Dynamic navigation—The future of minimally invasive endodontics
Dynamic real-time surgical navigation digital imaging, diagnostics and impressions, and the use of computer-aided design/computer-aided manufacture (CAD/CAM) for prosthesis fabrication and lasers for soft and hard tissue augmentation are altering the developmental framework in dentistry. Nowhere is this more prevalent than in the foundational pillar of endodontics.
The magnification and illumination properties of surgical operating microscopes enhance the accuracy of freehand navigation access cavity preparation and microsurgical osteotomy. This has engendered a transformational shift to conservative, more restricted endodontic access cavity preparation.  This preserves coronal and radicular tooth structure by optimising the long-axis entry point, the drill angulation and the glide path to the terminus of the root canal space.
In spite of these advances, there are limitations in endodontic clinical scenarios where canals sclerotically regress in a coronal-apical direction and surgical access is space restricted. While the clinician’s experience is a positive factor, altered vertical and lateral angulation of the long-axis orientation of the endodontic access cavity presents iatrogenic risk. In endodontic microsurgery, a small bone volume or a misdirected osteotomy can injure the inferior alveolar nerve or perforate the maxillary sinus and other critical anatomical structures. [7, 8]
The advent of cone beam computed tomography (CBCT—DICOM files) and 3D printing has transformed pretreatment planning. DICOM files are converted into stereolithic files, which are used to create static navigation stents (CAD/CAM-fabricated). The stents direct the access cavity preparation and microsurgical orientation, thus avoiding removal of unnecessary tooth and bone structure (Figs. 1a & b).
Dynamic navigation offers new prospects for computerguided endodontic protocols. Enhanced accuracy owing to real-time feedback diminishes the complex impact of access cavity preparation of calcified canals, retreatment and microsurgical procedures. [9–11]
Each navigation protocol has disadvantages. With freehand navigation used for dentoosseous access and surgery, clinical judgement is the pilot. Freehand navigation depends upon visualisation of the anatomical scenario from information provided by casts and radiographs. Significantly more time is required with a freehand navigation technique in contrast to a guided technique. Determining the canal path position is more complex.
Stereolithic stents (static navigation) require a medium field of view CBCT scan. Polyvinylsiloxane impressions of the arch to be treated are poured and a digital 3D scan of the stone model merged with the patient’s DICOM files. The use of an intra-oral scanner is preferable.
In the case of dynamic navigation, virtual planning of the endodontic access preparation or the osteotomy can be affected by the resolution of the CBCT scan. Flaws in the process of fiducial integrated stent fabrication can result in inaccurate image acquisition.
Dynamic navigation facilitates real-time computer guidance technology using an imported CBCT data set. This is analogous to the use of GPS and satellite navigation. An innovative computer-guided technology, Trace and Place (TaP), has been developed by the Canadian company ClaroNav. TaP obviates the need for a fiducial stent, with the resultant increase in the accuracy of dentoosseous penetration. An optical tracking device (Fig. 2) tracks a Jaw-Tracker, the optical tracking tag connected to the patient’s jaw, and a Drill-Tag, which is the optical tracking tag connected to an instrument specific to the procedure. The tip is super imposed on the CBCT scan, which is mapped to the patient’s jaw.
The heightened level of accuracy of TaP technology enhances the facility of treatment for restricted access cavity preparation and minimises the size of cortical window osteotomies (high-speed; Piezotome, ACTEON). Ultrasonic tips used for root end retro-preparation can also be tracked by dynamic navigation software.
TaP workflow planning and trace registration
Estimates place the global population over 65 at 615 million. 13 Years of dentate and periodontal disease can impact on the pulp, the periapex and the periradicular tissues. With longevity will come increasing numbers of a mosaic of endodontic procedures, as age and treatment induce sclerotic changes in the root canal space. As such, the use of dynamic navigation will prove to be of significance in a myriad of endodontic treatment protocols.
Prior to the appointment
The first stage of TaP workflow is the importation of the patient’s CBCT data set (as DICOM file) into the dynamic navigation planning software to reveal the dentition. The screen shows the streaming video, panoramic view, target view, depth indicator, and buccolingual and mesiodistal section views (Fig. 3). The access point of entry, the axis orientation/angulation and the depth of the access cavity are planned. For microsurgical procedures, the Piezotome pathway is based on the dimensions of the osseous pathology surrounding the root apex (Figs. 4a–c). The planning stage can be done at any time prior to the procedure, provided the CBCT scan is consistent with the current dentate condition. As a preliminary step prior to the trace registration, three to six trace starting points (landmarks) are chosen and marked on visible and accessible teeth. When the computer mouse is positioned over the 3D model, a 2D cross-sectional view appears. The red crosshair sticks to the landmark, its centre on the surface (Fig. 5). The software advises the clinician if it suspects that the landmark is in an incorrect position.
The Jaw-Tracker (mandible or maxilla) or Head-Tracker (maxilla) is securely fastened to the jaw to be treated (Fig. 6). It should be noted that the Jaw-Tracker can be positioned at a distance from the rubber dam, unlike a Jaw-Tracker attached to a fiducial stent, which is more positionally restricted. Once the three landmarks have been determined, the optical tracking sensor tracks the Tracer- Tag/ Tracer- Tool as it is brushed around the landmarks on the facial, lingual and occlusal surfaces in a manner similar to applying etching or bonding solutions. The software shows the number of points contacted as a percentage (Fig. 7).
Calibration of the drill
The Drill-Tag is attached to the handpiece, and the drill axis and drill tip are calibrated. The optical tracking sensor continuously tracks the Drill-Tag, and the software shows the position of the drill or Piezotome. The software will issue a warning if the Drill-Tag or the Jaw-Tracker is out of view of the camera (Figs. 8a & b).
Dentoosseous real-time navigation
The navigation screen is active when the system identifies the calibrated instrument as it approaches the patient’s jaw. The target view measures the distance between the instrument’s tip and central axis of the designated access penetration point, the glide path or the osteotomy. The central axis length of the planned procedure is represented by the centre of the static white target, and the tip of the drill is in dicated by the moving black cross following the drill tip movement. The real-time direction of the drill is represented as a cone in the head of the handpiece (Figs. 9a & b).
During the drilling, the moving cross and cone are tracked. The cone will turn green when the instrument tip is within 0.5 mm and has an angulation of less than 3° to the planned glide path or osteotomy. When the drill tip reaches a distance of 1 mm from the apical or horizontal extent of the planned depth landmark, the depth indicator turns yellow.
Dynamic navigation is an additional value chain in digital workflow sequencing. Minimally invasive protocols are the trajectory of dentistry’s future. Dynamic navigation is proving to be both the pilot and co-pilot of this new milestone in patient-centric care. All innovation requires seminal exploration of both the incentives for and barriers against prior to acceptance of a new technology as a contributing protocol. Early adoption is osmotic: general acceptance occurs by diffusion. Improvements in the resolution of computer screens, optical markers and the reference array will herald an unprecedented level of accuracy in endodontic procedures. Digital has replaced analogue as the societal norm. The transition in the dental profession is in process.
Editorial note: A list of references is available from the publisher. This article was published in roots—international magazine of endodontics Vol. 15, Issue 3/2019.