Dynamic Navigation in Endodontics

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In many different areas of dentistry, there is an increasing tendency of using computer-controlled, navigated surgical and therapeutic methods in the daily routine. The technology originating from implantology has reached other areas of dentistry, particularly, endodontics. Its potential uses include endodontic procedures such as bone trephination, root end resection and root canal localization.

For guided approaches in dentistry, basically there are two types of management options called static and dynamic navigation. During intervention, static navigation uses a surgical template generated by preoperative CBCT imaging, computer-guided design, and 3d printing or CAD-CAM. The disadvantage of this method is that after the fabrication of the template, the angle, size, and depth cannot be modified. Other potential problems include fabrication-related costs and time factor consisting of time consumed for fabrication and design.

Dynamic navigation shows real-time positioning of drills or instruments on preoperative CBCT data. In this construction, positions and locations can be designed and correlated with reference points with the help of computer programs and preoperative CBCT data. In this improved setup, an optical motion tracking system provides feedback during surgery, and therefore the designed information is linked to the real clinical situation and the equipments used for the intervention. In summary, it facilitates the traceability of instrument position.

According to some publications, this method reduces the number of surgery-related errors and, considering the outcome of interventions, it is more accurate than manual (or freehand) placement. Based on the observations of Bun San Chong et al., the critical points of implantat surgery, such as injury of critical anatomical structures (e.g., nerve canal, position of the adjacent tooth), can be minimised. This method also provides flexibility for the person performing the surgery, as in case of unexpected need of modifications, these can be done any time during the intervention. 

Components of Dynamic Navigation System (DNS):

The basic components of any dynamic navigation systems are as follows: 

• Handpiece attachment or drill-tag (Fig 1)
• Patient jaw attachment or jaw-tag (Fig 2)
• The system cart (Fig 3), which consists of the cameras, a computer with a navigation software

Workflow of Dynamic Navigation:

To guide the drilling, navigation system must precisely map the drill tip to the CT image of the jaw used for planning the implantation. Sensors are attached on the body of the handpiece and the extraoral clip attached to the fiducial markers. It achieves this in three steps (Fig 4), performed in the following order: 

1. Trace Registration: CBCT images are matched with the teeth, through the Jaw Tracker or Head Tracker mounted on the patient, by registering the CBCT scan to the teeth and/or bone. For trace registration, a calibrated tracer (like a stylus pen or ball burnisher) tracked by the Micron Tracker camera is slid along the tooth surface, in brushing motion, while the system samples point along its path. The collected “cloud of points” is then automatically matched in the best possible way with the outer surface of the teeth in the CBCT scan. Minimum 3 and maximum 6 teeth can be traced for better accuracy. An accuracy check should be performed in all 3 directions (anteroposterior, laterolateral, and occlusogingival) to verify registration accuracy in all 3 axes. 
2. Calibration: Mapping the drill tip to the DrillTag. The drilling axis calibration is done once, prior to the start of the operation by placing the handpiece chuck over a pin in the JawTag. After each drill change, the drill tip location is calibrated by touching a dimple on the calibrator. 
3. Tracking: Mapping the DrillTag (Handpiece attachment) to the JawTag (Jaw attachement). This is dynamic and is done throughout the operation by the optical tracking system. Continuous tracking is very important to achieve planned treatment outcomes. Tracking camera should be placed at position to provide broad operating field view during the treatment. Extension arm of navigation device may help to achieve broad view of operating field.

Dynamic navigation in Non-surgical Endodontics

Nonsurgical endodontic treatments have several rules for correct implementation. In line with modern endodontic requirements, it should be kept in mind in every situation that during an intervention, as little as possible tooth material should be sacrificed. This is also called minimally invasive approach. The borders of the cavity as well as the access opening and orifice should be prepared with the most conservative method. Unfortunately, in real clinical situations, the person performing the surgery has to deal with several problems. Often removal of excessive tooth material is required for successful exploration of a severely stenotic, calcified canal. However, this significantly weakens tooth tissue, threatens structural integrity, and carries the risk of perforation. 

Therefore in everyday practice, each effort which facilitates the work of the person performing the surgery (i.e., makes preparation of a small cavity possible) decreases iatrogenic harm, preserves structural integrity, while at the same time meets all the expected access requirements. 

To date, endodontics preferred static navigation. Relatively few publications are available concerning dynamic navigation. Bun San Chong et al. evaluated the use of dynamic navigation. They examined extracted teeth with intact crown and root. Metal restorations appearing as artefacts on the images were removed and replaced by glasionomer cement. After proper preparation (simulation of canal calcification), periapical Xray examination and CBCT were performed and integrated into the selected navigation program. After proper planning, intervention was done with the help of navigation. 

After the intervention, results made the preparation of a minimally invasive cavity possible, the risk of canal perforation decreased, therefore those teeth which were difficult to treat could be conserved. The disadvantages of the system are well-represented by the fact that due to the need for more CBCT imaging, single-use devices and expensive other materials are used. 

