Basic Research—Technology
Incidence of Dentinal Cracks after Root Canal Preparation with Twisted File Adaptive Instruments Using Different Kinematics Ertugrul Karatas¸, DDS, PhD,* Hakan Arslan, DDS, PhD,* Meltem Alsancak, DDS,* € Damla Ozsu Kırıcı, DDS,* and I_ brahim Ersoy, DDS, PhD† Abstract Introduction: The purpose of the present study was to assess the effect of root canal instrumentation using Twisted File Adaptive instruments (Axis/SybronEndo, Orange, CA) with different kinematics (adaptive motion, 90 clockwise [CW]–30 counterclockwise [CCW], 150 CW–30 CCW, 210 CW–30 CCW, and continuous rotation) on crack formation. Methods: One hundred five mandibular central incisor teeth were selected. Fifteen teeth were left unprepared (control group), and the remaining 90 teeth were assigned to the 5 root canal shaping groups as follows (n = 15): adaptive motion, 90 CW–30 CCW, 150 CW–30 CCW, 210 CW–30 CCW, continuous rotation, and hand file. All the roots were sectioned horizontally at 3, 6, and 9 mm from the apex with a low-speed saw under water cooling, and the slices were then viewed through a stereomicroscope at 25 magnification. Digital images of each slice were captured using a camera to determine the presence of dentinal cracks. Results: No cracks were observed in the control group, and the continuous rotation group had more cracks than the reciprocation groups (90 CW–30 CCW, 150 CW–30 CCW, and 210 CW–30 CCW) (P < .05). Both the continuous rotation and adaptive motion groups had significantly more dentinal cracks than the hand file group (P < .05). Regarding the different sections (3, 6, and 9 mm), there was a significant difference between the experimental groups at the 9-mm level (P < .05). Conclusions: The incidence of dentinal cracks is less with TF Adaptive instruments working in 210 CW–30 CCW reciprocating motion compared with working in continuous rotation and adaptive motion. (J Endod 2015;41:1130–1133)
Key Words Cracks, kinematics, root canal instrumentation, Twisted File Adaptive system
I
nstrumentation with nickel-titanium instruments could result in some complications such as perforations (1), canal transportation, ledge and zip formation (2), separation of instruments (3), and dentinal cracks (4–10). Vertical root fracture, which might occur as a result of a dentinal crack (11), can lead to extraction of the tooth (12). Recently, a new system has been introduced called Twisted File Adaptive (TF Adaptive) (Axis/SybronEndo, Orange, CA) that uses continuous rotation when it is exposed to minimal or no applied load. The TF Adaptive instrument can change to a reciprocation mode, with specifically designed clockwise and counterclockwise angles, which vary from 600 –0 up to 370 –50 when it engages dentin and a load is applied. Because the incidence of dentinal cracks after root canal instrumentation may differ according to the preparation technique (13), design (9) and taper (14) of the file, and instrumentation length (15), it might be speculated that the root canal instrumentation with different movement kinematics (continuous rotation, reciprocation with different angles, and adaptive motion) may change the incidence of dentinal defects. To date, no studies have determined the incidence of dentinal microcracks resulting from the use of the TF Adaptive instruments with different kinematics. Therefore, the purpose of the present study was to assess the effect of root canal instrumentation using TF Adaptive system instruments with different kinematics (adaptive motion, 90 clockwise [CW]–30 counterclockwise [CCW], 150 CW–30 CCW, 210 CW–30 CCW, and continuous rotation) on crack formation. The null hypothesis was that there would be no differences in crack formation among the groups.
Materials and Methods Extracted human mandibular central incisors with single canals and similar lengths were selected and kept in purified filtered water. The soft tissue remnants and calculi on the external root surface were removed mechanically, and the coronal portions of all the teeth were removed using an Isomet low-speed saw (Isomet 1000; Buehler, Lake Bluff, IL) under water cooling to achieve a final 13-mm length for each tooth. All the roots were observed with a stereomicroscope (Novex, Arnhem, Holland) with 15 magnification to detect any pre-existing external defects or cracks. Proximal radiographs were taken, and a tooth having more than a single root canal and apical foramen, root canal treatment, internal/external resorption, immature root apices, caries/cracks/fractures on the root surface, and/or root canal curvature more than 10 was excluded from the study. In all the teeth, the canal width near the minor apical foramen was compatible with a size 10 K-file (Dentsply Maillefer, Ballaigues, Switzerland).
