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Table of Contents   
ORIGINAL ARTICLE  
Year : 2011  |  Volume : 14  |  Issue : 3  |  Page : 264-268
Change of working length in curved molar root canals after preparation with different rotary nickel-titanium instruments


1 Department of Conservative Dentistry and Endodontics, Swami Devi Dyal Dental College and Hospital, Panchkula, India
2 Department of Conservative Dentistry and Endodontics, College of Dental Sciences, Davangere, India
3 Department of Prosthodontics, Sen lech Swami Devi Dyal dental College and hospital, Panchkula, India
4 Department of Conservative Dentistry and Endodontics, Swami Devi dyal dental College and hospital, Panchkula, India

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Date of Submission19-Sep-2010
Date of Decision11-Oct-2010
Date of Acceptance19-Feb-2011
Date of Web Publication10-Oct-2011
 

   Abstract 

Aim: The purpose of this study was to investigate change of working length in curved molar root canals after preparation with Profile, ProTaper and K3 Rotary Nickel-Titanium (Ni-Ti) instruments.
Materials and Methods: One hundred and eighty maxillary and mandibular molars were divided into group I having root curvature angle <300 and group II having root curvature angle >300 comprising 90 teeth in each group based on Schneider's method. Group II and I were further divided into sub group A, B and C having 30 teeth each based on type of instrument used. Profiles, ProTaper and K3 Rotary Ni-Ti files were used to prepare mesial and buccal roots of molars. Radiography platform was made to allow technique for constant object to film distance and object to sensor distance. Conventional access opening was prepared in each tooth. Preoperative and postoperative working length was measured to an accuracy of 0.1 of mm on Dexis 3.0 direct digital radiograph's onscreen measurement device.
Results: Mean loss of working length varied from 0.28 to 0.92 mm. Highest working length loss was seen in ProTaper followed by K3 files and Profiles, which is statistically significant.

Keywords: Angle of curvature; direct digital radiography; loss of working length; Ni-Ti; rotary instruments

How to cite this article:
Khurana P, Nainan MT, Sodhi KK, Padda BK. Change of working length in curved molar root canals after preparation with different rotary nickel-titanium instruments. J Conserv Dent 2011;14:264-8

How to cite this URL:
Khurana P, Nainan MT, Sodhi KK, Padda BK. Change of working length in curved molar root canals after preparation with different rotary nickel-titanium instruments. J Conserv Dent [serial online] 2011 [cited 2019 Apr 21];14:264-8. Available from: http://www.jcd.org.in/text.asp?2011/14/3/264/85809

   Introduction Top


Shaping of root canals is necessary to facilitate obturation. The most appropriate canal shape according to Schneider should have gradually increasing taper, with the smallest diameter at the apical construction terminating larger at the coronal orifice. [1] Ideal preparation form with Rotary instruments has three-dimensional continuously tapering cone in multiple plane with sufficient apical enlargement. [2]

Buehler et al developed Ni-Ti alloy in 1963 in Silver springs, MD. He had used about 55 wt% Nickel and 45 wt% Ti and less than 2 wt% Co. [3]

Walia et al 1988 was first to investigate Nickel-Titanium (Ni-Ti) endodontic instruments by fabricating 15-size triangular cross-section file Ni-Ti orthodontic alloy wire. They observed that Nitinol files have two to three times more elastic flexibility than that of stainless steel files as well as superior resistance to fracture in clockwise and counter clockwise torsion. [4] Root canal treatment causes stress to Ni-Ti files and a stress-induced Martensitic transformation takes place from the Austenitic to the Martensitic phase. [5] This ability of Ni-Ti alloys to undergo extensive deformation resulting from a stress-assisted phase transformation, with the reverse transformation occurring on unloading is called super-elasticity. Ni-Ti files also have ability to revert back to its original straight form without any signs of lasting deformation, this property is called shape memory. [5]

