Introduction In an endodontic treatment, the root canal system is our road map to success. In the past, we have been thinking only vertically. Many students were taught that the first concern in root canal preparation was “working length”. Now, we understand that the critical issue is three-dimensionality. Root canals exist as multiple inter-relationships. Root canal systems are not cylinders but ribbons, sheets and banners. Eccentrically and abnormality are “normal”. Almost 30 years ago, Schilder introduced the concept “cleaning and shaping”. These 2 concepts are inseparable. The secret to successful clinical endodontics is proper shaping.
Cleaning: Refers to the removal of all contents of the root canal system before and during shaping. Substrates, microflora, bacterial products, foods, caries etc. Shaping Refers to a specific cavity form with particular design objectives. The shape permits vertical pluggers to fit freely within the root canal system and to general hydraulics
maximum cushion of gutta-percha and sealer into all foramina. The purpose of this seminar is to provide the rationale and techniques for proper cleaning and shaping of the root canal system, which will enable the clinician to obturate the system. As with many aspects of dental profession, such as a denture being no better than the initial impression, or an inlay being no better than the tooth preparation, it 2
follows that canal obturation will be no better than the cleaning and shaping of the entire system. Generally speaking, the 2 main objectives in canal cleaning and shaping are: Biologic
shaping of the canal is the
procedures is to remove all
pulp tissue remnants and
infected dentin. BIOLOGIC OBJECTIVES 1. Confine all instrumentation within the root canal space to maintain its spatial integrity. Repeated
constriction is unwarranted. It causes peri-radicular inflammation and often destroys the normal biologic constriction of the root apex.
2. Avoid pushing contaminated debris past the confines of the apical constriction. ď‚ž Many instances of post treatment pain and swelling can be attributed to necrotic tissue and micro-organism and their toxins being inoculated into the peri-radicular tissues
response. 3. Remove all the potential irritants from the entire canal system. ď‚ž This avoids recurrent peri-radicular inflammatory and creates a condition that permits prompt, uneventful healing. 4. Establish the exact W.L and completely clean and shape the canal system during the first treatment visit. 5. Create sufficient width in the coronal half of the canal system to allow for copious flushing and debridement.
MECHANICAL OBJECTIVES 1. Develop a continuously tapering conical form in the root canal preparation. The final preparation of this system should be an exact replica of the original canal configuration in shape, taper, and flow only larger. Only too often, canals are simply “bored out” with the clinician failing to consider the spatial relationship of the canal to the overall root anatomy. 2. Prepare a sound apical dentine matrix at the DC junction. This provides the resistance form to the intraradicular cavity preparation. This also prevents the overextension of instruments and controls the apical movement of gutta-percha sealer during obturation.
3. Prepare the canal to taper apically, with the narrowest crosssectional diameter at the apical termination (apical dentin matrix). ď‚ž The apical third of the canal preparation must provide a tapering / parallel, spatial configuration in order to ensure a firm seating of the gutta-percha and sealer. ď‚ž The
especially of the apical 1/3 rd , must provide a retentive cavity to enhance condensation procedures. 4. Confine cleaning and shaping procedures to the canal system, thereby maintaining the spatial integrity of the apical foramen. ď‚ž Adherence to this principle prevents violation of the peri-radicular tissues. This principle is evident when foramina are transported (moved) during excessive apical instructions.
External transportations takes 2 Internal forms
beyond the apical matrix.
occurs becomes mud
Ripping of the Direct apical
foramen begins with a
a ledge or apical / blockage
External transmission is caused by failing to precurve files, or being too heavy handed 5. Remove all residue of cleaning and shaping procedures that could prevent patency of the apical foramen i.e. dentin shavings and tissue debris. ď‚ž Recapitulation is essential to all cleaning procedures ignoring this important step will often lead to ledges, loss of canal length, dev of false canals etc.
Preparatory procedures 1)
MAF-Master apical file Is the largest file that binds slightly at correct WL after straight line assess. It is determined by passively placing the successively larger files at the C.W.L. until correct size is reached which binds at the tip.