From the *Department of Endodontics, Faculty of Dentistry, Ataturk University, Erzurum, Turkey; and †Department of Endodontics, Faculty of Dentistry, S¸ifa University, _Izmir, Turkey. Address requests for reprints to Dr Ertugrul Karatas¸, Department of Restorative Dentistry and Endodontics, Faculty of Dentistry, Ataturk University, Erzurum 25240, Turkey. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2015 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2015.02.029
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Basic Research—Technology According to these criteria, 105 mandibular central incisor teeth were selected, and the teeth were randomly divided into 6 groups (n = 15). The root width was measured buccolingually and mesiodistally 5 mm from the apex, and the homogeneity of the 6 groups was assessed using an analysis of variance (P = 1.000). A size 10 K-file was introduced into the canals of all samples until the tip of the file became visible at the apical foramen. The distance between the tip of the file and the reference plane was defined as the canal length, and the working length (WL) was established by subtracting 1 mm from this length. A silicone impression material was used for coating the surface of the roots to simulate the periodontal ligament, and all the roots were then embedded in acrylic blocks. Fifteen teeth were left unprepared (control group). Seventy-five teeth were instrumented using TF Adaptive instruments (SM1 [20/.04], SM2 [25/.06], and SM3 [35/.04]) at the full WL. The remaining 15 teeth were instrumented with hand files. The irrigation was performed using a syringe and a 27-G needle (Hayat, Istanbul, Turkey) placed 1 mm from the WL. After each instrument change, 2 mL sodium hypochlorite was used for irrigation and a total of 10 mL sodium hypochlorite was used for each canal.
Group 1 (Adaptive Motion) The root canals were instrumented using the TF Adaptive instruments (SM1 [20/.04], SM2 [25/.06], and SM3 [35/.04]) with an Elements Motor (SybronEndo, Glendora, CA). Group 2 (90 CW–30 CCW) In this group, root canal preparation was performed using an electric motor (Satelec Endodual; Acteon, Merignac, France) that allows the user to modify and set the reciprocating angles in both CW and CCW directions. The angle of reciprocation was set at CW = 90 and CCW = 30 for root canal preparation. Group 3 (150 CW–30 CCW) The root canals were instrumented using a motor (Acteon) at a reciprocation range of 150 CW and 30 CCW (angle of progression for each reciprocation was 120 ). Group 4 (210 CW–30 CCW) The root canals were instrumented using an Acteon motor at a reciprocation range of 210 CW and 30 CCW (angle of progression for each reciprocation was 180 ).
Figure 1. A representative image of the slice with a dentinal crack.
All the root canal preparations were performed by 1 operator and the assessments of the cross sections were performed by 2 other examiners who were blinded to all the experimental groups. All the roots were sectioned horizontally at 3, 6, and 9 mm from the apex with a low-speed saw under water cooling. The slices were stained with a dye (VOCO Caries Marker, Cuxhaven, Germany) to enhance the detection of cracks. The slices were then viewed through a stereomicroscope at 25 magnification. Digital images of each slice were captured using a camera (Coolpix 4500; Nikon, Tokyo, Japan) to determine the presence of dentinal cracks. A ‘‘crack’’ was defined if an incomplete crack (a line extending from the canal wall into the dentin without reaching the outer surface of the root), a complete crack (a line extending from the root canal wall to the outer surface of the root) (Fig. 1), or a craze line (other lines that did not reach any surface of the root or extend from the outer surface into the dentin but did not reach the canal wall) were present in the root dentin. ‘‘No crack’’ was defined as root dentin devoid of craze lines, complete cracks, and incomplete cracks (Fig. 2). More than 1 crack per slice was possible. However, the data were collected as present/absent of a crack. The chi-square test was used for statistical analysis of differences among the experimental groups (P = .05).
Group 5 (Continuous Rotation) In this group, the root canals were prepared using an Acteon motor at continuous rotation. Group 6 (Hand File) The coronal flaring was performed with #2 and #1 Gates Glidden drills (Mani Inc, Tachigiken, Japan). K-files were used in a crown-down sequence by using #35 .02 taper, #30 .02 taper, #25 .02 taper, and #20 .02 file until 1 mm short of the WL. Thereafter, each root canal was prepared to the WL according to the following sequence: #20 .02 taper, #25 .02 taper, #30.02 taper, and #35 .02 taper (15). Group 7 (Control) In this group, the teeth were left unprepared. In all groups, the root canals were instrumented at a speed of 250 rpm using an 8:1 reduction handpiece except for the TF Adaptive group. (In this group, the instruments were used with the TF Adaptive program of their motor.) JOE — Volume 41, Number 7, July 2015
Figure 2. A representative image of the slice without any dentinal cracks.
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Basic Research—Technology TABLE 1. Number of Cracks in the Different Cross-section Slices Absolute number of cracks 9 mm (%)
6 mm (%)
3 mm (%)
Total cracked roots per group (%)
7 (47)a 3 (20)abc 3 (20)abc 0 (0)c 6 (40)a 3 (20)abc 0 (0)bc .008
4 (27) 3 (20) 3 (20) 3 (20) 6 (40) 1 (7) 0 (0) .130
2 (13) 0 (0) 1 (7) 0 (0) 3 (20) 1 (7) 0 (0) .199
13 (29)ab 6 (13)bc 7 (16)bc 3 (7)cd 15 (33)a 5 (11)c 0 (0)d .000
TF Adaptive 90 CW–30 CCW 150 CW–30 CCW 210 CW–30 CCW Continuous rotation Hand files Control P value
CCW, counterclockwise; CW, clockwise; TF Adaptive, Twisted File Adaptive. Values with the same letters were not statistically different at P = .05. Note that >1 crack per slice was possible.
