Abstract
Objectives: To evaluate the clinical application of the dental operating microscope (DOM) in the management of complicated root canal therapy. Methods: 345 teeth with 546 root canals which could not be successfully managed by conventional methods received therapy under the DOM with ultrasonic instruments by the same endodontists. The aetiology of the canals included calcification, broken instrument, missed canal and canal perforation. The teeth and canals successfully managed were then calculated. Results: 406 canals were successfully managed with a rate of 74.4%; 246 teeth were successfully managed with a rate of 71.3%. The rates in each category of the complicated root canals were: 74.0% for calcified canals, 72.3% for canals blocked by broken instruments, 82.5% for missed canals and 72.7% for canal perforations. Conclusions: The clinical application of the DOM is an effective way of managing complicated root canal therapy.
Key words: Root canal therapy, canal calcification, separated instrument, missed canal, canal perforation, dental operating microscope
INTRODUCTION
Root canal therapy is the first treatment plan for pulpitis and periodontitis1. However, canal calcification, separated instruments, missed canals or canal perforation may cause the therapy to be more difficult, even resulting in its failure. The dental operating microscope (DOM) provides the clinician with superior lighting and magnification and the ability to treat cases that previously may have been deemed untreatable or which may have resulted in a compromised prognosis2. Michaelides3 stated that the enhanced illumination and visibility enables endodontists to improve the predictability of their procedures. Khayat4 listed the advantages of using a microscope for detection of coronal and radicular cracks and fractures, patient education with pictures displayed on the monitor, location of calcified and additional canals, bypassing ledges, removal of separated instruments, and viewing perforations for repair.
The introduction of the DOM to China was very late but clinicians strove to acquire considerable experience in operating the equipment and have gained good outcomes. The purpose of this paper is to report the successful treatment of complicated cases with the aid of DOM.
MATERIALS AND METHODS
Case selection
About five hundreds patients came to the Dental Operating Microscope Center of Affiliated Stomatology Hospital of Nanjing Medical University from January 2008 to December 2010. They were transferred from general clinic services and other hospitals as their teeth could not be successfully treated due to canal calcification, separated instruments, missed canals or canal perforation. A recent and concise, comprehensive medical history and dental history were conducted. Then standard periapical radiographs were taken using a DDR system (Sidexis; Siemens AG, Bensheim, Germany) or a Micro-CT (NewTom VG, QR SRL, Verona, Italy) by an experienced radiographic operator. The peroperative radiographs were analysed carefully. Initially, most patients received treatment from the endodontists of the DOM Center by conventional methods but about 500 patients’ teeth could not be successfully treated and so it was suggested that treatment with DOM be undertaken.
A preoperative conversation was conducted which included discussion over the course of treatment, expenses, prognosis and other details. The exclusion criteria were patients who could not accept the treatment because of their weak physical status, and those who gave up treatment due to the longer time needed for the therapy or the higher charge. This left 332 patients with 345 teeth; 129 males and 203 females with a mean age of 40.4 ± 16.1 years (9–77 years).
Treatment methods
The teeth were isolated with a rubber dam (Coltène-Whaledent AG, 9450 Altstätten/Switzerland) and the DOM (OPMI pico; Carl Zeiss, Germany) and the Ultrasonic instrument (P5 Satelec; France) were used in the therapy.
Calcification
The colours of the normal chamber floor and the calcified dentine were identified under the DOM. A DG-16 explorer (DG-16; Hu-Friedy, USA) or a Micro-Opener (Densply Maillefer, Ballaigues, Switzerland) was used to locate and probe the canal orifice before the canal orifice was enlarged using an ultrasonic tip (Satelec; Pierre Rolland, France) or a Gates Glidden drill (28 mm; MANI, INC, Japan). The calcification in the coronal and middle two-thirds was removed by the ultrasonic tip. During the therapy, Vitapex (Neo Dental Chemical Products CO., Ltd, Tokyo, Japan) was injected into the canals as the radiopaque material, and the radiographs were taken to adjust the direction of the ultrasonic tip. CT images were used in a few cases to help adjust the direction of the ultrasonic tip. A 10# K-file (21 mm/25 mm; MANI, INC) or a C-Pilot file (21 mm/25 mm; VDW GmbH, Munich, Germany) coated with root canal lubricant (Densply Maillefer) was inserted into the apical portion of the canal, and was twisted back and forth with small amplitude. A slight ‘tug back’ often signals the negotiation of the canal. If the file tip reached the apical constriction of the canal or the distance between the file tip and radiographic apex of the root was <2 mm, the treatment was considered to have been a success otherwise the treatment was considered to have failed.