Pre curving of instruments A precurved file is a valuable tool for feeling canal passages and for moving around calcification, ledges and around curved foramina. It is used also in an attempt to alleviate the diverse effects of canal curvature. The primary difficulty is limited areas coronal to the curvature. May be done with a cotton wool roll, commercial devices.
Methods of Cleaning and Shaping Cleaning
motions, flowing, rhythmic, and energetic. In order to use files and reamers efficiently, the movements require distinction. There are 6 distinctive motions of files and reamers. A)
Follow: Usually performed with files. Are used initially during cleaning and shaping or any time an obstruction blocks the foramen. Irrigating,
curving al the way to the tip of the instrument, and multiple curves in multiple directions of the instrument are all part of follow. A)
Follow-withdraw Files are used.
This motion is used once the foramen has been reched and the next step is to create the path from access cavity to foramen. The motion is follow, then withdraw or “follow and pull” or “follow and remove”. It is simply an in – or – out, passive motion that makes no attempt to shape the canal. B)
Cart Refers to the extension of a reamer, to or near the radiographic terminus. The reamer should gently and randomly touch the dentinal walls and “cart” away debris.
Carve Is for shaping. Reamers are used.
The key is not to press the instrument apically but simply and to touch the dentin with a precurves reamer and shape on withdrawal randomly. D)
Smooth Is accomplished with files. In the past, most endo procedures were performed with a smoothing or circumferential filing motion. If the previous four motions are followed smoothing is rarely required.
Patency Is achieved with files/ reamers. It means that the portal of exit has been cleared of any debris in the path.
Motion of instrumentation / envelopes of motion: A)
Filing: Indicates a push-pull action with the instrument. The inward passage of the file is powered by the hand and the rigidity of the file. A canal wall can be damaged very quickly by this motion (use of passive insertion and pulling withdrawal from canal). This is an effective technique with H-file since they do not engage during the insertion action and cut efficiently during the withdrawal motion.
Disadvantages: With H-file that it can easily cut three middle of a curvature and cause strip perforation. B)
instrument. The instrument must be restrained from
insertion to generate a cutting effect. Instrument # is increased when this motion is employed. C)
Turn-and-pull Is a combination of reaming and filling, the file is inserted with a ¼ turn clockwise and inwardly directed hand pressure (i.e. reaming) positioned into the canal by this action, the file is subsequently withdrawn (i.e. filling). The rotation during placement sets the cutting edges of the file into dentin and the non-rotating withdrawal breaks local the dentin that has been engaged.
Disadvantages: Hourglass canal shapes were observed by Weine. According to Schilder Clockwise rotation of a half-revolution followed by withdrawal. The file is not inserted towards the apex,
rather, he gradually allows the preparation to progress out of the canal. ¼ turn to right followed by straight pull out D)
Watch-winding Is the back-and-forth oscilation of a file (30-60°) right and (30-60°) left as the instrument is pushed into the canal. It is an expanded use of the insertion technique described by Ingle as “Vaiven”. This back-and-forth movement causes the files and reamers to plane the walls efficiently. In a way, this is a predecessor to the balanced force technique, as the 30-60° of clockwise rotation pushes the file tip and working edges into the canal and the 30-60° of counter clockwise motion partially cuts away the engaged dentin.
Watch-winding and pull When used with H-files, watch winding cannot cut dentin with the backstroke. It can only wiggle and wedge the edges tightly into the wall. With each clockwise turn, the instrument moves apically until it meets resistance and must be freed with a pull stroke.
Balanced force technique This calls for oscillation of the preparation instruments right and left with different arcs in either direction. To insert an instrument, it is rotated to the right (clockwise) a quarter turn. This pulls the instrument into the canal and positions the cutting edges into the walls. Next, it is rotated left (counterclockwise) at least 1/3 rd of the revolution to unthread the instrument and drive it from the canal.