Results Table 1 summarize the results. No cracks were observed in the control group, and the difference between the control group and the experimental groups was statistically significant (P < .001). The continuous rotation group had more cracks than the reciprocation groups (90 CW–30 CCW, 150 CW–30 CCW, and 210 CW–30 CCW) (P < .05). The adaptive motion group was associated with significantly more cracks compared with the 210 CW–30 CCW group. Both the continuous rotation and adaptive motion groups had significantly more dentinal cracks than the hand file group (P < .05). There was no statistically significant difference among the reciprocation groups (P > .05). Regarding the different sections (3, 6, and 9 mm), there was a significant difference between the experimental groups at the 9-mm level (P < .05). The continuous rotation and adaptive motion groups had significantly more cracks than the 210 CW–30 CCW and control groups in the coronal section (P < .05). There was no significant difference among the reciprocation, hand file, and control groups at the 9-mm level in terms of crack formation. In the 6-mm and 3-mm sections, there was no significant difference in the crack formation among the groups (P > .05). In all reciprocation groups, especially in the 90 CW–30 CCW, some of the TF Adaptive files were distorted after a single use. In contrast, in the continuous rotation and adaptive motion groups, none of the TF Adaptive files were distorted.
Discussion In the present study, the effect of the TF Adaptive instruments with different movement kinematics on crack development was evaluated. According to the results, all of the kinematics compared in the current study was associated with dentinal cracks. In addition, because the different movement kinematics produced different amounts of dentinal crack, the null hypothesis was rejected. Saber Sel and Abu El Sadat (16) have evaluated the effect of altering the reciprocation range of the WaveOne instrument (Dentsply Maillefer) on its fatigue life and shaping ability. They concluded that decreasing the reciprocation range of WaveOne instruments resulted in an increased cyclic fatigue resistance with less canal transportation. It might be speculated that the root canal instrumentation with different progression ranges may change the incidence of dentinal defects. Thus, the present study compared 90 CW–30 CCW, 150 CW–30 CCW, and 210 CW–30 CCW reciprocation angles with adaptive and continuous rotation motion in terms of crack formation. These angles were selected because of their different progression range (60 , 120 , and 180 in the 90 CW–30 CCW, 150 CW–30 CCW, and 210 CW–30 CCW groups, respectively). 1132
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According to the results of the present study, the adaptive motion group produced more cracks than the 210 CW–30 CCW group. However, there was no significant difference among the TF Adaptive, 90 CW–30 CCW, and 150 CW–30 CCW groups. The TF Adaptive instrument uses continuous rotation when it is exposed to minimal or no applied load. When the file engages dentin or a load is applied, it changes to a reciprocation mode, with the angles of 600 CW–0 CCW up to 370 CW–50 CCW. However, it is unclear whether the kinematic of adaptive movement was reciprocation or the continuous rotation during root canal preparation. Therefore, there is a lack of clarity on the progression range of adaptive movement. On the other hand, the reciprocation groups had certain progression ranges. The progression range of 210 CW–30 CCW group was 180 , whereas it was 60 and 120 in the 90 CW–30 CCW and 150 CW–30 CCW groups, respectively. Thus, it can be speculated that decreasing the reciprocation range of TF Adaptive instruments might have resulted in an increased incidence of dentinal crack formation. In the present study, continuous rotation caused more cracks than reciprocation. Applying a rotational force to the root canal wall can create microcracks and craze lines in root dentin (5). Continuous rotation might have increased the stress concentration on the root canal wall because of applying more rotational forces to the root canal wall, resulting in more crack formation. In addition, it has been reported that the dentinal cracks can be related to instrumentation techniques (13). Adorno et al (13) evaluated the effect of preparation techniques on crack development in the apical root canal wall, and they found that the crown-down technique was associated with more cracks than the step-back technique at a level of 1 mm short of the apical foramen. Although most nickel-titanium systems work in a crown-down manner, reciprocal systems simulate the balanced force technique (17). Liu et al (7) evaluated the incidence of dentinal cracks after root canal instrumentation with different file systems and reported that reciprocating motion caused less dentinal damage than continuous rotation motion. Although a direct comparison cannot be performed, this finding may be assumed to be similar to our results. Abou El Nasr and Abd El Kader (18) evaluated dentinal damage with single-file systems (WaveOne and ProTaper) using different kinematics and concluded that the alloy from which the material is manufactured is a more important factor in determining the dentin damaging potential of single-file instruments than the motion of instrumentation. Similarly, Kansal et al (19) assessed dentinal damage during root canal instrumentation using reciprocating and rotary files (WaveOne and ProTaper) and concluded that dentinal cracks are produced irrespective of motion kinematics. However, in the present study, all the roots were prepared with the same type of instrument; thus, a direct comparison could not be performed between the JOE — Volume 41, Number 7, July 2015
