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BIOMECHANICAL PREPARATION-I INTRODUCTION The second component of root canal treatment is canal preparation. Once the proper working length is established the endodontic canal preparation is chemo mechanical process. The term cleaning and shaping was associated with pervious endodontic teaching. In 21st century this has been changed to shaping and cleaning. Instruments used to readily shape the canal to permit the ingress of chemical agents into the root canal system.

Definition and objectives: Schilder introduced the concept of cleaning and shaping 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 root canal contents before and during shaping which includes substrates, micro-flora, bacterial products, food, caries etc. Shaping: Is the development of a logical cavity preparation that is specific for the anatomy of each root (Raiden et al, JOE 1998). Shaping refers to specific root canal form with particular design and objectives. It involves carving and predetermined removal of root canal structure to achieve a uniform, tapering, homogenous design.

The final design should be in such a way that it should permits effective irrigation and captures a maximum amount gutta-percha and sealer into all foramina without any extrusion of gutta-percha. Generally speaking, the main two main objectives of cleaning and shaping are Biological: Biologically the goal is to remove all pulp tissue remnants and microorganisms and their substrates along with infected dentin. Mechanical: To shape the canal in 3 dimensional design. Biological objectives: 1) Confine all instrumentation within root canal space to maintain its spatial integrity. Repeated instrumentation, extending beyond the constriction is unwarranted. It causes peri radicular inflammation and often destroys the normal biological constriction of root apex. 2) Avoid pushing contaminated debris past the confines of the apical constriction. In many instances, post treatment pain and swelling can be attributed to necrotic tissue and microorganisms and their toxins being inoculated into peri radicular tissues as a result of indiscriminate cleaning procedure. This induces rapid immunological response. 3) Remove all the potential irritants from entire root canal system. It helps in uneventful healing. 4) Establish exact working length 5) Create sufficient within the coronal half of the canal system to allow for copious flushing and debridement.

Mechanical objectives: 1) Develop continuously tapering form of root canal preparation. The final preparation should be an exact replica of the original canal configuration in shape, taper, and flow but only larger. 2) Prepare a sound apical dentin matrix at the dentino cemental (DC) junction. It provides the resistance form to the intraradicular cavity preparation. This also prevent over instrumentation and apical movement of gutta-percha sealer. 3) Prepare the canal to taper apically, with narrowest cross sectional diameter at apical termination. The apical third of canal preparation, especially apical 1/3 must provide a tapering / parallel spatial configuration in order to ensure a firm seating of the gutta-percha. It must also provide retentive cavity to enhance condensation procedures. 4) Confine cleaning and shaping procedures to the canal system, there by maintaining the spatial integrity of apical foramen. The delicate foramen sometimes moves or transport due to improper sequencing of instruments, insufficient irrigation.

The foramina may be transport internally or externally. The external transportation of foramen may be caused due to failing to precurve the files. This may occur in two forms

- Direct perforation (Blockage of apical foramen) -

Teardrop shape (over use of instrument)

Internal transportation occurs when portal of exit; is moved internal to its external position by blocking the canal.

5) Keep the apical foramen size as small as possible. The operator must clean the foramen by maintaining its patency, but do not enlarge or distort it. When size of apical foramen increases it not only increases the risk of tearing but it increases potential for microleakage.

PROCEDURAL TERMS: 1) Master apical file (MAF) It is the largest file that binds lightly at correct working length after straight line access. The file which binds first or smallest file is called initial apical file. 2) Recapitulation: It is an important step especially in apical coronal techniques. It means the use of the instruments in the correct size, and sequence from smaller to larger and returning to smaller instruments from time to time before advancing to a larger size. Eg: After 15 no., 10 then 20, then use 10 and 15 and proceed to 25 and so on. This helps prevent packing of fillings and ensures patency of root canal through the apical foramen.

3) Anti curvature filling: Described by Abou-Rose – It is a controlled as directed preparation into safety zone of root canal away from the danger zones.