Root canal working length may be defined as the distance from a coronal reference point to the point of which canal preparation and obturation should terminate. Success has been found to be greatest in teeth in which the obturation material extended to within 2 mm of the radiographic apex but did not extend beyond the radiographic apex. [6] Regardless of the method once the appropriate working length has been established, maintaining consistency of that measurement throughout the course of endodontic treatment is crucial and obturate to the desired apical location. [7] This is particularly true in the instrumentation of curved canal. In vitro [8] studies have shown that changes in WL commonly occur during the cleaning and shaping of curved root canals. The rotary instruments used in study were, Profile (Tulsa Dental) rotary files have cross-sectional geometry of three equally spaced "U-Shaped" grooves. It has a 20 0 negative rake angle at the cutting edge and flat radial lends to cut dentin in a planing motion. [9] ProTaper system (Dentsply, Switzerland) has convex triangular cross-section. This design along with progressive taper present in these instruments, result in reduced contact area between dentin and the cutting blade of the instrument. [10] K3 rotary file system (Sybron Endo, CA) was designed by Dr. John McSpadden has asymmetrical cross-section. A series of three radial bands with a relief behind two of the three lands allows reduced friction on the canal wall. A slight positive "rake" angle provides more cutting efficiency. [11] The purpose of this in vitro investigation was to compare pre and postinstrumentation change in WL in curved molar root canals prepared by Profile, ProTaper and K3 Rotary Ni-Ti files.


   Materials and Methods Top


Selection of teeth comprised of 180 extracted human maxillary and mandibular molars. The teeth were free of caries, had closed apices, without dilacerations and without any restorations. The teeth following extraction were cleaned free of debris and calculus and were then stored in normal saline.

Radiographical platform was made to allow technique for a more constant object to film distance and object to sensor distance. [12] It allows the application of a more constant source to object distance. Radiographical technique followed was the paralleling technique. The paralleling technique produces improved images as the result of placing the film parallel with the long axis of the tooth and the control X-ray tube is directed at right angle to the teeth and film. These factors result in images with less magnification and increased definition. Cold cure acrylic material was used for fabrication of block of length equal to the metal sheet attached to the clamp (in setting stage) with height of 25 mm and width of 30 mm, respectively. While acrylic material was in setting stage rectangular block of modeling wax having dimension of length 20 mm, width 17 mm and height 17 mm was kept in the center of acrylic block. Metallic ruler was cemented to the clamp by means of cynoacrylate adhesive. Teeth were kept at the constant distance of 16 inch from X-ray tube and they were stabilized with the help of modeling wax. Once the radiographic platform was assembled, it was connected to the X-ray tube by the clamp, which was previously adjusted to the correct diameter. [13]

Measuring canal curvature

Conventional radiographs were taken in bucco lingual direction using E-speed film (Kodak), which was kept parallel to the teeth. Radiographs were taken for all the teeth; these radiographs were used to determine canal curvature. Tracing of the radiograph was done on cephalometric tracing paper and Schneider's method was employed to determine canal curvature. The Schneider's method employs first drawing a line parallel to the long axis of the canal in the coronal third; a second line is then drawn from the apical foramen to intersect the point where the first line left the long axis of the canal, the Schneider angle is the intersection of these lines. [14] The angle formed is then measured with protractor. Mesial root of mandibular molars and buccal roots of maxillary molars was measured. Most severe angle of the particular tooth was used to categorize the teeth. Grouping for study is done as follows 180 extracted human molar teeth were divided into two main groups having 90 samples each based on the curvature of root canal. Group I curvature less than 30 0 .Group II curvature more than 30 0 . Group II and I were further divided into subgroup A, B and C based on the design of rotary file used having 30 samples each. Profiles, ProTaper and K3 files were used to prepare sub group A, B and C, respectively.

