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Medicine

Guided Endodontics: Three-Dimensional Planning and Template-Aided Preparation of Endodontic Access Cavities

Published: May 24, 2022 doi: 10.3791/63781
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1, 1, 1, 2, 3, 1
1Department of Periodontology, Endodontology and Cariology, University Center for Dental Medicine Basel UZB, University of Basel, 2Center for Dental Imaging, University Center for Dental Medicine, University of Basel, 3Department of Conservative Dentistry and Periodontology, University Hospital of Würzburg

Summary

Guided endodontics describes a template-aided approach for access cavity preparation. The procedure requires cone-beam computed tomography and a surface scan to produce a template. An incorporated sleeve guides the drill to the target point. This allows the preparation of minimally invasive endodontic access cavities in calcified teeth.

Abstract

Pulp canal obliterations (PCO) are often a consequence of dental trauma, such as luxation injuries. Even though dentin apposition is a sign of vital pulp, pulpitis or apical periodontitis may develop in the long term. Root canal treatment of teeth with severe PCO and pulpal or periapical pathosis is challenging for general practitioners and even for well-equipped endodontic specialists. To ensure detection of the calcified root canal and avoid excessive loss of tooth structure or root perforation, static navigation using templates ("Guided Endodontics") was introduced a few years ago. The general workflow includes three-dimensional imaging using cone-beam computed tomography (CBCT), a digital surface scan, and superimposition of both in a planning software. This is followed by virtual planning of the access cavity and the design of a template that will guide the drill to the desired target point. To do this, a true-to-scale virtual image of the drill must be placed in a way that the tip of the drill reaches the orifice of the calcified root canal. Once the template has been fabricated using computer-aided design and computer-aided manufacturing (CAD/CAM) or a 3D printer, guided preparation of the access cavity can be performed clinically. For research purposes, a postoperative CBCT image can be used to quantify the accuracy of the access cavity performed. This work aims to present the technique of static guided endodontics from imaging to clinical implementation.

Introduction

Pulp canal obliterations (PCO) are signs of vital pulp, and are often observed after dental trauma1 or as a response to stimuli like caries, restorative procedures2, or vital pulp therapy3. When no clinical or radiographic signs of pathology are present, root canal treatment is not indicated. In the long term, however, the remaining pulp tissue can develop a pathosis4. In cases where clinical or radiographic signs of pulpal or apical pathology are present, non-surgical root canal treatment would be the treatment of choice for tooth preservation.

For a successful outcome of the root canal treatment, the preparation of an adequate access cavity is crucial. Teeth with PCO needing a root canal treatment are difficult to treat, even for dentists that are specialized in the field of endodontics5. Attempting to locate a calcified root canal may result in a high loss of tooth structure and thus weakening or even perforation of the root. This reduces the prognosis of the tooth, and extraction may be indicated6.

As template-based (static) navigation is already successfully used in oral implantology, its application in endodontics was first described in the literature a few years ago7. Since then, numerous case reports and studies have demonstrated the benefits of template-aided endodontic access cavity preparation in cases with PCO8,9.

The aim of this work is to present the technique of guided access cavity preparation using guided endodontics. For research purposes, a treatment evaluation (determination of angular and spatial deviation between planned and performed access cavity) is possible after a postoperative CBCT scan, which is also presented in this article.

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Protocol

Approval or consent to perform this study was not required since the use of patients' data is not applicable. In this study, DICOM data from a maxillary model consisting of extracted, de-identified human teeth are used. Teeth were extracted due to reasons not related to this study.

