Root canal preparations: Different techniques
Introduction
Root canal preparation is a crucial step in the conduct of endodontic treatment. It consists of removing as much of the root canal content as possible, cleaning, disinfecting and shaping the canal to allow and facilitate its obturation.
However, the pulpo-radicular anatomy and the almost systematic presence of canal curvatures complicate the implementation of these objectives.
This is the reason why many root canal preparation techniques have been described.
1. REMINDERS
1.1. Reminders on canal and root anatomy
The root canal and anatomy is complex: each tooth has its own particular anatomy.
In addition to the root complexity (number of roots, supernumerary roots, curvatures and double curvatures) there is also a canal complexity due to the shape of the canal itself (more or less conical, flattened or oval, C-shaped, etc.) and its ramifications with other canals or irregularities (calcifications): hence the notion of canal network.
Finally, the apical zone, where the limit of the endodontium represented by the apical constriction is located anatomically, histologically and physiologically, has particularities that must be perfectly known if they cannot be seen on the radiographic image: apical deltas, accessory canals, apical curves and eccentric apices represent traps that must be avoided and negotiated during canal preparation.
1.2. Classifications of canal morphology:
While endodontic therapy aims at apical sealing, it is the root canals that provide access to the apex; it is therefore of prime importance to be familiar with the different pathways that these root canals take to lead there.
These paths are none other than the different types of arrangements of the canal system.
- Dedeus classification : 1975, based on a technique of injecting Indian ink and diaphanization
From the main channel depart;
A side channel
* Located in the middle part of the root,
* It connects the main canal and the desmodont
A secondary channel:
*Located in an area between 1mm and 3mm from the apex,
* It connects the main canal and the desmodont
An accessory canal: branch of the secondary canal
Root canal preparations: Different techniques Root canal preparations: Different techniques
- FS WEINE classification
Type I: a single canal extending from the pulp chamber to the apex.
Type II: two separate channels that join together to form one channel
Type III: two separate and distinct channels
Type IV: a single canal originating from the pulp chamber and then dividing, shortly before the apex, into two distinct and separate canals which exit the root through two different foramina.
- Vertucci classification
Root canal preparations: Different techniques
1.3. Anatomy of the apical region:
Several anatomical structures are identifiable in the apical zone of the root:
- The apical foramen, which constitutes the main exit of the canal towards the periodontium;
- The apical dome represents the vertex of the tooth;
- The radiographic apex is the image projected onto a radiological medium (silver or digital = observed in 2D) of the root limit furthest from the crown.
- The anatomical apex is the most extreme apical point on the surface of the root (three-dimensional anatomical part).
- The first to study apical anatomy was Y. KUTTLER. His work, completed by that of PALMER, GREENE and then LAURICHESSE, made it possible to schematize the apical region:
• The apical part of the canal is formed by two cones (hourglass shape)
– One is the dentinal cone whose base is coronal and the apex is the cemento-dentinal junction (CDJ)
– The other is the cementum cone whose apex is the (JCD) at the joint of maximum narrowing of the previous one and the base is the foramen
- The (JCD) is therefore the histological border between the endodontium and the periodontium.
- The narrowing is located:
- At 0.524 mm from the apical foramen in adults, and
- At 0.629 mm in the elderly, due to the continuous apposition of cementum.
- The canal narrows with age, in its dentinal portion, but on the contrary, due to continuous cementum apposition which often occurs far from the foramen, the latter widens (681 nm against 502 in young people).
- The terminal cementum cone does not contain pulp but a desmodontal vasculo-nervous and fibrous bundle; it is the site of tissue repair after endodontic treatment.
- In the majority of cases (80%) the cementum cone is deviated distally in relation to the dentin cone, the foramen on the surface of the root is therefore almost never in the axis of the canal.
- In a radiographic and microscopic study of 1047 roots, Laurichesse et al demonstrated that the foramina occupied a central position on the terminal axis of the root in only 27% of cases.
- The operating stages of endodontic treatment
1. The preoperative X-ray(s).
2. Setting up the operating field after anesthesia, and possibly pre-endodontic coronal restoration if the tooth is dilapidated.
