Monday morning, the doctor walks into the clinic relaxed after the weekend and opens the appointment register. Call on my first case he remarks, full of enthusiasm and vigor and then what does he see-the first case is Oh no! My God-BMP. Good morning and welcome to today’s seminar on Biomechanical preparation during endodontic therapy. Let’s delve deeper under the following subheadings:
CONTENTS Introduction Definition and objectives Basic terms and motions of instrumentation General principles and Techniques of biomechanical preparation a) Hand
Apical coronal Coronal apical
b) Automated Curvatures and cleaning and shaping Advances in automated instrumentation and adjuvant techniques Conclusion and Bibliography INTRODUCTION Yes, the root canal system is complicatedly complex. Accessory and lateral canals, isthmuses, calcifications, curvatures and what not combine to form a daunting challenge to the astute clinician. Achieving not just vertical access but true 3 dimensional preparation is an issue that has and still vexes a majority of clinicians as evidenced by the myriad techniques and instrumentation that have spawned in the quest for ideal cleaning and shaping. Just as nothing is constant but change so too in the root canal nothing is predictable except the unpredictable. Along with diligent access preparation, canal location and working length determination only through biomechanical preparation, will ensure good obturation and healing. Understanding that a denture is as good as its initial impression, an inlay as good as the tooth preparation and an obturation as good as the biomechanical preparation, let us explore the rationale and techniques to achieve that perfect canal preparation. 1
DEFINITION AND OBJECTIVES: Schilder introduced the concept of â€œCleaning and Shapingâ€? almost 3-4 decades ago. Biomechanical preparation refers to the controlled removal of dentin and root canal contents by manipulation of root canal instruments and materials. It consists of cleaning and shaping. Cleaning: Refers to the removal of all contents of the root canal system before and during shaping including substrates, microflora, bacterial products, foods, caries etc. Shaping: Refers to a specific root canal form with particular design objectives. It involves the carving and predetermined removal of root canal structure to achieve a uniform, tapering homogeneous design. The final shape permits effective irrigation, obturating instrumentation and general hydraulics required to transform and capture a maximum cushion of guttapercha and sealer into all foramina with three dimensionality and no extrusion being achieved. 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 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: Biological: Biologically, the goal of intracanal procedures is to remove all pulp tissue remnants and micro-organisms and their substrates along with infected dentin. Mechanical: Mechanically 3-D shaping of the canal is the objective which must be accomplished to achieve biologic cleaning. Biologic objectives include: 1. Confine all instrumentation within the root canal space (apical constriction) to maintain its spatial integrity. Repeated instrumentation extending beyond the constriction is unwarranted. It 2
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. Many instances of post treatment pain and swelling can be attributed to necrotic tissue and micro-organisms and their toxins being inoculated into the peri-radicular tissues as a result of indiscriminate cleaning procedures. This induces a rapid immunologic response. 3. Remove all the potential irritants from the entire canal system. This avoids recurrent peri-radicular inflammation and creates a condition that permits prompt, uneventful healing. 4. Establish the exact W.L and completely clean and shape the canal system. 5. Create sufficient width in the coronal half of the canal system to allow for copious flushing and debridement. Mechanical Objectives include: 1. Develop a continuously tapering 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 â€œbored outâ€? with the clinician failing to consider the spatial relationship of the canal to the overall root anatomy. 2. Prepare a sound apical dentin matrix at the DC junction. This provides the resistance form to the intraradicular cavity preparation. This also prevents the over-extension 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). 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. The three-dimensional shape of the preparation, especially of the apical 1/3rd, must provide a retentive cavity to enhance condensation procedures. 3
