Fig. 4.1
Nonrestorable roots of a mandibular second molar with a fragment in the apical third of the distal root. Tooth extraction is the treatment of choice in this case
Fig. 4.2
No intervention as the t reatment option for fragments revealed randomly during full-mouth periapical radiographic examination. (a) According to the patient’s history, the instrument fracture (arrow) occurred during RCT 15 years earlier. Prosthetic reconstruction was performed 5 years later. (b) The fragment in the periapical tissues can be attributed to the RCT performed, according to the patient’s history, 16 years earlier. Since then, the patient experienced no pain or discomfort in the area
4.2.2 Non-surgical Management
This approach can be divided into two phases. In the first phase as a general rule, efforts are made to retrieve the fragment and, if this is not possible, to bypass it. In cases where this is accomplished, as well as in cases where retrieval or bypassing fails and the appropriate conditions are met, the second phase follows. The second phase includes the instrumentation and obturation phase. In cases of retrieval or successful bypassing, instrumentation and obturation are performed up to the desired length; otherwise, the canal is instrumented and obturated up to the fragment, and the tooth is monitored clinically and radiographically.
4.2.3 Surgical Management
As a rule, surgical management with apicoectomy, hemisection, root amputation, or intentional reimplantation is performed when the conservative approach fails or is considered from the outset to lead to failure. It is the only reasonable alternative to extraction.
4.2.4 Tooth Extraction
This is performed when all other therapeutical options (non-surgical and surgical) have proved unsuccessful or are considered to be a failure.
4.3 Management Procedure
All procedures include the risk of creating additional errors that may eventually jeopardize the prognosis of the tooth. Therefore, the clinician should continuously reevaluate the progress of management procedures and consider alternative options when needed. The optimum management option is the retrieval of the fragment so that instrumentation and obturation can be accomplished to the desired length. There are certain steps to be followed prior to any decision and particularly initiation of efforts to retrieve the fragment. These include:
- 1.
Steps prior to any decision:
- (a)
Informing the patient
- (b)
Localization of the fragment
- (c)
Identification of the fragment
- (a)
- 2.
Initiation of management efforts:
- (a)
In primary teeth
- (b)
In permanent teeth
- (a)
4.3.1 Steps Prior to Any Decision
4.3.1.1 Informing the Patient
The patient should be informed about the incident, the procedures necessary for correction, the alternative management modalities, and the impact of this iatrogenic error as well as of all alternative treatment options on prognosis. It is important to explain that the fragment itself is not a direct cause of treatment failure but rather a possible indirect one, as it prevents adequate cleaning, shaping, and filling of the apical portion of the root canal. It must also be explained to the patient that each individual case has its own unique characteristics that dictate the management approach. By explaining and discussing the procedures and their potential complications with the patient, it may be possible to alleviate many of his/her worries and reduce medicolegal consequences.
Additionally, for medicolegal reasons, a detailed history with clinical pictures and radiographic documentation is necessary. It has also been proposed that the remaining segment of the instrument should be kept in the patient’s record (Cohen and Schwartz 1987). In cases of endodontic referrals related with primary or retreatment cases with fragments retained within the canal, it is of vital importance to diagnose them and consult the patient for their presence. Their presence carries a medicolegal risk, if not diagnosed preoperatively, because the iatrogenic error might be attributed to the clinician performing the new treatment. In all cases it is essential, for medicolegal reasons, to record accurately in the patient’s notes all the information given to the patient.
4.3.1.2 Localization of the Fragment
Localization of the fragment provides fundamental information for decision-making regarding the potential management of the fragment. There are three different conditions under which a dentist needs to detect, identify, and localize a fragment. These are:
- 1.
Localization of a fragment caused by the treating dentist
- 2.
Localization of a fragment in a referral case
- 3.
Localization of retained fragment in retreatment cases
- 1.
Localization of a fragment caused by the treating dentist . Instrumentation must be stopped immediately after an instrument fracture. It might then be necessary for the clinician to thoughtfully interpret more than one periapical radiograph obtained with different horizontal angulations to confirm the incident, to reveal the location of the fragment in the root canal, and to appreciate the thickness of the remaining dentinal walls and, if present, the depth of an external concavity. The advantage in this case is that the exact type and size of the fragment are known as well as the exact stage of instrumentation when the error occurred.
- 2.
Localization of a fragment in a referral case . In some cases, information obtained by the referring dentist concerning the fragment and the instrumentation stage when the fracture occurred is very illuminating, but in many cases it is not. Thorough interpretation of periapical radiograph(s) obtained before commencing any treatment is again absolutely essential.
- 3.
Localization of retained fragment(s) in cases of root canal retreatments . In these cases, preoperative detection of retained fragments is crucial for a decision-making process regarding the treatment plan and also for medicolegal reasons. Once again periapical radiography is the principal form of radiography used. The radiographic diagnosis of fragment bypassed and retained in a root canal or retained within a canal obturated to the level of the fragment may be challenging. The material composition of the fragment, the size and length of the fragment, as well as the technical characteristics of the obturation and the type of the obturation material used (gutta-percha and sealer) are among the factors that influence the radiographic ability to detect the presence of a fragment. An ex vivo study that compared the diagnostic ability to radiographically detect, with conventional and digital radiography, fractured SS and NiTi instruments located at the apical third of root canals, filled with either AH 26 (Dentsply DeTrey GmbH, Konstanz, Germany) or Roth (Roth International Ltd., Chicago, IL, USA) sealers in extracted human teeth, showed that the type of sealer did not affect the ability to detect the retained instruments (Rosen et al. 2014). The sensitivity in detecting fractured segments of SS instruments was significantly higher than NiTi in the vicinity of both AH26 and Roth sealers. In the same study (Rosen et al. 2014), it was also found that there was no difference between the diagnostic ability of conventional and digital radiography in the detection of both NiTi and SS fragments, in the two different sealers (AH26 and Roth). Another study that compared the diagnostic efficacy of CBCT imaging and periapical radiography for the detection of retained fragments, located at the apical third of filled canal up to the fractured instrument with laterally condensed gutta-percha and AH 26 sealer or Roth sealer, revealed that CBCT imaging is inferior to periapical radiography (Rosen et al. 2016). This was attributed to the production of artifacts by the gutta-percha and the metallic nature of the fragment. The researchers concluded that the ongoing efforts in developing techniques for artifact reduction will probably result in the need to reassess these results as newer technological developments in CBCT artifact reduction algorithms become available. They also emphasize the need for further studies to assess the effect of factors, such as various sealer types, obturation techniques, and CBCT voxel sizes, on the diagnostic efficacy for the detection of retained separated instruments in filled root canals (Rosen et al. 2016). Similarly Ramos Brito et al. (2017) compared the detection of fractured instruments in root canals with and without filling by periapical radiographs from three digital systems and CBCT images with different resolutions. They concluded that in unfilled canals, a single periapical radiograph may properly diagnose the location of a fractured instrument inside a root canal. This accuracy of periapical radiographs was lower in filled canals, while CBCT imaging showed the worst performance for the detection of fractured instruments in filled canals (Ramos Brito et al. 2017).