1. Virtual access cavity planning

  1. Start the digital planning program.
  2. Right-click on Expert to choose the advanced mode.
  3. Right-click on New to open a new case.
  4. Select the folder with DICOM image data to import the image data to the software.
  5. Adjust the Hounsfield Units (HU) thresholds if necessary for optimal visualization (check in the small window in the lower left).
  6. Click on Create Dataset to complete the data import.
    NOTE: Here, DICOM data from a maxillary model consisting of extracted, de-identified human teeth are used.
  7. Choose the type of planning by left-clicking on Maxilla or Mandible and name the planning.
  8. Click on Edit Segmentations to start the image segmentation process.
    NOTE: A new window opens automatically for the segmentation process.
  9. Choose the axial view by left-clicking on Axial in the upper left box.
  10. Click on Density Measurement to measure the high radiopaque tooth surface and the surrounding non-radiopaque states (air). Calculate the mean values between both densities. (Figure 1).
    NOTE: The mean value needs to be calculated manually; there is no integrated tool in the software.
  11. Click on 3D Reconstruction.
  12. Set the lower threshold to the determined mean value (Figure 2A).
  13. Segment the dentition with the Flood Fill Tool and name the segmentation as desired (Figure 2B).
    NOTE: When the flood fill tool is selected and active, the desired area can be segmented by a left click in the 3D-view.
  14. Complete the segmentation by clicking on Close Module.
  15. Add a model scan by selecting Add > Object > Model Scan.
    NOTE: A surface scan needs to be generated beforehand (e.g., utilizing an intra-oral scanner, which provides the data as an stl-file).
  16. Import the stl File from the digital surface scan.
  17. Choose Align to Other Object.
  18. Select the performed segmentation (Figure 2C).
  19. Choose three different matching points for landmark registration in the 3D view in both datasets, the segmentation, and the surface scan.
    NOTE: Spatial distribution of the points will facilitate the semi-automatic matching of the data.
  20. Verify correct registration in all planes and complete registration.
    NOTE: Manual corrections can be required if deviations between CBCT and surface scan are apparent. If required, left-click and drag to adjust the alignment spatially, and right-click and drag to adjust angular deviation in the displayed planes (Figure 3)
  21. Add an implant (the utilized endodontic bur must be imported to the software's implant database beforehand) to plan the access to the root canal.
  22. Position the bur in the desired angulation and to the required depth, and verify in all planes (Figure 4A).
  23. Add the corresponding sleeve to the bur (the utilized sleeve system must be added to the database beforehand via Extras > Edit Custom Sleeve System).
    NOTE: The sleeve must not be in contact with the crown of the tooth. If the sleeve is in contact, a longer bur needs to be selected to provide space between the sleeve and tooth structure (Figure 4B).
  24. Select Object > Add > Surgical Guide to design the template as preferred (Figure 5A).
  25. Export the template as an stl file and manufacture it with a 3D printer (Figure 5B, Supplementary File 1).
    ​NOTE: After completing the 3D print, rework the template according to the manufacturer's instructions for the printer and printing material used. The accurate removal of support material is crucial for the fit of the template on the dental arch, and thus also for the accuracy of the preparation of the access cavity.

2. Access cavity preparation

  1. Check the fit of the template on the dentition (Figure 5C).
    NOTE: Inspection windows can be added during the design process to enhance visual control of the fit and seat.
  2. Check the fit of the sleeve in the template.
  3. Mark the enamel at the access cavity site. Dye (e.g., caries detector) may be used at the bur's tip (Figure 6A, B).
  4. Remove the enamel at the access cavity site without using the template or endodontic bur. Use a diamond bur instead until dentin is exposed (Figure 6C).
  5. Place the sleeve containing the template on the dental arch.
  6. Insert the bur into the handpiece that was used for the planning.
  7. Perform the access cavity preparation with template guidance (Figure 6D).
    ​NOTE: The access cavity should be prepared intermittently. The drill and the cavity should be cleaned of debris to counteract heat generation. Hand files can be used to check if the root canal orifice can be entered before the apical position is reached. The apical position will be defined by the bur stop. Hand files can be used to search or enter the canal orifice. Once the canal orifice is located, conventional root canal treatment utilizing hand files and/or rotary instruments can be performed.