Separated instruments
The preoperative radiographs were used to determine the type of the separated instrument, its position, length and distance from the canal orifice and the apical foramen, as well as the degree of curvature and the thickness of the root canal. A 10# file was placed in the root canal to establish the distance between the canal orifice and the separated instrument. The coronal portion of the canal was flared with Gates Glidden drills or ultrasonic tips under the DOM. Straight-line access was created to allow visualisation of the separated instrument. A tunnel was created around the coronal aspect of the separated instrument using ultrasonic tips, or by using the K files to bypass the fragment, and then the separated instrument was loosened and flushed out of the root canal. During the operation, cotton pellets were placed in the other canal orifices to prevent the separated instrument from flowing into those canals. If possible, an attempt was made to remove the separated instrument with the help of a Masserann trephine (Micro-Mega, Besancon, France), pliers (Hu-Friedy, Germany) or Hedstrøm files (21 mm/25 mm; MANI, INC) at all stages5., 6.. The definition of a successful treatment was that the fragment was completely removed. If the fragment was not removed or just a portion of the fragment was removed, the treatment was considered to have failed.
Missed canal
Radiographs taken from mesial and/or distal angles helped to determine if the canal that had been located was centred in the root, keeping in mind that an eccentrically located canal is highly suggestive of the presence of a further canal yet to be found7. In a few cases, CT images were used. Dentine covering an orifice was removed with an ultrasonic tip under the DOM. A DG-16 explorer or a Micro-Opener was used to locate and probe the canal orifice. When detecting root canal orifices under the DOM, two main features were very important for canal location. The first was the presence of a groove in the pulpal floor, serving as a map for canal location. Second, there was a colour difference between the dentine of the pulpal floor and calcified dentine that was around the canal orifices8. If the missed canal was located and was negotiated, the treatment was considered to have been a success otherwise the treatment was considered to have failed.
Perforation
Radiographs and an electronic apex locator (Raypex 5; VDW GmbH) were used to detect root perforations9. The margin of the perforation was trimmed with a small round bur or an ultrasonic tip under the DOM. Paper points (DAYADING, Beijing, China) were used for haemorrhage control. Coronal perforations may be repaired with glass ionomer cement (3M ESPE, USA) or amalgam (AT&M Biomaterials Co., LTD, Beijing, China) with minimal tamping action in a perfectly dry field. The middle and apical perforations were repaired with mineral trioxide aggregate (MTA; Dentsply, DeTrey GmbH, Germany). The MTA was placed in the perforation with an MTA Gun System (Densply Maillefer) and compacted with Schilder pluggers (Hu Friedy, Chicago, IL, USA). A cotton pellet moistened with saline was placed in the perforation against the MTA. The definition of a successful treatment was that the perforation was repaired and the root canal therapy was completed, otherwise the treatment was considered to have failed.
The successfully treated teeth and canals were recorded, and the success rate was calculated. Statistical analysis was not performed, because results of this study were not being directly compared with a similar previous or concurrent study.
RESULTS
A total of 345 teeth with 546 root canals received treatment; 406 canals were successfully managed (74.4%), 246 teeth were successfully managed (71.3%). The rates in each category of the complicated root canals were: 74.0% for calcified canals, 72.3% for canals blocked by broken instruments, 82.5% for missed canals and 72.7% for canal perforations (Table 1, Figure 1., Figure 2., Figure 3., Figure 4.). No severe complications occurred during the treatments.
Table 1.
The therapy results of the teeth and root canals under a DOM (%)
| Type | Teeth | Root canals | |||
|---|---|---|---|---|---|
| Coronal | Middle | Apical | Total | ||
| Calcification | 155/231 (67.1) | 130/148 (87.8) | 143/196 (73.0) | 37/75 (49.3) | 310/419 (74.0) |
| Separated instruments | 50/64 (78.1) | 10/10 (100) | 30/38 (78.9) | 7/17 (41.2) | 47/65 (72.3) |
| Missed canal | 25/29 (86.2) | 27/32 (84.4) | 6/8 (75.0) | 0 (0) | 33/40 (82.5) |
| Perforation | 16/21 (76.2) | 13/16 (81.3) | 3/6 (50.0) | 0/3 (0) | 16/22 (72.7) |
| Total | 246/345 (71.3) | 406/546 (74.4) | |||
a/b: a, the successful therapy of the teeth or canals; b, all of the teeth or canals which need treatment.
