- Email: [email protected]
Evaluation of the Efficiency of a New File Removal System in Comparison With Two Conventional Systems
Basic Research—Technology
Evaluation of the Efficiency of a New File Removal System in Comparison With Two Conventional Systems Yoshitsugu Terauchi, DDS,* Le O’Leary, DDS,† Izumi Kikuchi, DDS, PhD,* Mami Asanagi, DDS,* Takatomo Yoshioka, DDS, PhD, Chihiro Kobayashi, DDS, PhD,* and Hideaki Suda, DDS, PhD* Abstract A novel file-removal system (FRS) was designed to address weak points of conventional file-removal methods. The purpose of this study was to compare fileremoval time and dentin removal rates among the FRS, the Masserann kit (Micro-Mega, Besancon, France), and an ultrasonic file-removal method. Ninety extracted mandibular incisors with separated nickel titanium files were divided into 3 groups of 30 teeth each. Groups 1, 2, and 3 had file-removal attempts made by using the Masserann kit, a CPR-7 titanium ultrasonic tip (ObturaSpartan Corp., Fenton, MO), and the FRS, respectively. Each group had three operators removing the separated files. Pre-/postoperative digital radiographs were downloaded into image analyzing software that calculated the amount of dentin removed. The FRS needed less time and had less dentin loss than the others (p ⬍ 0.05). There were statistical differences between the experienced operator and less experienced operators regarding the file-removal time and the dentin removal rates (p ⬍ 0.05). (J Endod 2007;33:585–588)
Key Words Dentin-removal rate, file removal, file-removal time, masserann kit, separated nickel titanium file, ultrasonic tip
*From Pulp Biology and Endodontics Section, Tokyo Medical and Dental University, Tokyo, Japan; and †Advanced Microendodontics, P.C., Plano, TX. Address requests for reprints to Dr. Yoshitsugu Terauchi, 1557-4 Shimotsuruma Yamato city, Kanagawa prefecture, Japan 242-0001. E-mail address: [email protected]. 0099-2399/$0 - see front matter Copyright © 2007 by the American Association of Endodontists. doi:10.1016/j.joen.2006.12.018
N
ickel titanium (NiTi) rotary files are now widely used for cleaning and shaping of the canal system. The inherent characteristics of greater elasticity and resistance to torsional fracture of the NiTi alloy have allowed clinicians to efficiently obtain predictable results with nonsurgical endodontic treatment (1). One of the most dreaded complications with NiTi files is the separation of the instrument during use. In general, instruments used in rotary motion separate by two distinct modes: torsional and flexural (2). Various factors have been associated with the following iatrogenic mishaps: operator experience (3), rotational speed (4), canal curvature (5), instrument design and technique (6, 7), torque (8), manufacturing process (9), repeated use (10), and absence of glide path (11). Although there is a higher demand for removal of NiTi separated files, to date no standardized procedure for successful instrument removal has been established (3). For many years, the traditional method of retrieving instrument fragments among clinicians was to use the Masserann kit (Micro-Mega, Besancon, France) (5– 8). This system is very effective in the retrieval of instrument fragments located within the straight part of the canal (5– 8). It cannot be applied to cases involving fragments located in the midroot or apical third of the root or in severely curved canals because the technique involves the removal of considerable amounts of sound dentin, which can weaken the root structure and increase the risk of perforation (9, 10). Most recently, the use of ultrasonic tips has been found to be the most effective method for removing separated instruments from root canals without sacrificing a great deal of sound dentin (11). However, in the use of ultrasonic tips, difficult cases are occasionally encountered in which the separated file cannot be retrieved from the canal even though it is seen to be loose. The challenge is that the separated part of the file tends to engage on the outside wall of a curved canal. These cases ultimately require longer treatment time, and the process of troughing around the separated instrument is repeated until either an iatrogenic error occurs, such as strip perforation, canal transportation, zipping, or ledging, or the fragment is finally extruded out of the canal. Nagai et al. (12) reported that the time required for ultrasonic file removal varied from 3 to 40 minutes, whereas the Masserann’s method varied from 20 minutes to several hours, depending on canal shapes. In addition, it has been observed that removal of NiTi instruments with ultrasonics is more difficult than removal of stainless-steel instruments because there is a greater tendency for NiTi instruments to fracture repeatedly (13). This study was conducted as a series following our previously published case report (14). We developed a new file removal system (FRS) with the intended goal of minimizing both the dentin removal rate and the time required to remove the separated instruments. The purpose of this study was to compare the file-removal time and the dentin removal rates among the FRS, the Masserann kit, and the ultrasonic tip, and among operators with different experience levels.