3. The creation or redevelopment of the access cavity.
4. Catheterization and assessment of working length.
5. Removal of the canal contents and shaping of the canal network with permanent antiseptic, solvent and biocompatible irrigation.
6. Final flushing of the canal
7. Drying of the canal before three-dimensional root canal obturation.
2. Definition
Chemomechanical canal preparation: “Instrumental preparation of root canals with the joint use of various irrigation solutions to benefit from their antiseptic, solvent and demineralizing action”
3. The two main concepts of formatting
Two schools, one Scandinavian and the other so-called American, propose different concepts which dictate different principles:
- Scandinavian School = “Standardized” Approach 1960 by John Ingle
The concepts of this method take into account a greater protection of the periapical periodontium.
In the standardized technique, the goal is to achieve apical widening and create an “apical box” or “apical stop” to block the root canal filling materials.
The Scandinavian school recommends stopping the preparation 1 or 2 mm from the radiological apex and instrumenting the canal up to a diameter of 60 to 80/100 in order to create an “apical box”.
In infected teeth, this school advises against endodontic TRT in a single session.
Root canal preparations: Different techniques Root canal preparations: Different techniques
- American School = Approach based on conicity = Schilder (1974)
The Schilderian technique advocates maintaining the apical foramen as narrow as possible and creating a taper from the apical preparation limit.
The apical part of the canal is funnel-shaped.
Root canal preparations: Different techniques Root canal preparations: Different techniques
4. The objectives of root canal preparation
4.1. Biological objectives:
– Remove bacterial irritants as well as all organic tissues that are likely to act as an ideal substrate for the development of residual microorganisms in the canal and which would inevitably lead to failure in the more or less long term.
– Maintain the shaping inside the canal and do not instrument beyond the dentin structure (bone, apical lesion, etc.).
– Prevent any propulsion of infected or necrotic products into the periapical area.
– Try as much as possible to complete the endo TRT in a single session.
4.2. Mechanical objectives:
According to the American school:
- Create a regular taper from the apex to the canal entrance.
- The diameter of the prepared canal should be minimal at the apical level, and maximal at its coronal end.
- The apical foramen should be maintained in its original position.
- The apical opening should be kept as narrow as possible.
5. Different phases of root canal preparation
Canal preparation can be divided into two phases:
- A coronary phase;
- A root phase;
The coronal phase: This corresponds to the preparation of the access cavity.
The root phase corresponds to:
- Catheterization.
- Determination of working length (LT)
- Widening or shaping under abundant irrigation.
5.1. Catheterization
– Initial penetration is the active exploration of the canal system.
Allow :
- Initial exploration of the canal system.
- Evaluation of the canal lumen.
- Visualize internal anatomy.
- Determine the working length (LT).
- Catheterization instruments:
- Most authors agree to use the K type file n=° 6, 8, 10, 15
- MMC instruments are particularly well suited for this function.
- K pins can be used as an alternative
- Operating mode
- The root canal system should be lubricated with irrigants before the instrument is inserted.
- All instruments must be pre-bent before insertion into the canal.
- Any initial penetration is done by a continuous linear movement of the instrument in the apical direction, associated with a rotation of 1/8 turn clockwise with return to the starting position by a reverse 1/8 turn.
5.2. Determination of working length
- Definition
The LT is defined as the distance between a predetermined reference point on the crown that is a reproducible horizontal flat (usually the incisal edge for an anterior tooth and a cusp apex for a posterior tooth) and a point corresponding to the limit of the cleaning, shaping, and obturation action.
- Choice of apical limit
The root canal preparation must be located at the cemento-dentin junction and will have a pointed shape, this cone constitutes the dentin matrix intended to receive the obturation
Depending on the distance from the radiological apex it will be located:
– In the case of a straight root, 0.5 mm from the radiological apex.
– In the case of curvature, even if slight, it is 1 mm from the radiological apex.
– On a living adult tooth, it is at the level of the CDJ
– On a tooth with an unedited apex, it is 1 mm from the shortest edge
- Materials required for establishing working length
Retroalveolar photographs, undistorted, showing the entire tooth.
