File Delivery by Drs. Allen Ali Nasseh and Anne Lauren Koch

Categories: Endodontics;
File Delivery for Dental Endodontic Treatment 

Endodontic treatment of a severely curved mesial buccal root on a maxillary molar

by Drs. Allen Ali Nasseh and Anne Lauren Koch

One of the more interesting aspects of how dentistry has performed during the pandemic is how well endodontics has done in dental practices. At first glance this may seem surprising, but it makes total sense. Not only do emergency patients increase the endodontic patient load, but numerous clinicians with holes in their schedule also decided to do some “endo” to fill in the time.

Certainly, providers need to feel confident in their skills before they attempt challenging cases in any field, but with such an increased interest in endodontics, it is an appropriate opportunity to review how we address difficult molar cases.

The following case involves a severely curved mesial buccal root on a maxillary molar that was treated using the EndoSequence Blend Protocol. We created this technique specifically for use with the EndoSequence file system, which we co-developed, but the steps we describe would also be applicable for use with similar files from other brands. It uses a combination of non-heat-treated austenitic EndoSequence files coronally, followed by the use of EndoSequence Scout heat-treated files apically. This allows a combination of efficiency and flexibility to address a different part of the root canal.

Here, we’ll use multiple images to explain the thought process behind our endodontic treatment protocol.

File Delivery for Endodontic Treatment
Fig. 1

A 36-year-old patient presents with a chief complaint of needing a root canal in his upper tooth. The patient had a previous formocresol pulpotomy to address pain and discomfort; upon examination, it was noted that the tooth had a severely curved mesial buccal root in addition to the previous pulpotomy.

Note: The presence of a prior pulp cap can complicate the procedure if there is any coronal calcification associated with the previous pulp therapy. This is something to be mindful of as one begins the procedure.

File Delivery for Endodontic Treatment
Fig. 2

A CBCT was obtained to fully evaluate the root anatomy and to formulate an endodontic treatment plan to manage the 90-degree curvature on the mesial root. The axial section shows the presence of an MB2 canal, while the coronal section through the MB root demonstrates that MB1 and MB2 join somewhere midroot.

Note: The vast majority of mesial buccal canals (MB1 and MB2) do join together. This is why, for many years, molar endodontics worked, even though we weren’t fully aware of the prevalence of additional canals.

File Delivery for Endodontic Treatment
Fig. 3

Following access through the original temporary filling, access is modified to gain straight-line access to the orifice of each canal before creating straight-line access to the body of each root. The use of ball-shaped ultrasonic tips can be a great help along with regular tapered tips.

Note: It’s important to remember that proper straight-line access is imperative for instrumenting a severely curved canal. Good access is key for clinical success.

File Delivery for Endodontic Treatment
Fig. 4

Higher magnification shows the isthmus connecting the MB1 and MB2 canals. Even though MB2 joins MB1 in this case, it’s important to instrument this portion of the root canal to ensure proper cleaning and disinfection.

Note: Ultrasonics are a great help in this part of the procedure, because of their ability to clean in a three-dimensional manner.

File Delivery for Endodontic Treatment
Fig. 5

Once coronal access has been adequately prepared to allow straight-line access to each orifice, coronal flaring is achieved using an orifice opener such as a 16-millimeter 20/.08 EndoSequence file in each canal.

Note: Coronal flaring at this point in the procedure will facilitate rotary instrumentation by effectively opening the canal in the coronal third.

File Delivery for Endodontic Treatment
Fig. 6

After initial preparation of each canal to a Size 15/.06 EndoSequence CM, a finishing file was used in each canal, based on its determined size after apical gauging. The palatal and DB canals were quite large, and a single EndoSequence 35/.04 file was used in these straighter canals.

Note: Heat-treated files such as the EndoSequence CM, with their inherent flexibility, will do all the “hard work,” but we like to complete the preparation with a non-heat-treated file because the instrument will not distort and, consequently, will ensure a better match with the gutta-percha master cone.

File Delivery for Endodontic Treatment
Fig. 7

The severely curved MB roots had to be prepared to a smaller apical diameter, using heat-treated files to address the flexibility necessary to instrument such curvatures. Consequently, the MB roots were instrumented to only Size 20/.06 EndoSequence CM.

Note: While this size initially may seem small, we must consider the fact that with a .06 taper, the canal size 1mm back from the apex is 26mm in diameter. MB2 canals that join the main MB1 canal generally are narrower than a stand-alone MB2 canal.