Materials and Methods Ninety extracted human mandibular incisors with straight roots were used in the study. It was visually recognized that all the experimental teeth had completely developed root apices. The clinical crowns were removed, and conventional access cavities were prepared with high-speed diamond burs. The working length was established by inserting a #15 K file into the canal until the tip was visualized at the apex. The root canals were prepared to the canal terminus by using 25-mm long greater taper rotary
JOE — Volume 33, Number 5, May 2007
New File-Removal System
585
Basic Research—Technology TABLE 2. File-Removal Time in Minutes (Mean⫾Standard Deviation) With Multiple Comparisons Among the Operators and Among the Experimental Groups Operator 1 Operator 2 Operator 3
Group 1
Group 2
Group 3
8.1 ⫾ 4.4 16.1 ⫾ 9.3 24.0 ⫾ 16.8 c
20.5 ⫾ 18.7 19.2 ⫾ 12.0 29.1 ⫾ 20.4 c
5.5 ⫾ 3.5 a 4.6 ⫾ 1.6 b 11.1 ⫾ 3.1a,b c
EDTA solution, followed by 5.25% sodium hypochlorite, after which the canals were dried with paper points.
Figure 1. Magnified views of each instrument. (a) CBA. (b) CBB. (c) Ultrasonic tip. (d) Loop device. Vertical bar on the right side corresponds to 1 mm in length.
nickel-titanium files with #20/.06 taper (Dentsply/TulsaDental, Tulsa, OK) on an Endo-Mate TC electronic motor (NSK Inc., Tochigi, Japan). A separated instrument was then created in the canal by notching a greater taper rotary file with #20/0.10 taper to a depth of half the instrument thickness and at 3 mm from the tip by using a low-speed diamond disk. The notched instrument was then used in the canal at 250 rpm until it separated in the apical one third of the canal. The coronal end of the separated instrument measured approximately 0.5 mm at 3 mm from the tip. The teeth were then divided into 3 groups of 30 samples each: groups 1, 2, and 3 for separated file removal with the Masserann kit, a CPR-7 titanium ultrasonic tip (Obtura-Spartan Corp., Fenton, MO), and the FRS, respectively. The CPR titanium ultrasonic instruments are known for their long lengths and thin diameters, allowing them to work well in severely restricted space. The CPR-7 (0.4 mm in diameter) was selected because it was the first instrument from the CPR series (from largest to smallest) that had adequate length and diameter to passively reach the separated files under the condition of this study. These experiments were performed by three operators. Operators 1 and 2 had 8 to 9 years of clinical endodontic experience at the time of the study, and they both had no previous experience with the instruments used in this study. Operator 3, the first author of this study, had 14 years of clinical endodontic experience and 5 years of familiarity with all the file-removal instruments involved in this study. File-removal attempts continued until the entire separated file was removed, regardless of secondary fracture occurring during the procedure. If the separated file was extruded out of the apex or the canal was perforated, the attempt was cancelled. This procedure was continued until each operator successfully removed 10 separated files in each group. File-removal attempts were also cancelled when the procedure exceeded 90 minutes. The irrigation protocol for each test group consisted of rinsing the canals intermittently with 17% TABLE 1. Number of Unsuccessful Cases Because of Perforation (P), Overtime Attempt (T), Overtime Attempt With Secondary Separated File Fracture (S), and a Separated File Pushed out of the Apex (A) Operator 1 Operator 2 Operator 3
586
Terauchi et al.
Group 1
Group 2
Group 3
P,P P —
P,S P,T,A —
— — —
Group 1 The Masserann kit was used according to the manufacturer’s instructions. The Peeso reamer (Mani, Inc., Tochigi, Japan) was chosen over the Gates Glidden (Mani, Inc.) drill for straight-line access based on the assumption that the parallel configuration of the bur would help maintain a straight pathway down the canal and possibly conserve the dentin during the process. A staging platform was created with a #4 Peeso reamer, 1.3 mm in diameter, which would make room for the entry of the smallest (1.2 mm in diameter) extractor down the canal. After the access, the trephine bur (1.1 mm in diameter) was worked in a counter-clockwise direction to further expose the coronal portion of the fragment. Once an adequate amount of file was exposed and confirmed under a microscope (Opmi 111; Zeiss, Oberkochen, Germany), the Masserann extractor was used to retrieve the separated instrument. Group 2 Straight-line radicular access was achieved with a # 2 Peeso reamer (0.9 mm in diameter). The CPR-7 was then activated at the lowest power setting (Spartan Ultrasonic Endo J15; Obtura-Spartan Corp., Fenton, MO) and trephined circumferentially in a counter-clockwise direction to expose the coronal aspect of the file in dry conditions as recommended by Ruddle (15). This procedure was continued until the obstruction was freed and floated out of the canal by the ultrasonic tip. Group 3 The FRS involved three steps comprising three different techniques and four newly designed instruments (14) (Fig. 1). Each step was performed sequentially until the separated file was removed. The details of the techniques can be obtained from our previously referenced case report (14). The procedure was timed from the moment the file-removal process began up to the point when the separated file was removed from the canal, and it was rounded off to the nearest whole minute. A standard urethane jig was designed to hold an X-ray tube head at a fixed distance from a DEXIS digital radiographic sensor (Provision Dental Systems, Palo Alto, CA). The head of the X-ray tube was fixed in the aperture of the urethane jig, and the digital radiographic sensor was placed in the wall on the opposite side perpendicular to the X-ray tube. Mesiodistal (MD) and labiolingual (LL) planes were created on the TABLE 3. Dentin Removal Rates (%) in the Mesiodistal (MD) Direction (Mean⫾Standard Deviation) With Multiple Comparisons Among the Operators and Among the Experimental Groups Operator 1 Operator 2 Operator 3