3. Treatment evaluation

  1. Use the preoperative CBCT settings to create postoperative image data.
  2. Start a new case planning.
  3. Import the image data analog to the preoperative planning.
  4. Click on Edit Segmentations.
  5. Set the lower threshold to the determined mean value, which was calculated for the preoperative data.
  6. Use the Flood Fill Tool to segment the dentition.
  7. Complete the segmentation by clicking on Close Module.
  8. Open the preoperative planning.
  9. Select Plan > Treatment Evaluation.
  10. Select Postoperative Volume Dataset (Figure 7A).
  11. Load the correct postoperative dataset and choose the generated segmentation.
  12. Align pre- and postoperative CBCT data by choosing three different regions for landmark registration.
    NOTE: Spatial distribution of the points will facilitate the semi-automatic matching of the data (Figure 7B).
  13. Verify correct registration in all planes and complete registration.
    NOTE: Manual corrections can be required if deviations between CBCT and surface scan are apparent (Figure 8).
  14. Place the virtual endodontic bur in the direction of performed access cavity preparation, and check in all the planes (Figure 9).
    NOTE: If the diameter of the calcified canal is larger than the diameter of the utilized endodontic bur, adjustment in the apical-coronal direction is not feasible. Thus, treatment evaluation can be determined for angular and lateral deviation only, not for apical or three-dimensional deviation.
  15. Select Finish, and the software will calculate the deviation automatically, showing the results in a table. Moreover, the deviation between planned and performed access cavity preparation can be visualized in a 3D-rendered view.

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Representative Results

Figure 10A shows the occlusal view of a prepared endodontic access cavity in a first maxillary molar after template-aided access cavity preparation of the mesio-buccal canal. Figure 10B shows the insertion of three endodontic handfiles to confirm successful root canal detection after preparation of the palatal and disto-buccal access cavities. After matching the postoperative CBCT data to the preoperative planning data, virtual bur placement generates information about the deviation (Figure 11A). Here, the angular deviation is 0.7°, 0.74 mm 3D deviation at the base of the bur, and 0.87 mm 3D deviation at the tip of the bur. For better visualization, the deviation can be shown in different planes or a 3D-rendered view (Figure 11B).

Figure 1
Figure 1: Segmentation preparation. Measurement of the HU density for the tooth enamel and the surrounding material. Calculate the mean value. Red circle: button for the density measuring tool. Left-click to activate, which allows density measurements in the axial view by left-clicking and holding in the desired area. Please click here to view a larger version of this figure.

Figure 2
Figure 2: Segmentation process and preparation for alignment with surface data. (A) 3D view of preoperative CBCT data. The lower threshold has been adjusted to the determined mean value. (B) The flood fill tool was utilized to perform a segmentation of the tooth structure (color blue) and was named "Maxillary Teeth". (C) The performed segmentation can be selected (here: "Maxillary Teeth") for the registration step. Please click here to view a larger version of this figure.

Figure 3
Figure 3: Alignment of CBCT and surface scan datasets. Verify in all planes that matching is accurate and complete the registration step. Note the "camouflage pattern" between segmentation and surface scan data in the 3D reconstruction, which indicates a highly precise matching of the data. Please click here to view a larger version of this figure.

Figure 4
Figure 4: Access cavity planning. (A) An endodontic bur is virtually placed to the root canal orifice of a maxillary second premolar, providing straight-line access. (B) A suitable sleeve can be added to the endodontic bur. There must be enough space between the sleeve and coronal tooth structure to avoid interference when later placing the template on the dental arch. Please click here to view a larger version of this figure.

Figure 5
Figure 5: Template for static navigation. (A) The entire template has been designed (here, a maxillary study model with multiple planned access cavities in the posterior tooth area). It is now ready to be exported and 3D printed. (B) The template has been 3D printed. (C) The sufficient fit of the template on the dental arch is checked. Please click here to view a larger version of this figure.