Advantages: ď‚ž Simultaneous apical and counter-clockwise rotation of file strikes a balance between the tooth structure and instrument elastic memory. This balance locates the instrument very near the canal axis, even in severely curved canals, so this technique avoids transportation. ď‚ž It works effectively without pre-curving.
Techniques for preparing root canals: Apical coronal technique
In which the WL is established In which the coronal portion of and the full length of the canal is the
determining the WL
debridement of the coronal
Roane (balanced force)
deeper penetration of irrigant early in the preparation.
Tends to shorten the effective WL and determining the
enlargement will reduce the problem
Allows better control over apical instrumentation.
Apical coronal 1) -
Standardized preparation: Done in narrow canals with circular cross-sections. WL determined. Smallest instrument adjusted to WL. Sequentially enlarged entire canal. Obturation with silver cone.
Risk of extrusion of debris.
Alteration of WL.
Vertical root # is overinstrumentation is carried out.
Step back preparation: WL determined. Instrument that fills to correct WL is chosen. Enlarge 3 No’s larger at the apex. 18
Reduce the WL length by 1mm and continue to enlarge canal / flaring. Recapitulate, irrigate for patency. Coronal preparation done using GGD. Disadvantages: -
Extrusion of debris.
Alteration of W.L.
Tendency for canal deviations.
Roane Technique (Balanced Force)
Three of its main features are: -
Canals are prepared to predesigned dimensions of which 3 are recognized and are 45, 60 and 80 according to the size of apical preparation.
These dimensions refer to the size of the file used at the third step back.
Each step-back from the master apical file at the PDL is 0.5mm shorter than the previous one. This is termed as the “apical control zone”.
Flex R files are used.
WL determined to the radiographic apex with the largest file placed without force. This helps in determining the selection of predesigned preparation (45, 60, 80).
Coronal apical technique 1) Step down technique: -
Is a modification of the step-back technique.
Prepare the coronal portion to 16-18 mm /beginning of the curve with anti-curvature filling. GGD’s are used to refine the coronal part. Determine WL. Using step-back, complete the apical preparation. Disadvantages: -
Perforation. Through this technique overcomes most of the disadvantages
of the step-back technique.
2) Double Flared Technique: Determine W.L. Prepare till 14 mm / coronal to the curve. Irrigate and clean. Go 1mm deeper, maintaining instrumentation coronal to the curve and file. Again 1mm deeper. Continue till WL is achieved. Prepare using step-back Indications: -
For straight canals or
For straight portions of curved canals.
Contra indications: -
In calcified canals.
In young permanent teeth with open apices.
3) Crown-down pressureless technique: -
For curved canals without causing deviations. Rotary action is used to cut dentine with the apical part of files.
Determine WL and prepare till # 35 till 16mm (widen the canal with smaller files first) Reduce size + go down and enlarge till apex. Change to #40 + repeat. 4) Canal master technique: -
Its aim is to aid the maintenance of curves using a rotary instrument designed so that only the apical 1-2mm is engaged in dentine removal.
Avoids the need for recapitulation.
The apical 0.75mm of the hand instrument is safe-ended to facilitate maintenance of canal curvature. Determine WL Prepare to the beginning of the curve Use canal master in step-back fashion.
Consists of reaming the apical third and filing the coronal two-thirds.
The coronal preparation is obturated using gutta-percha.
CURVATURE-THE ENGINE OF COMPLICATIONS -
As an instrument is curved, elastic forces develop internally. These forces attempt to return the instrument to its original shape and are responsible for straightening of the final canal shape and location.
These internal elastic forces (i.e. restoring forces) act on the canal wall during preparation and influence the amount of dentin removed. They are particularly influential at the junction of the instrument tip and its cutting edges. This region is the most efficient cutting surface along an instrument, and when activated by the restoring forces, it removes more tissue. This phenomenon is responsible for apical transportation and its consequences.