4. Confine cleaning and shaping procedures to the canal system, thereby maintaining the spatial integrity of the apical foramen. Adherence to this principle prevents violation of the periradicular tissues. This principle is evident when foramina are transported (moved) (zip and elbow)during excessive apical instrumentation. This can be internal or external transportation. 5. Remove all residue of cleaning and shaping procedures that could prevent patency of the apical foramen i.e. dentin shavings and tissue debris. This will help prevent complications like ledges, loss of canal length, development of false canals etc. Recapitulation is essential to all cleaning procedures as ignoring this important step will often lead to ledges, loss of canal length, dev of false canals etc. Procedural terms: 1) MAF-Master apical file: It is the largest file that binds slightly at correct WL after straight line access. 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. The file binding at first or smallest file to bind is initial apical file. 2) Pre curving of instruments Precurving of stainless steel instruments is mandatory while negotiating curved canals. It is a valuable tool for feeling canal passages and for moving around calcifications, ledges and around curved foramina. It helps to prevent procedural problems and perform adequate shaping in curvatures. Precurving can be done either with cotton or gauze or using commercialy available devices utilizing the diagnostic x-ray. 3) Recapitulation : An essential step especially in apical coronal techniques â€“ it means the use of instruments in the correct size sequence smaller to larger and returning to smaller instruments from time to time before advancing to a larger size. E.g. after 15 no. 10mm them proceed to 20, then use 10 and 15 and proceed to 25 and so on. This helps prevent packing of dentinal filings and ensures patency of root canal through to the apical foramen. 4) Anticurvature filing-Filing away from curvatures and danger areas described in detail under curvatures. Basic terms of Motions of instrumentation â€“ BMP is a dynamically delicate motion â€“ flowing, rhythmic and energetic. Various motions involved are: 4
Methods of Cleaning and Shaping Cleaning and shaping are dynamically delicate 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, precurving different kinds of curves, curving all the way to the tip of the instrument and multiple curves in multiple directions of the instrument are all part of follow. A)
Files are used. This motion is used once the foramen has been reached 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 – and – out passive motion that makes no attempt to shape the canal. B)
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. C)
Carve Reamers are used for shaping. The key is not to press the instrument apically but simply to touch the dentin with a precurved reamer and shape on withdrawal randomly.
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. 5
Also included are 2 other terms given by Ruddle-Gauging and Tuning. Gauging refers to the knowing the cross sectional diameter of the foramen that is confirmed by the size of the instrument that “snugs in” at working length. Tuning is ensuring that each sequentially larger instrument uniformly backs out of the canal by 0.5 mm. Also included is scouting that refers to using instruments to gauge and estimate the root canal anatomy, form and variations and is same as follow. Motion of instrumentation / envelopes of motion: A)
Filing: Indicates a push-pull motion of the instrument. The inward passage is powered by hand and file rigidity. Cutting is done during withdrawal or pull stroke. Done using files and usually in circumferential manner. Reaming Indicates clockwise / right-hand rotation of an instrument. The instrument must be restrained from insertion to generate a cutting effect. Instrument # is increased when this motion is employed. It is a rotating-pushing motion limited to a quarter to half turn.
Turn-and-pull(Combination) 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. 6
¼ turn to right followed by straight pull out D)
Watch-winding Is the back-and-forth oscillation of a file (30-60°) right and left as the instrument is pushed into the canal. It is an expanded use of the “Vaiven” technique described by Ingle. This back and forth motion can be combined with a pull stroke and effectively planes walls. It has various advantages like canal centering, not necessitating precurving and balancing tooth structure cutting with instrument mechanics. 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.
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. General Guidelines for cleaning and shaping: 1.
Direct straight line access should be obtained.
rubber dam is a prerequisite and microscopes are an asset.
Accurate length determination is a prerequisite. Remember canal length may shorten on instrumentation of curved canals.
Instruments should be used sequentially with recapitulation.
Instrument stops and reproducible reference points should be used.
Do not force instruments and regularly inspect and debride instruments.
Use copious irrigation and instrument in wet canals. Various chemical aids can be used to supplement preparation like RC prep, EDTA, Glyde etc.
Confine instruments to root canal and do not force debris apically.