Circumferential filing: Here instrument is first moved toward buccal side of the canal, then reinserted and moved mesially. This continues around the preparation to the lingual aspect and then to distal until all walls has been rasped





BASIC TERMS OF MOTIONS OF INSTRUMENTATION: BMP is a dynamically delicate motion. The motion should be flowing, rhythmic and energetic. There are 6 distinct, 6 motion of files and reamers. A) Follow: is usually performed with files. They are used initially during cleaning and shaping or any time an obstruction blocks the foramen. B) Follow-withdraw: It is a simple in and out motion performed with file. C) Cart: Extension of reamer to or near the radiographic terminus. D) Smooth: It refers to finishing the preparation with files. It is usually performed with circumferential filing motion. E) Patency: Refers to cleaning the portal of exit of root canal with small size


F) Gauging: refers to knowing the cross sectional diameter of the foramen that is confirmed by the size of the instruments that fits snugly at working length. G) Tuning: It is ensuring that each sequentially larger instrument uniformly backs out of canal by 0.5mm. H) Scouting: It is estimating the gauge and anatomy of root canal with help of instrument.

I) Filing / rasping: This term refers to push and pull action with instruments.

J)Reaming: Indicates clockwise / right hand rotation of an instrument. It is a rotating, pushing, motion limited to quarter to half turn. The instrument must be restrained from insertion to obtain cutting action. Reamers can be used in this motion. The instrument fracture is increased when this motion is employed.

K) full:


Turn is



combination of reaming and filling. Here file is inserted with ¼ clock wise and inwardly directed hand pressure (reaming) into canal by this action and file is withdrawn (filling).

Disadvantage: 1) Hourglass shape canal observed by Weine according to Schilder. According to Schilder, while performing this motion the file is not inserted toward apex rather it gradually moves the canal contents out of canal. Instead of this he suggested recombining half revolution in clockwise direction followed by withdrawal. a. Watch-winding: It is a back and forth oscillation of file (30-60°) to right and left as instrument pushed into the canal. It is an effective motion very useful during shaping procedures. 30-60° to right side rotation pushes the file tip and working edges into canal and 30-60° left side

counter clockwise rotation cuts away the engaged dentine. Therefore it is a predecessor of balanced force technique.

Advantages: 1. Canal






instrument. 2. It is less aggressive compared to the turn and pull motion. Because here file is not pushed far into the apical region, there is less chance of apical loading. b. Watch winding and pull: This is primarily used with Hedstrom files, when using H. files watch winding cannot cut dentin, it can only wiggle and wedge the horizontal unidirectional edges tightly into canal walls.

The file should inserted with right and left back and forth motion (rocking) until you meet resistance then file must be freed by pull stroke.

GENERAL GUIDE LINES FOR CLEANING AND SHAPING: 1) Direct straight line access 2) Rubber dam isolation 3) Accurate working length is very important 4) Use instruments sequentially with recapitulation 5) Instrument stops and reproducible reference points should be used.

6) Do not force the instruments and regularly inspect and debride instruments. 7) Use copious irrigation and instrument in wet canals. Various chemicals can be used like RC-Prep, EDTA, Glyde etc. 8) Confine instruments in root canal and do not force debris apically. 9) How much canal should be enlarged? a. Anatomical structure b. Accessibility of canal c. Skill of operator In adequate enlargement: limits cleaning, debridement, disinfection, obturation. Excessive enlargement: perforations, spatial movement of apical foramen and procedural problems. Earlier two guide lines are used -

Enlarge canal at least 3 sizes larger than that of first instrument which binds in the canal.


Enlarge the canal until clean, white dentinal shavings appear in flutes of instrument.

But these criteria is not valid today The root canal enlarged atleast till 25-30 number in the apical potion and no. 40 or larger in middle or coronal portion of root canal, will permit effective irrigation.


Standardized preparation


Stepback and its modifications


Roane balanced force technique.

Coronal apical -

Step down


Double flare


Crown down presureless


Canal master and technique

Hybrid technique: Step back and step down combination.