Figure 1.
(1) Pre-operative radiograph. Calcification in the coronal third of the distolingual canal of the mandibular first molar (arrow) and periapical radiolucencies. (2) Working radiograph. The calcification of the canal was negotiated. (3) Postoperative radiograph. Obturated tooth with laterally condensed gutta-percha. (4) Eight months recall showing good healing.
Figure 2.
(1) Pre-operative radiograph. A separated instrument in the middle third of the mesiolingual canal of tooth number 25 (arrow). Distal canal is blocked by gutta-percha. (2) The radiograph showing that the fragment has been removed. (3) Postoperative radiograph. Obturated tooth with laterally condensed gutta-percha.
Figure 3.
(1) Pre-operative radiograph. Bifurcation (arrows) of the root canal in a mandibular first premolar. (2) Instruments in place demonstrating the number of canals. Three completely separated mesiobuccal and distobuccal and lingual canals. (3) Working length film. (4) Postoperative radiograph. Canal filled with gutta-percha by lateral and vertical condensation.
Figure 4.
(1) Pre-operative radiograph. Perforation occurred during post (arrow). (2) Post-operative radiograph. MTA has been positioned at the perforation. A plastic post and a temporary crown have been placed.
DISCUSSION
The DOM gives intimate detail of the operation area that otherwise would be under-illuminated and under-magnified, or would which would require guesswork with accompanying risks. With the help of the DOM complicated root canal therapy becomes easy.
Canal calcification was the most common reason for the need for complicated root canal therapy. In this study, 231 teeth with 419 root canals were calcified (Table 1); the majority, 344 (82.1%) of calcified canals had calcification in the coronal and middle two-thirds. Of these, 79.4% (273/344) were successfully negotiated. However, in comparison, only 49.3% (37/75) of such canals with calcification in the apical third were successfully negotiated, indicating that the nearer to the apex the calcification occurs the more difficult it is to negotiate. The location of the calcified canal orifice and the identification of the colour of the normal chamber floor and calcified dentine under the DOM were key aspects in the treatment10., 11.. One of the dangers in searching for calcified canals is the possibility of perforation and so the direction of the ultrasonic tips should be adjusted accurately according to the radiographs. Another risk factor may be that vital pulp remains under the calcification, which may mislead the clinician.
Instrument separation during treatment often leads to considerable anxiety, even inducing conflicts between the clinician and patient. The removal of separated instruments from root canals can be difficult and time-consuming, with a reported success rate ranging from 55 to 79%12. The ultrasonic technique, in conjunction with magnification and illumination, is usually the first option in such cases13. The advantage of an ultrasonic instrument is that it has the ability to vibrate the obstruction loose while causing minimal damage to the canal wall14. In this study, 47 separated instruments were removed from root canals, with a success rate of 72.3% (Table 1); all of the removed fragments were stainless steel instruments. Of the 18 irremovable separated instruments, 12 were in the apical one-third of the canals, indicating that the nearer to the apex the more difficult it is to be removed. Of the 18 irremovable separated instruments, 10 fragments were NiTi instruments, indicating that the removal of fractured NiTi instruments (ProTaper, Dentsply Maillefer, Ballaigues, Switzerland) may be more difficult compared with stainless steel instruments6.
It should be remembered that root canal perforations can occur during attempts to remove separated instruments5, especially when fragments are located at and beyond the canal curvature. The next risk factor is that when ultrasonic vibration is used in an attempt to loosen the fractured instrument from the root canal, the instruments have a greater tendency to fracture repeatedly. The third risk factor is that if the separated instrument is in the apical third of the canal, there is a possibility of extruding the instrument through the apical foramen. Finally, when the fragment is loosened from the root canal, it may flow into the other canals.