The updated joint position statement of the American Association of Endodontists and the American Academy of Oral and Maxillofacial Radiology on the Use of Cone Beam Computed Tomography in Endodontics 2015 Update recommends among other the following:
Recommendation 1: Intraoral radiographs should be considered the imaging modality of choice in the evaluation of the endodontic patient. Recommendation 8: Limited Field Of View Cone beam computed Tomography (FOV CBCT) should be the imaging modality of choice for nonsurgical retreatment to assess endodontic treatment complications, such as overextended root canal obturation material, separated endodontic instruments, and localization of perforations. (Nair et al. 2016)
Recommendation 8 seems to be challenged, in part, by a recent work (Rosen et al. 2016) which has found CBCT to be inferior to periapical radiography for the detection of fractured endodontic instruments surrounded by endodontic sealer. It appears that artifacts originated from the gutta-percha and the endodontic instruments might have played a part. It is certain that the identification of a fractured instrument is not an easy task; factors such as the size and type of the fragment, the type of sealer, and the possible gaps around the fragment may be of significance in its identification. As research advances, a clearer view of this challenging task may evolve.
In line with Recommendation 1, it is strongly believed that periapical radiography as the principal radiographic modality for detection, identification, and localization of intracanal instrument fragments is justified. The use of CBCT to assess the canal shape and the available space around the fragment, in unfilled portions of canals, especially when the dental operating microscope does not allow direct visualization, could be justified when it is perceived to be of valuable assistance in selecting optimal management strategies.
Under all these three different conditions in which the operator is asked to detect, identify, and localize the presence of a fragment, the clamp of the isolation (metallic or plastic) might interfere with the radiographic portrayal of the fragment. Additionally, the clamp might prevent the clinician from following the course of manipulations required during management efforts and inhibit his/her ability to estimate the amount of root canal wall dentin removed. Therefore, in all cases, it is advisable, once the RCT or retreatment has started, to retain the rubber dam by placing the clamp, whenever possible, on an adjacent tooth (Fig. 4.3) or by using dental floss or rubber strips.
Fig. 4.3
(a) Preoperative radiograph of maxillary first molar with an instrument fragment in the distobuccal canal. (b) Placement of the plastic clamp on the tooth with the fragment during efforts to negotiate the fragment with a small file hinders management efforts. (c) Placement of the clamp on the adjacent second molar results in a clearer view
The potential locations of the fragment, irrespective of the type of the instrument, are the following:
-
One end of the fragment protruding into the pulp chamber and the other within the root canal (Fig. 4.4).
-
Both ends of the fragment within the root canal (Fig. 4.5).
-
One end of the fragment within the root canal and its tip extending into the periapical area (Fig. 4.6).
-
The fragment extending from the coronal third to the periapical area (Fig. 4.7).
-
The fragment is lodged outside the canal in the periapical region (Fig. 4.8). Rarely, it can also be extruded in adjacent anatomical structures.
Fig. 4.4
Fragment protruding into the coronal chamber
Fig. 4.5
Fragment with both ends within the root canal
Fig. 4.6
Fragment with one end within the root canal and its tip extending into the periapical area
Fig. 4.7
Fragment extending from the coronal third into the periapical region
Fig. 4.8
Fragments extruded beyond the confines of the tooth
4.3.1.3 Identification of the Fragment
The type of instrument fractured and the size of the fragment must be recorded on the patient’s chart. In retreatment cases with retained instrument fragment(s) or referrals with no relevant details on the patient’s chart, their radiographic appearance will assist in their identification. Thus, familiarity with the radiographic appearance of instruments used within root canal and particularly NiTi and stainless steel (SS) instruments is essential.
4.3.2 Initiation of Management Efforts
Upon completion of the patient briefing and the localization and identification of the fragment, management efforts start. It is absolutely essential before any attempt is made to ensure that there is plenty of available time for both the patient and the clinician in order to avoid additional stress on both sides. The management efforts differ in primary and permanent teeth:
- 1.
Initiation of management efforts in primary teeth
- 2.
Initiation of management efforts in permanent teeth
4.3.2.1 Initiation of Management Efforts in Primary Teeth
The recommended management is retrieval of the fragment or tooth extraction, depending on the fragment’s location and the stage of the primary tooth’s root resorption (Table 4.1). In all cases, the clinician must very carefully consider whether removal attempts are necessary at all. The much thinner radicular dentin, compared to that in permanent dentition, requires caution and the selection of a noninvasive or the least invasive technique for removal of the fractured instrument. In cases where retrieval is not possible but the fragment can be bypassed, instrumentation and obturation with the fragment retained within the sealing material and recall examinations are not recommended. Additionally, if bypassing is not possible, obturation up to the fragment and follow-up of the case are also not recommended. Patients do not always conform to recall appointments. In cases of appointment failure, there is the risk that the metallic fragment will remain in the jaw after the resorption of the root of the primary tooth. This may affect the permanent successor, and theoretically, it might even be found in the oral cavity after the exfoliation of the primary tooth and inadvertently swallowed or inhaled. Extraction followed by space maintenance is often considered the treatment of choice. Obviously the latter is decided in close collaboration with pedodontist and orthodontist.
