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

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 PCO^8,9.

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.

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.

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 informatio...

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 plann...

Materials

List of materials used in this article

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