Conventional access cavity was prepared in each tooth, with No. 2, 4 and 6 round burs and taper fissure bur was used to refine the access cavity. Each root canal was located with an endodontic explorer. Pulp extirpation was done with barbed broach. The canals were made patent with 08, 10 and 15 no K-file.

Measurement of preoperative working length

No 10K file is placed in the canal and working length was measured 0.5 mm short of apical foramen of tooth. Teeth were then placed in resin block and stabilized with modeling wax. Sensor is kept parallel to the teeth at distance of 5 mm from the teeth. Estimated canal length to an accuracy of 0.1 of a millimeter using unlimited number of clicks, one at the occlusal reference point, then the remaining clicks following the curvature of the canal to the most apical extend of apical foramen, on the DDR'S (direct digital radiograph) on screen measurement device, later 0.5 mm was reduced from total measurement. [15]

Mesial root canals of mandibular molars and buccal root canals of maxillary molars were measured. All the canals were prepared using crown-down technique in sequence recommended by manufacturers. Files were mounted on a low-speed, high-torque electric motor (TC motor 3000) with a contra-angle 20:1 reduction hand piece (WH 975, Austria). Light pressure during instrumentation procedure was used together with back and forth movements of an amplitude of between 2 and 3 mm. Usage time for each instrument was maintained between 5 and 10 seconds. For Profile which were used as control are more elastic than other Ni-Ti files and they remain centered within the canal during instrumentation, due to three passive radial land. [16] Profile orifice shapes No.4 (0.07 / 50), No.3 (0.06/40), 0.06/30, 0.06/25, 0.04/30, 0.04/25 files were used in sequence recommended by manufacturer. [16] ProTaper rotary Ni-Ti endodontic instruments were used in crown down technique. [10] K3 rotary Ni-Ti endodontic instruments were used as recommend by manufacturer. [11] Orifice shapes of size (0.10/25) and (0.08/25) was used to enlarge coronal third. To enlarge middle third of canal 0.06 taper files of size 40, 35, 30, 25. For apical finishing 0.04 /25 and 0.04 /30 was used.

Postoperative working length

After the root canal preparation was completed canals were thoroughly irrigated and dried. Last used rotary file till working length in each group was placed in the canal and teeth were transferred to the acrylic block and stabilized with modeling wax. Later acrylic block was transferred to the metallic sheet attached to the metal clamp and the metal clamp was attached to the X-ray tube head at the distance of 16 inch from X-ray source which was held perpendicular to the teeth and sensor. Postoperative estimated canal length was measured to an accuracy of 0.1 of millimeter on Dexis 3.0 DDR's (Direct digital radiographs) on screen measurement device by unlimited click with first click at occlusal reference point and last click at the most apical extent of working length. Pre and postoperative working length change was measured and compared for any loss in working length. The teeth in which file had fractured postoperative working length was not determined.


   Results Top


Loss of working length was compared in 148 molar teeth, teeth in which rotary file had fractured working length loss was not determined. In Group I Profiles (control) showed mean loss of working length was 0.28 mm with ± standard deviation (SD) 0.12. Percentage reduction of 1.5% was observed. Paired t-test showed value of 16.5 and P-value < 0.001 which was highly significant. In Group II Profiles (control) showed mean loss of working length 0.39 with SD ± 0.13; loss of working length was 2.0%, paired t-test 19.8 and P-value < 0.001, HS. In case of ProTaper files in Group I mean loss of WL was 0.78 ± SD 0.16, loss was 4.2%, paired t-test 34.0 and P-value < 0.001, HS. In Group II ProTaper files showed mean loss of WL equal to 0.92 SD 0.17, loss of 4.7%, paired t-test 35.8 and P-value < 0.001, HS. In case of K3 files in Group I mean loss of WL 0.77 ± 1.40 SD, t-3.95 and P-value < 0.001, HS. K3 files in Group II mean loss of working length was 0.52 ± 0.17 SD, and loss of 2.8%, Paired t-value 25.2 and P-value< 0.001 HS [Table 1], [Table 2], [Figure 1]. Mean loss of working length varied from 0.28 to 0.92 mm. Highest working length loss was seen in ProTaper followed by K3 files and Profiles; which was statistically significant.
Figure 1: mean loss of working length in relation to angulation and instrument use