Table 4.1
Recommended management of fractured instruments in the primary dentition based on the location of the fragment
|
Location of the fragment
|
Management phase I
|
Management phase II
|
|
|---|---|---|---|
|
Fragment with one end protruding into the pulp chamber and the other in the r. c.a
|
 |
In all cases, retrieval of the fragment
|
RCT
|
|
Fragment with both ends within the r.c.
|
 |
Retrieval of the fragment
|
RCT
|
|
Failure to retrieve the fragment
|
Tooth extractionb
|
||
|
Fragment with its tip extending into the periapical area
|
 |
Tooth extractionb
|
|
|
Fragment extending from the pulp chamber into the periapical area
|
 |
Retrieval of the fragment
|
RCT
|
|
Failure to retrieve the fragment
|
Tooth extractionb
|
||
|
Fragment lodged outside the r.c.
|
 |
Tooth extractionb and removal of the fragment
|
|
To our knowledge, there are only three case reports with successful retrieval of fractured instruments in primary teeth with ultrasonics under the dental operating microscope (Patel et al. 2015; Pk et al. 2016). To minimize unnecessary removal of tooth structure, low intensity ultrasonic vibrations of the fragment through a DG 16 endodontic explorer was used to loosen and retrieve the fragment in two of them (Pk et al. 2016). In the third case (Patel et al. 2015), the tip of the ultrasonic instrument activated at a low power setting was placed in intimate contact with the 3 mm fragment located in the middle third of the root of a maxillary central incisor in a 5-year-old boy. A case is also presented in a book (Lambrianidis 2001) where the primary tooth with a fragment with its one end extending into the periapical tissues was extracted (Fig. 4.9). To our knowledge, there is no case in the literature with follow-up of a fragment retained in the root canal of primary tooth after the completion of RCT.
Fig. 4.9
(a) Preoperative radiograph. (b) Radiographic confirmation of the fragment’s presence and identification of its location. (c) Extraction of tooth. The tip of the fragment protruding into periapical tissues is discernible (with permission from Lambrianidis 2001)
4.3.2.2 Initiation of Management Efforts in Permanent Teeth
Initially an attempt is made to retrieve the fragment (Figs. 4.10, 4.11, and 4.12), if this attempt fails to bypass it (Figs. 4.13 and 4.14) and if this attempt also fails to instrument and obturate the canal up to the fragment (Figs. 4.15, 4.16, and 4.17). In all cases, the tooth in question is scheduled for follow-up. The recommended management varies according to the fragment’s location, the pulpal and periapical status at the initiation of the treatment, and the instrumentation stage when the fracture occurred (Table 4.2).
Fig. 4.10
(a) Clinical appearance of a healthy 45-year-old woman presented with swelling and fever lasting 3 days, despite self-administered antibiotics (amoxicillin 625 mg ×3 for 3 days). According to her dental history, she had a continuous discomfort since the RCT and bridge work performed 18 months earlier. (b) Preoperative radiograph revealed the presence of an endodontic instrument fragment with both ends within the root canal “covering” approximately the whole length of the canal. (c, d) Retrieval of the fragment, instrumentation, and dressing of the root canal with Ca(OH)2 for 14 days. (e) Immediate post-obturation radiograph. (f) Clinical picture of the day of completion of RCT (Courtesy of Dr. K. Mastoras)
Fig. 4.11
(a) Preoperative radiograph of a left maxillary first molar . (b) Fragment of an irrigation needle in the mesiobuccal canal. (c) Removal of the fragment. (d) Working length determination radiograph. (e) Radiograph appearance after the completion of the RCT and the rehabilitation of the tooth (Courtesy of Dr. P. Mourouzis)
Fig. 4.12
(a) Preoperative radiograph showing three fractured instruments at the apical third of the root canal of a lower mandibular right second premolar tooth with a diagnosis of chronic apical periodontitis . (b) A staging platform was created around the most coronal aspects of the fragments by using modified Gates Glidden drills (sizes #2–4). Thereafter, an RT3 (EMS) ultrasonic tip was activated at low power settings, which trephined dentin in a counterclockwise motion around the fragments. With this action and the vibration being transmitted to the fragments, two of them began to loosen, and they were removed from the canal. (c) Working length determination radiograph showing one fragment inside the canal. (d) The third fragment, as it can be clearly seen in the master cone radiograph, was removed during copious irrigation in the course of root canal instrumentation. (e) Immediate post-obturation radiograph showing complete obturation of the root canal and temporary restoration with glass ionomer cement (Fuji II GC Corporation, Tokyo, Japan) and Cavit (Courtesy of Dr. T. Zarra)
Fig. 4.13
(a) Preoperative radiograph. (b) Fragment at the middle third of the mesiolingual canal of a first mandibular molar. (c) Bypassing of the fragment. (d) Immediate post-obturation radiograph. The fragment can hardly be seen within the obturation material
Fig. 4.14
(a) Fragment of the tip of a notched irrigation needle . (b) Bypassing the fragment and obturation of the root canal with the fragment in place (Courtesy of Dr. K. Kodonas)
Fig. 4.15
(a) Preoperative radiograph of a crowned mandibular first molar with incomplete RCT and apical periodontitis. (b) Removal of the crown, fracture at the apical third of the distobuccal canal, of a 2 mm K-file which could not be bypassed and retrieved. This was followed eventually by instrumentation and obturation of this canal up to the fragment. (c–e) The scheduled recall clinical and radiographic follow-up at 3, 9, and 30 months, respectively, revealed uneventful healing
Fig. 4.16
(a) Preoperative radiograph. (b) Master cone radiograph. The fragment of the NiTi instrument can be seen at the apical third of the mesiobuccal canal. (c) Instrumentation and obturation up to the fragment. The fragment can hardly be identified at the immediate post-obturation radiograph. (d) Six-month recall radiograph (Courtesy of Dr. Ch. Beltes)
Fig. 4.17
(a) Two fragments of NiTi instruments at the apical third in a severely curved canal. (b) Instrumentation and obturation up to the fragments. Note that some sealer extruded through the apical and lateral foramina (Courtesy of Prof. P. Beltes)
Table 4.2
Recommended management of fractured instruments in permanent dentition based on the location of the fragment, the pulpal status, and the instrumentation stage when the fracture occurred
|
Location of the fragment
|
Management phase I
|
Pulpal status
|
Instrumentation stage when fracture occurred
|
Management phase II
|
|||
|---|---|---|---|---|---|---|---|
|
Vital
|
Non-vital
|
Early stage
|
Late stage
|
||||
|
Fragment with one end protruding into the pulp chamber and the other into the r.c.a
|
 |
In all cases, retrieval of the fragment
|
(N/A)b
|
N/A
|
N/A
|
N/A
|
RCT
|
|
Fragment with both ends within the r.c.
