Advances in Biomechanical Preparation

INTRODUCTION
During the last few years, endodontics has seen an accelerated advancement in the technology used to clean and shape canal systems. As with any procedure, equipment and techniques naturally improve in efficiency with time as new instruments are manufactured that overcome the limitations and weaknesses of those that were previously available. In terms of endodontic rotary files, the newer generations of files are more flexible and resistant to cyclic fatigue than ever before.1 In conjunction, as research and understanding of debris removal and infection in canal systems has improved, the concept of canal irrigation has become more sophisticated.2 Gone are the days of essentially squirting bleach in a tooth with a conventional needle syringe and gutting roots with stiff and cumbersome files. Any clinician performing root canal therapy today should be excited by the current advances in file design and irrigation.

File Design
In 1988, the concept of manufacturing rotary endodontic files from nickel-titanium (NiTi) wire was introduced.3 Since then, the marketplace for NiTi rotary files has exploded with new products being offered by an increasing number of manufacturers. With nearly 2 and a half decades of rotary files being used in endodontics, much has changed. Ruddle et al4 classified these files into different generations largely based on file shape, metallurgy, and motion. The evolution started with first generation rotary files characterized by passive cutting radial lands and fixed tapers. From there, later generations of files were produced with advanced features such as active cutting edges, reciprocating motion, and offset centers of rotation. The metallurgy used in NiTi production also has been advanced, and as Ruddle et al4 discussed, proprietary heat treatments to files has likewise contributed to an improvement in their strength and flexibility. Regardless of the file system used, the newer generations of files are more flexible and resistant to separation than at any time in the history of endodontics. The following 2 cases illustrate the safety and efficiency that newer generation files possess.

CASE 1
A 34-year-old male patient presented with a chief complaint of intense pain to temperature stimulation and chewing in the upper left quadrant. Tooth No. 15 was diagnosed with an irreversible pulpitis with symptomatic apical periodontitis (Figure 1a). Exceptional root curvature was noted on the preoperative radiograph.

CASE 1
Figure 1. Tooth No. 15 with curves. (a) Preoperative radiograph. (b) Postoperative radiograph.

After administering local anesthesia, a rubber dam was placed to isolate the tooth, and access was made. The ProTaper Gold SX file (Dentsply Sirona) was used to open up the canal orifices and remove the coronal inflamed pulp tissue. A 10 K-file was used to scout the canals, and working length was determined using the Root ZX (J. Morita USA). A glide path was created using 10 and 15 K-files, and 6% sodium hypochlorite (NaOCl) was used to flush debris. Following the establishment of a glide path, the chamber was filled with NaOCl and the series of ProTaper Gold instruments S1 through F2 (Dentsply Sirona) were used sequentially to the apex in all canals. Copious irrigation with NaOCl was used after each file before proceeding to the next. Once instrumentation was completed, the smear layer was removed with 17% EDTA followed by a NaOCl flush. The canals were dried and sealed with a System B Heat Source downpack (Kerr Endodontics) and Obtura III Max (Obtura Spartan). The postoperative radiograph shows the ability of one of the most advanced rotary file systems on the market to shape anatomically narrow and curved canals while minimizing the risk for iatrogenic accidents (Figure 1b).

CASE 2
A 48-year-old female patient presented with a history of previous root canal therapy on teeth Nos. 14 and 15 (Figure 2a). Tooth No. 14 was symptomatic to chewing and causing spontaneous pain. A periapical radiograph revealed a large apical lucency on tooth No 14. While the quality of the treatment on tooth No. 15 appeared less than ideal, the tooth was asymptomatic, and the patient elected to only treat tooth No. 14 to alleviate her symptoms. The mesial root of No. 14 was noticeably arched, and the possibility of a missed second canal was of concern.

CASE 2
Figure 2. Upper left quadrant periapical radiograph. (a) Preoperative radiograph.
(b) Postoperative radiograph.

After anesthesia and rubber dam isolation, access was made into tooth No. 14. The ProTaper Gold F1 file was used along with chloroform to remove the bulk of the gutta-percha from the canals. Small hand K-files were used with chloroform to remove the remaining gutta-percha at the apices. An untreated second mesiobuccal (MB) canal was found. The working length was determined using the Root ZX apex locator. The ProTaper Gold series of files S1 through F3 was used to instrument the canals in the presence of copious 6% NaOCl irrigation. Stainless steel hand K-files up to size 45 were used to finish the apical preparation of the palatal root. Once instrumentation was completed, 17% EDTA followed by 6% NaOCl was used to remove the smear layer. With the canals and chamber filled with NaOCl, the EndoActivator (Dentsply Sirona) was used in each canal to improve the penetration and disinfecting action of the irrigant. The canals were dried and sealed with a System B Heat Source downpack and Obtura III Max. The postoperative radiograph shows the treated second MB canal and presents another example of the ability of today’s more advanced file systems to safely shape curved canals in anatomically complex teeth (Figure 2b).

Irrigation
Instrumentation alone is not enough to clean a canal system. Irrigation is needed to flush debris from teeth and aid in disinfection. Traditionally, endo­dontics has relied on the delivery of antimicrobial irrigants into the root canal system by the use of some form of a luer lock syringe and a needle. Canal anatomy is complex, and it is increasingly apparent that conventional needle irrigation fails to effectively deliver an irrigant into many of the fins and anastomoses present in teeth.2

Recently, different irrigation techniques and devices have been developed to improve the cleaning of the root canal system. Ultrasonic or sonic activation, negative pressure irrigation, photon-induced photoacoustic streaming, lasers, and sound wave-induced hydrodynamic forces have all been promoted within the last few years to improve the penetration and efficiency of canal irrigation.5 Regardless of the device used, the concept is the same. Improvement in the removal of debris and bacteria is achieved by actively moving the irrigating solution in the root canal system. The following 2 cases demonstrate the ability to clean complicated anatomical canal spaces using an activated irrigation technique.