STANDARDIZED TECHNIQUE: By John Ingle (1961) done in narrow canals with circular cross sections. Standardized files are used

W.L determined ↓ Smallest instrument adjust to WL

↓ Sequentially enlarged the canal ↓ Obturate with silver points accepted


WL determined

Dentine removed by size 15 reamer

Dentine removed by size 20 reamer

Dentine removed by size 25 reamer

Disadvantages -

Risk of extrusion of debris


Alteration of WL


Difficult to debride complex canals


Possibility of canal deviation


Vertical root fracture if over instrumentation carried out

STEP BACK PREPARATION: (Telescopic or serial root canal preparation) Introduced by Klem Developed by Weine, Martin, Walton, and Mullaney. Indicated: Canal with narrow apical constriction and Steps:

Determine working length ↓ Take the instrument which fits into C.W.L. and file circumferentially and till next instrument reaches WL irrigate. ↓ Repeat until no 25 or two sizes larger than the fill which binds at apex.

↓ Once no. 25 file reaches to WL then each larger size file should used to prepare canal by reducing 1mm (Explain using diagram) ↓ After each file it is very important to recapitulate with smaller number file (No.25) with copious irrigation to maintain patency. ↓ Refine coronal preparation with G.G Ds (No.1, 2, 3)


WL determined

Stepping back by 2mm from WL at size 35

Sequentially enlarged canal Stepping back by 1mm from WL at size 30 till #25 to full wl in circumferential manner

Stepping back by 5mm from Refining coronal flare with WL at size 50 GG 1,2,3

Advantages: -

Less periapical trauma


More debris removal


Greater flare, more G.P. peak


No over extrusion of G.P due to develop of apical matrix


Increase condensation pressure can exerted → fills more accessory and lateral canals.

Disadvantages: -

Apical blockage


Alteration of W.L.


Tendency for canal deviation.

PASSIVE STEP BACK PREPARATION: Passive step back preparation was proposed by Torabinajad in 1994. Here the combination of rotary and hand instruments are used for root canal preparation. Here enlargement of root in apical to coronal without application of force i.e., rotating at 1/8 to Âź turn. Advantage: Reduces the risk of apical transportation. MODIFIED STEP BACK: Here after apical preparation, the step back procedures begin 2-3mm up the canal. This provides short almost parallel retention form to receive primary gutta-percha.

BALANCED FORCE TECHNIQUE: Introduced by Roane and Sabala in 1985. -

Flex R files are commonly used for this technique.


Canals are enlarged to 3 predesignated sizes 45, 60, 80 according to size of apical preparation.


This dimension refers to the size of the file used at third step back.


Each step back from master apical file at PDL is 0.5mm shorter than previous one. This apical preparation zone is called apical control zone.

Here we preparing canal not till apical constriction or foramen but to radiographic length corresponding to the PDL. Thus it will prepare its own apical constriction. Here instrument is used in an oscillatory motion i.e., right and left with different arc in different direction. To insert an instrument it is rotated quarter turn in a clockwise direction (right) with gentle inward pressure. It pulls the instrument into the canal and engages the cutting edges equally in all directions into the surrounding walls. Next the instrument rotated counter clockwise (left) at least 1/3 of revolution. This motion unthreads the instrument and drives it out from canal. In order to prevent this and obtain cutting action clinician must press inward pressure while giving this rotation.

Once the file has reached the desired WL length the files is made free by one or more counter clockwise rotation. Then file is removed from canal with slow clockwise rotation, which effectively loads debris into flutes and removes away from the canal. Caution: The inward pressure and rotating force should always very light. Steps: 

Irrigate coronal part of canal.

Determine the largest file which will reach radiographic apex without force. This will helps in the selection of predesigned preparation i.e., 45, 60, 80.

Now Flex-R files are used to the apex create apical control zone.

Smoothing and accentuating flare of coronal two third is done using Gates glidden drill (i.e., 2, 3, 4, 5, 6). The Gates Glidden drill should remain 3-6 short of working length.