|
  |
Retrieval
|
N/A
|
N/A
|
N/A
|
N/A
|
RCT
|
|
Bypass
|
N/A
|
N/A
|
N/A
|
N/A
|
RCT. The fragment is incorporated in the filling material
Follow-upc
|
||
|
Failure to retrieve, bypass
|
+
|
−
|
+
|
Instrumentation and obturation up to the fragment
Follow-upc
|
|||
|
+
|
−
|
−
|
+
|
||||
|
+
|
+
|
||||||
|
+
|
+
|
||||||
|
Fragment with its tip extending into the periapical area
|
 |
Retrieval
|
N/A
|
N/A
|
N/A
|
N/A
|
RCT
|
|
Bypass
|
+
|
+
|
RCT. The intracanal segment of the fragment is incorporated in the filling material
Follow-upc
|
||||
|
+
|
+
|
||||||
|
+
|
+
|
||||||
|
+
|
+
|
||||||
|
Failure to retrieve, bypass
|
+
|
+
|
Instrumentation and obturation up to the fragment
Follow-up
|
||||
|
+
|
+
|
||||||
|
+
|
+
|
||||||
|
+
|
+
|
||||||
|
Fragment extending from the pulp chamber to the periapex
|
 |
Retrieval
|
N/A
|
N/A
|
N/A
|
N/A
|
RCT
|
|
Bypass
|
N/A
|
N/A
|
N/A
|
N/A
|
RCT. The intracanal segment of the fragment is incorporated in the filling material
Follow-upc
|
||
|
Failure to retrieve, bypass
|
N/A
|
N/A
|
N/A
|
N/A
|
Surgical endodontics
|
||
|
Fragment lodged outside the r.c.
|
 |
In all cases
|
N/A
|
N/A
|
N/A
|
NA
|
RCT
Follow-upc
|
4.3.3 Retrieval of the Fragment
The retrieval of a fractured instrument or any metallic object from the root canal has been a problem for dentists for decades. Various techniques and instruments, which quite often have to be used in combination, have been advocated for retrieving fragments. Technological advances in vision and particularly the dental operating microscope seem to be a key factor in a successful outcome as it can increase visibility through the use of magnification and light, enabling clinicians to visualize the coronal portion of most fractured instruments. The combination of microscope, ultrasonics, and advances in mechanical techniques used to retrieve foreign objects from the root canal ensures safety and increased efficacy. The techniques proposed for the retrieval of fractured instruments from the root canal employ either chemical or mechanical means. Other methods include the electrolyte method, the softened gutta-percha technique, the use of the Multisonic Ultracleaning System, and the laser irradiation (Table 4.3).
Table 4.3
Means and techniques proposed for retrieval of instrument fragments from the root canal
|
Means
|
Techniques
|
||
|---|---|---|---|
|
Chemical
|
|||
|
Mechanical means
|
Technique using ultrasounds
|
||
|
Endosonic filing
|
|||
|
The file bypass technique
|
|||
|
Holding techniques
|
The Masserann technique
|
||
|
The Feldman and coauthors technique
|
|||
|
The Meitrac Endo Safety System
|
|||
|
The Instrument Removal System (IRS)
|
|||
|
The Endo Rescue
|
|||
|
The Endo Extractor System
|
|||
|
Tube techniques
|
The Endo Extractor
|
||
|
The Cancellier Extractor Kit
|
|||
|
Hypodermic surgical needle
|
With cyanoacrylate
|
||
|
With Hedstroem file
|
|||
|
The separated instrument removal system
|
|||
|
The Micro-Retrieve & Repair System
|
|||
|
Mounce extractors
|
|||
|
Canal Finder System technique
|
|||
|
Micro-forceps grasping technique
|
|||
|
Wire loop technique
|
|||
|
Gutta-percha
|
Softened gutta-percha technique
|
||
|
Multisonic Ultracleaning
|
Multisonic Ultracleaning System
|
||
|
Electrolysis
|
Electrolytic technique
|
||
|
Laser
|
Laser-assisted removal of fractured instruments
|
||
4.3.4 Chemical Means
The use of chemical means is aimed at:
-
Decalcification of root canal wall dentin around the fractured instrument with a weak acid (usually EDTA) in order to facilitate subsequent removal or bypass of the fragment with mechanical means
-
Corrosion of the metallic fragment and its “dissolution” or reduction of its cross section (with iodine compounds) in order to facilitate its retrieval or bypass with mechanical means
It is thus clear that the use of chemical means is not actually a technique for managing fragments within the root canal but a preparatory stage that may facilitate their management with mechanical means. Historically, potassium iodine (Lugol), crystallic iodine, iodine trichloride, crystals of iodine, iron chloride solution, and nitrohydrochloric acid have been some of the chemical proposed and most frequently used to intentionally corrode metallic objects in the root canal (Stasinopoulos 1978; Hülsmann 1993). There is a significant reduction in their use nowadays due to:
-
Their ineffectiveness
-
The fact that any chemical used in the root canal may be harmful to the periapical tissues if inadvertently extruded through the foramen or to the gingivae if it leaks
-
The allergic reaction to iodine compounds (Schafer 2007)
-
The well-known staining potential of iodine compounds
4.3.5 Mechanical Means
Several mechanical approaches have been proposed for the retrieval of instrument fragments from the root canal (Table 4.3). They sometimes employ simple mechanical means such as the use of a magnet (Grossman 1974) in the expectation that it might “attract” the fragment or a barbed broach wrapped in cotton wool and introduced into the root canal in the hope that the broken piece will become enmeshed in the cotton and will thus be pulled out as the broach is withdrawn (Feldman et al. 1974; Stasinopoulos 1978). These two techniques and particularly the magnet have had very limited success in retrieving fragments. Furthermore, wrapped cotton wool on a barbed broach might be effective only when the fragment is loose in the straight portion of a canal.
The proposed mechanical means, regardless of how sophisticated they may be, all operate on the same basic principle, which is to flare the canal coronal to the fragment, create space around it in order to free the fragment or at least its coronal segment, and at a second stage to retrieve it.
Regardless of the mechanical removal means and technique or combination of techniques to be employed in all cases, there are certain common steps to be followed:
-
A radiograph and in some cases more than one radiograph with different angulations are obtained to confirm the presence of the fragment, to reveal its location in relation to the root canal curvature, if present, and to estimate its size and length if unknown.
-
The access cavity is redefined to allow better visualization and unobstructed manipulations.
-
Cotton pellets are placed over other exposed orifices in multi-canal teeth to prevent dislodgment of the fragment into another root canal (see Chap. 7).
