Predictable root canal treatment of calcified maxillary incisor using a 3D-printed drill-guide
Gergely Benyõcs, DCD

ABSTRACT

Compared to operating freehand, using any type of guidance results in better accuracy, especially in borderline situations. CBCT and scanners are widely available in dental practices or by office independent services. Planning and 3D printing for endodontic surgical and non-surgical purposes can be carried out by companies, serving this method for guided implant placement. This case report describes the step by step procedure of a challenging root canal treatment of an upper central incisor with pulp and root canal calcification. Using a 3D printed static drill guide with a corresponding drill and CNC sleeve, allowed for predictable treatment while maximizing the retention of dentin.

Key words: guided endodontic, 3D printed template, static guidance, conservative endodontics, minimally invasive endodontics, patient-centered approach.

INTRODUCTION

Pulp canal calcification (PCC) occurs as a sequela of dental trauma or in elderly patients.1-3 PCC usually develops because of the formation of secondary and tertiary dentin. From another standpoint, orthodontic treatment may also trigger or accelerate the apposition of secondary dentin.4-5 

Although PCC is considered a sign of pulp vitality and that root canal treatment should not be undertaken unless there is clinical and radiographic evidence of pulp necrosis, it remains that in the long-term, necrosis usually affects up to 33% of teeth with PCC.6 Access and shaping becomes very challenging in these cases and a high failure rate ensues, especially in narrower teeth.7 The American Association of Endodontists rates the treatment of teeth with PCC as having a “high difficulty” level.8 Even with magnification, the search for the elusive root canal may lead to excessive dentin removal that will in turn jeopardize biomechanics and reduce the long-term prognosis.9 

The widespread of digital dentistry, specifically 3D scanning and printing, allows today for a new approach to teeth affected by PCC using a printed guide that will serve as guide to the bur.10-11 The following case report will illustrate this technique.

CASE REPORT

A 48-year old female patient was referred to our office with history of spontaneous pain and sensitivity upon biting on the upper right central incisor. Anamnesis revealed no history of trauma and the medical history was not contributory.

Clinical examination revealed discoloration of tooth #11 and the presence of a purulent swelling in the vestibule facing the apex of that tooth. (Fig.1) Palpation and percussion were positive. Pulp testing was negative. Radiography supplied by the patient revealed a radiolucent lesion around tooth 11. A reduction of the pulp canal lumen as well as pulp chamber and root canal calcification were also noted. The diagnosis was pulp necrosis with acute apical abscess. 

The situation was explained to the patient and treatment options were presented including non-surgical root canal treatment, surgical endodontics or extraction followed by an implant solution to the patient. All risks were discussed, understood and the first option, non-surgical root canal treatment, was chosen. Due to the complexity of the case, 3D-printed static guidance was suggested, and since 2 days were needed for planning and printing, an emergency incision and drainage was carried out, and an analgesic (diclofenac 50mg, TID for 3 days, Novartis Hungary) was prescribed. A small FOV (5×5) cone-beam computed tomography (CBCT) (CS8100 3D, Carestream, Onex Corporation, Toronto, Ontario, Canada) was carried out and an impression was taken (Aquasil Soft Putty Regular Set, Ultra Plus XLV, Dentsply Sirona, Miford, USA). 

A model was cast and scanned in the laboratory (iMetric d104i, Imetric 4D Imaging, Courgenay, Switzerland). STL files with scan data and DICOM files with CBCT data were uploaded to a planning software (CoDiagnostix, Dental Wings, Chemnitz Germany). After segmentation and alignment, a virtual drill path was established and the virtual bur was adjusted accordingly. The drill path was aligned to involve the first visible part of the root canal. (Fig.2)

The guide was printed (Form 2, Formlabs, Sommerville, USA) and the custom sleeve, planned and made by computer numerical control (CNC) machining was inserted.

Guided access preparation and root canal treatment

The stability of the guide was first checked on the cast then in situ. Dimensional stability of the 1mm guide drill (Meissinger pilot implant bur, Hager & Meisinger, Neuss, Germany) was also controlled. (Fig. 3, 4) The entry point of the access was marked with a bur (EndoExplorer EX1, Komet Dental, Lemgo, Germany) through the sleeve. In order not to destroy the sleeve, its diameter had to be narrower than 1mm, then the restoration was removed by freehand preparation. (Fig.5)

The dentine was drilled using the guide. In order to allow for cooling, drilling was interrupted after each 1-2mm, the drill was cleaned and the cavity flushed with saline. Once the planned depth was reached, the guide was removed and a rubber dam was placed. The tooth was further isolated using a liquid dam (Ultradent, South Jordan, Utah, USA). The root canal was discovered lateral to the tip of the bur. (Fig.6-7).