Basic Research—Technology results of the previous studies and the present study. Moreover, different instruments with alloys and designs may produce different amounts of dentinal cracks (16, 18). According to the result of the present study, the TF adaptive motion and continuous rotation groups produced more dentinal cracks than the hand file group. This is in agreement with Liu et al (15), who concluded that rotary instruments caused more dentinal defects than hand instruments. There was no significant difference among the hand file and reciprocation groups in terms of dentinal crack formation. However, all the reciprocation groups, except the 210 CW–30 CCW group, produced more dentinal cracks than the control group. The tapered files may generate an increased stress on the dentin wall (14). Wilcox et al (11) concluded that the likelihood of root fracture increases with the amount of tooth structure removed. It was found that the amount of dentin removed by tapered files at the coronal part of the root canal is more than at the apical part of the root canal (20). Regarding the different sections, there was no significant difference among the groups at the 3- and 6-mm levels. However, at the 9-mm level, the continuous rotation and adaptive motion groups produced significantly more cracks than the 210 CW–30 CCW and control groups. The taper of the files might have led to more crack formation at the 9-mm level in the continuous rotation and adaptive motion groups. In the present study, the TF Adaptive system was selected for root canal preparation in all groups. To our knowledge, there are no data about dentinal crack formation after using these instruments with different kinematics. Moreover, the TF Adaptive system instrument can work in both continuous rotation and reciprocating motion. However, there was no significant difference between the adaptive motion and continuous rotation groups (P > .05). There are conflicting reports about the use of the dyeing method in the assessment of cracks. Wright et al (21) reported that methylene blue provides discrimination between cracked and noncracked resected roots. In contrast, Von Arx et al (22) reported that staining alone may not necessarily enhance the detection of cracks because the dye cannot flow into craze lines unless there is a break in the surface. In the present study, a dye was used to enhance the detection of cracks as used previously (23).
Conclusion Within the limitations of this in vitro study, it can be concluded that all the kinematics used in the present study caused dentinal crack formation. The incidence of dentinal cracks is less with TF Adaptive instruments working in 210 CW–30 CCW reciprocating motion compared with working in continuous rotation and adaptive motion.
Acknowledgments The authors deny any conflicts of interest related to this study.
JOE — Volume 41, Number 7, July 2015
References 1. Tsesis I, Rosenberg E, Faivishevsky V, et al. Prevalence and associated periodontal status of teeth with root perforation: a retrospective study of 2,002 patients’ medical records. J Endod 2010;36:797–800. 2. Aydin B, Kose T, Caliskan MK. Effectiveness of HERO 642 versus Hedstrom files for removing gutta-percha fillings in curved root canals: an ex vivo study. Int Endod J 2009;42:1050–6. 3. Cuje J, Bargholz C, Hulsmann M. The outcome of retained instrument removal in a specialist practice. Int Endod J 2010;43:545–54. 4. Capar ID, Arslan H, Akcay M, et al. Effects of ProTaper Universal, ProTaper Next, and HyFlex instruments on crack formation in dentin. J Endod 2014;40:1482–4. 5. Yoldas O, Yilmaz S, Atakan G, et al. Dentinal microcrack formation during root canal preparations by different NiTi rotary instruments and the self-adjusting file. J Endod 2012;38:232–5. 6. Topcuoglu HS, Demirbuga S, Tuncay O, et al. The effects of Mtwo, R-Endo, and D-RaCe retreatment instruments on the incidence of dentinal defects during the removal of root canal filling material. J Endod 2014;40:266–70. 7. Liu R, Hou BX, Wesselink PR, et al. The incidence of root microcracks caused by 3 different single-file systems versus the ProTaper system. J Endod 2013;39:1054–6. 8. Hin ES, Wu MK, Wesselink PR, et al. Effects of self-adjusting file, Mtwo, and ProTaper on the root canal wall. J Endod 2013;39:262–4. 9. Burklein S, Tsotsis P, Schafer E. Incidence of dentinal defects after root canal preparation: reciprocating versus rotary instrumentation. J Endod 2013;39:501–4. 10. Karatas E, Gunduz HA, Kirici DO, et al. Dentinal crack formation during root canal preparations by the Twisted File Adaptive, ProTaper Next, ProTaper Universal, and WaveOne instruments. J Endod 2015;41:261–4. 11. Wilcox LR, Roskelley C, Sutton T. The relationship of root canal enlargement to finger-spreader induced vertical root fracture. J Endod 1997;23:533–4. 12. Tamse A, Fuss Z, Lustig J, et al. An evaluation of endodontically treated vertically fractured teeth. J Endod 1999;25:506–8. 13. Adorno CG, Yoshioka T, Suda H. The effect of working length and root canal preparation technique on crack development in the apical root canal wall. Int Endod J 2010;43:321–7. 