The golden era of root canal shaping

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The golden era of root canal shaping

Dr Ahmed Shawky says: “The MG3 Gold with low shape memory and high cutting efficiency allows (...) to manage different cases with an excellent margin of safety and predictability.” (Image: VanoVasaio/Shutterstock)

Tue. 6. September 2022

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After access preparation and location of anatomy, the next challenge facing the endodontic clinician is to select the proper file alloy and sequence for the shaping procedure in order to be able to shape the anatomy safely and predictably and without any procedural errors. This article will show the advantages of the MG3 instruments (Shenzhen Perfect Medical Instruments) and how we can customise the sequence of these files according the anatomy encountered and case difficulty for predictable root canal shaping with a high safety margin.

Files

First, I will go through the components of the basic assortment of the MG3 Gold file system (Fig. 1). The main advantage of this file system is the presence of different designs and cross sections in the same instrument kit, a smart thing for dealing with different anatomies.

The MG3 Gold files are machined with a variable pitch and helix (Fig. 2), allowing efficient coronal evacuation of debris and preventing a screw-in tendency. This also reduces the torsional load on the instrument that would otherwise occur because of debris accumulation or excessive friction with the root canal walls.

Fig. 1

Fig. 1

Fig. 2

Fig. 2

Starter file (orifice modifier, 20/0.10)

This file has a short working segment (9 mm) and 19 mm length. This improves accessibility in restricted areas (Fig. 3). It is used for mechanical pre-flaring or orifice modification for elimination of coronal dentine resistance. It has a convex triangular cross section, which increases the blade strength, giving the instrument a high cutting efficiency. With this cross section, the instrument is subjected to excessive torsional load; therefore, this instrument must be used in brushing motion towards the outer walls and not pecking motion.

Gliders (16/0.02 and 19/0.02)

Another advantage of this system is that it has two glide path files (Fig. 4). They can be used sequentially, depending on case difficulty. Sometimes, only one is used. The rectangular cross section provides four blades for better centring ability, avoiding transportation, and for high cutting efficiency for reproducible glide path preparation.

The small size and taper of these files make them extremely flexible for negotiating mechanically difficult curvatures. Owing to the small size of the gliders, it is recommended to use them with brushing motion ahead of pecking motion to avoid torsional failure.

 

Fig. 3

Fig. 3

Fig. 4

Fig. 4

Shaping files 20/0.04 and 25/0.06

The cross section of these shaping files is triangular (Fig. 5). This design provides sharp blades for enhanced cutting efficiency and reduces the metal core of the instrument, as the size is increased to maintain flexibility. The heat treatment imparts a wear-resistant surface with superior cutting behaviour and enhances cyclic fatigue resistance.

The 25/0.04 file can be used in body shaping and can be used as a finishing file in cases with anatomical limitations, such as severely curved canals. The 25/0.06 file can be used for pressureless pre-flaring and as a shaping or finishing file.

Shaping file 35/0.04

The cross section of this shaping file is off-centre rectangular (Fig. 6). This design provides sharp blades for enhanced cutting efficiency and reduces the contact points of the instrument with the root canal walls. This reduces the torsional load on this larger size and provides better clearance of debris.

The off-centre design also makes the instrument move in swaggering motion for better canal tracing and for avoiding transportation. The 35/0.04 file is an optional file for increasing the preparation size in large root canals. It is used in zone pecking motion.

Fig. 5

Fig. 5

Fig. 6

Fig. 6

Additional information

Non-assorted refills of all sizes are available for the clinician to customise his or her treatment sequence up to ISO tip size 50. All files are available in lengths of 21, 25 and 31 mm (except the starter file, being of 19 mm in length).

The recommended operation speed is 300–350 rpm, and the recommended torque is 2 Ncm for the glide path and shaping files and 3 Ncm for the starter file. Markings indicate taper: one marking for 2%, two for 4% and three for 6%. Precisely calibrated working length markings are engraved on each instrument shank at 18, 19, 20 and 22 mm for easy reproduction of the recorded working lengths in each canal, especially in multi-rooted teeth of different lengths.

How to use the MG3 Gold instruments

Case 1 (Fig. 7)

The patient presented to the clinic and was diagnosed with symptomatic irreversible pulpitis and apical periodontitis of a mandibular third molar. After access preparation, only one large mesial orifice was identified. Ultrasonic modification revealed the presence of two mesial canals originating from a single mesial orifice (sub-pulpal bifurcation).

Mechanical pre-flaring with the 25/0.06 MG3 Gold file, followed by mechanical body shaping with the 25/0.04 file, created a smooth glide path down the two separate mesial canals despite coronal restriction. Following the reproducible glide path, shaping with the 20/0.04, 25/0.04 and 25/0.06 files was not a difficult task.

Fig. 7

Fig. 7

Case 2 (Figs. 8 & 9)

A patient with a mandibular third molar diagnosed with irreversible pulpitis and symptomatic apical periodontitis was referred to my practice. Under high magnification, the canal entrances were negotiated using medium-power ultrasonic instruments and D-perfect C Files (Shenzhen Perfect Medical Instruments). Special care was given to the coronal portion of the root canal, especially to the mesiobuccal canal, owing to the scouted double curvatures. Pressureless mechanical pre-flaring was done to reduce the coronal interferences (cervical dentinal triangle—red triangle), which can place huge stress on the shaping files, leading to procedural errors such as instrument separation and transportation, thereby increasing the difficulty of an initially straightforward case.

Mechanical pre-flaring in such a case can be done using either the starter file (20/0.10) or the apical 3–4 mm of the 25/0.06 shaping file or even both. The mode of action of these files is brushing motion towards the outer walls.

Fig. 8

Fig. 8

Fig. 9

Fig. 9

Case 3 (Figs. 10 & 11)

The patient presented with a mandibular first molar with advanced symptomatic pulpitis and apical periodontitis. Taking into consideration the constricted appearance of the root canals on the digital radiograph, MG3 Gold was the best suited for the situation owing to the high cutting efficiency. Mechanical pre-flaring with the 25/0.06 file was done to facilitate body shaping using the 25/0.04 file and a secured mechanical glide path to a final size of 30/0.04 in the five-canaled molar.

Fig. 10

Fig. 10

Fig. 11

Fig. 11

Conclusion

When dealing with anatomy, variability is the rule. This is the reason that the endodontic practitioner must be able to modify the sequence of the instruments and treatment approach according to the anatomy. The introduction of new file systems like MG3 Gold with low shape memory and high cutting efficiency allows the clinician to manage different cases with an excellent margin of safety and predictability.

Editorial note:

This article was published in roots—international magazine of endodontics vol. 18, issue 1/2022.

Endodontics Root canal therapy

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