Advantages: This balance maintains the file in central even in curved canal.

It avoids transportations (Montgomery 1988) Disadvantage: Strip perforations.


WL determined

Size 40, 1mm short of WL

Enlarge the canal to size 25 to full WL

Size 30, 0.5mm short of WL

Size 45, 1mm short of WL

Gates Glidden size 26 to compare the complete flare


Suggested by Schilder in 1974


Goerig named and explained technique in detail.

Principle: Coronal aspect of root canal prepared and cleaned before the apical part. Steps: 1) Prepare coronal part of canal to depth 16-18mm or beginning of curve using H.file i.e, starting from 15, 20 and 25. 2) Refine coronal portion of preparation with no 1, 2, 3 G.Gs. -

Find out working length


Now using step back technique to complete the preparation.

Advantages: – Reduces the canal curvature enabling straighter access to the apical region. – Allows early debridement of the coronal part of the canal which may contain bulk of organic debris. – Enables better and deeper penetration of irrigant early in the preparation. – Allows better control over apical instrumentation. – Less extrusion of debris

Disadvantages: 1) Formations of ledges, apical blockage and perforations.


16-18mm coronal part of canal prepared with H-file

Coronal flare prepared with GG 123

WL determined enlarge till no.25 to full WL

Prepare apical portion by step back

DOUBLE FLARE TECHNIQUE OR HYBRID TECHNIQUE: Steps: Determine working length ↓ Introduce larger instrument coronal to curve in canal. This instrument should fit loosely in the canal. ↓ Irrigate introduce next size instrument 1mm deeper than the previous one ↓ Again go 1mm deeper with next size instrument ↓ Continue till working length is established (Confirm with radiograph) ↓ Now prepare the canal by step back technique Indications: - For straight canals. - Straight portion of curved canals. Contraindications: -

In calcified canals


Young permanent teeth with open apices.


WL determined

File with size 10 to 1mm deeper than size 15 (now at WL)

Introduce larger file about 14mm coronal portion of the canal

File with no. 30, 1mm deeper than size 35

Prepare the canal with size 25 at Prepare apical portion of canal by full WL step back preparation.

CROWN DOWN PRESSURELESS TECHNIQUE: Indication: Curved canals. Aim: Facilitate preparation curved canals without causing the deviation Here the rotary action is used to prepare the canal. Steps: -

Determine the radicular access by placing no.35 file till the 16mm of coronal portion of canal. If this file is not going inside the canal instrument canal with smaller instrument.


Determine provisional W.L. 3mm short of apex using radiograph.


Place no.35 file as far it goes without apical force. At this point turn two full revolutions without apical force.


Now use next smaller size (no. 30) in a same way.


Repeat the sequence till you reached provisional W.L.


Determine definitive working length.


Now prepare the canal starting from no.40 till the W.L. reached.


Again start with no. 45


Then with No. 50

Advantage: - Less extrusion of debris -

Effective in maintaining canal shape.


Less chance of alteration of W.L. CROWN DOWN PRESSURELESS TECHNIQUE

Determine radicular access

Prepare the canal 15 no. file at full WL

Widen 16mm of coronal portion of canal till 35 no.

Repeat the sequence with 45

Prepare the canal with 30 no. file without apical force

Prepare the canal 20 no. file at full WL


Prepare the canal with 10 no. file without apical force

Repeat the sequence starting with size 50

Repeat the sequence starting with size 40

Prepare the canal 25 no. file at full WL

Here root canal preparation is done using a special instrument which cuts only at apical 1-2mm of root canal. They come in both hand held and mechanized. The apical 0.75mm of the hand instrument is safe ended and helps in maintain of curvature. Steps: -

Determine working length


Prepare to the beginning of the curve using rotary instrument i.e., starting from no. 50 to 80.


Now prepare the curve in step back fashion.

Advantage: Avoids the need of recapulation. Disadvantage: The instruments have tendency to fortune.