Angulator or film holder:
– It helps to position the film and keep it fixed during the exposure:
– it allows reproduction of the size of anatomical structures and their relationship with minimal distortion and deformation
– Allows the same incidence to be reproduced over time.
- Working Length Measuring Techniques
- Indirect technique
- Bisection and rule of three:
A catheter with a STOP is introduced into the canal, an X-ray is taken, instrument in place.
On the image, we measure the L of the tooth and the instrument up to the stop (LR(x))
We knew the real L of the instrument up to the stop;
To know the real L of the tooth we applied the proportional rule:
L Rx of the tooth x Actual L of the instrument to the stop
Actual tooth length = —————————————————————
L Rx of the instrument until the stop
- Ingle Technique
- On an X-ray, we measure the length of the tooth; we decrease 2.5 mm, we obtain the length D.
- We measure on the X-ray the difference between D and the apical constriction in place, we will obtain D1
- To obtain the working length called D2: D2 = D + D 1 – 0.5 mm.
- Graduated Probes
- These are probes graduated in 1 mm and which allow us, after taking an X-ray with the probe in place, to directly read the length of the canal.
- Electronic method
- Apex locators are electronic devices that measure working length by measuring the electrical resistance between the apical region and the oral mucosa.
- Electronic determination of LT:
- Placement of the lip electrode
- Powering on the locator, the 2nd electrode is placed in contact with the instrument which is advanced into the canal
- Signal indicating the foramen;
- Millimetered, indicated length measured with 1 millimeter ruler
- To check the measurement, the instrument must be advanced beyond the foramen (0.5mm), the locator will indicate an overshoot, and the instrument is then raised (1.5 to 2mm), then advanced again towards the foramen; the exact value will be displayed again.
- LT= found value – 0.5 mm
- This measurement should be confirmed by a Rx file in place.
- False measurements
o Presence of saliva leaks,
o Lip hook in contact with a metal element,
o Electrode in contact with the lip, cheek or tongue,
o Electrode or endodontic instrument in contact with a metal element
o Use of an instrument with a diameter that is too small in relation to the apical diameter of the canal,
o The presence of abundant purulent apical exudate,
o Immature teeth (open apices) can also result in an inaccurate or erroneous measurement.
5.3. Irrigation
– Irrigation plays an essential role in the disinfection process of the endodontic system and is an integral part of the shaping sequences.
- Remember that instrumental shaping does not clean the canal but allows the irrigation solution to reach the deep areas of the canal and therefore ensure its disinfection.
- While the instruments shape the main canal, it is the irrigation solutions that ensure the cleaning of the entire canal system.
- Role of irrigation
- Destruction of bacteria by the antiseptic action of irrigation solutions.
- The removal of organic and inorganic debris and bacteria that become suspended during shaping.
Evacuation of compacted debris and bacteria within non-instrumented areas of the canal network.
- Dislocation and evacuation of bacterial biofilm adhering to the canal walls and having escaped mechanical instrumental maneuvers
- Root canal irrigation methods
- Passive irrigation
- This is the irrigation delivered by the syringe, it allows the supply of the irrigation solution inside the canal and the evacuation of debris by pushing back into the space left free coronally,
- The syringe needle is inserted until it touches the walls and then withdrawn slightly to create a reflux space.
- The irrigation solution is renewed after each instrumental passage.
- During irrigation, the needle is driven by a low amplitude back and forth movement.
- The effectiveness of this method depends on several parameters:
- Canal taper and apical Ф
- Needle tip gauge.
- Pressure (using side-opening needles helps to better manage irrigant penetration)
- Irrigant volume: must be abundant and renewed.
- Active irrigation
- This is the irrigation obtained by inserting a moving instrument into the canal filled with irrigation solution to cause a place of pressure and depression.
- It helps to optimize the solvent power of the irrigant.
- Agitation can be done in 3 ways:
- Dynamic manual activation: the gutta master cone + low amplitude vertical movement (100mvt/mn)
- Sound activation: sonic insert
- Ultrasonic activation: ultrasonic file
6. Root canal preparation techniques
6.1. Manual preparation
6.1.1 Classic preparation
– In this technique, the goal was to reach the apical foramen and prepare this apical area first.