Figure 6
Figure 6: Access cavity preparation. (A) Dye (here: caries detector) at the bur's tip is used to mark enamel at the access cavity site. (B) Enamel has been marked through the template and sleeve. (C) Enamel at the access cavity site has been removed using a diamond bur in a contra-angle handpiece. (D) After sleeve insertion, the template is placed on the dental arch, and the guided endodontic access cavity can be performed with the endodontic bur in a contra-angle handpiece. Please click here to view a larger version of this figure.

Figure 7
Figure 7: Preparation for treatment evaluation. (A) Choose Postoperative Volume Dataset as a data source for treatment evaluation. (B) Landmark registration between pre- and postoperative CBCT data. Choosing anatomically prominent regions (cusp tips, marginal ridges) as landmarks and their spatial distribution can facilitate semi-automatic registration. Please click here to view a larger version of this figure.

Figure 8
Figure 8: Postoperative CBCT alignment. Matched pre- and postoperative data is shown in all planes and in 3D reconstruction. Note the "camouflage pattern" between the datasets in the 3D Reconstruction, which indicates a highly precise matching of the data. Please click here to view a larger version of this figure.

Figure 9
Figure 9: Marking of the access cavity. For treatment evaluation, a virtual bur is placed in the direction of access cavity preparation, which can be withdrawn from the postoperative CBCT data ((A) coronal plane, (C) sagittal plane). Confirm adequate bur positioning in both planes ((B) coronal plane, (D) sagittal plane). Please click here to view a larger version of this figure.

Figure 10
Figure 10: Clinical view after access cavity preparation. (A) Template-aided endodontic access cavity preparation of a maxillary first molar of the mesio-buccal canal. (B) After disto-buccal and palatal root canals are accessed in the same manner, handfiles are inserted to confirm successful root canal detection. Please click here to view a larger version of this figure.

Figure 11
Figure 11: Treatment evaluation. (A) After correct matching of pre- and postoperative CBCT data and correct bur placement, the software calculates the angular and spatial deviation between planned and performed access cavity preparation. The results are presented in a table. (B) Visualization of the deviation is also provided in sagittal or coronal view, or in 3D reconstruction. Please click here to view a larger version of this figure.

Supplementary File 1: A sample stl file of the template. Please click here to download this File.

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Discussion

The introduction of template-aided access cavity preparations in endodontics has brought immense progress to non-surgical endodontic treatment in teeth with PCO. Conventional access cavity preparation can be very time consuming5 and is prone to error in cases with severe PCO. In vitro studies and clinical case reports demonstrate the feasibility of the guided endodontics approach, generating satisfying results in terms of root canal detection and an overall low deviation between the planned and performed access cavities8. However, the implementation of guided endodontics should be limited to cases where the conventional freehand access cavity preparation is accompanied by a higher risk of iatrogenic errors, since the use of ionizing radiation (CBCT) is required10.

To minimize the deviation between the planned and finally performed access cavity, a few factors need to be considered. When performing full-arch surface scans, local deviations and inaccuracies may occur11. This can lead to a certain degree of error in the CBCT data matching process, thus leading to deviations in access cavity preparation. Hence, highly precise surface scanners would also provide more accurate results for the guided endodontics approach. Different planning software and types of template manufacturing (additive versus subtractive) were investigated and found to have an influence on the outcome as well12.

