DT News - India - CHF technique prevents common endodontic mishaps

Dr. Sourav Banerjee

Tue. 23 April 2024

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The Conceptual Hybrid Flare (CHF) technique is a novel technique developed to revolutionize the cleaning and shaping of root canals making the endodontic procedures more predictable, and also preventing and managing the commonest mishaps viz file separation, canal transportation, ledging, zipping, and perforation. The following editorial by Dr. Sourav Banerjee is an easy-to-read summary of his original copyrighted research.

One fine morning I get up and find a message popping up on my mobile screen that reads, “A new amazing file has been launched.” My eyes glitter in ecstasy and I run after acquiring them assuming it is the savior I have been waiting for that would solve all of the problems I face during root canal treatment procedures. It is not only with me but it happens with many clinicians who are not satisfied with the endodontic procedures they perform. The bottom line that most of us miss is files are there to make way for the irrigants; they shape the canals such that subsequent disinfection of the complex canal system can be achieved. Hence the predecessor of predictable Endodontics is a predictably achievable Biological goal and to that is predictable mishap-free Shaping of the canals.

Endodontics has evolved considerably over the last few decades. The intent among people to save natural teeth has pushed researchers to develop materials and techniques that make the Root Canal Treatment (RCT) procedure more precise and predictable. The gateway to successful endodontic treatment is adequate cleaning and shaping of the canals. An adequately shaped canal ensures optimum activated irrigation & disinfection to achieve the biological goal. The shaping procedure is one of those aspects of endodontic treatment that has witnessed most of the changes from file design to metallurgy to various shaping techniques. All of these efforts are aimed at achieving mishap-free shaping of the canals.

The Conceptual Hybrid Flare (CHF) technique is a novel technique developed to revolutionize the cleaning and shaping of root canals making the endodontic procedures more predictable, and also preventing and managing the commonest mishaps viz file separation, canal transportation, ledging, zipping, and perforation. CHF focuses on quality patient care keeping the procedure easy and predictable for the clinician.

The Concept

The concept took shape as a result of finding a solution to various mishaps that happened during the shaping of the root canals. The technique was conceived keeping in mind a predictable way to avoid mishaps and complications. Over a decade, through my interactions in my lectures, training programs, and workshops I observed that the majority of clinicians faced similar challenges while performing RCTs, and presented similar doubts and concerns. I inferred that the clinicians were getting entangled in multiple variables and a simple straightforward approach should mitigate the issue.

Let me enumerate the common concerns I kept hearing:

when to change the files,
how to know how many times a file be reused,
how to evaluate to which size the canal should be prepared,
how to shape severely curved canals,
how to shape calcified canals,
how to be sure that transportation is not happening while shaping,
how to prevent post and inter-operative flare-ups,
how to prevent over-instrumentation,
why there is a sudden loss of working length (WL),
how to decide when or at what file size should the shaping end in the first time and during re-treatments.

An endodontic procedure demands considering the following variables pre-operatively:

the file design
the file metallurgy
the canal curvature on the intraoral periapical radiograph (IOPAR)
the visible patency of the canals and the pulp chamber
calcifications if any in the pulp chamber and /or encroaching the canal orifices
the periapical area on the IOPAR
the lateral width of the canal

Critical aspects considered in the development of the CHF Technique:

depth of penetration of the endodontic irrigation needle is recommended to be within 1 mm of the EW
the action of hypochlorite solution (hypo) is time-dependent
that hypo needs to be in contact with the tissues for dissolution and disinfection, to which better flow, low surface tension, and adequate space are needed
that removal of the smear layer and disruption of the biofilm is the cornerstone of the endodontic biological goal and that ultrasonic activation is considered most effective in achieving it; to allow acoustic streaming to happen adequate space is needed
the above-stated goals need to be achieved in the critical apical few millimeters that house near total of the ramifications and finer anatomies those offshoots from the main canal system (CHF Technique effectively addresses all the above 5 critical aspects along with conservation of the tooth structure as the essential prerequisite)

While developing the technique the critical part was to incorporate the fundamentals of shaping the root canals simultaneously keeping it simple and safe.

The two most vital aspects that are prioritized:

predictable shaping of the canals, offsetting all the major probable mishaps
to make the technique biologically acceptable and evidence-based

This technique adequately answers all the above concerns. The technique is designed to achieve the biological goal by enabling the creation of optimum size in the critical apical zone that would allow placement of irrigation needles to the required depth and also allow ultrasonic activation of the same. The technique requires all preparation to end at 25.06 size thereby creating a 0.31 mm space at D1 as this is the required optimum size to achieve adequate activated irrigation at the same time being conservative and safe.

