Revisiting Fundamental Skills in Endodontic Therapy: Patency, Chelation, and File Curving

By Alan H. Gluskin, D.D.S., and Craig A. Dunlap, D.D.S.

Introduction

According to a recent survey, 83% of universities allow their students to perform first molar root canal treatment (1).  However, 55% of the pre-doctoral directors in the United States and Canada do not feel that their graduates will be competent to perform a molar root canal treatment after graduation (1).  This percentage has increased by 20% compared to a similar study, which was done 10 years ago (2).  All participating dental schools reported that they have adopted nickel-titanium rotary instrumentation (1), which has resulted in a reduction of the fundamental hand instrumentation concepts in the dental curriculum.

In the rapidly evolving field of endodontics, technological advancements have revolutionized treatment protocols and improved patient outcomes. From rotary nickel-titanium instruments to 3D imaging techniques, these innovations have undoubtedly enhanced the efficiency and predictability of root canal treatments. However, amidst this progress, it is crucial not to overlook the fundamental hand skills that formed the bedrock of successful endodontic therapy, including maintaining patency, effective chelation, and proper file curving techniques. These skills, when mastered, significantly enhance the quality of root canal treatments and contribute to long-term success. By revisiting these core competencies, dental students can ensure a solid foundation upon which to build their more advanced techniques and technological applications.

Patency: The Gateway to Thorough Cleaning

Patency is defined as the ability to pass a small file through the apical foramen without resistance and is a critical concept in endodontic therapy. Maintaining patency throughout the cleaning and shaping process ensures that the entire length of the root canal system is accessible and can be adequately treated. Further, achieving and maintaining patency of the apical foramina has been shown to double the odds of periapical healing (3).  As such, apical patency is a cornerstone of meticulous and precise endodontic practice.

Benefits of Patency:

1. Prevents apical blockage: By regularly passing a small file through the apical foramen, practitioners can prevent the accumulation of debris that might otherwise lead to blockage of the canal space.
2. Facilitates more effective irrigation: Patency relieves vapor lock inside the canal (4) which allows for irrigating solutions to reach the full working length, enhancing their cleaning efficacy.
3. Reduces the risk of procedural errors: Maintaining patency helps avoid the formation of ledges, transportations, or perforations that can occur when the original canal path is lost, blocked, and/or ledged.
4. Improves the accuracy of working length determination: A patent canal allows for more precise electronic apex locator readings and radiographic interpretations (5).

Achieving and maintaining patency requires a delicate touch and precise control. Practitioners must develop the tactile sensitivity to navigate the intricacies of root canal anatomy without causing damage to the apical tissues. This skill is particularly crucial in cases with complex anatomies, such as severely curved canals or those with apical deltas.

Chelation: The Chemical Assistant

Chelation plays a vital role in the chemical aspect of root canal preparation. Chelating agents, such as EDTA (Ethylenediaminetetraacetic acid) and products containing EDTA, aid in the removal of the smear layer and soften dentin, facilitating easier instrumentation. The smear layer, a 1-2 µm thick layer of organic and inorganic debris produced during instrumentation, can harbor bacteria and inhibit the penetration of irrigants and sealers, and compromise disinfection.

Importance of Proper Chelation:

1. Enhances removal of inorganic debris: EDTA binds to calcium ions in dentin, effectively dissolving the inorganic components of the smear layer.
2. Improves the penetration of irrigants and medicaments: By removing the smear layer, chelating agents allow for better penetration of antimicrobial solutions into dentinal tubules.
3. Facilitates better adhesion of filling materials: A clean dentin surface promotes better bonding of sealers and obturation materials to the canal walls.
4. Contributes to disinfection that is more thorough: The removal of the smear layer exposes bacteria in dentinal tubules, making them more susceptible to antimicrobial agents such as sodium hypochlorite.

Mastering the use of chelating agents requires an understanding of their chemical properties and the ability to judge the appropriate duration and method of application. For instance, EDTA is typically used as a 17% solution and is most effective when allowed to remain in the canal for 1-5 minutes. However, prolonged exposure should be avoided as this can lead to excessive dentin erosion (6), particularly in young patients with thin dentin walls.

Chelation complements mechanical instrumentation and significantly improves the overall quality of root canal treatment. It is important to note that chelation should be used in conjunction with sodium hypochlorite irrigation, as EDTA alone does not have significant antimicrobial properties, nor does it possess tissue-dissolving properties (6).