CASE 3
A 41-year-old female patient presented with pain to chewing associated with tooth No. 19. A periapical radiograph revealed a large periradicular radiolucency (Figure 3a). Tooth No. 19 was diagnosed as necrotic with symptomatic apical periodontitis.

Following anesthesia and rubber dam placement, access was made through the existing crown. The ProTaper Gold SX was used to coronally enlarge the orifices. A 10 K-file was used to scout the canals, and working length was determined using the Root ZX. A glide path was created using 10 and 15 K-files, and 6% NaOCl was used to flush debris. Following the establishment of a glide path, the chamber was filled with NaOCl, and the series of ProTaper Gold instruments S1 through F3 were used sequentially to the apex in all canals. Copious irrigation with NaOCl was used after each file before proceeding to the next. Once instrumentation was completed, the smear layer was removed with 17% EDTA followed by a NaOCl flush. With the canals and chamber filled with NaOCl, the EndoActivator was used in each canal to improve the penetration and disinfecting action of the irrigant. The canals were dried and sealed with a System B Heat Source downpack and Obtura III Max.

CASE 3
Figure 3. Lower left quadrant periapical radiograph. (a) Preoperative radiograph. (b) Postoperative radiograph.

Figure 3b shows the complex anatomy that was cleaned and obturated in tooth No. 19. Accessory and lateral canals in the mesial root became evident after obturation. The bulging area in the mid-portion of the canal in the distal root, which could not be completely instrumented by files without removing excessive dentin, was cleaned and well obturated. In areas where files cannot touch, irrigation delivery is the key to success.

CASE 4
An 18-year-old patient presented with a necrotic tooth No. 9 (Figure 4a). The tooth was anesthestized, rubber dam placed, and access preparation performed. Working length was determined using the Root ZX apex locator. The canal was filled with NaOCl, and the series of ProTaper Gold instruments S1 through F3 were used sequentially to the apex in the canal. Copious irrigation with NaOCl was used after each file before proceeding to the next. Hand K-files sizes 35 and 40 (Kerr Endodontics) were used to finish apical preparation. Once instrumentation was completed, the smear layer was removed with 17% EDTA followed by a NaOCl flush. With the canal filled with NaOCl, the Endoactivator was used to improve the penetration and disinfecting action of the irrigant. The canal was dried and sealed with a System B Heat Source downpack and Obtura III Max.

CASE 4
Figure 4. Periapical radiograph of tooth No. 9. (a) Preoperative radiograph. (b) Postoperative radiograph.

The postoperative radiograph in Figure 4b demonstrates how even a seemingly “simple” anterior tooth can benefit from advanced irrigation techniques. Complex accessory canals visibly appeared after obturation in the apical area of the root. Smear layer removal and active irrigation contributed to better cleaning and disinfection in this seemingly straightforward case.

CLOSING COMMENTS
The cases presented here demonstrate the treatment outcomes that are possible with modern endodontic technology. With all the advances in endodontic instrumentation and techniques that have occurred recently, it can be overwhelming to keep pace with everything in the marketplace. Clinicians can find themselves lost in a quandary trying to decide which file system to use. In addition, with the realization that conventional needle irrigation by itself is not as effective as newer ways to rinse and clean a canal system, one can be left feeling uncertain of the quality of their patient care. Irrigation is critical to endodontic success and should not be overlooked.

What works for one clinician may not work well for another. The best advice to find the technique that is right for you is to attend large dental conventions to get a chance to try some of the latest advances endodontics has to offer firsthand. The newer files offered are all more flexible and stronger than older generations, so find the one that is best suited for the types of teeth you choose to treat.

It is an exciting time in the specialty of endodontics, and as amazing as things seem now, one can only wonder what future advancements are in the works.


References

1. Hieawy A, Haapasalo M, Zhou H, et al. Phase transformation behavior and resistance to bending and cyclic fatigue of ProTaper Gold and ProTaper Universal instruments. J Endod. 2015;41:1134-1138.
2. De-Deus G, Barino B, Marins J, et al. Self-adjusting file cleaning-shaping-irrigation system optimizes the filling of oval-shaped canals with thermoplasticized gutta-percha. J Endod. 2012;38:846-849.
3. Walia HM, Brantley WA, Gerstein H. An initial investigation of the bending and torsional properties of Nitinol root canal files. J Endod. 1988;14:346-351.
4. Ruddle CJ, Machtou P, West JD. The shaping movement: fifth-generation technology. Dent Today. 2013;32:94-99.
5. Sigurdsson A, Garland RW, Le KT, et al. 12-month healing rates after endodontic therapy using the novel GentleWave System: a prospective multicenter clinical study. J Endod. 2016;42:1040-1048.


Dr. Beach graduated magna cum laude from the University of Florida College of Dentistry in 2003 and completed his endodontic residency there in 2005. He is currently a Diplomate of the American Board of Endodontics and maintains a private practice in Wesley Chapel, Fla. He frequently provides continuing educational lectures at local, state, and national study clubs and conventions. He can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it..

Disclosure: Dr. Beach reports no disclosures.

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