14. Bier CA, Shemesh H, Tanomaru-Filho M, et al. The ability of different nickel-titanium rotary instruments to induce dentinal damage during canal preparation. J Endod 2009;35:236–8. 15. Liu R, Kaiwar A, Shemesh H, et al. Incidence of apical root cracks and apical dentinal detachments after canal preparation with hand and rotary files at different instrumentation lengths. J Endod 2013;39:129–32. 16. Saber Sel D, Abu El Sadat SM. Effect of altering the reciprocation range on the fatigue life and the shaping ability of WaveOne nickel-titanium instruments. J Endod 2013; 39:685–8. 17. Kocak S, Kocak MM, Saglam BC, et al. Apical extrusion of debris using self-adjusting file, reciprocating single-file, and 2 rotary instrumentation systems. J Endod 2013; 39:1278–80. 18. Abou El Nasr HM, Abd El Kader KG. Dentinal damage and fracture resistance of oval roots prepared with single-file systems using different kinematics. J Endod 2014;40: 849–51. 19. Kansal R, Rajput A, Talwar S, et al. Assessment of dentinal damage during canal preparation using reciprocating and rotary files. J Endod 2014;40:1443–6. 20. Akhlaghi NM, Kahali R, Abtahi A, et al. Comparison of dentine removal using V-taper and K-Flexofile instruments. Int Endod J 2010;43:1029–36. 21. Wright HM Jr, Loushine RJ, Weller RN, et al. Identification of resected root-end dentinal cracks: a comparative study of transillumination and dyes. J Endod 2004;30:712–5. 22. von Arx T, Kunz R, Schneider AC, et al. Detection of dentinal cracks after root-end resection: an ex vivo study comparing microscopy and endoscopy with scanning electron microscopy. J Endod 2010;36:1563–8. 23. Arslan H, Karatas E, Capar ID, et al. Effect of ProTaper Universal, Endoflare, Revo-S, HyFlex coronal flaring instruments, and Gates Glidden drills on crack formation. J Endod 2014;40:1681–3.
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Incidence of Dentinal Cracks after Root Canal Preparation with Twisted File Adaptive Instruments Using Different Kinematics Ertugrul Karatas¸, DDS, PhD,* Hakan Arslan, DDS, PhD,* Meltem Alsancak, DDS,* € Damla Ozsu Kırıcı, DDS,* and I_ brahim Ersoy, DDS, PhD† Abstract Introduction: The purpose of the present study was to assess the effect of root canal instrumentation using Twisted File Adaptive instruments (Axis/SybronEndo, Orange, CA) with different kinematics (adaptive motion, 90 clockwise [CW]–30 counterclockwise [CCW], 150 CW–30 CCW, 210 CW–30 CCW, and continuous rotation) on crack formation. Methods: One hundred five mandibular central incisor teeth were selected. Fifteen teeth were left unprepared (control group), and the remaining 90 teeth were assigned to the 5 root canal shaping groups as follows (n = 15): adaptive motion, 90 CW–30 CCW, 150 CW–30 CCW, 210 CW–30 CCW, continuous rotation, and hand file. All the roots were sectioned horizontally at 3, 6, and 9 mm from the apex with a low-speed saw under water cooling, and the slices were then viewed through a stereomicroscope at 25 magnification. Digital images of each slice were captured using a camera to determine the presence of dentinal cracks. Results: No cracks were observed in the control group, and the continuous rotation group had more cracks than the reciprocation groups (90 CW–30 CCW, 150 CW–30 CCW, and 210 CW–30 CCW) (P < .05). Both the continuous rotation and adaptive motion groups had significantly more dentinal cracks than the hand file group (P < .05). Regarding the different sections (3, 6, and 9 mm), there was a significant difference between the experimental groups at the 9-mm level (P < .05). Conclusions: The incidence of dentinal cracks is less with TF Adaptive instruments working in 210 CW–30 CCW reciprocating motion compared with working in continuous rotation and adaptive motion. (J Endod 2015;41:1130–1133)
Key Words Cracks, kinematics, root canal instrumentation, Twisted File Adaptive system
I
nstrumentation with nickel-titanium instruments could result in some complications such as perforations (1), canal transportation, ledge and zip formation (2), separation of instruments (3), and dentinal cracks (4–10). Vertical root fracture, which might occur as a result of a dentinal crack (11), can lead to extraction of the tooth (12). Recently, a new system has been introduced called Twisted File Adaptive (TF Adaptive) (Axis/SybronEndo, Orange, CA) that uses continuous rotation when it is exposed to minimal or no applied load. The TF Adaptive instrument can change to a reciprocation mode, with specifically designed clockwise and counterclockwise angles, which vary from 600 –0 up to 370 –50 when it engages dentin and a load is applied. Because the incidence of dentinal cracks after root canal instrumentation may differ according to the preparation technique (13), design (9) and taper (14) of the file, and instrumentation length (15), it might be speculated that the root canal instrumentation with different movement kinematics (continuous rotation, reciprocation with different angles, and adaptive motion) may change the incidence of dentinal defects. To date, no studies have determined the incidence of dentinal microcracks resulting from the use of the TF Adaptive instruments with different kinematics. Therefore, the purpose of the present study was to assess the effect of root canal instrumentation using TF Adaptive system instruments with different kinematics (adaptive motion, 90 clockwise [CW]–30 counterclockwise [CCW], 150 CW–30 CCW, 210 CW–30 CCW, and continuous rotation) on crack formation. The null hypothesis was that there would be no differences in crack formation among the groups.