-
Maintenance of constant vision during management efforts. The Stropko Irrigator (Fig. 4.18) (DCI Intl, Portland, OR) placed into a three-way syringe (DCI, Adec, Midmark, Vista, etc.) is particularly useful, but it is important to regulate the air pressure going into the three-way syringe. An SPR pressure regulator (www.stropko.com) can be utilized to reduce the airflow to between 2 and 7 psi (14–50 kPa) for a controlled precise delivery. This removes dentinal dust as it is created to maintain constant vision and ensure, even in depths of the root canal, a good drying action more effectively than paper points. Its proximal end is positioned into the three-way syringe, and its distal end has Luer Lock threads for securely attaching different length and gauged canuli. Its small tips do not impede visibility during use under the microscope. In addition to the good drying action achieved with the Stropko Irrigator, paper points are avoided and thus the risk of contamination if inadequately manipulated by the operator (Pessoa de Andrade et al. 2014) and of cellulose fiber shedding (Brown 2016) associated with their use. This shedding is of outmost importance as it is substantially documented that these cellulose fibers if inadvertently extruded beyond the foramen are associated with intense persistent periapical inflammation and treatment failure (Koppang et al. 1989; Nair et al. 1990; Sedgley and Messer 1993; Nair 2006) as they cannot be degraded by human body cells (Nair 2006).
-
Frequent working radiographs are mandatory to check the level of retrieval and amount of dentin loss. It must, however, always be kept in mind that radiographic evaluation of the residual dentin thickness during management efforts can be misleading because of the inherent inaccuracy of radiographic interpretation.
-
Upon removal of the fragment, the canal is renegotiated with #6- to #10K-files to the apical foramen, and canal instrumentation and obturation follow. Instrumentation manipulations must be performed with caution, as the likelihood of another iatrogenic error in this clinical situation is very high.
Fig. 4.18
(a) The Stropko Irrigator . (b) Stropko Irrigator (XL length, 3.5 in), Stropko Irrigator (original size, 2 in), and Stropko Irrigator Adapter (for older syringes)
Prior to the detailed presentation of the proposed techniques, it should be noted that instrument fragments extending above the root canal orifice (Fig. 4.19) can usually be easily removed with a hemostatic forceps, Steiglitz forceps at 45° or 90° angles (Hu-Friedy), Peet silver point forceps (Silvermans, New York, NY), Endo Forceps (Roydent Dental Products, USA), Advanced Micro Endo Forceps 45° (Roydent Dental Products, USA), a Castroviejo needle holder, a Perry plier, ultrasonics, or even a spoon excavator. The micro alligator forceps commonly used by otolaryngologist can also be used.
Fig. 4.19
(a, b) Clinical and radiographic examination revealed access cavity with no temporary filling in the right maxillary central incisor and a fragment of an endodontic instrument extending from the coronal orifice to the apex “covering” approximately the whole length of the root canal. The treating dentist left the access cavity unsealed and invited his patient to “clean” the canal with an instrument he had given her nearly a year before when she began treatment with him. She had fractured the instrument within the canal 3 months earlier, and since then, she had started taking antibiotics repeatedly (amoxicillin 625 mg ×3) for 4 days each time. (c, d) The fragment was retrieved with forceps. (e, f) Instrumentation, calcium hydroxide dressing for 10 days, and obturation of the root canal with the cold lateral compaction technique of gutta-percha and 811 sealer (Roth International Ltd., Chicago, IL, USA) followed (Courtesy of Dr. M. Kasambali)
4.3.6 Ultrasonics
Ultrasound is a sound energy with a frequency above the range of human hearing, which is 20 kHz. Ultrasonic vibration is currently the most widely used method for retrieving foreign objects from the root canal. The vast majority (98.5%) of endodontists practicing in the UK that responded to a questionnaire concerning their opinions and attitudes toward the intracanal fracture of endodontic instruments use ultrasonics (Madarati et al. 2008). Fragments of instruments, silver cones, or intraradicular posts (Krell and Neo 1985; Meidinger and Kabes 1985; Souyave et al. 1985; Stamos et al. 1985; Nagai et al. 1986; Jeng and ElDeeb 1987; Berbert et al. 1995; Nehme 1999; Tzanetakis et al. 2008; Cuje et al. 2010; Fu et al. 2011; Nevares et al. 2012) can be loosened by ultrasonics and then removed. It is obviously implied that the technique requires intimate contact of the vibrator tip with the metallic object to be retrieved. Initially hand files or spreaders were activated by ultrasonic devices to manage fractured instruments (Krell et al. 1984; Souyave et al. 1985; Nehme 1999). D’Arcangelo et al. (2000) reported two cases with successful removal of fragments using hand instrumentation with SS K-files and K-files mounted on the handpiece of an ultrasonic device. In one of them, four fragments were removed. Currently most ultrasonic companies have tips specifically designed to remove fractured instruments (Fig. 4.20). Therefore, a selection of specially designed ultrasonic tips is available. They have a contra-angled design with alloy tips manufactured from a range of metal alloys, such as SS and titanium alloys, and can be coated with an abrasive such as diamond or zirconium nitride in order to increase the cutting efficiency of the tip. Tips are available in different angles, lengths, and sizes to enable use in various parts of the root canals. As a general rule, the deeper the fragment is located in the canal, the longer and thinner the ultrasonic tip that should be used. These long, thin tips must be used at very low power settings to prevent tip breakage.
Fig. 4.20
ProUltra ENDO Tips (Dentsply Tulsa Dental, Tulsa, OK). The 1–5 Ultrasonic Endo Tips are zirconium nitride coated to harden them and improve clinical performance. These tips are designed for the removal of dentin and restorative materials along the lateral sides of the instruments. The ProUltra ENDO 6–8 have increased strength due to their titanium alloy construction and can be used to the full length of the root canal due to their longer lengths and smaller diameter
Tips should be carefully chosen. Clinicians choose tips in accordance with the ultrasonic scaler they use. This is because the resonance frequency of the tips must match the working frequency of the devices. Obviously, this applies with respect to devices of the same brand. Lack of compatibility will lead to tip fracture. To our knowledge, there is only one study on resonance compatibility between endodontic ultrasonic (endosonic) tips for fractured instrument removal and ultrasonic devices of different brands (Shiyakov and Vasileva 2014). The authors of this study concluded that combinations of different brands of instruments and ultrasonic devices are possible but information regarding resonance compatibility should be carefully checked.
