Get smart – technological innovations in endodontics. Part 1: 3D imaging, 3D treatment planning and guided endodontics

3D radiographic imaging

Dental radiography, commonly in the form of peri-apical and dental panoramic radiographs, has limitations, such as anatomical noise from superimposition of orofacial structures, compression of three-dimensional (3D) objects into a two-dimensional (2D) image, and geometric distortion due to variation in angulation and position of films/sensors.20 Thus, small lesions, confined to cancellous bone and hidden by the overlying cortical plate, may escape detection.20^,21^,22

Cone beam computed tomography (CBCT), a relatively new digital imaging modality, may be used to overcome these limitations by providing 3D imaging across multiple planes.20^,22 Several studies have highlighted the accuracy and sensitivity of CBCT compared with 2D radiography at detecting endodontic disease.20^,22^,23^,24^,25^,26 CBCT, by providing visual guidance in 3D, has enhanced the understanding and interpretation of complex anatomical structures, benefiting diagnosis and treatment planning.20^,22^,26^,27^,28^,29^,30^,31

Various guidelines have been published to assist clinicians in case selection and to promote the safe use of CBCT in endodontics.32^,33^,34^,35^,36

CBCT should always be used on a case-by-case basis, justified, and the potential benefits should outweigh the risks.33^,34^,36^,37 When a CBCT scan is prescribed, the radiation dose should be kept ‘as low as reasonably achievable (ALARA)’ by limiting the field of view, adjusting the voxel size, current, and exposure time, allowing a pulsed and restricted arc of exposure.33^,34^,36

While there are significant advantages with 3D imaging, it is the use and application of the data, for example 3D treatment planning and guided endodontics (see later), that make this technological innovation a game changer in patient management. As the source of 3D imaging data, CBCT scans underpin the accuracy and function of secondary devices or software that may be used for planning and/or performing treatment. These volumetric data exist in a Digital Imaging and Communications in Medicine (DICOM) format to facilitate exchange between the different manufacturers and platforms.38

3D treatment planning

3D virtual planning software, such as SICAT Endo (Dentsply Sirona, Salzburg, Austria), have been specifically designed for the assessment of root canal anatomy and pre-operative root canal working length determination. Relying on data from CBCT scans, the precursor software 3D Endo (Dentsply Sirona) is able to accurately determine the working length of root canals by tracing and computing the measurement in 3D, thereby accounting for canal curvatures and complexities.39 Data from 3D radiographic imaging processed by 3D planning software can assist clinicians in treatment planning, for example in complex cases requiring endodontic treatment, through identification of root canal anatomy and determination of root canal working lengths.20^,31 A study demonstrated the usefulness of 3D planning software and CBCT for the evaluation of the root canal anatomy and working length determination.31 The use of these digital technologies was reported to reduce stress levels for operators during treatment.31 Another study compared the accuracy between root canal working length readings measured using 3D Endo (Dentsply Sirona) software, pre-operatively, and an electronic apex locator, intra-operatively, in human extracted single-rooted teeth.40 This study found no statistical difference between the measurements and suggested that, for cases with a pre-operative CBCT scan available, 3D Endo software could be used to accurately determine the working length of root canals.40

An earlier study by Segato et al41 supported the combined use of measurements from 3D Endo (Dentsply Sirona) software and electronic apex locators for accurate determination of the root canal terminus. Further research is required involving multi-rooted teeth and different CBCT image settings that may influence the accuracy of these measurements. In the future, incorporation of artificial intelligence (see Part 2) software may permit automated detection of features pertinent to treatment planning and management, such as the presence of untreated or additional canals, pre-operative working length, apical size diameter, and apical pathosis.

Matched data from CBCT scans and optical (intra-oral/plaster model) scans can also be used with implant planning software, for example, coDiagnostiX (Dental Wings Inc, Montreal, Canada) for treatment planning and to help clinicians visualize root canal treatment complexities (Figure 1). 3D planning software, depending on equipment and treatment option chosen, can subsequently be used in guided endodontics (see later) for designing 3D printed guides for static guidance, or set parameters for dynamic guidance.