– The instrument is in contact with the canal walls over a large part of its working surface.
- Necessary instruments : pins, K files and H files.
- Technical
A pin is inserted with a ¼ turn clockwise rotation movement and then removed vertically.
Insertion of a K file of the same diameter with movement of the file on all the canal walls.
This action is repeated until the instrument passes freely through the canal.
The operation will be repeated until the entire instrumental sequence chosen previously has been played.
- Disadvantages
o Large instruments with less flexibility can cause curved canals to:
- Shoulder formation.
- Trajectory deviations with perforations
- Loss of working length
- Displacement of the foramen.
o The use of large instruments over the entire LT risks weakening the canal walls at the apical level.
- Indications
- Wide channels.
- Straight channels
- Contraindications
- Curved channels.
- Fine channels
6.1.2 Flame preparation: step back (Weine)
The pulp chamber is filled with an irrigating product.
Pass 1st instrument (usually 10 or 15) + widen over the entire LT
Move to the 2nd instrument immediately above, + widen over the entire LT
Move on to the 3rd instrument which will be immediately superior to the 2nd
Once this 3rd instrument fits freely over the entire LT, it will be called a master apical file (MAF).
Insert the following instrument over the entire LT -1mm
Work this instrument on this length
Re-scan the LAM to check canal patency
The operation is repeated in this way until the last instrument is used.
Irrigation will be carried out after each instrument has passed
6.1.3 Stair step preparation
Widening of the canals with an apical curvature located at the apical 1/3 and to avoid weakening the apical part.
Expand the channel over the entire LT to at least size 25.
The remainder of the canal from the curvature initiation will be prepared in the same way as the flame technique
Pre-curved instruments are used under irrigation
Go over the entire LT the LAM (emptiness of the canal)
- Benefits
- Allows the widerning of curved channels with greater safety.
- Prevents weakening of the apical part.
- Indications
- Curved channels.
6.1.4 Alternative preparation (Weine 1974)
- Alternates between K-type and H-type files.
- A summary by initial K file (K file 15 or even 10) separates each K+H pair.
- It is accompanied by abundant irrigation.
- Disadvantages
- Risks of instrumental fractures.
- Creation of stops.
- Indications
- Wide, straight channels.
- Contraindications
- Fine and curved channels.
6.1.5. Manual Crown-down technique (Marschal and Papin 1980)
- Crown-down involves cleaning and shaping the canal from the coronal third to the apical third.
- Knowing that the first instruments used in this technique were made of stainless steel.
- Root access preparation:
- An instrument of at least size 35 is inserted into the canal.
- Instruments 40 to 60 will be used along the length to where the 35 stopped.
- The gate forests are used in descending order.
- Establishment of a provisional operating length;
- Established from the preoperative radiograph 3 mm from the radiological apex.
- We work on this provisional length with instruments of decreasing size.
- Establishment of a definitive operative length:
- Radio instrument in place to definitively establish the operating length.
- We work with instruments smaller than No. 40 up to the apical limit under good irrigation.
- Advantage :
- Removal of cervical dentin which causes canal constrictions.
- Allows deeper and faster penetration of the irrigation solution.
- Allows for removal of most of the pulp and bacterial necrotic debris before approaching the apical 1/3 and therefore minimizes the risk of pushing bacterial or pulp irritants into the periapical repair space.
- The LT may or may not be modified during root canal instrumentation.
- Disadvantages
- Failure to follow the size sequence.
- Risk of choking.
- Inflexible instruments.
6.2. Continuous rotation root canal preparation
The current concept of root canal preparation arises from the association
1. The crown down
2. Continuous rotation or reciprocity
3. The use of nickel titanium instrumentation
4. Variable taper
- The crown down
It is therefore a question of dividing the canal shaping into several stages.
- First, the two coronal thirds are shaped in order to free the instruments from coronal constraints.
- The second step consists of a more controlled and gentle work in the apical area without pressure in the canal thus avoiding apical stops and displacements.