1) Pre-curving of instruments. 2) Anti-curvature filing -
bulky/safety zones and away from the thinner portions or danger zones of the root structure, where perforation or stripping of the canal walls can occur. Need: -
It is a method of applying instrument pressure so that shaping will occur away from the inside of the root curvature in the coronal and middle 1/3 rd of a canal.
Was described by Abou-Rose, Frank and Glick. They emphasized that during shaping procedures, files should be pulled from canals as pressure is applied to the outside canal wall.
dangerous midcurvature straightening in curved canals.
It maintains the integrity of canal walls at their thin portion and reduces the possibility of root perforation / stripping.
Maintains digital control over the instrument and the preparation of the curved canal is used.
Top of the handle is pulled into the curvature while the shank is pulled away (anticurvature)
Radicular access -
Was first promoted by Schilder.
This creates space in the more coronal regions of the canal which enhances placing and manipulating subsequent files as it increases the depth and effectiveness of irrigation.
May be accompanied by rotary instrument / circumferential filing.
Reversible Flaring / Pre-flaring -
Is the presently preferred development of flaring whereby the coronal portion of the preparation is flared before the completion of the apical portion.
In the standard flaring technique, the apical portion of the tooth is completed before any filling is performed.
In the reverse flaring and aspects of preparations are carried out.
Minimal filling at the tip ďƒ enlargement of the coronal part ďƒ apex is completed ďƒ apical flaring.
Irrigants are allowed to get down the canal earlier and farther to produce cleaning.
In curved canals, more effective preparation of the apical area is provided when the file has fewer obstructions in the coronal part.
Files, pluggers, filling material can penetrate to the apex more easily three a larger orifice.
Instruments used for Reverse Flaring -
0.4 taper instruments (Ni-Ti).
MeXIM Available in 5 instruments – 25.0.25 at Do (0.03, 0.04, 0.045, 0.05, 0.055 /mm – tapers). Used in gear reduction handpieces at 340 rpm. Made from Ni-Ti in H-style. Designed by MacSpadden. Ritano Files. Hand instrument with H-configuration with several tapers. Made in lengths shorter than 21mm.
Preparation using Automated Devices Disadvantages: -
Loss of tactile sense and lack of control of where and how much dentine is removed from the root canal wall.
Used in slow running standard handpiece e.g., GGD, Peeso, Canal master â€“ used only in the structure part.
Latest deviation is the new 16:1 gear reduction handpiece NiTi matic at 300rpm.
Ni-Ti files are used.
Used for preparation of severely curved canals.
Files are manufactured with an off-centre tip that facilitates negotiating around curvatures and ledges.
Reciprocal quarter turn: -
instrument three 90Â°. -
E.g. Giromatic (1964).
Endolift â€“ has a vertical component in addition to the rotation.
Disadvantages of Automated -
Hand instrument requires the same amount of time as automated.
Flare preparation with hand instrument tends to remove debris from within the canal system than automated.
Automated is difficult to use in the most post regions of the oral cavity.
There is greater propensity for the automated system to produce zipped canals, ledges etc.
A controlled power-assisted system designed to eliminate the original problems encountered by Giromatic appeared in 1981.
Uses stainless steel instruments with increased flexibility consist flute depth and curved canals and rounded tip to minimize and control ledges, zips, etc.
Has a vertical movement of 3-1 mm and free rotational movement.
Instrument used is canal master (H-file with a safe ended tip).
Vertical movement of 0.4-0.8 mm
3 instrument K-file with a safe ended tip. H-file. Universal file (flexible H-file with a safe-ended tip). IV)
Endosonic Air 3000
Reduces fatigue and stress during preparation.
- Requires H 2 O cooling
- Most common - No H 2 O cooling - May produce apical widening and ledges in curved canals.
Cleaning effect is by acoustic streaming.
Contents Introduction Mechanical & Biological Objectives Methods of Cleaning & Shaping Methods of Instrumentation Techniques for Preparing Root canal Hand Apical coronal
Automated Coronal Apical
Cleaning & Shaping in curved canals