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Table 1: Mean pre and postoperative loss of working length in relation to angle of curvature of root canal

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Table 2: Comparison between mean loss of working length in relation to instrument used

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   Discussion Top


The result of this study indicates that shorting of WL constantly occurs during the instrumentation of curved canals. Our finding suggested that Ni-Ti rotary files caused small but consistent changes in working length are in agreement with those of other investigators who evaluated length change associated with the use of Ni-Ti rotary files. Thompson and Dummer reported that working length decreased by mean of 0.5 mm in 33/40 canals when instrumented with Ni-Ti rotary files. [17] Schorder et al. reported loss of 0.17 mm in canal having curvature of 5 0 and 20 0 . [18] According to Davis et al. Ni-Ti files cause minimum change in working length due to the superior ability of Ni-Ti to remain centered within the canal during instrumentation when compared to stainless-steel instruments, which tend to straighten the curved canals. [19]

Mean loss of working length varied from 0.28 to 0.92 mm. Highest working length loss was seen in ProTaper followed by K3 files and Profiles (control group) which was statistically significant. Overall loss of working length was less than 1 mm in all the groups. Ni-Ti instruments have superior ability to remain centered within the canal during instrumentation compared to stainless steel files thus minimizing the straightening of the canal. The findings of both Dummer and Thompson and Bryant et al. reported that Ni-Ti rotary files caused small change up to 0.5 mm in canal configuration in accordance to the study. [17],[20]

Profiles which were used as control group showed minimum average loss of working length for Group I (< 30 0 ) to be 0.28 mm and 0.39 mm for Group II (>30 0 ), respectively. Iqbal et al. [21] suggested average loss of working length using profile Ni-Ti files to be 0.25 mm and other studies reported that working length decreased by mean of 0.5 and 0.63 mm. Berutti et al. [22] suggested profiles were more elastic than ProTaper they remain centered within the canal during instrumentation, thus minimizing the straightening of the canal. ProTaper files in Group I (<30 0 ) show loss of 0.78 and 0.92 mm for Group II. Bergman et al. [23] showed progressive tapered shaft design of ProTaper instrument showed higher dentine removal towards the furcation area of the root canal. Peter et al. [24] Micro CT evaluation of the shaped canal studies showed that the ProTaper tends to transport canals slightly larger than to file system with a passive cutting action. Nagaraja S. [25] conducted CT evaluation of rotary ProTaper files in curved canals and observed that it causes higher canal transportation and thinning of root dentine at middle and coronal levels Guelzow et al[26] study compared various parameters of root canal preparation using a manual technique and six different rotary Ni-Ti instruments. They concluded that Ni-Ti maintained the canal curvature and ProTaper created more regular canal diameter. K3 files mean loss of working length 0.77 mm for Group I and 0.52 mm for Group II. Schafer et al [27] showed loss of WL to be 0.18 mm for 28 0 and 0.35 mm for 35 0 Ayer et al [28] study compared the shaping ability of profile and K3 rotary instruments. Results showed that K3 removed more inner canal wall material along the length of the canal and more outer wall in the apical portion average loss of WL in Group II (>30 0 ) canals is slightly higher than Group I as more material is removed in outer aspect of coronal third and inner aspect of the apical third of canal. [28] The clinical impact of length changes that occur during instrumentation may be reduced if WL is verified immediately before obturation. Even if WL were shortened during cleaning and shaping procedures, length verification completed just before obturation would permit adjustments to the obturation material and reduce the risk to have overfill. Use of an electronic apex locator can be advantageous in this situation. It lends itself to rapid length determination, permitting repeated WL assessments throughout the procedure with little impact on treatment time. The mean change in working length distance occurring with rotary Ni-Ti instruments is less. [17],[18],[20] These changes may be probably due to a minor canal straightening during canal enlargement or lack of length control by the operator. [26] From the clinical point of view it seems questionable whether these comparably small changes of the working length have any relevance. [26],[18]


   Conclusions Top


Average loss of working length was small from 1.5 to 4.7%. Overall it was less than 1 mm. ProTaper showed highest working length loss followed by K3 files and Profiles (control group), which is statistically significant.