File Delivery for Endodontic Treatment
Fig. 8

After our irrigation protocol and smear layer removal, we can readily see both the MB1 and the MB2 canals.

Note: Notice how good straight-line access facilitates entry to the orifices.

File Delivery for Endodontic Treatment
Fig. 9

After a bioceramic sealer was placed in the individual canals, matching well-fitted master cones were fully seated to the respective apices and were confirmed. In the more oval-shaped palatal
canal, additional cones were placed alongside the master cone: Two additional Size 25 gutta-percha cones were passively placed next to the master cone to prevent pooling of the sealer. The gutta-percha cones were seared off at the level of the individual orifices and vertically compacted using a Size 10 plugger.

Note: The additional cones placed in the palatal canal were not laterally condensed. They were simply placed as supplemental or “confirmation cones” to occupy space and to properly disperse the sealer.

File Delivery for Endodontic Treatment
Fig. 10

The pulp chamber is cleaned of sealer, using the water spray from an ultrasonic, and subsequently dried.

Note: Water will not have a deleterious effect on the bioceramic sealer because BC Sealer is hydrophilic not hydrophobic..

File Delivery for Endodontic Treatment
Fig. 11

BC Liner was then placed with a thickness of 3mm to seal the chamber and the orifices. The immediate sealing of the root-canal system will help reduce coronal leakage from the  provisional restoration.

Note: If a surgical microscope (with a high-powered light) is used during the procedure, an orange filter is recommended to prevent premature setting of the BC Liner.

File Delivery for Endodontic Treatment
Fig. 12

After waiting 30 seconds for the material to self-etch and bond to dentin, it can be light-cured to expedite the process. Higher magnification shows the seamless bond to the walls, which provides an excellent seal under the provisional restoration.

Note: This can act as a base under a final restoration and has a compressive strength of over 260 megapascals.

File Delivery for Endodontic Treatment
Fig. 13

This angled postoperative image shows the high degree of curvature and the joining of the MB1 and MB2 canals in this root.

Note: This tooth has not only been treated in a proper endodontic manner, it has also been treated in such a way as to allow a good final restoration, thereby ensuring long-term success. After an endodontic procedure has been completed, it is critically important to have the tooth restored properly and in a timely manner.

File Delivery for Endodontic Treatment
Fig. 14

3D imaging of the final fill shows the high degree of curvature.

Note: The challenging anatomy in the apical 5mm is addressed through proper access and using heat-treated files as “scouts” in this area.

File Delivery for Endodontic Treatment
Fig. 15

Patient was seen for a one-year recall and the tooth was completely asymptomatic. The tooth was restored with a well-sealing coronal restoration.

Note: The long-term prognosis of this tooth is excellent!


This case is an example of how a well-conceived endodontic treatment plan can facilitate performing endodontic therapy on a difficult tooth. Diagnostic radiology made it clear that this tooth had a severely curved mesial root. Consequently, special consideration was given to straight-line access and the achievement of such, when combined with the use of heat-treated files in the apical half of each canal, allowed instrumentation to reach the apex of all canals. Obturation was performed using a bioceramic sealer and, when combined with a bioceramic provisional, resulted in an excellent base for the final restoration.


Author Bios
Dr-Allen-Ali-Nasseh Dr. Allen Ali Nasseh received his dental degree from Northwestern University Dental School and completed his postdoctoral endodontic training at Harvard School of Dental Medicine, where he also received a master’s degree in the area of bone physiology. He has been a clinical instructor in the postdoctoral endo department at Harvard School of Dental Medicine since 1994. Nasseh is the current president and CEO of Real World Endo and the editor of the Harvard Dental Bulletin and several other dental journals and periodicals. He has a solo private endodontic practice and an endodontic educational institute in downtown Boston.

Dr-Anne-Koch Dr. Anne Lauren Koch received her DMD and certificate in endodontics from the University of Pennsylvania School of Dental Medicine. She is the founder and past director of the new program in postdoctoral endodontics at the Harvard School of Dental Medicine. Before her endodontic career, Koch spent 10 years in the Air Force and held, among various positions, that of chief of prosthodontics at Osan and McGuire Air Force bases. In addition to having maintained a private practice limited to endodontics, Koch has lectured extensively in the United States and abroad and is the author of numerous articles on endodontics. She is a co-founder of Real World Endo.
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