The Role of CBCT and Guided Endodontics in Accessing a Calcified Maxillary Molar Using Computer Assisted Dynamic Navigation: A Case Report

Paula Andrea Villa-Machado, DDS; Julián González-García, DDS; and Felipe Augusto Restrepo-Restrepo, DDS

ABSTRACT

Background: Endodontic treatment is a major challenge when the root canals are partially obliterated. This can occur as a result of multiple causes that stimulate pulp canal obliteration (PCO) such as physiological processes, caries, extensive restorations, coronal wear or dental trauma.

Case description: Static-guided endodontic techniques have been reported as helpful in such cases, however, the interocclusal space required for the use of templates may contraindicate the use of this technique in posterior teeth. Dynamic navigation permits the trajectory of the instruments to be tracked in real time, allowing computer-guided endodontic accesses to be executed without the need for templates that may require wider interocclusal space, which can be beneficial for the treatment of posterior teeth.

Practical implications: This article reports a case in which the distobuccal canal of a maxillary second molar, which was obliterated up to the middle third of the root, was precisely and conservatively located with dynamic navigation.

Keywords: Cone beam computed tomography, guided endodontics, pulp canal obliteration, dynamic navigation

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AUTHORS

Paula Andrea Villa- Machado, DDS, is an associate professor of endodontics at the University of Antioquia in Medellín, Colombia. She is also a part of the POPCAD Research Group Laboratory of Immunodetection and Bioanalysis, Faculty of Dentistry, at the University of Antioquia in Medellín. Conflict of Interest Disclosure: Dr. Villa- Machado is a Navident key opinion leader.

Julián González-García, DDS, is an oral and maxillofacial radiologist with a private practice in Pachuca, Mexico. Conflict of Interest Disclosure: None reported.

Felipe Augusto Restrepo- Restrepo, DDS, is an associate professor of endodontics at the University of Antioquia in Medellín, Colombia. He is also a part of the POPCAD Research Group Laboratory of Immunodetection and Bioanalysis, Faculty of Dentistry, at the University of Antioquia in Medellín. Conflict of Interest Disclosure: None reported.

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Pulp canal obliteration (PCO) may be a consequence of physiological aging processes, dental pulp reactions to caries, dental wear, extensive restorations or dental trauma. [1,2] The endodontic treatment of these teeth is a great challenge. The use of 3D imaging with cone beam computed tomography (CBCT) is very helpful for the diagnosis and planning of the root canal treatment, and it has been indicated for the identification and location of obliterated canals. [3]

Computer-aided design (CAD) and computer-aided manufacturing (CAM) technologies enable the integration of tomographic images to design guides for endodontic access.

Guided endodontics has grown widely in recent years. It is suggested not only for the location of obliterated canals but also for the removal of fiber posts and some endodontic microsurgery cases. Its execution can be performed with static navigation. This implies obtaining the Digital Imaging and Communications in Medicine (DICOM) files from the CBCT and matching them with the Standard Tessellation Language files (.STL files) obtained from an intraoral scanner planning software. The guide can then be printed using a 3D printer. [4] Some limitations of this type of guide is its use in posterior teeth because sufficient interocclusal space is required for placement of the guide and the use of long drills in order to reach the canal. [5]

Computer-assisted dynamic navigation (C-AND) has been widely used to guide implant placement. C-AND tracks the instrument’s position in real time, and when integrated with the patient’s CBCT, allows real-time monitoring of the access path in the axial, sagittal and coronal space planes and grants to do the necessary corrections. It has recently been suggested as an aid to access narrow canals, resulting in less dentinal loss compared to freehand access, even with a tendency to be more accurate than static navigation. [6–8]

This system is composed of a laptop computer with the planning/guidance software, a MicronTracker stereoscopic camera and an LED light source that detect and track objects of interest. The objects are marked using small checkered target regions called Xpoints and must be attached to the handpiece (Drill Tag, Claron Technology, Toronto, Ontario) and to the patient’s jaw (head tracker for maxillary teeth and jaw tracker for mandibular teeth). Other system components are the tracer tool to register the CBCT scan to the patient and a unit to calibrate the location of the drills used during the clinical procedure (calibrator). [9]

When dynamic navigation is used, physical templates are not necessary, thus reducing the interocclusal space required to access with long instruments. This is an advantage when accessing posterior teeth. There is also the possibility to calibrate and use ultrasonic tips. [5]

This article describes a case in which the Navident dynamic navigation system was used to access the distobuccal (DB) canal of a partially obliterated maxillary second molar.

Case Report

A 58-year-old female was referred for root canal treatment of the maxillary left second molar with tenderness to percussion/palpation in the apical region, restored with a temporary crown. She had no underlying chronic medical illnesses or family history and was taking no medications. Preoperative CBCT images were obtained using a Veraview X800 Morita (Morita Corp., Tokyo) unit operated at 91.0 kVp, 7.9 mA, 40 x 40 mm of field vision, voxel size 80 μm and 17.9 seconds of exposure time examination, which revealed three roots and four canals with partial obliteration up to the root mid-third of the DB canal and periapical tissues of normal appearance.

A pulpal sensitivity test was done with a propane/butane spray (Endo-FROST, Coltene-Whaledent, Cuyahoga Falls, Ohio ) and cotton pellets with a negative response. A pretreatment diagnosis of pulpal necrosis with normal periapical tissues was made. Informed consent was obtained from the patient after the nature of the root canal treatment and possible discomforts and risks were fully explained.