If a canal is not detected, it cannot be cleaned and filled and is a potential cause of failure for the endodontic therapy15. The DOM allows better visualisation of the working field, ensuring that the anatomy of the tooth is more readily inspected. The dentine coverage can be removed precisely with an ultrasonic instrument16. This greatly enhances the clinician’s ability to locate extra root canals and therefore increase the likelihood of a successful outcome8., 17.. In this study, 40 root canal orifices were not detected with the naked eye whereas with the help of the DOM, 33 of those root canal orifices were detected successfully with a success rate of 82.5% (Table 1).
The second mesiobuccal canal (MB2) of maxillary molars and the distolingual canal of the mandibular first molars were detected easily. In this group, eight canal orifices were in the middle of the canals, and all of the teeth were mandibular premolars. The canal orifices of the multiple canal mandibular premolars were difficult to detect. Radiographs taken from mesial and/or distal angles help to determine missed canals. The clinician should master root canal morphology and potential variations and know the common missed canals, such as the MB2 of maxillary molars, the distolingual canal of the mandibular first molars, the lingual canal of mandibular anterior teeth and the multiple canals of mandibular premolars.
Root perforation is a procedural error that can have a profound effect on the prognosis of treatment18. It has been claimed that non-surgical treatment of perforation is limited because of the difficulty in determining the location of the perforation, its shape and size in addition to the lack of a matrix against which the sealing material can be packed without excess spreading into the periradicular tissues. The DOM is a helpful tool effective in detecting root perforations during orthograde root canal therapy and in surgical endodontic treatments. High magnification with coaxial illumination allows precise detection and visualisation of perforations along straight, non-curved root canals19. The selection of material used in perforation repair must be related to the type of perforation. Mineral trioxide aggregate (MTA) is proving to be an impressive material for both root-end filling and perforation repairs. Main et al.20 evaluated the success rate of root perforation repairs using MTA and concluded that MTA provided an effective seal for root perforations and showed promise in improving the prognosis of perforated teeth that would otherwise be compromised. In this study the coronal perforations were repaired with a good success rate (81.3%, Table 1). However, none of the apical perforations were repaired (0/3, Table 1) due to the difficulty of operation. The apical perforations were treated as new foramen according to routine endodontic principles and sealed with root canal filling materials.
Root canal perforations can occur at any time during therapy. Sudden bleeding and pain during instrumentation or post preparations in teeth are warning signals of a potential root perforation. The accurate detection of root perforations and determination of location are crucial to the treatment outcome. Radiographs taken at different angles with radio-opaque instruments or material (such as K file, Vitapex) in the root canal are the better options and may confirm the presence of a root perforation. Electronic apex locators can accurately determine the location of root perforations, making them significantly more reliable than radiographs9. Fresh perforations that occur during either operative or endodontic procedures are followed by haemorrhage. The first step is to control the haemorrhage by pressure or irrigation. An old perforation perhaps follows infection but the control the infection is a tough problem. Finally, the selection of material is a key aspect. The operation under the DOM should ensure that the material is not pushed into the periodontal tissues.
CONCLUSIONS
The clinical application of the DOM is an effective way to manage complicated root canal therapy and, in conjunction with ultrasonic instruments in clinical practice, the following guidelines are highly recommended:
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The clinician should participate in advanced training programmes and gain considerable experience in operating the DOM and the ultrasonic instruments skilfully to master root canal morphology and potential variation of the teeth, employing great patience.
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Not all cases are suitable to receive therapy under the DOM with ultrasonic instruments. The clinician should select cases in which patients are likely to be compliant and in which medical history is not a contraindication.
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The pre-operative radiographs should be analysed carefully. The location of the calcified canal orifice and the identification of the colour of the normal chamber floor and the calcified dentine under the DOM are the first key aspects. The coronal portion of the canal flared enough to create a straight line access is another key aspect.
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•
Working radiographs and CT images are very useful in helping to accurately adjust the direction of the ultrasonic instruments. In this study, a technique using ultrasonic tips to create a staging platform was consistently successful when part of the fractured instrument was located in the straight portion of the canal. The files should be combined with EDTA when negotiating the blocked canals. The key to repairing perforations is accurate detection and control of haemorrhage.
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•
If the therapy is not successful it is worth pausing the operation and resuming it at a later stage using a new approach.
Acknowledgements
We wish to thank Mrs Jingjing Ran for assisting with the English in the preparation of this paper.
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