In cases where the specific tips are not available, ultrasonic energy may be transmitted through the largest hand file reaching the fragment, an endodontic explorer or spreader, as proposed in earlier periods (Krell et al. 1984; Souyave et al. 1985; Nehme 1999).
The ultrasonic units currently available in dentistry are of two basic types with different action mechanisms. These are (Fig. 4.21):
-
Magnetostrictive. Magnetostriction converts electromagnetic energy into mechanical energy.
Fig. 4.21
Ultrasonic unit
Both types are clinically well accepted in dentistry. The piezoelectric type of ultrasonics is better suited to endodontic applications (Plotino et al. 2007). They offer more cycles per second, 40 versus 24 kHz, while the tips of these units work in a linear back-and-forth, “pistonlike” motion (Plotino et al. 2007). This movement is ideal for endodontics. This is particularly evident when removing posts and fractured instruments.
The stages that should be followed are (Fig.4.22):
-
Instrumentation of the root canal up to the fragment. Under direct microscopic vision, circumferential staging platform around the most coronal aspect of the fragment is prepared with modified (blunted) pre-selected #2–#4 Gates Glidden bur (Fig. 4.23) used in a crown-down fashion as described by Ruddle (2004). The maximum cross-sectional diameter of the pre-selected Gates Glidden bur must be slightly larger than the diameter of the fragment at its coronal aspect. Therefore, familiarization with the sizes of Gates Glidden burs is essential (Table 4.4). The modified Gates Glidden bur is carried into the pre-enlarged canal, rotated at a reduced speed of approximately 300 rpm, and directed apically until it makes light contact with the most coronal aspect of the fractured instrument. The platform is kept centered to allow better visualization of the fragment and the surrounding dentin root canal walls; therefore, equal amounts of dentin around the fragment are preserved, minimizing the risk of root perforation. Similarly modified LightSpeed NiTi rotary instrument (Lightspeed Technology Inc., San Antonio, TX) can be used. In a comparative study, it was found that the staging platform created with the latter was more centered in curved canals than the one created by Gates Glidden burs (Iqbal et al. 2006).
-
Copious irrigation to remove all debris and dentin chips. This is followed by thorough drying of the canal to facilitate excellent vision with the microscope prior to beginning ultrasonic procedures.
-
The pre-selected ultrasonic tip with the appropriate length to reach the fragment and a diameter that allows it to passively fit into the previously shaped canal is placed between the exposed coronal end of the fragment and the canal wall, in intimate contact with the fragment. It is then activated at lower power settings, to trephine dentin around the fragment in a counterclockwise motion. This is continued until a couple of millimeters of the coronal end of the fragment is freed and/or some movement of the fragment is noted (Fig. 4.24). Care must be exercised at this point to touch the fragment as little as possible and avoid removing a lot of dentin from the inner, less thick canal wall. Diamond-coated tips should be avoided for this troughing phase as they are very aggressive and may remove too much of the dentin wall. Occasionally the unscrewing force thus created might dislodge the fragment, which “jumps out” of the canal (Figs. 4.25 and 4.26). In cases of fragments in long roots with limited access and slender root morphology, titanium ultrasonic tips may be used. These are longer with smaller diameters, compared to the abrasively coated instruments. Also they are flexible, can cut only at their tip, and provide a smooth, less aggressive, cutting action that promotes safety when trephining deeper within a root canal. Blind trephining of dentin even with them must be avoided as it may cause iatrogenic errors.
Fig. 4.22
(a–h) Schematic illustration of fragment retrieval with ultrasonics. (a) Radiographic confirmation of the presence of a fragment and recognition of its location, size, and length. (b–d) Instrumentation of the root canal up to the fragment and creation of a staging platform with modified Gates Glidden bur. (e, f) Exposure of the coronal segment of the fragment with dry ultrasonic troughing around the fragment with the ultrasonic tip activated at lower power settings. (g) Ultrasonic vibration and removal of the fragment. (h) Once the fragment is removed, the canal is renegotiated with an ISO size #10K-file to the apical foramen, and canal instrumentation follows
Fig. 4.23
Modified Gates Glidden bur . Grinding or sectioning of the non-cutting tip perpendicular to their long axis at their maximum cross-sectional diameter transforms this end into a very efficient cutting tip. Therefore, modified Gates Glidden bur must be used with great care and preferably under direct microscopic vision
Table 4.4
Sizes of Gates Glidden burs
|
Gates Glidden bur
|
Size (mm)
|
|---|---|
|
#1
|
0.50
|
|
#2
|
0.70
|
|
#3
|
0.90
|
|
#4
|
1.10
|
|
#5
|
1.30
|
|
#6
|
1.50
|
Fig. 4.24
(a) Clinical picture of a hospitalized patient with extensive swelling, mild to severe pain, high fever, lymphadenopathy, and nausea. (b) Preoperative radiograph of a lower second mandibular molar with an incomplete RCT, an apical periodontitis, and a long SS fragment in the mesial root . (c) Preparation of staging platform and exposure of more than 3 mm of the coronal segment of the fragment with modified Gates Glidden burs (#2–#4) and ultrasonic tips (RT3, EMS). Despite this exposure, the fragment could not be retrieved, so it was bypassed, and more preexisting obturating material was removed. (d) Fragment as seen through the dental operating microscope. (e, f) The fragment was eventually retrieved with an RT3 tip (EMS) activated at lower power settings. (g) Canals were instrumented and obturated with gutta-percha and Roth 811 sealer (Roth International Ltd., Chicago, IL, USA) with the lateral compaction technique. (h) Clinical picture of the patient on the day of the root canal obturation
Fig. 4.25
(a) Preoperative radiograph of a mandibular second left molar with a fragment at the middle third of the mesiobuccal cana l . (b) Preparation of a staging platform around the most coronal segment of the fragment with modified Gates Glidden burs (#2–#4) and ultrasonic tips (RT3, EMS) until the fragment was visible with the aid of the dental operating microscope. (c, d) The platform was kept centered, and the ultrasonic tip trephined dentin in a counterclockwise motion around the fragment until the latter began to loosen and eventually “jumped” out of the canal. (e) The canals were then routinely prepared and obturated with warm vertical compaction of gutta-percha and AH26 (Dentsply DeTrey GmbH, Konstanz, Germany) sealer (Courtesy of Dr. G. Dehouniotis)
Fig. 4.26
(a) Immediate preoperative radiograph. (b) Operative microscope photography after staging platform creation and exposure of the coronal end of the fragment. (c) Fragment in the pulp chamber as seen through the dental operating microscope. Note the cotton pellet in orifice of the palatal canal. (d) Master gutta-percha cone radiograph. (e) Immediate postoperative radiograph (Courtesy of Dr. K. Kalogeropoulos)
When trying to remove a file that has a left-handed thread, the direction would be clockwise. It is crucial to avoid unnecessary stress on the ultrasonic tip in order to prevent its fracture (Fig. 4.27). All ultrasonic work inside the root canal is conducted in a dry environment, so the clinician has continuous visualization with the microscope of the energized tip and the fragment. Blind trephining of dentin may lead to undesirable complications. The Stropko Irrigator utilized by the dental assistant is particularly useful during ultrasonic use to collimate and direct a continuous stream of air and blow out dentinal dust.