Materials and Methods Extracted human mandibular central incisors with single canals and similar lengths were selected and kept in purified filtered water. The soft tissue remnants and calculi on the external root surface were removed mechanically, and the coronal portions of all the teeth were removed using an Isomet low-speed saw (Isomet 1000; Buehler, Lake Bluff, IL) under water cooling to achieve a final 13-mm length for each tooth. All the roots were observed with a stereomicroscope (Novex, Arnhem, Holland) with 15 magnification to detect any pre-existing external defects or cracks. Proximal radiographs were taken, and a tooth having more than a single root canal and apical foramen, root canal treatment, internal/external resorption, immature root apices, caries/cracks/fractures on the root surface, and/or root canal curvature more than 10 was excluded from the study. In all the teeth, the canal width near the minor apical foramen was compatible with a size 10 K-file (Dentsply Maillefer, Ballaigues, Switzerland).
From the *Department of Endodontics, Faculty of Dentistry, Ataturk University, Erzurum, Turkey; and †Department of Endodontics, Faculty of Dentistry, S¸ifa University, _Izmir, Turkey. Address requests for reprints to Dr Ertugrul Karatas¸, Department of Restorative Dentistry and Endodontics, Faculty of Dentistry, Ataturk University, Erzurum 25240, Turkey. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2015 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2015.02.029
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Basic Research—Technology According to these criteria, 105 mandibular central incisor teeth were selected, and the teeth were randomly divided into 6 groups (n = 15). The root width was measured buccolingually and mesiodistally 5 mm from the apex, and the homogeneity of the 6 groups was assessed using an analysis of variance (P = 1.000). A size 10 K-file was introduced into the canals of all samples until the tip of the file became visible at the apical foramen. The distance between the tip of the file and the reference plane was defined as the canal length, and the working length (WL) was established by subtracting 1 mm from this length. A silicone impression material was used for coating the surface of the roots to simulate the periodontal ligament, and all the roots were then embedded in acrylic blocks. Fifteen teeth were left unprepared (control group). Seventy-five teeth were instrumented using TF Adaptive instruments (SM1 [20/.04], SM2 [25/.06], and SM3 [35/.04]) at the full WL. The remaining 15 teeth were instrumented with hand files. The irrigation was performed using a syringe and a 27-G needle (Hayat, Istanbul, Turkey) placed 1 mm from the WL. After each instrument change, 2 mL sodium hypochlorite was used for irrigation and a total of 10 mL sodium hypochlorite was used for each canal.
Group 1 (Adaptive Motion) The root canals were instrumented using the TF Adaptive instruments (SM1 [20/.04], SM2 [25/.06], and SM3 [35/.04]) with an Elements Motor (SybronEndo, Glendora, CA). Group 2 (90 CW–30 CCW) In this group, root canal preparation was performed using an electric motor (Satelec Endodual; Acteon, Merignac, France) that allows the user to modify and set the reciprocating angles in both CW and CCW directions. The angle of reciprocation was set at CW = 90 and CCW = 30 for root canal preparation. Group 3 (150 CW–30 CCW) The root canals were instrumented using a motor (Acteon) at a reciprocation range of 150 CW and 30 CCW (angle of progression for each reciprocation was 120 ). Group 4 (210 CW–30 CCW) The root canals were instrumented using an Acteon motor at a reciprocation range of 210 CW and 30 CCW (angle of progression for each reciprocation was 180 ).
Figure 1. A representative image of the slice with a dentinal crack.