How much to enlarge is a priceless question- How large and how much to enlarge is dictated by the anatomic structure, accessibility of the canal and skill of the operator. Inadequate enlargement limits cleaning, debridement, disinfection and obturation while overzealous preparation leads to iatrogenic problems, unnecessary weaking of tooth and susceptibility to fracture, perforations, spatial movement of apical foramen etc. Earlier 2 guidelines were considered sacrosanct- enlarge a root canal at least 3 sizes beyond the size of the first instrument that binds and enlarge a canal until clean white dentinal shavings appear in the flutes. However, these are not considered valid criteria today by any researcher or clinician. Studies have shown that only enlargement upto 30 to 40 number permits effective irrigation though this may not be always possible. Thus enlarging the root canal should be 8
done based on myriad factors to achieve both biological and mechanical objectives.
Techniques for preparing root canals: Apical coronal technique
In which the WL is established In which the coronal portion of the canal and the full length of the canal is is prepared before determining the WL then prepared. e.g.
Roane (balanced force)
Allows early debridement of the coronal part of canal which may contain bulk of organic debris.
Enables better and deeper penetration of irrigant early in the preparation.
Tends to shorten the effective WL and determining the WL after such enlargement will reduce the problem of its alteration during preparation.
Allows better control over apical instrumentation.
Reduces the piston-in-acylinder effect responsible for debris extrusion
However, there are risks of ledging, blockage and perforation.
e.g. : -
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.
Unlikely to debride complex canals
Possibility of canal deviation.
To overcome deficiencies a hybrid technique consisting of reaming the apical third and filing the coronal twothird has been recommended with coronal preparation obturated with gutta percha. Step back preparation: WL determined. Instrument that fills to correct WL is chosen. Enlarge 3 No’s larger at the apex. Reduce the WL length by 1mm and continue to enlarge canal / flaring. 10
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:(Marshall and Papus) -
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. 11
Determine WL. Using step-back, complete the apical preparation. Disadvantages: -
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 12
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.
An amalgamation of various techniques can be used combing different desirable aspects and convenience to achieve thorough biomechanical preparation. 14
SPECIAL CONSIDERATIONS IN CURVATURES-CONVENTIONS AND COMPLICATIONS 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 -
Is the controlled and directed preparation into the 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.
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 1/3rd 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. This dimensionally applied pressure, prevents 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.
Radicular access Was first promoted by Schilder. 15
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.
Reverse 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 enlargement of the coronal part apex is completed 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. 16
Also for curved canals copious irrigation is mandatory.
Safe sided instruments and files dulled on one side can be employed or NiTi instruments can be used.
Extremely narrow canals require the use of smaller instruments and mid size Golden Medium files along with chemical chelators etc.
Double curved or bayonet shaped canals-Here after the apical foramen has been cleaned and shaped the middle third curve is eliminated with H-files taking care not to strip and perforate and then regular instrumentation carried out. This is done by introducing a small H-file at the junction of middle an apical third and filing away inner portion of the curve.
Dilacerated roots require coronal flaring and then using flexible and safe sided instruments.
Preparation using Automated Devices or Mechanical Instrumentation The lure of faster, easier and more efficient cleaning and shaping has spawned various types of automated devices. There is literally a revolution going on in automated devices with new brands and techniques introduced everyday. Disadvantages: -
Loss of tactile sense and lack of control of where and how much dentine is removed from the root canal wall.
Classification: I) Rotary -
Used in slow running standard handpiece e.g., GGD, Peeso, Canal master â€“ used only in the structure part.
Latest addition 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. 17
Myriad nickel titanium generation of instruments and devices like ProFile, ProTaper, Quantec, Light Speed, OS etc have been introduced.
Reciprocal quarter turn: -
This uses a special handpiece that contrarotates the 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. 18
H-file. Universal file (flexible H-file with a safe-ended tip). There are few basic guidelines for rotary shaping: 2) Straight line access. 3) Estimating the cross-sectional diameter. 4) Familarizing with specific root canal anatomy and seating. 5) Speed and sequencing with gear reduction and electric motor and using large to small files. 6) Lubrication and a light or feather touch equivalent to using sharp lead pencil. IV)
Endosonic Air 3000
Reduces fatigue and stress during preparation.
