after each use. Clearly this power of enlargement was insufficient to detect the deformation of NiTi files which is usually observe under scanning electron microscope. REFERENCE 1. Lam T, Lews D, Atkins D, Macfarlance R, Clarkson R, Whitehead M, Blockhurst P, Moule A. Changes in root canal morphology in simulated curved canals over-instrumented with a variety of stainless steel and Nickel-Titamiun files. Austral Dent J 1999, 44: (1): Bartha et al, Guelzow A, tamm 0, Marius P, Kielbassa A. Comparative study of six rotary nickel-titanium Restorative Dentistry 6

7 systems and hand instrumentation for root canal preparation. International Endodontic Journal 2005, 38 (10), Webber & Machtou, Pruett J, Clement D, Games D. Cyclic fatigue testing of nickel- titanium endodontic instruments. J of Endod 1997; 23, Roan J, abala C, Duncanson M. The balanced force concept for instrumentation of curved canals. J of Endod 1985; 11 (5), Calberson F, Deroose C, Hommez G, Raes H, DeMoor R. haping ability of GT rotary files in simulated resin root canals. Intern Endod J 2002; 35: Thompson, Dummer P. haping ability of HER0642_rotary_nickle- titanium instruments in simulated root canals: Part 2. Intern Endod J 2000; 33:(3) chafer E, Lohmann D.Efficiency of rotary nickel titanium FlexMaster instruments compared with stainless steel hand KFlexofile Part 1. haping ability in simulated curved canals. Intern Endod J 2002; 35: chafer E, Florek H. Efficiency of rotary nickel-titanium K3 instruments compared with stainless steel hand K-flexofile. Part l.haping ability in simulated curved canals. Intern Endod J 2003; 36 (3), chafer E, Vlassis M.Comparative investigation of two rotary nickels titanium instruments: ProTaper versus RaCe. Part 1.haping ability in simulated curved canals. Intern Endod J 2004; 37(4) onntag D, Mareike 0, Kathrin K, Vitus. Root canal preparation with the NiTi systems K3. Mtwo and ProTaper. Aust Endod J Tepel J, chafer E. Endodontic hand instruments: cutting efficiency, instrumentation of curved canals, bending and torsional properties. Endod Dent Traumatol 1997;13, Hulsmann M, chade M, chafers F. A comparative study of root canal preparation with HERO 642 and Quantec C rotary NiTi instruments. Intern Endod J 2001; 34: Kum K, pangberg L, Cha B, Il-Young J, eung J, Chan Young L. haping ability of three ProFile rotary instrumentation techniques in simulated resin root canals. J of Endod 2000; 26: Paque F, Musch U, Hulsmann M. Comparison of root canal preparation using RaCe and ProTaper rotary NiTi instruments. Intern Endod J 2005; 38: Kavanagh D, Lumley P. An in vitro evaluation of canal preparation using Profile.04 and.06 taper instruments. Endod Dent Traumatol 1998; 14: Haikel Y, erfaty R, Bateman G, enger B, Allemann C. Dynamic and cyclic fatigue of engine-driven rotary nickel titanium endodontic instruments. J of Endod 1999; 25: Fife D, Gambarini G, Britto L. Cyclic fatigue testing of ProTaper NiTi rotary instruments after clinical use. Oral urgery Oral Medicine Oral Pathology Oral Radiology and Endod 2004;97 (2) Bryant, Dummer P. haping Ability of.04 and.06 Taper ProFile Rotary Nickel-Titanium Instruments in imulated Root Canals. Intern Endod J 1999; 32: Yancy A, Tygesen H, teiman R, Ciavarro C. Comparison of distortion and separation utilizing Profile and Pow-R Nickel-Titanium rotary files. J of Endod 2001; 27: Thompson, Dummer P. haping ability of Profile.04 taper eries 29 rotary nickel-titanium instruments in simulated root canals. Part 1. Intern Endod J 1997; 30 (1) Ehab E, Azza H, Abeer M. Defects in Hero-haper Rotary Nickel Titanium Instruments before and after use. An EM study. Ainshams Dent J 2005; 8: 2: June. 24. Ugur I, Cumhur A, Ozgur U, Ozgur T, Tayfun A. Evaluation of the surface characteristics of used and new ProTaper instruments: An atomic force microscopy study. J of Endod 2007; 33 (11). Restorative Dentistry 7