Group 1
Group 2
Group 3
162.7 ⫾ 17.6 164.9 ⫾ 23.0 158.8 ⫾ 27.0 a
147.8 ⫾ 25.6 138.2 ⫾ 28.1 135.7 ⫾ 17.3 a
130.2 ⫾ 15.0 117.6 ⫾ 14.5 125.7 ⫾ 13.2 a
JOE — Volume 33, Number 5, May 2007
Basic Research—Technology TABLE 4. Dentin Removal Rates (%) in the Labiolingual (LL) Direction (Mean⫾Standard Deviation) With Multiple Comparisons Among the Operators and Among the Experimental Groups Operator 1 Operator 2 Operator 3
Group 1
Group 2
Group 3
162.8 ⫾ 33.0 176.6 ⫾ 19.0 164.5 ⫾ 18.1 c
154.1 ⫾ 28.7 156.4 ⫾ 40.8 121.3 ⫾ 14. c
144.8 ⫾ 12.9 a 128.8 ⫾ 21.3 b 113.6 ⫾ 9.6 a,b c
sample roots with quick self-curing acrylic resin (Unifast; GC Dental Products Corp., Aichi, Japan) to stabilize the sample roots for radiographic superimposition. Cross lines were drawn on both planes of the sample roots and the plate of the digital radiographic sensor holder with a black oil-based marker so that they could be placed back in the same positions for pre- and postoperative radiographs in both the MD and the LL directions. The standardized digital radiographs were downloaded in JPEG format from the DEXIS digital radiographic system and imported into the image analyzing software (Photoshop 6.0, Adobe Systems, Inc., San Jose, CA) to compare the pre- and postoperative radiographs. This was accomplished by outlining the periphery of the entire canal on the image, and the number of the pixels within this outline representing the canal space was then recorded. The determination of the dentin removal rate for each case was calculated by dividing the value of the canal space on the preoperative pixels into that of the postoperative pixels. Outcomes of each value for both the working time and the dentin removal rates were analyzed by Fisher’s Protected Least Significant Difference (PLSD) at 0.05 significance level.
The time needed for file removal in group 3 ranged from 2 to 17 minutes, whereas group 1 varied from 2 to 70 minutes and group 2 from 4 to 80 minutes. The removal time varied as a result of the root canal shape and the wedging severity of the fragment (12). From an observational point of view, even when using a microscope, it was difficult to predict when the separated files in groups 1 and 2 would be dislodged from the canals. In group 3, when a separated file was seen swaying in the canal during step 2, it was highly expected that the fragment would be removed before long using the loop device. In group 3, 23 of 30 separated files were successfully removed with ultrasonics without resorting to the loop device, which indicated that ultrasonic vibration alone is very effective in removing separated files from straight roots. Two cases in group 2 had secondary fracture, and they ultimately required longer time to complete the file-removal process. Overapplication of ultrasonic vibration to a separated file could cause secondary fracture, resulting in more complication because extra time is then required for removal of the remaining fragment. In fact, Hulsmann and Schinkel (16) reported a shorter fragment was more difficult to retrieve than a longer fragment.
Results Ninety of 98 separated files consumed in all the groups were successfully removed. The number of unsuccessful cases and causes for failure are listed in Table 1A. Mean file-removal time in minutes, mean dentin removal rates (%) of MD and LL directions with standard deviations and multiple comparisons among the operators and among the experimental groups were determined by using Fisher PLSD and are listed in Tables 2-4. Representative samples in each group are shown in Figure 2. The results showed that there were significant differences between operators 1 and 3 as well as operators 2 and 3 in the fileremoval time and in the LL dentin removal rates (p ⬍ 0.05). Group 3 had the shortest mean file-removal time, whereas group 2 had the longest. Group 1 had the largest mean dentin removal rate, whereas group 3 had the least.
Discussion In the results, there were no statistically significant differences between operators 1 and 2 in both dentin removal rates and working time. However, between operator 3 and the other operators, there were significant differences in the working time and the dentin removal rate in the LL direction. The results showed operator 3 had the longest file-removal time and the lowest dentin removal rate among all the operators in each group, which shows that operator 3 was very careful not to sacrifice too much dentin during the process. The removal of a large amount of dentin loosens the file from the canal wall, thus making the file-removal attempts much easier. Unfortunately, excessive loss of dentin does increases the risk of iatrogenic accidents such as canal perforation, as in the case of operators 1 and 2 having five cases for groups 1 and 2. Even though operator 3 had the longest file-removal time, there was more preservation of dentin when compared with the other operators. Operator 3 was successful in removing all separated files in all groups without any procedural errors. The success is probably because of the operators’ experience in removal of separated files.
