PRINCIPLES AND TECHNIQUES OF CANAL SHAPING
I- Definition
Endodontic treatment (ET) is a clinical procedure that is applied from the coronal end to the apical end of a canal network of a tooth or root and which consists, after etiological, positive and differential diagnosis:
– to eliminate and neutralize all organic substances contained in the canal network (debridement, trimming),
– to widen the main channel,
– to block the canal network.
II- Objectives
a. Biological objectives:
- Trimming:
- Removal of all living or dead pulp tissue
ii. Respect for the periapex:
- No toxic irritation (do not propel necrotic debris beyond the foramen):
- No mechanical irritation
- No chemical irritation
b. Mechanical objectives:
i. Conicity: it allows:
- Instrument control in the apical region.
- Irrigation, by better penetration of the syringe needle inside the canal
- Three-dimensional shuttering
- Penetration of compaction instruments into the apical region
ii. Tracing : the shape of the prepared canal must be traced, in a wider form, on its original anatomy.
iii. Position of the foramen : the apical foramen should be maintained in its original spatial position on the root surface and kept as small as possible
III-Operative times of canal preparation
i-Anesthesia:
It is essential if the pulp is alive, it allows for operating comfort.
ii- operating field : the best way to do it is by dam
iii-access cavity: it is specific to each type of tooth, it must allow:
- easy penetration of endodontic instruments
- easy removal of root canal debris
- provide a reservoir for the irrigation solution
iiii-catheterization (initial penetration):
- A) Choice of type and number of the first penetration instrument: Weine recommends reserving a No. 08 K file for calcified canals and using No. 15 or even No. 20 as the first instrument, depending on the case.
- B) Pre-curvature of the instruments : Two types of pre-curvature can be achieved using the Maillefer instrument: an apical pre-curvature (mandatory) “or tight pre-curvature of 30 to 40°”
- and/or a regular “progressive” pre-curvature of the entire blade
- C) Initial canal exploration techniques:
1-manual techniques: a K file is introduced into the canal until it is blocked, a 1/8 turn movement is given to the instrument with a slight apical push then another 1/8 turn movement in the opposite direction is given to the instrument to facilitate its removal, the maneuver is repeated until reaching the apical limit, a chelator can be used.
2-mixed techniques : it aims to eliminate obstacles at the level of the coronal 2/3 of the canal using a rotating instrument (Gates-Glidden, Les Orifices Openers) and explore the apical 1/3 using a manual K file
iiiiii-Determination of working length
A.DEFINITION OF WORKING LENGTH:
- it is the distance which joins a precise point of a crown or a free edge of a tooth to the apical limit of the preparation
- It is important to mark the operative length on the instrument before introducing it into the canal using a stop relative to a coronal reference point, preferably healthy and flat and not likely to be jeopardized during treatment.
B. Measurement techniques:
1. Empirical methods : Based on the operator’s tactile sense and experience or on the patient’s painful sensation when exceeding the apical limit,
2. Radiographic methods:
- Bisection and rule of three:
The length of the tooth will be determined by the following formula: L= [(AC)/B ]- D
- D= (0.5 to 2mm) depending on the age of the patient (this is the length of the apical foramen)
- A = Radiological length of the tooth
- B= Radiological Length of the instrument to the Stop
- c: Length of the instrument to the stop.
- b-Parallel techniques and measurement : since the technique presents real dimensions of the radiological image, the working length will be taken directly on the image
- c-The BEVERIDGE technique:
-1st step : examine the pre-op image and measure the canal length
-2nd step: report the presumptive length on the instrument and take a file radio in place .
Several situations may arise
- The file appears to have reached the set limit (0.5 mm or 1 mm) of the radiographic apical end.
- The file is below the chosen limit: the instrument is then pushed to the missing length.
- The file is beyond the chosen limit, it is immediately removed by its excess length compared to the chosen apical limit.
- d- software measurement (RVG): Thanks to the RVG, it is possible to measure the working length using specific software based on digital data
3. Electronic determination of LT:
Definition: An apex locator is actually an ohmmeter connected to two electrodes:
- An oral electrode, in contact with the skin, represents the measurement of the resistance of the periodontal ligament; the other, fixed to the endodontic catheterization instrument, measures the intracanal resistance. The electrodes are connected to a box on which we can read on a dial with a needle, by a light and/or sound indicator, digital screen, the achievement of the canal length.
Benefits
- They reliably and accurately determine the position of the apical foramen.
- Deduce the position of the apical constriction (cemento-dentin junction)
- Protect against apical overshoots.
- Reduce radiation exposure to the patient
- Reduce operating time
Disadvantages
- High cost.
- Some models work poorly with teeth that have a very open apex or very wide canals.
- Need evidence for files by means of X-rays
B. choice of working limits
- Living tooth: LT at the physiological apex, the foramen must be spared from any instrumentation because it only contains the desmodont which is a key element in healing
- Necrotic tooth: LT at the radiological apex
IV-Root shaping techniques
1-Concepts of root canal preparation
Schilder’s A-Concept (flame preparation)
This involves reaming the canal, eliminating all irregularities, of course to the detriment of the root dentin structure. This preparation is also characterized by the creation of a “stop cone” at the apical narrowing, in order to avoid any risk of excess filling material. Originally designed to allow condensation of hot gutta
Weine’s B-Concept: Step-back preparation (1977)
This involves preparing the canal starting with the apical portion of the canal and going towards the coronal part of the canal from the catheterization to file no. 25 ( master apical file ), from this number any file that follows must be subtracted 1 mm from the working length.