- Early widening of the coronal two-thirds offers several advantages:
– the immediate penetration of a greater volume of irrigation solution into the body of the canal, which will constitute a sort of reservoir, thanks to this coronal reservoir, the constitution of a space for the rise of debris which are suspended during irrigation
– a reduction in apical repression, since a large part of the pulp debris and bacteria has previously been eliminated.
– The files working apically pass through an irrigation reservoir into a portion of the canal already cleaned and disinfected.
– Better tactile sensitivity which allows to optimize the work of the tip of the pre-curved instruments to explore the apical zone without coronal friction, thus allowing to detect for example the curvatures not visible on the X-ray and the doubling of the canal;
– increased accuracy of electronic apex locators, whose measurement is more reliable when the file is in contact with the dentinal walls at the apical level
– Each part of the canal is approached in the following manner: exploration, pre-widening then shaping.
– Canal exploration is always carried out with small diameter manual steel files.
– Pre-widening can be performed with larger diameter steel hand files or with rotary or hand-held nickel-titanium instruments.
– Shaping is then carried out using nickel-titanium instruments, rotary or manual.
Under no circumstances should a nickel-titanium instrument be forced into a canal portion that has not been previously explored and pre-expanded.
1. Initial negotiation : after estimating the length of the work on a well-angulated preoperative radiograph, the initial exploration of the canal is always performed with small diameter hand steel files.
Instrumental dynamics:
– a file is inserted into the canal with a crawling movement, i.e. a rotational movement alternately clockwise and counterclockwise until it is sheathed by the canal walls, the instrument is never forced in the apical direction, when blocked the instrument is removed on site by a small alternating translational movement.
2. Pre-enlargement : its purpose is to secure, after the initial manual exploration, the canal trajectory before the passage of the rotating shaping instruments
– Available pre-widening files are PathFile®, Scout-RaCe®, ProGlider G.files or MTwo®.
-They can be used with any Nickel-titanium root canal shaping system, in continuous rotation at low speed in a slow and regular movement without pressure in the apical direction, in case of too much resistance, the file is removed from the canal, cleaned using a compress soaked in sodium hypochlorite, the canal is irrigated and the apical descent movement is repeated.
3. Shaping the coronal two-thirds : Many instruments are available to the practitioner for preparing the coronal two-thirds of the canal.
– Currently, rotary NiTi instruments are the instruments of choice for quickly and safely shaping the coronal portion of canals.
– Almost all systems on the market offer coronal shaping instruments. They have two common characteristics: they are more tapered and shorter than the other instruments in the series, which are designed to work more apically.
– The instruments must be guided by the canal on the way down and by the practitioner’s hand on the way up.
– Regardless of the system, instruments with a large taper are used first to pave the way for instruments with a smaller taper, up to the level where the canal has been pre-widened.
– A special feature concerns the MTwo® system for which coronal-apical preparation is not recommended: all the instruments in the sequence are used successively up to the working length.
– Regardless of the system used, the instruments are frequently cleaned and the canal irrigated with sodium hypochlorite between each pass of the files.
4. Shaping the apical third
– This step will also be carried out in two stages: an exploration and pre-expansion phase, followed by a shaping and finishing phase.
A – Exploration phase of the apical third
A K 10 hand steel file is pre-curved and used to explore the apical area.
Important! This step is important because it allows you to:
– gather information on the anatomy of the apical zone
– accurately and definitively determine the working length using an electronic apex locator and an X-ray if necessary;
– confirm the patency of the apical foramen.
– Once the apical area has been explored (K 08 and/or K 10 file), the working length determined, the foramen permeabilized (K 10 file at working length + 1 mm) and the canal pre-widened in its apical area (K 15 file or low-conicity NiTi rotary file), shaping can be carried out extremely reliably with the instruments of the system chosen by the practitioner.
- Single-use single-instrument preparation
– the one Shape concept:
Method:
6.3. New concepts
A. Mono-instrumental shaping in reciprocal movement
- Definitions and characteristics
– It is an alternating movement of different amplitude in one direction and in the other.