JOE — Volume 33, Number 5, May 2007
Figure 2. (a) Representative sample from group 1. (a1, a2) Pre-and postoperative radiographs from the LL view. a2 sample has an arrow pointing to a trenched out area created by a trephine bur. (a3, a4) Pre-and postoperative radiographs from the MD view. (b) Representative sample from group 2. (b1, b3) Pre- and postoperative radiographs from the LL view. (b2) Radiograph showing a secondary fracture during file-removal attempts from the LL view. (b4, b6) Pre-and postoperative radiographs from the MD view. (b5) Radiograph showing a secondary fracture during file-removal attempts from the MD view. (c) Representative sample from group 3. (c1, c2) Pre- and postoperative radiographs from the LL view. (c3, c4) Pre- and postoperative radiographs from the MD view.
New File-Removal System
587
Basic Research—Technology There were significant differences in the dentin removal rates among all the groups. Group 1 had the largest instruments out of the three groups for file removal, whereas group 3 had the smallest instruments. The ultrasonic tip used for group 3 was two times thinner than group 2. The differences between groups 2 and 3 are the diameter of the tip and its ability to work in tight spaces. The dentin removal rates were directly in proportion to the instrument size, even though the time needed for file removal in each group was significantly different. The allotted working time for removal of the separated instruments was set at 90 minutes because this parameter would give adequate time for each system to prove itself and it’s also a reasonable chair time for treatment. Suter et al. (13) had recommended that removal attempts of separated instruments from root canals should not exceed 45 to 60 minutes because the success rates may drop with increased treatment time. They suggested that the lowered success rate could be because of operator fatigue or overenlargement of the canal, which compromises the integrity of the tooth and increases the risk of perforation. With any bench-top study, what we can glean from the findings is the potential of the system. Therefore, under the condition of this study, the FRS was found to be very effective in reducing file-removal time and dentin removal rates. Clinicians inexperienced in separated file removal tend to sacrifice more dentin than an experienced clinician.
References 1. Walia H, Brantley WA, Gerestein H. An initial investigation of the bending and torsional properties of nitinol root canal files. J Endod 1988;14:346 –51. 2. Cohen S, Hargreaves K. Pathways of the pulp, ed 9. St. Louis: Mosby, 2006.
588
Terauchi et al.
3. Mandel E, Adib-Yazdi M, Benhamou L-M, et al. Rotary NiTi profile systems for preparing curved canals in resin blocks: influence of operator on instrument breakage. Int Endod J 1999;32:436 – 43. 4. Sano S, Miyake K, Osada T. A clinical study on the removal of the broken instrument in the root canal using Masserann kit. Kanagawashigaku 1974;9:50 –7. 5. Masserann J. Removal of metallic fragments from the root canal. J Br Endod Soc 1971;5:55–9. 6. Feldman G, Solomon C, Notaro P, Moskowitz E. Retrieving broken endodontic instruments. J Am Dent Assoc 1974;88:588 –91. 7. Krell KV, Fuller MW, Scott GL. The conservative retrieval of silver cones in difficult cases. J Endod 1984;10:269 –73. 8. Yoldas O, Oztunc H, Tinaz C, Alparslan N. Perforation risks associated with the use of Masserann endodontic kit drills in mandibular molars. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2004;97:513–7. 9. Friedman S, Stabholtz A, Tamse A. Endodontic treatment: case selection and techniques. J Endod 1990;16:543–9. 10. Yared G. In vitro study of the torsional properties of new and used Profile nickel titanium rotary files. J Endod 2004;30:410 –2. 11. Ward JR, Parashos P, Messer HH. Evaluation of an ultrasonic technique to remove fractured rotary nickel-titanium endodontic instruments from root canals: an experimental study. J Endod 2003;29:756 – 63. 12. Nagai O, Tani N, Kayaba S, Osada T. Ultrasonic removal of broken instruments in root canals. Int Endod J 1986;19:298 –304. 13. Suter B, Lussi A, Sequeira P. Probability of removing fractured instruments from root canals. Int Endod J 2005;38:112–23. 14. Terauchi Y, O’Leary L, Suda H. Removal of separated files from root canals with a new file removal system: case reports. J Endod 2006;32:789 –97. 15. Ruddle CJ. Nonsurgical retreatment. J Endod 2004;30:827– 45. 16. Hulsmann M, Schinkel I. Influence of several factors on the success or failure of removal of fractured instruments from the root canal. Endod Dent Traumatol 1999; 15:252– 8.