Fig. 4.27
Fractured ultrasonic tips . (a) Fracture of RT3 (EMS) at its tip. (b) Fracture of RT3 (EMS) at its shank. (c) Fracture of ProUltra Endo Titanium Tip
NiTi and SS instruments respond differently to ultrasonic vibration. SS fragments absorb the ultrasonic energy bodily and will show movement early on (Cohen et al. 2005). NiTi instruments are brittle and often break up into fragments (Fig. 4.28) when subjected to direct ultrasonic energy, particularly if the fragment is tightly locked. This renders the procedure considerably more difficult. Heat-generated and cyclic fatigue created by high-frequency waves of the ultrasonic tip transferring to the fragment could be contributing factors to secondary fracture (Terauchi et al. 2013). Secondary fracture of fragments appeared to be reduced when the ultrasonic tip was applied to the inner curvature of the canal (Terauchi et al. 2013).
Fig. 4.28
Secondary breakage of NiTi fragment . (a) Working length radiograph. (b) Staging platform and exposure of approximately 1–2 mm of the coronal end of the NiTi fragment. (c) Secondary fracture of the initial fragment following the use of an RT3 tip (EMS) at a low power setting
If the fragment cannot be retrieved but is loosened and completely bypassed, vibration can be transmitted through a hand SS K-file introduced alongside the space pre-created with hand files between the fragment and the dentin wall. This vibration, at lower power settings, of the K-file further loosens the fragment, which can eventually be washed out with the irrigant (Figs. 4.29 and 4.30). Care must be exercised to activate ultrasonically K-file(s) thinner than the last hand file used to bypass the fragment. An Ultrasonic Endo File Adapter (Fig. 4.31) needs to be threaded onto the ultrasonic handpiece so that its chuck will grasp the 0.02 SS K-file by tightening the nut with the wrench provided. It must be emphasized that K-files for the ultrasonic unit are more cost-effective and less aggressive and could be pre-bent more easily than ultrasonic tips.
Fig. 4.29
(a) Preoperative radiograph showing a fractured instrument at the apical third of the mesiobuccal root canal of tooth #46 with a diagnosis of chronic apical periodontitis . (b) A staging platform was created around the most coronal aspects of the fragments by using modified Gates Glidden drills (#2–4). Thereafter, an RT3 (EMS) ultrasonic tip was activated at low power settings, which trephined dentin in a counterclockwise motion around the fragments. With this action and the vibration being transmitted to the fragments, the fragment began to loosen. At this stage, it was bypassed with size #10 up to size -25K-files and “washed out” (arrow) to the floor of the pulp chamber with the irrigant. (c) Master cone radiograph. (d) Final radiograph showing complete obturation of the root canal and temporary restoration with a cotton pellet and Cavit (Courtesy of Dr. T. Zarra)
Fig. 4.30
(a) Preoperative radiograph showing two instrument fragments at the apical third of the mesiobuccal root canal of left maxillary first molar not visible with the operative microscope. (b, c) After coronal pre-flaring, the fragments were released and removed blindly with the U-files activated at low power settings, at the internal curvature. (d) Final radiograph showing complete obturation of the root canals and adhesive restoration of the access cavity with flowable composite (Courtesy of Dr. M. Leineweber)
Fig. 4.31
The Ultrasonic Endo File Adapter manufactured under a variety of names and brands has been designed to function on most brands of piezoelectric-type dental ultrasonic scalers. It accepts SS or NiTi files that are between sizes 15 and 40 after the handle or latch hub has been removed
4.3.7 Endosonic Filing
With this method proposed in the 1980s (Souyave et al. 1985; Nagai et al. 1986), the steps to be followed are:
-
An endosonic file #15 or #20, attached to the handpiece and monitored under the dental operating microscope, is inserted into the root canal up to the coronal end of the fragment and energized ultrasonically to create a trough around this end of the fragment.
-
A small K-file, pre-curved at its tip, is then gently pushed down to bypass the fragment.
-
When the fragment can be bypassed at least to its midpoint, it may be dislodged by simultaneous irrigation and agitation with the endosonic file. A low power setting is used initially, but this can be adjusted upward depending on the fragment.
4.3.8 The File Bypass Technique
This technique does not require any special or sophisticated instrument. It utilizes endodontic instruments available in all dental practices. In this technique, an effort is made to establish patency to the apical foramen bypassing the fragment and subsequently, when the access of the instruments up to the apex is ensured, to try to retrieve the fragment by a filing motion. It is a technically challenging procedure, depending solely on the tactile sensitivity and sheer perseverance of the practitioner. The likelihood of creating another iatrogenic error such as fracture of a second file, ledge formation, perforation, or transportation is very high, and thus the whole procedure must be performed with great caution.
For this purpose (Fig. 4.32):
-
The root canal is instrumented up to the fragment. Straight-line access and visualization of the coronal aspect of the instrument should be tried whenever possible.
-
Copious irrigation follows to remove as much residual tissue and debris as possible.
-
The instrumented part of the canal is flooded with EDTA to be carried with the small instrument to follow and soften root dentin.
-
A small sharp bent is made to a fine hand K-file (ISO 6 or 8 and maximum 10) either with a cotton plier (Fig. 4.33) or with the SS Endo File Bender (SybronEndo, Orange, California) if available. The bent file is then inserted into the root canal and using very gentle apical pressure is rotated up to one-fourth of the turn until its tip “is blocked” in the narrow space between the fragment and the root canal wall (Fig. 4.34). The probing manipulations continue until the fragment is bypassed and the tip of the file reaches the apex. The path of the instrument is followed radiographically, and the procedure is stopped in the event of misdirection since there is an increased risk of ledge formation or root perforation. The apex locator at this stage can only verify that the tip has reached the periodontal ligament but cannot differentiate whether this is beyond the apex or at a perforation site. The file is not removed at this point. With great caution, very small in and out movements are made with copious irrigation with the file in place. Very often, it is necessary to repeat the same procedure with a new file of the same size with an identical small sharp bent.