All the root canal preparations were performed by 1 operator and the assessments of the cross sections were performed by 2 other examiners who were blinded to all the experimental groups. All the roots were sectioned horizontally at 3, 6, and 9 mm from the apex with a low-speed saw under water cooling. The slices were stained with a dye (VOCO Caries Marker, Cuxhaven, Germany) to enhance the detection of cracks. The slices were then viewed through a stereomicroscope at 25 magnification. Digital images of each slice were captured using a camera (Coolpix 4500; Nikon, Tokyo, Japan) to determine the presence of dentinal cracks. A ‘‘crack’’ was defined if an incomplete crack (a line extending from the canal wall into the dentin without reaching the outer surface of the root), a complete crack (a line extending from the root canal wall to the outer surface of the root) (Fig. 1), or a craze line (other lines that did not reach any surface of the root or extend from the outer surface into the dentin but did not reach the canal wall) were present in the root dentin. ‘‘No crack’’ was defined as root dentin devoid of craze lines, complete cracks, and incomplete cracks (Fig. 2). More than 1 crack per slice was possible. However, the data were collected as present/absent of a crack. The chi-square test was used for statistical analysis of differences among the experimental groups (P = .05).
Group 5 (Continuous Rotation) In this group, the root canals were prepared using an Acteon motor at continuous rotation. Group 6 (Hand File) The coronal flaring was performed with #2 and #1 Gates Glidden drills (Mani Inc, Tachigiken, Japan). K-files were used in a crown-down sequence by using #35 .02 taper, #30 .02 taper, #25 .02 taper, and #20 .02 file until 1 mm short of the WL. Thereafter, each root canal was prepared to the WL according to the following sequence: #20 .02 taper, #25 .02 taper, #30.02 taper, and #35 .02 taper (15). Group 7 (Control) In this group, the teeth were left unprepared. In all groups, the root canals were instrumented at a speed of 250 rpm using an 8:1 reduction handpiece except for the TF Adaptive group. (In this group, the instruments were used with the TF Adaptive program of their motor.) JOE — Volume 41, Number 7, July 2015
Figure 2. A representative image of the slice without any dentinal cracks.
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Basic Research—Technology TABLE 1. Number of Cracks in the Different Cross-section Slices Absolute number of cracks 9 mm (%)
6 mm (%)
3 mm (%)
Total cracked roots per group (%)
7 (47)a 3 (20)abc 3 (20)abc 0 (0)c 6 (40)a 3 (20)abc 0 (0)bc .008
4 (27) 3 (20) 3 (20) 3 (20) 6 (40) 1 (7) 0 (0) .130
2 (13) 0 (0) 1 (7) 0 (0) 3 (20) 1 (7) 0 (0) .199
13 (29)ab 6 (13)bc 7 (16)bc 3 (7)cd 15 (33)a 5 (11)c 0 (0)d .000
TF Adaptive 90 CW–30 CCW 150 CW–30 CCW 210 CW–30 CCW Continuous rotation Hand files Control P value
CCW, counterclockwise; CW, clockwise; TF Adaptive, Twisted File Adaptive. Values with the same letters were not statistically different at P = .05. Note that >1 crack per slice was possible.
Results Table 1 summarize the results. No cracks were observed in the control group, and the difference between the control group and the experimental groups was statistically significant (P < .001). The continuous rotation group had more cracks than the reciprocation groups (90 CW–30 CCW, 150 CW–30 CCW, and 210 CW–30 CCW) (P < .05). The adaptive motion group was associated with significantly more cracks compared with the 210 CW–30 CCW group. Both the continuous rotation and adaptive motion groups had significantly more dentinal cracks than the hand file group (P < .05). There was no statistically significant difference among the reciprocation groups (P > .05). Regarding the different sections (3, 6, and 9 mm), there was a significant difference between the experimental groups at the 9-mm level (P < .05). The continuous rotation and adaptive motion groups had significantly more cracks than the 210 CW–30 CCW and control groups in the coronal section (P < .05). There was no significant difference among the reciprocation, hand file, and control groups at the 9-mm level in terms of crack formation. In the 6-mm and 3-mm sections, there was no significant difference in the crack formation among the groups (P > .05). In all reciprocation groups, especially in the 90 CW–30 CCW, some of the TF Adaptive files were distorted after a single use. In contrast, in the continuous rotation and adaptive motion groups, none of the TF Adaptive files were distorted.
Discussion In the present study, the effect of the TF Adaptive instruments with different movement kinematics on crack development was evaluated. According to the results, all of the kinematics compared in the current study was associated with dentinal cracks. In addition, because the different movement kinematics produced different amounts of dentinal crack, the null hypothesis was rejected. Saber Sel and Abu El Sadat (16) have evaluated the effect of altering the reciprocation range of the WaveOne instrument (Dentsply Maillefer) on its fatigue life and shaping ability. They concluded that decreasing the reciprocation range of WaveOne instruments resulted in an increased cyclic fatigue resistance with less canal transportation. It might be speculated that the root canal instrumentation with different progression ranges may change the incidence of dentinal defects. Thus, the present study compared 90 CW–30 CCW, 150 CW–30 CCW, and 210 CW–30 CCW reciprocation angles with adaptive and continuous rotation motion in terms of crack formation. These angles were selected because of their different progression range (60 , 120 , and 180 in the 90 CW–30 CCW, 150 CW–30 CCW, and 210 CW–30 CCW groups, respectively). 1132
Karatas¸ et al.