JOE — Volume 33, Number 5, May 2007
Evaluation of the Efficiency of a New File Removal System in Comparison With Two Conventional Systems Yoshitsugu Terauchi, DDS,* Le O’Leary, DDS,† Izumi Kikuchi, DDS, PhD,* Mami Asanagi, DDS,* Takatomo Yoshioka, DDS, PhD, Chihiro Kobayashi, DDS, PhD,* and Hideaki Suda, DDS, PhD* Abstract A novel file-removal system (FRS) was designed to address weak points of conventional file-removal methods. The purpose of this study was to compare fileremoval time and dentin removal rates among the FRS, the Masserann kit (Micro-Mega, Besancon, France), and an ultrasonic file-removal method. Ninety extracted mandibular incisors with separated nickel titanium files were divided into 3 groups of 30 teeth each. Groups 1, 2, and 3 had file-removal attempts made by using the Masserann kit, a CPR-7 titanium ultrasonic tip (ObturaSpartan Corp., Fenton, MO), and the FRS, respectively. Each group had three operators removing the separated files. Pre-/postoperative digital radiographs were downloaded into image analyzing software that calculated the amount of dentin removed. The FRS needed less time and had less dentin loss than the others (p ⬍ 0.05). There were statistical differences between the experienced operator and less experienced operators regarding the file-removal time and the dentin removal rates (p ⬍ 0.05). (J Endod 2007;33:585–588)
Key Words Dentin-removal rate, file removal, file-removal time, masserann kit, separated nickel titanium file, ultrasonic tip
*From Pulp Biology and Endodontics Section, Tokyo Medical and Dental University, Tokyo, Japan; and †Advanced Microendodontics, P.C., Plano, TX. Address requests for reprints to Dr. Yoshitsugu Terauchi, 1557-4 Shimotsuruma Yamato city, Kanagawa prefecture, Japan 242-0001. E-mail address: [email protected]. 0099-2399/$0 - see front matter Copyright © 2007 by the American Association of Endodontists. doi:10.1016/j.joen.2006.12.018
N
ickel titanium (NiTi) rotary files are now widely used for cleaning and shaping of the canal system. The inherent characteristics of greater elasticity and resistance to torsional fracture of the NiTi alloy have allowed clinicians to efficiently obtain predictable results with nonsurgical endodontic treatment (1). One of the most dreaded complications with NiTi files is the separation of the instrument during use. In general, instruments used in rotary motion separate by two distinct modes: torsional and flexural (2). Various factors have been associated with the following iatrogenic mishaps: operator experience (3), rotational speed (4), canal curvature (5), instrument design and technique (6, 7), torque (8), manufacturing process (9), repeated use (10), and absence of glide path (11). Although there is a higher demand for removal of NiTi separated files, to date no standardized procedure for successful instrument removal has been established (3). For many years, the traditional method of retrieving instrument fragments among clinicians was to use the Masserann kit (Micro-Mega, Besancon, France) (5– 8). This system is very effective in the retrieval of instrument fragments located within the straight part of the canal (5– 8). It cannot be applied to cases involving fragments located in the midroot or apical third of the root or in severely curved canals because the technique involves the removal of considerable amounts of sound dentin, which can weaken the root structure and increase the risk of perforation (9, 10). Most recently, the use of ultrasonic tips has been found to be the most effective method for removing separated instruments from root canals without sacrificing a great deal of sound dentin (11). However, in the use of ultrasonic tips, difficult cases are occasionally encountered in which the separated file cannot be retrieved from the canal even though it is seen to be loose. The challenge is that the separated part of the file tends to engage on the outside wall of a curved canal. These cases ultimately require longer treatment time, and the process of troughing around the separated instrument is repeated until either an iatrogenic error occurs, such as strip perforation, canal transportation, zipping, or ledging, or the fragment is finally extruded out of the canal. Nagai et al. (12) reported that the time required for ultrasonic file removal varied from 3 to 40 minutes, whereas the Masserann’s method varied from 20 minutes to several hours, depending on canal shapes. In addition, it has been observed that removal of NiTi instruments with ultrasonics is more difficult than removal of stainless-steel instruments because there is a greater tendency for NiTi instruments to fracture repeatedly (13). This study was conducted as a series following our previously published case report (14). We developed a new file removal system (FRS) with the intended goal of minimizing both the dentin removal rate and the time required to remove the separated instruments. The purpose of this study was to compare the file-removal time and the dentin removal rates among the FRS, the Masserann kit, and the ultrasonic tip, and among operators with different experience levels.