- Requires H2O cooling
- Most common - No H2O cooling - May produce apical widening and ledges in curved canals.
Cleaning effect is by acoustic streaming. 19
I) Microbrushes: Advancement in small wire technology, injection molding, bristle materials and bristle attachment have enabled the creation of endodontic microbrushes. These can be activated by rotary or ultrasonics and are primarily intended for finishing root canals. They contain 16mm bristle with D0 diameter of 0.4, 0.5, 0.6 and 0.8. Rotary brushes are run at about 300 rpm while ultrasonic ones are run with NaOCl and 17% EDTA. II) Lasers: In 1971, Weichman and Johnson were probably the first to suggest the use of laser in endodontics. Initially Nd:YAG and CO2 lasers were used. They are mainly advocated as a coadjunct for microbial reduction and to readily root surface. Recently, argon lasers, excimer laser, holmium:YAG laser, diode laser and erbium : YAG laser with various wavelength have been investigated. These can be delivered using a optical fibre 200-400Âľm diameter equivalent to # 20-40 file cooling systems with air water sprays may accessory this. Levy compared the laser technique with a step back procedure finding the form better. The technique was: 1.
Enlarge apical region with # 15 file + copious irrigation.
Preparation begins with the laser energy level set at 150milli joules.
Fibre optic is inserted to W:L and enlargement done circumferentially first apically tehn moving coronally to enlarges upto #60 instrument.
The avg. time to complete the preparation was 1 minute. Although hand instruments left some walls untouched and smear layer was found covering walls, laser preparation showed remarkable cleanliness. However Levy also found melting of dentin and closing off of tubules and melting of silicon fiber optic. Similarly various other lasers have been experimented with. Currently wavelength at UV plaster appears promising. The ArF excimer laser at 193nm and XeCl (308nm) laser appear well suited. Second harmonic alexandrite laser (377nm) also shows promise. 20
Mainly today lasers are advocated for cleaning or sterilizing the root canal and shaping is a modality under investigation. The laser is excellent at satisfying the root canal. Future promises of efficient preparation, sterile canals, shorter treatment time and minimum effort with maximum result are fuelling laser research at break neck speed. Potential disadvantages of cost, safety, coolants, effective control etc have to be overcome. Lasers have a definitive future in endodontics only the direction has to be delineated. Non instrumented root canal cleansing: Lussi et al introduced devices to cleanse the root canal without instrumentation. The 1st device reported in 1993 consisted of a ‘pump’ that inserted an irrigant (like NaOCl) creating bubbles and cavitation that loosened debris. This process was followed by negative pressure (suction) that removed debris. More recently a smaller new improved machine was introduced. Also ozone pumps like healizae have been veritified in cleansing root canal systems. Finalizing the preparation: After cleaning and shaping by any of the mind baggling variety of techniques it is necessary to finagling the preparation and manage the smear layer. Through a controversial topic, if divided to be removed, smear layer removal and final finishing is accomplished cutter with EDTA and ultrasonics, EDTA and microbrushes with NaOCl or other newly available chemicals for its management to provide a root canal now ready for obstruction. CONCLUSION: “Try cleaning a house after a wild party.” Cleaning and shaping root canals is just more difficult. The complex anatomy, convoluted curvatures, non-negotiable interconnections and hard to reach nooks and crevices make for a challenging and daunting task. “Purity is considered the hallmark of sanctity”. Obtaining clean and sterile root canals is the secret of good healing. Also the revolution of automated endodontic combined with advances in hand instrumentation have changed the long we shape and clean canals. Thus combining the art of proper shaping and the science of immaculate cleaning will culminate in ideal biomechanical preparation that will lay the foundation for ideal obturation and healing and ultimately successful therapy. Bibliography: 21
1. Endodontics – Stock, Gulabivala, Walker, Goodman. 2. Endodontics – Ingle and Bakeland. 3. Endodontic practice – Grossman, Oliet, Rio. 4. Endodontics – Cohen and Burn. 5. DCNA.