According to the results of the present study, the adaptive motion group produced more cracks than the 210 CW–30 CCW group. However, there was no significant difference among the TF Adaptive, 90 CW–30 CCW, and 150 CW–30 CCW groups. The TF Adaptive instrument uses continuous rotation when it is exposed to minimal or no applied load. When the file engages dentin or a load is applied, it changes to a reciprocation mode, with the angles of 600 CW–0 CCW up to 370 CW–50 CCW. However, it is unclear whether the kinematic of adaptive movement was reciprocation or the continuous rotation during root canal preparation. Therefore, there is a lack of clarity on the progression range of adaptive movement. On the other hand, the reciprocation groups had certain progression ranges. The progression range of 210 CW–30 CCW group was 180 , whereas it was 60 and 120 in the 90 CW–30 CCW and 150 CW–30 CCW groups, respectively. Thus, it can be speculated that decreasing the reciprocation range of TF Adaptive instruments might have resulted in an increased incidence of dentinal crack formation. In the present study, continuous rotation caused more cracks than reciprocation. Applying a rotational force to the root canal wall can create microcracks and craze lines in root dentin (5). Continuous rotation might have increased the stress concentration on the root canal wall because of applying more rotational forces to the root canal wall, resulting in more crack formation. In addition, it has been reported that the dentinal cracks can be related to instrumentation techniques (13). Adorno et al (13) evaluated the effect of preparation techniques on crack development in the apical root canal wall, and they found that the crown-down technique was associated with more cracks than the step-back technique at a level of 1 mm short of the apical foramen. Although most nickel-titanium systems work in a crown-down manner, reciprocal systems simulate the balanced force technique (17). Liu et al (7) evaluated the incidence of dentinal cracks after root canal instrumentation with different file systems and reported that reciprocating motion caused less dentinal damage than continuous rotation motion. Although a direct comparison cannot be performed, this finding may be assumed to be similar to our results. Abou El Nasr and Abd El Kader (18) evaluated dentinal damage with single-file systems (WaveOne and ProTaper) using different kinematics and concluded that the alloy from which the material is manufactured is a more important factor in determining the dentin damaging potential of single-file instruments than the motion of instrumentation. Similarly, Kansal et al (19) assessed dentinal damage during root canal instrumentation using reciprocating and rotary files (WaveOne and ProTaper) and concluded that dentinal cracks are produced irrespective of motion kinematics. However, in the present study, all the roots were prepared with the same type of instrument; thus, a direct comparison could not be performed between the JOE — Volume 41, Number 7, July 2015
Basic Research—Technology results of the previous studies and the present study. Moreover, different instruments with alloys and designs may produce different amounts of dentinal cracks (16, 18). According to the result of the present study, the TF adaptive motion and continuous rotation groups produced more dentinal cracks than the hand file group. This is in agreement with Liu et al (15), who concluded that rotary instruments caused more dentinal defects than hand instruments. There was no significant difference among the hand file and reciprocation groups in terms of dentinal crack formation. However, all the reciprocation groups, except the 210 CW–30 CCW group, produced more dentinal cracks than the control group. The tapered files may generate an increased stress on the dentin wall (14). Wilcox et al (11) concluded that the likelihood of root fracture increases with the amount of tooth structure removed. It was found that the amount of dentin removed by tapered files at the coronal part of the root canal is more than at the apical part of the root canal (20). Regarding the different sections, there was no significant difference among the groups at the 3- and 6-mm levels. However, at the 9-mm level, the continuous rotation and adaptive motion groups produced significantly more cracks than the 210 CW–30 CCW and control groups. The taper of the files might have led to more crack formation at the 9-mm level in the continuous rotation and adaptive motion groups. In the present study, the TF Adaptive system was selected for root canal preparation in all groups. To our knowledge, there are no data about dentinal crack formation after using these instruments with different kinematics. Moreover, the TF Adaptive system instrument can work in both continuous rotation and reciprocating motion. However, there was no significant difference between the adaptive motion and continuous rotation groups (P > .05). There are conflicting reports about the use of the dyeing method in the assessment of cracks. Wright et al (21) reported that methylene blue provides discrimination between cracked and noncracked resected roots. In contrast, Von Arx et al (22) reported that staining alone may not necessarily enhance the detection of cracks because the dye cannot flow into craze lines unless there is a break in the surface. In the present study, a dye was used to enhance the detection of cracks as used previously (23).
Conclusion Within the limitations of this in vitro study, it can be concluded that all the kinematics used in the present study caused dentinal crack formation. The incidence of dentinal cracks is less with TF Adaptive instruments working in 210 CW–30 CCW reciprocating motion compared with working in continuous rotation and adaptive motion.
Acknowledgments The authors deny any conflicts of interest related to this study.
JOE — Volume 41, Number 7, July 2015
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