Materials and Methods Ninety extracted human mandibular incisors with straight roots were used in the study. It was visually recognized that all the experimental teeth had completely developed root apices. The clinical crowns were removed, and conventional access cavities were prepared with high-speed diamond burs. The working length was established by inserting a #15 K file into the canal until the tip was visualized at the apex. The root canals were prepared to the canal terminus by using 25-mm long greater taper rotary
JOE — Volume 33, Number 5, May 2007
New File-Removal System
585
Basic Research—Technology TABLE 2. File-Removal Time in Minutes (Mean⫾Standard Deviation) With Multiple Comparisons Among the Operators and Among the Experimental Groups Operator 1 Operator 2 Operator 3
Group 1
Group 2
Group 3
8.1 ⫾ 4.4 16.1 ⫾ 9.3 24.0 ⫾ 16.8 c
20.5 ⫾ 18.7 19.2 ⫾ 12.0 29.1 ⫾ 20.4 c
5.5 ⫾ 3.5 a 4.6 ⫾ 1.6 b 11.1 ⫾ 3.1a,b c
EDTA solution, followed by 5.25% sodium hypochlorite, after which the canals were dried with paper points.
Figure 1. Magnified views of each instrument. (a) CBA. (b) CBB. (c) Ultrasonic tip. (d) Loop device. Vertical bar on the right side corresponds to 1 mm in length.
nickel-titanium files with #20/.06 taper (Dentsply/TulsaDental, Tulsa, OK) on an Endo-Mate TC electronic motor (NSK Inc., Tochigi, Japan). A separated instrument was then created in the canal by notching a greater taper rotary file with #20/0.10 taper to a depth of half the instrument thickness and at 3 mm from the tip by using a low-speed diamond disk. The notched instrument was then used in the canal at 250 rpm until it separated in the apical one third of the canal. The coronal end of the separated instrument measured approximately 0.5 mm at 3 mm from the tip. The teeth were then divided into 3 groups of 30 samples each: groups 1, 2, and 3 for separated file removal with the Masserann kit, a CPR-7 titanium ultrasonic tip (Obtura-Spartan Corp., Fenton, MO), and the FRS, respectively. The CPR titanium ultrasonic instruments are known for their long lengths and thin diameters, allowing them to work well in severely restricted space. The CPR-7 (0.4 mm in diameter) was selected because it was the first instrument from the CPR series (from largest to smallest) that had adequate length and diameter to passively reach the separated files under the condition of this study. These experiments were performed by three operators. Operators 1 and 2 had 8 to 9 years of clinical endodontic experience at the time of the study, and they both had no previous experience with the instruments used in this study. Operator 3, the first author of this study, had 14 years of clinical endodontic experience and 5 years of familiarity with all the file-removal instruments involved in this study. File-removal attempts continued until the entire separated file was removed, regardless of secondary fracture occurring during the procedure. If the separated file was extruded out of the apex or the canal was perforated, the attempt was cancelled. This procedure was continued until each operator successfully removed 10 separated files in each group. File-removal attempts were also cancelled when the procedure exceeded 90 minutes. The irrigation protocol for each test group consisted of rinsing the canals intermittently with 17% TABLE 1. Number of Unsuccessful Cases Because of Perforation (P), Overtime Attempt (T), Overtime Attempt With Secondary Separated File Fracture (S), and a Separated File Pushed out of the Apex (A) Operator 1 Operator 2 Operator 3
586
Terauchi et al.
Group 1
Group 2
Group 3
P,P P —
P,S P,T,A —
— — —
Group 1 The Masserann kit was used according to the manufacturer’s instructions. The Peeso reamer (Mani, Inc., Tochigi, Japan) was chosen over the Gates Glidden (Mani, Inc.) drill for straight-line access based on the assumption that the parallel configuration of the bur would help maintain a straight pathway down the canal and possibly conserve the dentin during the process. A staging platform was created with a #4 Peeso reamer, 1.3 mm in diameter, which would make room for the entry of the smallest (1.2 mm in diameter) extractor down the canal. After the access, the trephine bur (1.1 mm in diameter) was worked in a counter-clockwise direction to further expose the coronal portion of the fragment. Once an adequate amount of file was exposed and confirmed under a microscope (Opmi 111; Zeiss, Oberkochen, Germany), the Masserann extractor was used to retrieve the separated instrument. Group 2 Straight-line radicular access was achieved with a # 2 Peeso reamer (0.9 mm in diameter). The CPR-7 was then activated at the lowest power setting (Spartan Ultrasonic Endo J15; Obtura-Spartan Corp., Fenton, MO) and trephined circumferentially in a counter-clockwise direction to expose the coronal aspect of the file in dry conditions as recommended by Ruddle (15). This procedure was continued until the obstruction was freed and floated out of the canal by the ultrasonic tip. Group 3 The FRS involved three steps comprising three different techniques and four newly designed instruments (14) (Fig. 1). Each step was performed sequentially until the separated file was removed. The details of the techniques can be obtained from our previously referenced case report (14). The procedure was timed from the moment the file-removal process began up to the point when the separated file was removed from the canal, and it was rounded off to the nearest whole minute. A standard urethane jig was designed to hold an X-ray tube head at a fixed distance from a DEXIS digital radiographic sensor (Provision Dental Systems, Palo Alto, CA). The head of the X-ray tube was fixed in the aperture of the urethane jig, and the digital radiographic sensor was placed in the wall on the opposite side perpendicular to the X-ray tube. Mesiodistal (MD) and labiolingual (LL) planes were created on the TABLE 3. Dentin Removal Rates (%) in the Mesiodistal (MD) Direction (Mean⫾Standard Deviation) With Multiple Comparisons Among the Operators and Among the Experimental Groups Operator 1 Operator 2 Operator 3