-
The remaining portion of the root canal apical to the fragment is instrumented under copious irrigation. The size 10 file is followed by careful use of the size 15 and size 20 files. Prior to the use of the size 15 file, it is suggested (Zeigler and Serene 1984) to use to full working length the size 10 file shortened by 1 mm. In this way, the cross section at the tip of the shortened file is bigger than that of the size 10 file and smaller than that of the size 15 file, with the flexibility though of the size 10 file. This eases the use of the size 15 file that will follow. The same is repeated with file sizes 15 and 20. Golden medium sizes are mostly helpful in such cases. Care must be exercised to avoid placing any instrument directly on top of the fragment as it might push the fragment deeper into the canal and also impede the patency gained. In such cases, patency has to be regained by starting again with the initial file which, having been pre-bended, succeeded in bypassing the fragment.
Fig. 4.32
(a–h) Schematic illustration of instrument fragment retrieval with the file bypass technique. (a) Radiographic confirmation of the presence of a fragment and recognition of its location, size, and length. (b) Instrumentation of the root canal up to the fragment. (c) Efforts to bypass it with a pre-curved size #8Κ-File. (d) After bypassing, filing continues with larger-sized instruments trying to “engage” the fragment in their flutes and to retrieve it. (e–g) Sometimes engagement and retrieval of the fragment are facilitated with the simultaneous insertion (braiding technique) of two and occasionally more instruments in the root canal, preferably Hedstroem files. (h) Once the fragment is removed, the canal is renegotiated with an ISO size 10K-file to the apical foramen, and canal instrumentation follows
Fig. 4.33
Schematic illustration of creation of small sharp bend with cotton pliers
Fig. 4.34
Pre-bent K-file during the attempt to bypass a fragment in the apical third of a distal root in a mandibular first molar
Some characteristic cases of instrument fragments managed with the file bypass technique are presented (Figs. 4.35, 4.36, 4.37, and 4.38).
Fig. 4.35
(a) Preoperative radiograph of a retreatment case with two fragments, one in each buccal root of a maxillary left second molar . (b) Removal of the fragments with the file bypass technique. (c) Immediate post-obturation radiograph. Note the ledge formed
Fig. 4.36
(a) Preoperative radiograph of a referred case with two fractured instruments. (b) Bypassing of the instruments and retrieval of one of the fragments with the file bypass technique, while the other, which became loose with the technique, was suctioned during sodium hypochlorite irrigation . (c) Pre-final radiograph with gutta-percha cones in place. (d) Immediate post-obturation radiograph. (e) Three-month recall radiograph (Courtesy of Dr. A. Chouliara)
Fig. 4.37
(a) Preoperative radiograph. A fragment can be seen (arrow) apically to the obturation material of the initial RCT. (b) Fragment retrieved with the file bypass technique. (c) Immediate post-obturation radiograph. (d) Three-month recall radiograph
Fig. 4.38
(a) Preoperative radiograph of a first mandibular molar with incomplete RCT and apical periodontitis. (b) Radiograph with a fragment in the apical third of the mesiobuccal canal fractured during retreatment procedure. (c) Immediate post-obturation radiograph following bypassing of the fragment, instrumentation up to the desired length, and dressing of the root canal with Ca(OH)2 for 2 weeks. (d, e) Recall radiograph at 8 and 21 months, respectively, shows healing (Courtesy of Prof. J. Molyvdas)
The objective of this procedure is to free the fragment through filing, to engage it in the flutes of the file, and to retrieve it. The capture and removal of the fragment are facilitated by the braiding technique, with which two (rarely three) files are gently screwed into the canal alongside the fragment and then wound around each other until the fragment is tightly grasped and withdrawn. Although the braiding technique was initially described using ISO size #15 files, the largest size possible should be used to decrease the risk of file fracture (Pitt Ford et al. 2002).
It is generally accepted that not all bypassed fragments are retrieved. The frequency with which bypassing but not retrieval happens in clinical practice is not substantially documented in the literature. There are many cases in the literature and in the author’s archives of fragments that have been bypassed but not retrieved. In these cases if despite bypassing, the removal of the fragment is not possible, the instrumentation continues. The instrumentation technique and the master apical file that will be used for the root canal segment apical to the fragment respect all the rules of instrumentation. The obturation that follows incorporates the fragment within the filling material.
NiTi instruments are not used at all with this technique due to the increased risk of fracture. Bypassing efforts and cleaning and shaping of the canal accommodating the fragment are better completed by hand K-files to avoid further instrument fracture.
4.3.9 Holding Techniques
The concept of these techniques is to expose the coronal portion of the fragment (Fig. 4.39) using a range of trephine drills or ultrasonic tips prior to the use of a second instrument that will engage the coronal aspect and withdraw the fragment from the canal.
Fig. 4.39
(a) Preoperative radiograph in which a fragment with both ends within the root canal is visible at the apical root third. (b) Exposure of approximately 2 mm of the coronal segment of the fragment
Among the holding techniques , the most characteristic and well known are:
-
The Masserann technique
-
The Feldman et al. (1974) technique
-
The Meitrac Endo Safety System
-
The Instrument Removal System (IRS)
-
The Endo Rescue
-
The Endo Extractor System
4.3.10 The Masserann Technique
The Masserann technique (Masserann 1966, 1971), being used for the removal of fractured instruments, has also been used for the retrieval from the root canal of metallic objects such as silver cones and posts. The available kit (Masserann endodontic kit, Micro-Mega, Besancon, France) consists of (Figs. 4.40 and 4.41):
-
An assortment of 14 color-coded, end-cutting, tubular trepan burs of increasing size
-
Two sizes of tubular extractors (1.2 and 1.5 mm)
-
A gauge that assists in predicting the size of the bur and the extractor to be used
Fig. 4.40
(a) The Masserann kit (Masserann endodontic kit, Micro-Mega, Besancon, France). (b) The special trepan burs are concave. (c) The trepan burs may be used on a handpiece or manually
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