WL determined

Prepare the canal with size 50 to full WL

Prepare the beginning of the curve using canal master-U (size 50)

Size 55 1mm shorter than WL

Size 80 in instrument to beginning of curve

Prepare the canal with size 20 to full WL

Size 60 2mm shorter than WL

Size 80 4mm shorter than WL


As an instrument is curved an internal elastic forces are developed. These force the attempt to return the instrument to its original shape. This mainly acts at the junction of instrument tip and cutting edges. This force is mainly responsible for alteration or straightening of the final canal shape and location. Guidelines precautions: 1) Pre-curving of instruments therefore facilitate easy insertion and prevent ledging. Curvature can be estimated by reviewing the diagnostic radiograph or use of small number files. Precurving can be done by grasping the blade with a gauze sponge and carefully bending with the blades of files until desired curvature is attained. 2) Anti-curvature filing – Described by Abou-Rass et al, Frank and Glick. It is controlled or directed preparation into safety zones of root canal away from danger zones method of applying instrument pressure so that shaping occur away from the inside of root curvature especially in coronal and middle 1/3rd of canal. The file should be moved away from the inside of curve, so that the cutting flutes are only against the safer part of root canal. 3) Radicular access: Described by Schilder. It creates more space in coronal portion of canal which enhances placing and manipulating subsequent files and increases the depth of irrigation. It is done by using rotary instrument / circumferential filing.

4) Double or Bayonet shaped canal: First clean the apical foramen with no.10 file. No introduce small H.file to junction of middle and apical third of canal and file the inner portion of curve.

5) Dilacerated canal: ďƒ˜ Enlarge cervical and middle third of canal first. ďƒ˜ Now introduce small H-file to beginning of curve and do circumferential filing. Irrigate and recapitulate with small no. 10 file.

This should performed till middle and cervical third of canals opens so that apical third can be instrumented without forcing the instruments. Now the prepare the canal using no.15 file by dulling its outer portion in apical third and inner portion in middle third of instrument. It will prevent the transportation of apical foramen and over instrumentation. Reverse flaring / preflaring: Here coronal portion of root canal flared before the completion of apical portion. Advantage: ďƒ˜ Effective penetration of irrigate which produce more cleaning. ďƒ˜ It removes the dentine interferences in coronal part






instrumentation in apical area. ďƒ˜ Plugger and filling materials penetrate to apex more easily through large orifice. Instrument used are:


0.4 taper Ni-Ti instrument.


Me-XIM i. Made up Ni-Ti ii. Available in different taper iii. Run in greater reduction hand piece at 340rpm.

6) Extremely narrow canals: Smaller instruments and mid sized Golden medium files along with chemical chelators. ROOT CANAL PREPARATION USING AUTOMATED DEVICE: Preparation of root canal using hand instruments is hard work and time consuming. So most of the operator used engine driven instruments for cleaning of root canal. Many of automated devices are available all of which has advantages and disadvantages. None of these are most predictable as compare to hand instruments. Classification: Based on type of movement of cutting instruments 1) Rotary: Eg: Gates Glidden, Peesoreamer, Canal master. They are used in the straight part of canal with very slow speed. For this group now new 16:1 gear handpiece is added. It runs at 300rpm. It runs Ni-Ti files. They mainly used for preparation of curved canals.

Reciprocal quarter turn: In this type the instrument activated by 90 째 reciprocate arc.

Giromatic handpiece Reciprocal quarter turn

Example: -

Giromatic – first introduced i. Giro-pointer 16mm long orifice opener ii. Giro-broach iii. Giro-file H. configuration iv. Giro-reamer





The giromatic hand piece rotates the instrument in the high speed of 1000cycles /min.



The instrument packs the debris in the canal.


Preparation takes longer time and had a tendency to create ledges and flaring in apex


Less effective compared to hand instruments (Grossman)


Difficult in use narrow canals.

Vertical: In this the hand piece produces vertical movement (0.3-1mm) with free rotational movement.

Vertical movement with free rotation



Canal finder system: For this canal master U and H file with safe ended tip may be attached.