Group 1
Group 2
Group 3
162.7 ⫾ 17.6 164.9 ⫾ 23.0 158.8 ⫾ 27.0 a
147.8 ⫾ 25.6 138.2 ⫾ 28.1 135.7 ⫾ 17.3 a
130.2 ⫾ 15.0 117.6 ⫾ 14.5 125.7 ⫾ 13.2 a
JOE — Volume 33, Number 5, May 2007
Basic Research—Technology TABLE 4. Dentin Removal Rates (%) in the Labiolingual (LL) Direction (Mean⫾Standard Deviation) With Multiple Comparisons Among the Operators and Among the Experimental Groups Operator 1 Operator 2 Operator 3
Group 1
Group 2
Group 3
162.8 ⫾ 33.0 176.6 ⫾ 19.0 164.5 ⫾ 18.1 c
154.1 ⫾ 28.7 156.4 ⫾ 40.8 121.3 ⫾ 14. c
144.8 ⫾ 12.9 a 128.8 ⫾ 21.3 b 113.6 ⫾ 9.6 a,b c
sample roots with quick self-curing acrylic resin (Unifast; GC Dental Products Corp., Aichi, Japan) to stabilize the sample roots for radiographic superimposition. Cross lines were drawn on both planes of the sample roots and the plate of the digital radiographic sensor holder with a black oil-based marker so that they could be placed back in the same positions for pre- and postoperative radiographs in both the MD and the LL directions. The standardized digital radiographs were downloaded in JPEG format from the DEXIS digital radiographic system and imported into the image analyzing software (Photoshop 6.0, Adobe Systems, Inc., San Jose, CA) to compare the pre- and postoperative radiographs. This was accomplished by outlining the periphery of the entire canal on the image, and the number of the pixels within this outline representing the canal space was then recorded. The determination of the dentin removal rate for each case was calculated by dividing the value of the canal space on the preoperative pixels into that of the postoperative pixels. Outcomes of each value for both the working time and the dentin removal rates were analyzed by Fisher’s Protected Least Significant Difference (PLSD) at 0.05 significance level.
The time needed for file removal in group 3 ranged from 2 to 17 minutes, whereas group 1 varied from 2 to 70 minutes and group 2 from 4 to 80 minutes. The removal time varied as a result of the root canal shape and the wedging severity of the fragment (12). From an observational point of view, even when using a microscope, it was difficult to predict when the separated files in groups 1 and 2 would be dislodged from the canals. In group 3, when a separated file was seen swaying in the canal during step 2, it was highly expected that the fragment would be removed before long using the loop device. In group 3, 23 of 30 separated files were successfully removed with ultrasonics without resorting to the loop device, which indicated that ultrasonic vibration alone is very effective in removing separated files from straight roots. Two cases in group 2 had secondary fracture, and they ultimately required longer time to complete the file-removal process. Overapplication of ultrasonic vibration to a separated file could cause secondary fracture, resulting in more complication because extra time is then required for removal of the remaining fragment. In fact, Hulsmann and Schinkel (16) reported a shorter fragment was more difficult to retrieve than a longer fragment.
Results Ninety of 98 separated files consumed in all the groups were successfully removed. The number of unsuccessful cases and causes for failure are listed in Table 1A. Mean file-removal time in minutes, mean dentin removal rates (%) of MD and LL directions with standard deviations and multiple comparisons among the operators and among the experimental groups were determined by using Fisher PLSD and are listed in Tables 2-4. Representative samples in each group are shown in Figure 2. The results showed that there were significant differences between operators 1 and 3 as well as operators 2 and 3 in the fileremoval time and in the LL dentin removal rates (p ⬍ 0.05). Group 3 had the shortest mean file-removal time, whereas group 2 had the longest. Group 1 had the largest mean dentin removal rate, whereas group 3 had the least.
Discussion In the results, there were no statistically significant differences between operators 1 and 2 in both dentin removal rates and working time. However, between operator 3 and the other operators, there were significant differences in the working time and the dentin removal rate in the LL direction. The results showed operator 3 had the longest file-removal time and the lowest dentin removal rate among all the operators in each group, which shows that operator 3 was very careful not to sacrifice too much dentin during the process. The removal of a large amount of dentin loosens the file from the canal wall, thus making the file-removal attempts much easier. Unfortunately, excessive loss of dentin does increases the risk of iatrogenic accidents such as canal perforation, as in the case of operators 1 and 2 having five cases for groups 1 and 2. Even though operator 3 had the longest file-removal time, there was more preservation of dentin when compared with the other operators. Operator 3 was successful in removing all separated files in all groups without any procedural errors. The success is probably because of the operators’ experience in removal of separated files.