Guided endodontics

During non-surgical root canal treatment, the access cavity should be prepared according to access requirements while avoiding unnecessary and destructive tooth tissue removal.42 The advent of the ‘minimally invasive endodontics’,43^,44 in line with the ‘minimal invasive dentistry’ concept, means that access cavities should be kept as conservative as possible. Instead of the traditional endodontic cavity, conservative/contracted endodontic cavity and ultraconservative ‘ninja’ endodontic cavities have been advocated.45 However, there are a number of clinical scenarios that hamper the desire to be conservative. For example, in order to locate the root canal system of teeth with a calcified root canal system (pulp canal obliteration), dens invaginatus or dilacerated roots,46^,47^,48 increasing amounts of tooth tissue may need to be removed, compromising structural integrity, risking perforation and a negative treatment outcome.49 Thus, any strategy or technique that allows for the preparation of minimal access cavities, preserving tooth structural integrity with reduced risk of procedural errors and still meets ideal shaping and preparation objectives50 would be extremely beneficial. Similarly, for apical surgery, where access to the root-end is constrained due to tooth position, a thick cortical bone plate, and/or close proximity to critical anatomical structures, any method or technique that permits minimally invasive osteotomies, safe removal of lesions and accurate resection of root-ends would be equally helpful.

In dental implant surgery, the use of some form of guidance system, to ensure placement at the desired location, depth and angulation, has been an area of interest for some time. The advent of 3D imaging has led to the development of techniques to improve the accuracy of dental implant surgery by using guidance based on CBCT-acquired data. The guided implant placement concept has been adopted and adapted to endodontics. Guided endodontics mean that challenging cases requiring endodontic treatment may be managed with greater accuracy, reduced risk of procedural errors and iatrogenic injuries. Guided endodontics relies on careful pre-operative treatment planning software and matched data acquired from CBCT and optical scans, and depending on the treatment modality, may be classified as static or dynamic.

Static guidance

Static guidance refers to use of a removable stent (Figure 2), for example fabricated using 3D printing involving computer-aided design/computer-assisted manufacture (CAD/CAM) and additive manufacturing techniques, based on the matched data from pre-operative CBCT and optical scans. 3D printed stents, designed on 3D planning software, may be tooth-, mucosa-or bone-supported, and encode the depth and angulation required to accurately perform treatment procedures.

Several case reports and studies have been published documenting the transfer of 3D imaging data to implant planning software and 3D printers for the design and production of printed stents in endodontic treatment.47^,48^,51^,52^,53^,54^,55^,56^,57^,58 The use of guidance stents has been reported to be minimally invasive, reducing operating time, allowing greater accuracy, better patient comfort and facilitating operator skill development. Thus, challenging endodontic cases where there is increased risk of procedural errors may be treated safely without compromising outcome. However, the use of 3D printed stents has several drawbacks that limit its wider adoption. These include additional treatment planning time, production cost of the stents, access difficulties for patients with limited mouth opening and in the molar tooth regions.59^,60 Most importantly, unchangeable (static) operational parameters, such as angle and size of guide sleeves, may afford no or very limited leeway for intra-operative corrections and the requirement for multiple stents for each canal in a multi-rooted tooth (Figure 2).56^,59^,61^,62

Dynamic navigation

Dynamic guidance, based on computer-aided surgical navigation technology and analogous to global positioning systems or satellite navigation, has been used in an attempt to overcome the limitations of static guidance in dental implant surgery. Dynamic guidance uses matched 3D imaging data to provide real-time visual feedback to the operator with the help of optical motion tracking cameras. Chong et al59 demonstrated the potential of Navident (ClaroNav Technology Inc, Toronto, Canada), a dynamic guidance system designed for implant placement, in non-surgical root canal treatment for minimally invasive access cavity preparation and canal location (Figure 3). Recent case reports documented the application of dynamic guidance in facilitating precise performance of a minimally invasive osteotomy and root-end resection during apical surgery,63 and conservative access cavity preparation, with canal location, during non-surgical root canal treatment.64

Unlike static guidance, dynamic guidance relies on meticulous treatment planning and there are still, albeit lower, cost and time considerations. Although proof-of-concept has been demonstrated63 there are a number of issues to consider before the technology can be fully used in everyday endodontic practice. The treatment planned virtually has to be transferred to the actual patient; visualization and real-time guidance of the treatment plan and real-time monitoring of procedural steps are still displayed on 2D computer monitors. Therefore, having to concentrate on the 2D display monitor forces the clinician to look away from the patient and even from their own hands, contrary to normal in which the operator directly faces the patient. Apart from being unnatural, this working position hampers hand-eye co-ordination; it is also inefficient and risks mishaps. A possible solution to this problem may be the use of augmented or mixed reality (see Part 2) to complement dynamic guidance.

Conclusions

Technological developments, such as 3D imaging, 3D treatment planning and guided endodontics, may help manage complex endodontic cases and can play an important role in dental education.