In another case report, intraoperative navigation used in neurosurgery was administered for the removal of a broken endodontic instrument. In this case, navigation significantly helped the person performing the surgery to find and remove the fragment.

Step-by-Step Workflow 

1. Take a CBCT scan of the entire arch with high resolution and small field of view (FOV). Import scan data to dynamic navigation system. 
2. Plan endodontic treatment on CBCT file in the dynamic navigation software. Plan virtual drill path for non surgical treatment. Keep diameter of vitual path as minimal as possible (not more than 1.0 mm). For endodontic microsurgery, plan ostoeomy site and size. Level and angulation of root end resection can also be planned, simultaneously. 
3. Install the patient tracker (JawTracker or HeadTracker). It should be placed within range of camera tracking system. Endodontic microscope should be used carefully to avoid any errors during use of dynamic navigation. 
4. Register the CBCT scan to the patient using Trace registration in one of the following ways: (i) Tracing directly on the CBCT scan, (ii) Using an intra-oral scan superimposed or matched with the CBCT scan, (iii) Using the NaviBite (when the tooth and its neighbouring teeth have full coverage metallic restorations). 
5. The patient tracker (JawTracker) placement and tracing should be completed prior to placement of the rubber dam. Rubber dam isolation should be performed and rubber dam and clamp should not exert any force on the patient tracker. 
6. Calibrate handpiece (slow-speed, high-speed or piezoelectric handpiece) and bur (drill) with calibrator. Registration accuracy should be evaluated before drilling. (Fig 5,6)
7. During drilling, follow the planned path and complete the treatment. If multiple drills have to be used, calibrate each drill before using it intraorally and perform accuracy check everytime. 
8. For endodontic microsurgery, similar tracing and calibration has to be performed. Calibrate bone saw before use and also calibrate its dimensions for better accuracy. Usually, osteotomy and root-end resection are performed simultaneously with a precise bone saw cut. If accuracy check results are poor, re-trace the CBCT and perform the treatment.

Dynamic navigation in endodontic surgery 

Dynamic navigation contributes to continuous development in the field of endodontic surgery. To date, only one case report is available in the literature, where Navident dynamic navigation system was used. In this case, dynamic navigation system made exact root apex localization and accurate apicoectomy possible in a minimally invasive manner. Improvement of targeted surgical navigation systems facilitates surgical maneuvers and decreases the risk of iatrogenic harm. 

Gambarini et al. presented dynamic navigation through the surgery of a 34year-old patient. The patient refused removal of a crown on tooth 12. His tooth was sensitive to percussion, and periapical rarefaction was seen. His treating physicians decided to perform root-end resection. CBCT image made the accurate, step-by-step planning of the surgical intervention possible. The big advantage of the system is that during the operation, steps can be modified. The person performing the surgery can accurately check and correct any errors on the spot, since the instruments are calibrated and strictly observed during surgery. One of the challenges of root-end resection is to distinguish root apex from the surrounding bone. With the help of navigation, this problem can easily be solved with minimum invasivity. Another benefit of microsurgery is the minimization and eventual elimination of inclination. 

In summary, endodontic surgical interventions performed with dynamic navigation are very forward-looking, as several sources of error such as nonminimally invasive intervention, inaccuracy of localization, and injury of critical anatomical structures can be eliminated. In addition to advance planning, errors detected during surgery can immediately be addressed. The posture of the person performing the surgery also improves as he/she clinician concentrates on the display, and the learning curve is fast.^,6

References

1. Block MS, Emery RW, Cullum DR, Sheikh A. Implant Placement Is More Accurate Using Dynamic Navigation. J Oral Maxillofac Surg. 2017 Jul;75(7):1377-1386.
2. Chong BS, Dhesi M, Makdissi J. Computer-aided dynamic navigation: a novel method for guided endodontics. Quintessence Int. 2019;50(3):196-202.
3. Chong BS, Dhesi M, Makdissi J. Computer-aided dynamic navigation: a novel method for guided endodontics. Quintessence Int. 2019;50(3):196-202.
4. Sukegawa S, Kanno T, Shibata A, Matsumoto K, Sukegawa-Takahashi Y, Sakaida K, Furuki Y. Use of an intraoperative navigation system for retrieving a broken dental instrument in the mandible: a case report. J Med Case Rep. 2017 Jan 15;11(1):14.
5. Gambarini G, Galli M, Stefanelli LV, Di Nardo D, Morese A, Seracchiani M, De Angelis F, Di Carlo S, Testarelli L. Endodontic Microsurgery Using Dynamic Navigation System: A Case Report. J Endod. 2019 Sep 9. pii: S0099-2399(19)30544-8. doi: 10.1016/j.joen.2019.07.010. [Epub ahead of print]
6. Kinariwala, N., Antal, M.A., Kiscsatári, R. (2021). Dynamic Navigation in Endodontics. In: Kinariwala, N., Samaranayake, L. (eds) Guided Endodontics . Springer, Cham. https://doi.org/10.1007/978-3-030-55281-7_9