JOE — Volume 33, Number 5, May 2007
Figure 2. (a) Representative sample from group 1. (a1, a2) Pre-and postoperative radiographs from the LL view. a2 sample has an arrow pointing to a trenched out area created by a trephine bur. (a3, a4) Pre-and postoperative radiographs from the MD view. (b) Representative sample from group 2. (b1, b3) Pre- and postoperative radiographs from the LL view. (b2) Radiograph showing a secondary fracture during file-removal attempts from the LL view. (b4, b6) Pre-and postoperative radiographs from the MD view. (b5) Radiograph showing a secondary fracture during file-removal attempts from the MD view. (c) Representative sample from group 3. (c1, c2) Pre- and postoperative radiographs from the LL view. (c3, c4) Pre- and postoperative radiographs from the MD view.
New File-Removal System
587
Basic Research—Technology There were significant differences in the dentin removal rates among all the groups. Group 1 had the largest instruments out of the three groups for file removal, whereas group 3 had the smallest instruments. The ultrasonic tip used for group 3 was two times thinner than group 2. The differences between groups 2 and 3 are the diameter of the tip and its ability to work in tight spaces. The dentin removal rates were directly in proportion to the instrument size, even though the time needed for file removal in each group was significantly different. The allotted working time for removal of the separated instruments was set at 90 minutes because this parameter would give adequate time for each system to prove itself and it’s also a reasonable chair time for treatment. Suter et al. (13) had recommended that removal attempts of separated instruments from root canals should not exceed 45 to 60 minutes because the success rates may drop with increased treatment time. They suggested that the lowered success rate could be because of operator fatigue or overenlargement of the canal, which compromises the integrity of the tooth and increases the risk of perforation. With any bench-top study, what we can glean from the findings is the potential of the system. Therefore, under the condition of this study, the FRS was found to be very effective in reducing file-removal time and dentin removal rates. Clinicians inexperienced in separated file removal tend to sacrifice more dentin than an experienced clinician.
References 1. Walia H, Brantley WA, Gerestein H. An initial investigation of the bending and torsional properties of nitinol root canal files. J Endod 1988;14:346 –51. 2. Cohen S, Hargreaves K. Pathways of the pulp, ed 9. St. Louis: Mosby, 2006.
588
Terauchi et al.
3. Mandel E, Adib-Yazdi M, Benhamou L-M, et al. Rotary NiTi profile systems for preparing curved canals in resin blocks: influence of operator on instrument breakage. Int Endod J 1999;32:436 – 43. 4. Sano S, Miyake K, Osada T. A clinical study on the removal of the broken instrument in the root canal using Masserann kit. Kanagawashigaku 1974;9:50 –7. 5. Masserann J. Removal of metallic fragments from the root canal. J Br Endod Soc 1971;5:55–9. 6. Feldman G, Solomon C, Notaro P, Moskowitz E. Retrieving broken endodontic instruments. J Am Dent Assoc 1974;88:588 –91. 7. Krell KV, Fuller MW, Scott GL. The conservative retrieval of silver cones in difficult cases. J Endod 1984;10:269 –73. 8. Yoldas O, Oztunc H, Tinaz C, Alparslan N. Perforation risks associated with the use of Masserann endodontic kit drills in mandibular molars. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2004;97:513–7. 9. Friedman S, Stabholtz A, Tamse A. Endodontic treatment: case selection and techniques. J Endod 1990;16:543–9. 10. Yared G. In vitro study of the torsional properties of new and used Profile nickel titanium rotary files. J Endod 2004;30:410 –2. 11. Ward JR, Parashos P, Messer HH. Evaluation of an ultrasonic technique to remove fractured rotary nickel-titanium endodontic instruments from root canals: an experimental study. J Endod 2003;29:756 – 63. 12. Nagai O, Tani N, Kayaba S, Osada T. Ultrasonic removal of broken instruments in root canals. Int Endod J 1986;19:298 –304. 13. Suter B, Lussi A, Sequeira P. Probability of removing fractured instruments from root canals. Int Endod J 2005;38:112–23. 14. Terauchi Y, O’Leary L, Suda H. Removal of separated files from root canals with a new file removal system: case reports. J Endod 2006;32:789 –97. 15. Ruddle CJ. Nonsurgical retreatment. J Endod 2004;30:827– 45. 16. Hulsmann M, Schinkel I. Influence of several factors on the success or failure of removal of fractured instruments from the root canal. Endod Dent Traumatol 1999; 15:252– 8.
JOE — Volume 33, Number 5, May 2007