File Curving: Customizing for Canal Anatomy

The ability to properly curve endodontic files is a crucial skill that allows practitioners to navigate complex root canal anatomies effectively. Pre-curving files enables better access to curved canals and reduces the risk of procedural errors such as ledging, transportation, or perforation. This skill becomes particularly important when dealing with molars, which often present with significant curvatures in their roots.

Techniques and Considerations in File Curving:

1. Assessing canal curvature through radiographs and tactile feedback: Prior to curving the file, practitioners should carefully analyze preoperative radiographs and use initial exploratory files to gauge the degree and direction of canal curvature.
2. Selecting appropriate file sizes and materials for curving: Smaller, more flexible files (e.g., sizes 08, 10, 15) are typically easier to curve and are less likely to ledge or transport the canal during use.
3. Applying consistent and controlled pressure during curving: The file should be curved gradually using finger pressure or a sterile gauze. Additionally, delicate cotton pliers carefully used can create gentle and rounded curves. Avoid using heavy pliers or other instruments that might create sharp bends, which may weaken the file and make it more susceptible to breakage.
4. Understanding the limitations and potential risks of excessive curving: Over-curving the file can lead to file separation or creation of false paths. It is crucial to maintain a balance between achieving the desired curvature and preserving file integrity.
5. Gauging the size of the apical foramen: Many times, a curve is present at the canal terminus.  Properly curving a file allows the clinician to appropriately gauge the size of the foramen and ensure the presence of an apical constriction (7) which helps ensure canal cleanliness while helping minimize extrusion.

The Synergy of Fundamental Skills

While each of these skills—patency maintenance, effective chelation, and file curving—are important in their own right, the true advantage lies in their synergistic application. When used in conjunction, they create a comprehensive approach to root canal therapy that addresses both the mechanical and chemical aspects of treatment (8),(9).

For example, maintaining patency allows for more effective delivery of chelating agents to the apical third of the canal, where smear layer removal is often most challenging. Similarly, proper file curving techniques enhance the practitioner’s ability to maintain patency in curved canals, reducing the risk of creating blockages or ledges.

Moreover, these skills complement modern technologies rather than being replaced by them. For instance, while rotary instruments have greatly improved the efficiency of canal shaping, the ability to pre-curve hand files remains crucial for initial canal negotiation, for glide path creation, and for managing complex anatomies that rotary instruments cannot safely reach or negotiate (10), (11).

Conclusion

In an era where technology often takes center stage, it is crucial to remember and cultivate the fundamental hand skills necessary for predictable endodontic therapy. Patency, chelation, and file curving form the foundation upon which all advanced techniques and technologies are built. By mastering these skills, endodontic practitioners develop the foundational knowledge necessary to navigate a wide range of clinical scenarios, from straightforward cases to more complex cases.

As educators and practitioners, we must continue to emphasize the importance of these skills in training programs and clinical practice. Although we should continue to adopt and embrace new technologies, we should not neglect the fundamental tactile skills that allow for nuanced treatment approaches. The art of endodontics lies in the hands of the practitioner, guided by knowledge, experience, and a mastery of these fundamental skills.

In conclusion, as we continue to advance the field of endodontics with new technologies and materials, let us not forget the timeless value of these core competencies. By maintaining a strong foundation in these fundamental skills, we ensure that our technological advancements are built upon a solid base of sound clinical practice, ultimately leading to better patient care and improved treatment outcomes.

References

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11. Plotino G, Nagendrababu V, Bukiet F, Grande NM, Veettil SK, De-Deus G, Aly Ahmed HM. Influence of Negotiation, Glide Path, and Preflaring Procedures on Root Canal Shaping-Terminology, Basic Concepts, and a Systematic Review. J Endod. 2020;46(6):707-29.

Alan H. Gluskin, D.D.S., is currently Professor, Department of Endodontics, Arthur A. Dugoni School of Dentistry, University of the Pacific in San Francisco, California. He served as Chairperson of the Endodontic Department for over 30 years. He is at present a Fellow of the International College of Dentists and the American College of Dentists.

Craig A. Dunlap, D.D.S., is an associate professor, vice chair of the endodontic department, and pre doctoral director at the University of the Pacific, Arthur A. Dugoni School of Dentistry in San Francisco.