 
   References Top

1.Sheilder H. Cleaning and shaping the root canal. Dent Clin North Am 1971;18:269-96.  Back to cited text no. 1
    
2.Walsh H. The hybrid concept of nickel-titanium rotary instrumentation. Dent Clin North Am 2004;48:183-202.  Back to cited text no. 2
    
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14.Schneider WE. A comparison of canal preparations in straight and curved root canals. Oral Surg Oral Med Oral Pathol 1971;32:27-35.   Back to cited text no. 14
    
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17.Thompson SA, Dummer MN. Shaping ability of profile .04 Taper series 29 rotary Nickel-Titanium instruments in simulated root canals. Int Endod J 1997;30:1-7.   Back to cited text no. 17
    
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19.Davis RD, Marshall G, Baumgartner JC. Effect of early canal flaring on working length change in curved canals using rotary Nickel titanium versus stainless steel instruments. J Endod 2002;28:438-42.  Back to cited text no. 19
    
20.Bryant S, Dummer P, Pitoni C, Bourba M, Moghal S. Shaping ability of .04 and .06 taper ProFile rotary nickel-titanium instruments in simulated root canals. Int Endod J 1999;32:155-64.  Back to cited text no. 20
    
21.Iqbal MK, Floratos S, Hsu YK, Karabucak B. An in vitro comparison of Profile GT and GTX nickel-titanium rotary instruments in apical transportation and length control in mandibular molar. J Endod 2010;36:302-4.  Back to cited text no. 21
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22.Berutti E, Chiandussi G, Gaviglio I, Ibba A. Comparative Analysis of Torsional and Bending stresses in Two Mathematical Models of Nickel-Titanium Rotary Instruments:ProTaper versus ProFile. J Endod 2003;29:15-9.  Back to cited text no. 22
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23.Bergmans L, Van Cleynenbreugel J, Beullens M, Wevers M, Van Meerbeek B, Lambrechts P. Progressive versus constant tapered shaft design using Ni-Ti rotary instruments. Int Endod J 2003;36:288-95.   Back to cited text no. 23
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24.Peters OA, Peters CI, Schonenberger K, Barbakow F. ProTaper rotary root canal preparation: effects of canal anatomy on final shape analyze by micro CT. Int Endod J 2003;36:86-92.  Back to cited text no. 24
    
25.Nagaraja S, Sreenivasa Murthy BV. CT evaluation of canal preparation using rotary and hand NI-TI instruments: An in vitro study. J Conserv Dent 2010;13:16-22.  Back to cited text no. 25
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26.Guelzow A, Slamm O, Martus P, Kielbassa. Comparative study of six rotary Nickel-Titanium systems and hand instrumentation for root canal preparation. Int Endod J 2005;38:743-52.  Back to cited text no. 26
    
27.Schafer E, Florek H. Efficiency of rotary nickel-titanium K3 instruments compared with stainless steel hand K-Flexofile. Part 1. Shaping ability in simulated curved canals. Int Endod J 2003;36:199-207.  Back to cited text no. 27
    
28.Ayar LR, Love RM. Shaping ability of Profile and K3 rotary Ni-Ti instruments when used in a variable tip sequence in simulated curved root canals. Int Endod J 2004;37:593-601.  Back to cited text no. 28
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DOI: 10.4103/0972-0707.85809

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