Root Canal Treatment Protocol

Under local anesthesia with lidocaine 2% with epinephrine 1:80,000 (New Stetic, Guarne, Antioquia, Colombia) and rubber dam isolation of the tooth, endodontic treatment was performed using the following protocol:

Under an operating microscope (Zumax OMS3200, Zumax Medical, Suzhou New District, China), first the palatine, mesiobuccal and mesiobuccal 2 (MB2) canals were located and cleaned and shaped. The distobuccal canal was not found, and after an intraoperative CBCT (FIGURE 1), DICOM files were obtained and uploaded to the Navident planning software to map the dentition.

To create the virtual guide, a 1 mm diameter path indicator was placed over the tooth to the required length to reach the visible distal root canal, and its position was adjusted in the 3D (sagittal, coronal and axial) (FIGURE 2).

The head tracker was properly placed and secured on the patient’s head and the trace registration protocol was initiated in which a calibrated tracer tool is tracked by the MicronTracker camera while it is moved along the tooth surfaces. The system captures a cloud of points along this path to spatially orient the tool tag, therefore mapping the patient’s jaw to the CBCT scan. This tracing is finished by a full accuracy check performed by touching surfaces of the teeth with the tip of the tracer tool. Measurements from 0.0 mm to ± 0.03 mm allowed for verification of the accuracy of the trace in the three orthogonal planes (sagittal, coronal and axial).

Afterward, an optical tracking tag (Drill Tag) was attached to the highspeed handpiece and the selected drill as placed and calibrated to provide an optical triangulation tracking by the Micron Tracker stereoscopic camera. In this way, the Navident C-ADN system monitors in real time the deviation among the actual planned location and the trajectory of the drill tip as it penetrates through the tooth’s structure.

Once the planned length was reached, an endodontic K-File #0.8 (Dentsply- Maillefer, Ballaigues, Switzerland) was used to confirm the location and patency of the canal (FIGURE 3). From then on, the device was no longer needed and the root canal treatment was routinely performed, the working length was measured with an apex locator Root ZX II (J. Morita Manufacturing Corp., Kyoto, Japan) and the cleaning and shaping processes were performed with a HyFlex Controlled Memory (CM) system (Coltene- Whaledent) under abundant irrigation with 5.25% sodium hypochlorite. The root canal filling was completed with warm gutta-percha vertical compaction technique using AH Plus (Dentsply- Maillefer) as sealer material (FIGURE 4).

Discussion

Performing root canal treatment in teeth with PCO is considered a very complex treatment. 10 The endodontic access cavities must allow for complete location of the root canal system and direct access of the endodontic instruments to the root canal system, facilitate disinfection and complete debridement to avoid excessive loss of the dental structure. [11,12]

An alternative for root canal treatment in teeth with PCO may be endodontic microsurgery (EMS). Although the identification of the calcified root canal after apicoectomy and the retro preparation and disinfection of the contaminated apical canal might be challenging, EMS without a previously filled canal would not allow complete disinfection of the entire root canal system. [1,13] Due to the previous, the microsurgical approach was not considered as the first choice in the present report.

It has been suggested that C-ADN can be helpful to access narrow canals in a precise way, resulting in less tooth structure loss when compared to the freehand procedure and even more efficient and with greater precision than static guides that had showed evidence of unlocated canals in 8.3% of cases. [14] In addition, although it has been reported that the mean angular deviation associated with the use of static guides (10.04 degrees) is significantly higher than that of the dynamic navigation (5.58 degrees), 6 other authors have reported very low angular deviation (1.59 degrees) using printed templates. [15] A recent meta-analysis showed a high success rate (98.1%) locating the root canal using computer-assisted navigation techniques without statistically significant differences between static or dynamic computer-assisted navigation. Computerassisted static navigation techniques showed a slightly higher root canal location success rate (98.5%) than computer-assisted dynamic navigation techniques (94.5%). These results may be influenced by the small number of studies on the dynamic technique of computer-assisted navigation (two studies) with respect to the larger number of studies on the technique of static-assisted computer navigation (12 studies). [12]

Overall, both techniques are effective and better than the conventional freehand technique. [6,16] The advantages of C-ADN over static guides include fast planning using only CBCT images without the need for intraoral scanning or printed guides and the direction of the endodontic access cavity can be controlled, allowing for planning changes during in-office treatment. By contrast, some disadvantages of this technology are the cost of the equipment and a certain level of skill and experience required of the operator to maintain drilling from entry since it is difficult maintaining visibility of the system display when creating the endodontic access cavity. [6] However, augmented reality devices can reportedly be used to transfer over the virtual image displayed by the computer-aided dynamic navigation system while maintaining visibility of the therapeutic field. [17] In addition, virtual reality has been used to perform endodontic access cavities. 18

There have been a few case reports of guided accesses in molars, two with static guide techniques and one with C-ADN technique. The first one had enough interocclusal space to fit the template, the metallic sleeve and long drills. [10] The second one had a limited interocclusal space in which a modification of the technique using an intracoronal metallic pin was necessary to fit only the drill and succeed in the location of the canal. [19] The third one also had a limited interocclusal space in which they used a similar dynamic navigation system (X-guide) to locate the canal. 7 They all succeed in locating the canals in a predictable and safe way as in the presented case report.

Conclusion

C-ADN system Navident successfully locates the canals of PCO teeth in an accurate, safe, conservative and efficient way.

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THE CORRESPONDING AUTHOR, Paula Andrea Villa- Machado, DDS, can be reached at paula.villa@udeaedu.co.