C-Concept of Marshall and Pappin: Crown-Down preparation (1980)
The “crown-down” involves cleaning and shaping the canal from the coronal third to the apical third.
2-Root canal preparation techniques
a-Manual technique: (serial technique)
- Definition of the master apical file: it is the file of largest diameter which reaches the working length without constraint
- Definition of the permeability file: it is the file of smaller diameter which ensures canal permeability during preparation
- Principle:
This involves preparing the canal from catheterization to final shaping, using manual instruments of increasing diameter without ever skipping numbers under abundant irrigation.
The transition to the instrument of a higher Ø will only be made if the previous instrument is free in the canal, at the working length, up to 25/100 minimum, with a return to an instrument of a lower diameter if necessary.
- Instrumental sequence:
- K-Brooch or File: No. 15 20 25 (to LT) 30 (LT -1) 30 (LT -2)
- File H : 15 20 25 (at LT) 30 (LT -1) 35 (LT -2)
b-Mixed technique:
It takes place in 2 stages:
1st Phase of preparation of the coronal 2/3 of the canal
Its purpose is to eliminate any obstacles and coronal irregularities of the canal in order to facilitate the passage of manual instruments to the apical end and can be done:
- Either by running a sequence of Gate Gliden drills (n°1,2,3 and 4)
- either by passing Niti instruments (taper 08%, 06% then 4%)
- either by passing ultrasonic endodontic inserts
2nd phase: preparation of the apical 1/3 of the canal:
It is done by passing a sequence of manual instruments and respecting the same rules of the serial technique and the preparation must end with file n 30
c-Mechanized techniques:
They are made with Niti instruments mounted on a contra-angle itself connected to a motor, the latter offers the instruments a rotation speed and a torque adjustable and adapted to each instrumental system as well as a clutch system.
We can describe:
- Root canal preparation that meets the concept of Crown Down
- Variable Taper System The ProTaper® is currently the only instrument with variable taper. It is also a cutting instrument. Recent scientific studies have shown that the ProTaper® allows efficient and rapid root canal shaping of thin and curved canals without transporting the canal trajectory. The main advantage of variable taper is that it ensures flexibility adapted to the different instruments making up the system. Thus, a significant taper is given to the instrument only where work is desired in the canal.
- Instrumental sequence
- 1-Hand steel K files of diameter 10 and 15, coated with Glyde File Prep® are used for the initial negotiation and preparation of the accessible portion of the canal. This initial negotiation is not intended to bring these instruments to the apex but to ensure the patency of the canal.
- 2-The SI is used without exceeding the penetration depth of the K 15 file in order to widen and shape the portion of the canal permeabilized with the hand files.
- 3-Shaping File SX is used without pressure, with a back and forth and brushing motion on the opposite wall, in order to straighten the coronal access
- 4-the pre-curved 10 or 15 hand files are pushed towards the apical 1/3 to determine the working length and then widen this portion
- 5-The SI is advanced to the working length, by the same brushing movement associated with the back and forth, supporting the withdrawal against the canal walls
- 6-The S2 is then advanced to the working length, in the same way as the SI
- 7-The FI is advanced to the working length; The FI, as well as the other Finishing Files, are used in back and forth movements only.
- Constant taper system (eg FKG® system)
The instruments are numbered
- R1 (6% taper and 15/100 diameter)
- R2 (4% taper and 25/100 diameter)
- R3 (4% taper and 30/100 diameter)
- Instrumental sequence
- Bring the R1 back to the accessible portion of the canal
- Bring the R2 back to working length
- Bring the R3 back to working length
2-New concept of root canal preparation
- A-Reciprocity:
- The reciprocal movement consists of animating the files of high conicity with a clockwise/anticlockwise movement of variable amplitude. The screwing movement is greater in amplitude than the unscrewing movement, which avoids pushing debris in the apical direction. Several systems have been proposed, e.g.: WaveOne®, Reciproc®, etc.
operating protocol (EX; wave one): the preparation is single-instrumental
- After creating the access cavity and identifying the canal entrance, the canal is explored using a K 10 hand file, then pre-widened manually.
- Shaping the accessible portion of the channel with the reciprocal instrument (primary wave one: for thin channels, secondary wave one; for wide channels)
- Exploration of the apical portion of the canal with a K 10 file and pre-widening
- Shaping the 1/3apical with the wave one instrument
- B – Self Adjusting File® (SAF) System
- The SAF® instrument consists of a compressible hollow tube, 1.5 or 2 mm in diameter, composed of a nickel-titanium mesh,
- This “soft” instrument, since it has a hollow body, adapts to the shape of the canal into which it is introduced. The instrument is coupled to an irrigation system.
PRINCIPLES AND TECHNIQUES OF CANAL SHAPING
Operating protocol
- the canal is shaped to a minimum diameter of 20, using manual instruments .
- The SAF®, in active vibration mode, is then gently inserted into the canal up to the working length and then moved vertically back and forth under continuous irrigation.
PRINCIPLES AND TECHNIQUES OF CANAL SHAPING
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