The root canal treatment followed uneventfully and was done in a single session using stainless steel hand files up to size 25 (Ready Steel FlexoFiles, DentsplySirona Endodontics, Ballaigues, Switzerland), scouting before with 0.08 and 0.10 C-pilot files (VDW, Munich, Germany). 5.25% sodium hypochlorite was used for irrigation while shaping (Chlorax D 5.25%, Cerkamed, Stalowa Wola, Poland) and 17% EDTA as a final rinse (EDTA Solution Cerkamed). Saline was used in-between and after irrigants. Filling was done with gutta percha and AH Plus sealer (Dentsply Sirona Restorative, Konstanz, Germany) using the warm vertical condensation technique. (Fig.8-10) The orifice was sealed with glass-ionomer cement (Ketac-Molar, 3M-ESPE, Seefeld, Germany). The pulp chamber was filled with walking bleach material for 2 weeks (Opalescence-Endo, Ultradent) and covered with glass-ionomer cement.  Two weeks later, a glass fiber-reinforced resin post (1.35mm, Glasix, Nordin, Switzerland) was cemented using self-adhesive universal resin cement (Rely-x Unicem, 3M-ESPE) and a composite filling (Gradia-Direct, GC, Tokyo, Japan).

The symptoms disappeared and figure 11 and 12 show the 6-months and 2-years control respectively.

DISCUSSION

The modern endodontic approach tends towards being more conservative, less invasive procedures and techniques. This philosophy is becoming increasingly part of both graduate and post-graduate education. This is in accordance with the objectives of the endodontic treatment that is not only the prevention and/or elimination of apical periodontitis, but also the long-term preservation of sound dental structures and the lifetime retention of natural teeth. This is all the more important since the lifespan of the population is increasing and that teeth should be kept in function for more than 80 years. 

Restorations, composite fillings, and calcifications create challenges, and sometimes make it impossible to carry out endodontic treatments. In such complex situations, guided endodontics could be a useful approach for general dentists, and even for endodontists. In recent years, several publications proved the feasibility of static guidance, mostly on calcified incisors.10,12 This specific approach is interesting since for instance in lower incisors with no or only partially visible root canal, the failure rate was 71% during root canal treatment.7 The idea of guided endodontics could be the solution to avoid failures during access preparation. The widespread use of the operating microscope, improved heat-treated nickel-titanium files, and the use of CBCT as well as static and dynamic guidance made it possible to apply a patient-centered procedure to this case. The reason behind this is that the entry point of the access, the depth of drilling as well as the angulation of drilling are precisely implemented with this tool. Unnecessary tissue removal is avoided, one can get exactly where they want to. Nevertheless, care must be taken since inaccuracy during drilling has been reported in the literature and is evidenced in figures 6 and 7. The coronal pre-enlargement at the entrance is of significant importance in this technique, its size can be reasonably minimized while using variable tapered file. 

The methodology for creating a static guide is similar to the one used for guided implant placement. The accuracy of guided endodontics seems acceptable and allows an accurate access cavity preparation up to the apical third of the root utilizing printed templates for guidance.11 However, some factors should be considered before attempting static guidance. There should be enough interocclusal space to accommodate the additional 10mm drill or bur length, required by the guide ring position over the tooth. This can be ascertained by placing the guide bur in the patient’s mouth to check for available space. Metal restorations can also create problems while planning for this type of treatment as they can produce artifact that affect the accuracy of the DICOM file. However, with experience, the superimposition of scan data (STL files gained from an intra-oral scan or cast scan) can help overcome this occurrence. Static guides are not suitable for high-speed handpieces either. When drilling through enamel, ceramics and cast restorations, issues with cooling will be encountered. The point of entry should thus be marked with the help of the guide through the sleeve, then the guide should be removed and drilling through these hard substances should be carried out freehand. When the dentin is reached, the guide and corresponding may be used.

The main disadvantage of static guidance is that it is not suitable in acute cases. One should wait to receive printed or milled drill guides before scheduling an appointment with the patient. 

Considering this issues, static guidance can help us in certain situations, but not in all of them, at least for now. It does however help us minimize the footprint left following dental treatments and since there is to date no known material that possesses the mechanical characteristics of sound dentine, saving tooth structure is mandatory, especially in the peri-cervical region, to sustain long-term functional and parafunctional loads as well as possible further interventions if needed.

Dynamic guidance, however, may revolutionize our daily endodontic practice soon. Unlike static guidance, there is no need to print a guide. Planned on CBCT data, the avatar of the bur can be visualized on the screen in 3 planes and controlled real time in 3D to remove just as much tooth structure as is necessary for access preparation in endodontic treatment. However, new tools cannot replace expertise (that will have to acquired), proper diagnosis, and treatment planning. However, minimally invasive endodontics should not be self-purposed or for show on social media.

Disclaimer:

The author did not report any conflict of interest.