Furthermore, the quality and accuracy of the 3D printing process also play a role in minimizing deviations in access cavity preparation. In addition to the various processes in 3D printing13, the alignment of the printed object14 also plays a decisive role in manufacturing precision. Since additive manufacturing processes are subject to constant further development, the manufacturing process should be critically examined on a regular basis in order to achieve the highest possible precision. Also, the fitting precision between the bur and sleeve plays an important role in the accuracy of the entire procedure. To avoid heat development and allow the bur to slide smoothly, a certain amount of "loose fit" is necessary. Particularly when the distance from the sleeve to the apical target point is large, a small deviation at the bur's base might result in a larger deviation at the bur's tip. To avoid a possible disadvantage from a sleeve-based system due to reduced vertical space in the patient's mouth, a sleeveless guide system has been successfully described in a recent case report15. A further investigation comparing the accuracy of sleeve-containing versus sleeveless systems would be desirable for research in the field of guided endodontics in the future. Besides reduced vertical space, another limitation for template-aided preparation of endodontic access cavities is the presence of mobile teeth. To enable accurate planning and precise treatment, teeth with increased mobility can be splinted beforehand.

When the evaluation of the accuracy is performed utilizing postoperative CBCT data, it is important to assure that CBCT machine settings and the setting of the HU thresholds in the software are the exact same as in the preoperative data. It has been shown that different CBCT and threshold settings result in differing segmentation volumes16, therefore hindering the exact alignment of the imaging data and leading to incorrect results. Yet, even in an ideally matched dataset, error is unavoidable since the virtual bur is placed manually and underlies a subjective error. For the accuracy validation of oral implants, different methods were compared, and an automatic evaluation method was found to be superior to the manual matching method17. Hence, an automatic method should be considered to improve the quality of evaluation itself, and to create comparability between future research findings in the field of guided endodontics.

To the best of our knowledge, no commercially available software exists to date that automates the accuracy evaluation of access cavities. A difficulty that arises in comparison to the evaluation of implant positions is that access cavities are not radiopaque, and therefore, an automatic evaluation is difficult to implement.

Besides static navigation, dynamic navigation systems (DNS) were also described for endodontic purposes. DNS can circumvent the disadvantages of template-guided access preparation18, but require more equipment and are therefore still associated with high costs.

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Disclosures

All authors declare that they have no conflict of interest.

Acknowledgments

None.

Materials

Name Company Catalog Number Comments
Accuitomo 170 Morita Manufacturing NA CBCT machine
coDiagnostiX Dental Wings Inc Version 10.4 Planning software, which is mainly intended for implant surgery. Endodontic access cavities can be planned by adding the utlized bur to the implant database
Endoseal drill Atec Dental GmbH NA Carbide bur, which is used for the guided access cavity preparation
StecoGuide Endo-Sleeve steco-system-technik REF M.27.28.D100L5 Sleeves, which are inserted into the fabricated template
TRIOS 3 3Shape A/S NA Surface scanner
P30 Straumann NA 3D Printer
P pro Surgical Guide Clear Straumann NA Light-curing resin for the additive manufacturing