– The reciprocal movement consists of animating the files of high conicity with a clockwise/anticlockwise movement of variable amplitude.
– The main interest of reciprocal motion is the reduction of cyclic fatigue of the instruments. Indeed, a sequence of instruments animated by a reciprocal motion has a longer life than the same sequence used in continuous rotation.
– Furthermore, it allows perfect maintenance of the centering of the instrument in the canal.
– The secondary interest is that this movement virtually eliminates any screwing and suction effect
- Two different instruments use the reciprocal motion: WaveOne® (Dentsply-Maillefer) and Reciproc® (Dentsply-VDW)
- WaveOne® (Dentsply-Maillefer)
The system includes three instruments:
-WaveOne® primary, 25 in diameter and with a variable reverse taper of 8% over the apical 3 mm;
-WaveOne® thin, 21 in diameter and with a constant taper of 6%;
-WaveOne® large, 40 in diameter and with a variable reverse taper of 8% on the apical 3 mm.
The section of the instrument is triangular, concave at the tip and triangular at the coronal level.
- Reciproc® (Dentsply-VDW)
The system includes three instruments:
– Reciproc® 1, 25 in diameter and with a variable reverse taper of 8% over the apical 3 mm;
– Reciproc® 2, 40 in diameter and with a variable reverse taper of 6% over the apical 3 mm;
– Reciproc® 3, 50 in diameter and with a variable reverse taper of 5% over the apical 3 mm.
The section of the instrument is asymmetrical and has two cutting edges (section similar to that of the MTwo®)
- Operating protocol
Root canal shaping with these instruments follows the same strategy as continuous rotation:
– exploration (manual K file), pre-widening (manual K file or with PathFile®) then shaping of the two coronal thirds first and, then, exploration, pre-widening and shaping of the apical third.
B. Self Adjusting File® (SAF) System (ReDent-Nova)
-The SAF® instrument consists of a compressible hollow tube, 1.5 or 2 mm in diameter, composed of a nickel-titanium mesh, initially used for the manufacture of cardiac stents. This “soft” instrument, since it has a hollow body, adapts to the shape of the canal in which it is introduced. The instrument is coupled to an irrigation system
(VATEA, ReDent-Nova) which allows the irrigation solution to be delivered continuously within the instrument itself with a flow rate of 1 to 5 ml/min.
– The files are driven by a vertical vibratory movement of 3,000 to 5,000 vibrations per minute and 0.4 mm amplitude, obtained using a specific contra-angle.
C. Ultrasonic and subsonic canal preparation (parietal support technique)
- Material
- US Generators, special insert designed for endodontics
- A reservoir at Naocl
- Before use:
The use of US is only possible if:
- The channel is perfectly marked,
- Its measured length and manual widening leads to no. 15 (file k)
- Direct penetration with a US file inevitably leads to failure.
- During use:
- Avoid any pressure on the file
- 1st step: start to lower the file in place 1-2 mm
- 2nd step: operate the US irrigation
- 3rd step: lower the file to the length of the K-1 mm file
- These 3 times are accompanied by 3 types of alternating or simultaneous movements:
- Rotation during penetration as well as during withdrawal of the instrument to paint all the walls
- Prolonged back and forth to the apical limit
- Lateral translation movement.
D. Laser root canal preparation
Recently the potential of this technology has developed and several experiments have been conducted in endodontics .
The possibility of using the Laser in the canals is related to the physical properties of its irradiation which allows to remove tissue debris, microorganisms and other components of the canal.
Features of the Laser include:
– The wavelength, The dissipated energy, The use of an optical fiber which gives access to the canal networks .
- Protocol:
Initial penetration with K files (no. 10,15).
Suppression of interference in the 2/3 coronary with the laser fiber.
Manual preparation of the apical 1/3 (Helifile n°20,35)
Passage of the laser fiber over the entire length of the canal.
All these steps will be carried out under irrigation.
Conclusion
It is essential to understand that shaping is the cornerstone of successful endodontic treatment since it determines the quality of cleaning and filling of the root canal system.
Root canal preparations: Different techniques
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