Canal leader: It 4:1 speed reduction hand piece. It has a vertical movement of 0.4-0.8mm and contra lateral rotation which is restricted to 30째.

3 cutting instruments: -

K-file with safe ended tip




H-file with safe ended tip.

Random: These hand pieces will produce random lateral vibrational movement. This rotates at 20,000-25,000 rpm modified K-file can be attached to this hand piece.

Disadvantage: Handpiece some what bulky and difficult or especially when using in posterior part of the mouth.


Sonic air 1500


Mega sonic 1400

They operate at 1500-6500 cycles/minute. The vibrational wave form is generated in hand piece and it is transferred to shank of the file. Due to this file move both in lateral and vertical direction. The cleaning also enhanced by acoustic micro streaming at middle and tip of the shank.

Endosonic hand piece with file

It will accept 3 types of files - Rispisonic (coronal 2/3rd of canal) -

Heli-sonic file





For apical 1/ 3rd

ULTRA SONIC OSCILLATION: Here ultrasonic oscillations are produced in file shank. It consists piezoelectric unit which generate ultrasonic wave which activate magnetostrictive stack hand piece when activated produce movement of shaft.

Piezoelectric ultrasonic unit

Ultrasonic file holder

The greater amount of movement seen at file tip in a frequency 20,000 to 25,000 / second. Two types of files are available: -

Modified K file at tip


Diamond impregnated file.

File should activate only after insertion into the canal. File should moved circumferential motion with smooth push and pull stroke along the walls canal for a period of one minute with copious irrigation with NaOCl. This should repeat with 20, 25 no. files. Advantages: 1) More cleaning due to acoustic micro streaming.

Acoustic micro streaming

2) Chemical and bactericidal action of irrigant enhanced due heat which generated during movement of file.

LASERS: Weichman and Johnson are suggested use of laser in endodontics in 1971. Initially Nd: YAG, CO2 laser were used. Recently Argon laser, Excimer, Holmium, YAG laser, with various wave length are tried. Er: YAG laser at 8Hz &2W is widely used.

Fiber optic tip

Laser Unit Fiber optic tip inside the root canal

These can be delivered using optical fiber with 200-400mm diameter (equal to no 20-40 file) along with air water spray as a coolant. Action: By melting the dentin surface and vaporization of debris and pulpal tissue remnants. Straight / slightly curved, wide root canals are good indications.

Steps: -

W.L determined


Enlarge apical region with # 15 with copious irrigation (irrigants like)


Begin the preparation with laser energy level at 150milli joules.


Fiber optic inserted to W.L. and enlargement done circumferentially first apically then coronally to enlarge upto #60 instrument.


Four exposures of 15 seconds are made

The average time to complete the preparation is 1 minute. Levy compared the laser technique with a step back procedure and found the former is better. The recently: ArF Excimer at 193nm; XeCl at 308nm are also tried for root canal preparation. NON-INSTRUMENTATION





PREPARATION: Lussi et al (1993) introduced a device that cleanses the root canal without instrumentation. It consists of pump that is inserted with an irrigant (like NaOCl), it is attached to root canal through tubes. The cleaning is by bubbling and cavitation which loosened the debris in the canal. This debris removed out side by negative pressure (suction). Disadvantage: It cleans the root canal but it will not do any shaping.

SMEAR LAYER MANAGEMENT: When the blades of any file engage and cut dentine a smear layer of organic and inorganic debris formed in root canal. If the smear layer is removed then tighter interface between the obturation material and dentine walls is possible. If smear layer is left then root canal system is incompletely sealed and potential for microleakage and subsequent failure increases significantly. Various chemicals are available to removal of smear layer. -

17% EDTA




EDTA and micro-brushes can be used with rotary or ultrasonic hand pieces.

CONCLUSION “Cleaning and Shaping is a game and, as such, can be played at various skill levels. Visualizing and executing great play can move the clinician towards mastery and winning the inner game of endodontics.� - Ruddle


Bmp 1 corrected/ dental implant courses by Indian dental academy