The CHF technique has three variations:

LFS (long file sequence)
SFS (short file sequence) &
USS (ultra short sequence)

The technique functions as follows:- ➢ Orifice Shaping ➢ Glide Path ➢ Gradual Widening of the Glide Path ➢ Gradual Apical Preparations & Widening ➢ Gradual Mid Root Flaring ➢ Finishing

LFS Technique:

1. Canal Location (10.02) – S1

2. Orifice Shaping (8% or above OS) – S2

3. Establishing the glide path + SLC (10.02) -S3

4. First Complete Flare + First Apical Preparation (13.04/03) - S4

5. Second Apical preparation (15.02) – S5

6. Second Complete Flare + Third Apical Preparation (17.04) – S6**

7. Fourth Apical Preparation (20.02) – S7

8. First Mid Root Flaring (20.06) – S8 *

9. Apical Widening (20.04) -S9*

10. Second Mid Root Flaring (25.06) – S10

11. Fifth Apical Preparation (25.04) – S11

12. Final Flare / Finishing (25.06) – S12

SFS technique:

*S8 & S9 are missing in the SFS technique, which is recommended with file systems that do not have the 20.04 & 20.06 files in them. This approach somewhat increases the stress on the files and the canal wall and has only 10 steps.

8. Mid Root Flaring (25.06) – S8

9. Fifth Apical Preparation (25.04) – S9

10. Final Flare / Finishing (25.06) – S10

USS technique:

Ultra Short Sequence is recommended with file systems that do not have 17.04, 20.04, and 20.06. Hence, along with the *S8, S9 - even **S6 is missing.

6. First Mid Root Flaring (20.04) - S6

7. Third Apical Preparation (20.02) – S7

8. Second Mid Root Flaring (20.06) – S8

9. Fourth Apical Preparation (20.04) -S9

10. Final Flare / Finishing (25.06) – S10

The technique requires intermittent irrigation and irrigant exchange throughout the process and if needed as may be in constricted canals multiple repetitions in a single step. It is recommended to use 3% hypo for a balance between efficacy and safety. It is recommended to use EDTA 17% liquid intermittently for chelation and removal of the smear layer and accumulated hard tissue debris (AHTD). It is recommended to do activated chelation with EDTA followed by 5 ml of Hypo per canal preferably by CNPIE (Continuous Negative Pressure Irrigation & Evacuation) and or ultrasonic (US) activation followed by a final rinse with NS / distill water after the final flare. For PPI with side vented irrigation needles, a 30G irrigation needle is to be placed till D1 and the irrigant should be expelled at a flow rate of approximately 2ml/min.

How the CHF Technique works:

The technique allows each file to necessarily work in a particular area/segment of the canal, thereby reducing the length of engagement (LoE) of the file at any moment. This particularly reduces the chance of Tortional Failure (TF). The technique takes into account variables to govern the sequence of the files to be used. Studies have shown that stress on files working in a canal is high when the effective length of the file in contact with the canal wall is more and when the jump in percentage size is equal to or more than 50%. The CHF technique essentially solves these two issues adequately. This is one prescription technique that remains the same for all clinical situations.

There exists a lot of confusion among clinicians regarding which shaping technique to use in which clinical condition. Frequently it is observed that canals have curvature in other planes that are not appreciated in the 2-D radiographs. In such scenarios, there are high chances of file separation with even a slight flaw. In such circumstances,

CHF proves to be a favorable technique as it circumvents all the possible mishaps that could have been encountered. The technique is just like a prescription where the clinician has to just follow the prescribed sequence as it is. Let it be a calcified canal, or curved canal in any plane, it just works.

The technique has a mathematical explanation where it can clearly reveal which are the most stressed files in the sequence, those that need frequent inspection and replacement. Hence soft metallurgy plays an important role. The advantage of soft metallurgy is the flutes undergo deformation before separation, which can be easily noticed with a keen inspection. During the development phase, it was experienced that even if the file was rotated with only half of the required torque there was neither any excessive binding with the canal wall nor auto-reverse while the shaping happened unimpeded. By this alone, it may be appreciated that this technique inflicts minimum stress on the canal wall hence minimum transportation, crazing, and any other silent mishap could happen.

Why all shaping needs to end at 25.06%

This technique follows irrigation-centric shaping. The irrigation needle has a gauge of #30 so for effective placement till the WL the size should be at least #30 or more. The size prepared by a 25.06 file is #31 at D1. A 25.06 file keeps the apical size at D0 to 25 but adequately enlarges the canal at D1 to enable the placement of a 31G irrigation needle. Additionally the tapered shape aids in US activation with a size #20 tip.

US activation is a proven method to effectively remove the smear layer from the critical apical third. TDA (transverse displacement amplitude) of the US file needs adequate room (50-80 microns approx) to happen. Hence a 25.06 file provides the optimum room needed along with keeping the terminal preparation minimum possible.

Topics:

Endodontics

Tags:

Curved root canals Endodontic therapy Narrow root canals Root canal

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