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References

  1. Andreasen, F. M., Zhijie, Y., Thomsen, B. L., Andersen, P. K. Occurrence of pulp canal obliteration after luxation injuries in the permanent dentition. Endodontics & Dental Traumatology. 3 (3), 103-115 (1987).
  2. Fleig, S., Attin, T., Jungbluth, H. Narrowing of the radicular pulp space in coronally restored teeth. Clinical Oral Investigation. 21 (4), 1251-1257 (2016).
  3. Linu, S., Lekshmi, M. S., Varunkumar, V. S., Sam Joseph, V. G. Treatment outcome following direct pulp capping using bioceramic materials in mature permanent teeth with carious exposure: A pilot retrospective study. Journal of Endodontics. 43 (10), 1635-1639 (2017).
  4. Robertson, A., Andreasen, F. M., Bergenholtz, G., Andreasen, J. O., Noren, J. G. Incidence of pulp necrosis subsequent to pulp canal obliteration from trauma of permanent incisors. Journal of Endodontics. 22 (10), 557-560 (1996).
  5. Kiefner, P., Connert, T., ElAyouti, A., Weiger, R. Treatment of calcified root canals in elderly people: a clinical study about the accessibility, the time needed and the outcome with a three-year follow-up. Gerodontology. 34 (2), 164-170 (2017).
  6. Cvek, M., Granath, L., Lundberg, M. Failures and healing in endodontically treated non-vital anterior teeth with posttraumatically reduced pulpal lumen. Acta Odontologica Scandinavica. 40 (4), 223-228 (1982).
  7. Zehnder, M. S., Connert, T., Weiger, R., Krastl, G., Kuhl, S. Guided endodontics: accuracy of a novel method for guided access cavity preparation and root canal location. International Endodontic Journal. 49 (10), 966-972 (2016).
  8. Moreno-Rabié, C., Torres, A., Lambrechts, P., Jacobs, R. Clinical applications, accuracy and limitations of guided endodontics: a systematic review. International Endodontic Journal. 53 (2), 214-231 (2020).
  9. Buchgreitz, J., Buchgreitz, M., Bjørndal, L. Guided root canal preparation using cone beam computed tomography and optical surface scans - an observational study of pulp space obliteration and drill path depth in 50 patients. International Endodontic Journal. 52 (5), 559-568 (2019).
  10. Dula, K., et al. SADMFR guidelines for the use of cone-beam computed tomography/ digital volume tomography. Swiss Dental Journal. 124 (11), 1169-1183 (2014).
  11. Ender, A., Zimmermann, M., Mehl, A. Accuracy of complete- and partial-arch impressions of actual intraoral scanning systems in vitro. International Journal of Computerized Dentistry. 22 (1), 11-19 (2019).
  12. Krug, R., et al. Guided endodontics: a comparative in vitro study on the accuracy and effort of two different planning workflows. International Journal of Computerized Dentistry. 23 (2), 119-128 (2020).
  13. Chen, L., Lin, W. S., Polido, W. D., Eckert, G. J., Morton, D. Accuracy, reproducibility, and dimensional stability of additively manufactured surgical templates. The Journal of Prosthetic Dentistry. 122 (3), (2019).
  14. Tahir, N., Abduo, J. An in vitro evaluation of the effect of 3D printing orientation on the accuracy of implant surgical templates fabricated by desktop printer. Journal of Prosthodontics. , (2022).
  15. Torres, A., Lerut, K., Lambrechts, P., Jacobs, R. Guided endodontics: Use of a sleeveless guide system on an upper premolar with pulp canal obliteration and apical periodontitis. Journal of Endodontics. 47 (1), 133-139 (2021).
  16. Dong, T., et al. Accuracy of in vitro mandibular volumetric measurements from CBCT of different voxel sizes with different segmentation threshold settings. BMC Oral Health. 19 (1), 206 (2019).
  17. Oh, S. -M., Lee, D. -H. Validation of the accuracy of postoperative analysis methods for locating the actual position of implants: An in vitro study. Applied Sciences. 10 (20), 7266 (2020).
  18. Connert, T., Weiger, R., Krastl, G. Present status and future directions - Guided endodontics. International Endodontic Journal. , (2022).

Tags

Guided Endodontics Three-Dimensional Planning Template-Aided Preparation Endodontic Access Cavities Pop Canal Calcification Apical Pathosis Template Guided Access Preparation Tooth Preservation Minimally Invasive Less Experienced Operator Digital Planning Program DICOM Image Data Hounsfield Unit Thresholds Optimal Visualization Planning Type Selection Image Segmentation Process Density Measurement Radio Pack Tooth Surface 3D Reconstruction Dentition Segmentation Model Scan
Guided Endodontics: Three-Dimensional Planning and Template-Aided Preparation of Endodontic Access Cavities
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Cite this Article

Leontiev, W., Connert, T., Weiger,… More

Leontiev, W., Connert, T., Weiger, R., Dagassan-Berndt, D., Krastl, G., Magni, E. Guided Endodontics: Three-Dimensional Planning and Template-Aided Preparation of Endodontic Access Cavities. J. Vis. Exp. (183), e63781, doi:10.3791/63781 (2022).

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