CHAPTER 9: CLEANING & SHAPING THE ROOT CANAL SYSTEM

major objective of the root canal treatment procedure

to remove the contents of the pulp space and shape the walls of the canals to receive the filling material

cleaning

refers to the removal of all contents of the root canal system before and during shaping

which includes organic subtracts, microflora, bacterial by-products, food debris, caries, denticles pulp stones, previous root canal filling materials and dentinal shavings

shaping

refers to specific cavity form with five design objectives

• primary teeth: have minimal to no shaping – more on cleaning for RCT

• permanent teeth: After cleaning, there should be shaping or it could be done simultaneously

5 phases of root canal shaping

phase I - negotiating the canal (patency filling)

phase II - coronal pre-enlargement

phase III - working length measurement

phase IV - root canal shaping techniques

phase V - root canal working width

phase I - negotiating the canal (patency filling)

anesthetize → rubber dam isolation → access → patency filing

#6 pink, #8 gray, #10 violet – first files to introduce the canal with something small

phase II - coronal pre-enlargement

coronal third (orifice area) pre-enlargement using Gates Glidden, SX, and K-files

phase III - working length measurement

WL - reference point to the apical

rubber stopper – part of the instrument that indicates the length of the file (WL)

Endo Block – measures the instrument

phase V - root canal working width

width – taper of the preparation

apical gauging then obturation will follow

primary objectives of cleaning and shaping

remove infected soft and hard tissue

give disinfecting irrigants access to the apical canal space

create space for the delivery of medicaments and subsequent obturation

retain the integrity of radicular structures

ideal final apical size after rct

file #20, #30

can go bigger as it is a case-to-case basis

herbert schilder’s five mechanical objectives

never transport the foramen

make preparation in multiple planes

keep the apical foramen as small as is practical

develop a continuously tapering conical form in the root canal preparation

make the canal narrower apically with the narrowest cross-sectional diameter at its terminus

biological objectives

to completely debride the pulp space from:

• pulp tissue

• endotoxins

• dentinal debris

• bacteria / microorganisms

Enterococcus faecalis (E. Faecalis)

bacteria commonly found in root canal treated teeth

weine’s rules for canal preparation

preparation environment: always prepare canals in a wet environment to facilitate cutting efficiency and debris removal

instrument use: use instruments extravagantly, especially smaller files; employ patency files to establish and verify working length

canal shaping: enlarge the canal while preserving the general preoperative anatomy; create a shape sufficient for irrigation and obturation without over-preparing.

working length control: determine the working length and keep instruments within canal confines, stopping ~0.5 mm short of the radiographic apex; use an Electric Apex Locator (EAL) for precise apical position

motions of instrument manipulation

referred to as envelopes of motion; no motion is better than the other

• filling

• reaming

• turn and pull

• watch winding

• balanced force instrumentation

• anti-curvature filling

filling

the term indicates a push-pull action with the instrument

to scrape and smoothen the canal walls and used for shaping

similar to a nail file → push-pull or in-and-out of the canal; straightforward

risk: the inward passage of a K-type file under working loads is capable of damaging the canal wall very quickly, even when the slightest curvature is encountered

circumferential filling

enhances preparation when a flaring method is used by widening the orifice

first moved toward the buccal side, then reinserted and removed slightly mesially

continues around the preparation to the lingual aspect and then to the distal until all dentin walls have received rasping

(oval canals common in premolars; introduce the file along the circumference of the canal)

reaming

the term indicates clockwise or right-hand rotation of an instrument

twist it to the right then pull (may be risky but its subtle and goes unnoticed until an instrument fractures under the load)

to enlarge the canal and cut dentin; the rotating cutting edges cut dentin along the circumference, while the flutes collect and carry debris

divide the canal into 4 sections → insert the file → rotate slightly to the right (¼–½ turn) → push → repeat deeper → insert passively → rotate → pull out → repeat

turn and pull motion

a quarter turn to the right is followed by a straight outward pull

the arrow indicates a light inward force, which engages the file before rotation

sometimes, you can go a complete 360 turn clockwise then pull outward (more aggressive and actively cutting than reaming)

watch winding motion

to negotiate canals, achieve patency, and reduce instrument stress

back-and-forth oscillation of a file (30–60° right and 30–60° left) as the instrument is pushed forward into the canal

• procedure tips:

  • start with watch-winding to check canal patency

  • if the canal is constricted/narrow → continue with this motion

  • if the canal is wide → use filing motion

  • filing is performed last, after initial canal negotiation.

• clockwise rotation: pushes the file tip and working edges into the canal.

• counterclockwise rotation: partially cuts away engaged dentin.

balanced force technique

by james b. roane 1985

inward pressure and rotating force should always be very light.

stepwise motion: push → quarter turn to the right → push-pull → then turn ¾ counterclockwise

maintains canal curvature, safe in curved canals, reduces foramen transportation due to the balanced forces

• technique steps:

  • with apical pressure, perform a ¼ turn clockwise

  • again with apical pressure, perform a ¾ turn counterclockwise.

  • if done properly, a “click” is heard when the instrument cuts dentin.

  • repeat sequence 2–3 times.

anti-curvature filing

by Abou-Rass, Frank, and Glick.

to file away from the inner curve of a root to reduce the risk of strip perforation

technique in multirooted teeth: filing is concentrated on the bulky or safety zone using a push-and-pull motion, away from the danger zone.

• danger zone: always the inner surface of the tooth.

• safety zone reference:

  • if distal root, safety zone = mesial.

  • if mesial root, safety zone = distal.

strip perforation

recapitulation

re-instrumentation with a smaller instrument following each irrigation step

use of a smaller instrument to remove debris produced during instrumentation

prevents pushing debris beyond the apex and apical plug formation

every time you introduce a file inside the canal, you have to go back to the previously used file before proceeding to a bigger file; used in manual filing

example of its sequence:

• 6 → irrigate → 8→ irrigate → 6 → irrigate → 10 → irrigate → 8 → irrigate → 15 → irrigate → 10 → irrigate → 20 → irrigate → 15 → irrigate → 25 → irrigate → 20 → irrigate → 30

techniques of pulp space preparation

apical to coronal

coronal to apical

hybrid technique

apical to coronal

use of hand instruments

standardized preparation, roane balance force

step back preparation & modifications by (schilder, weine, passive step back)

involves preparation of the apical third initially followed by middle and coronal third of the canal using larger instruments

coronal instrumentation with reaming motion and apical instrumentation with circumferential filing

other term for apical to coronal

step – back

telescopic

serial root canal prep

advantages of apical to coronal

ability to prepare proper apical stop

popular technique employed with 2% SS files

conservation of tooth structure, especially in cervical third

disadvantages of apical to coronal

decreased volume of irrigating solution

procedural mishaps

apical plug formation

extrusion of debris into periapex

tendency to straighten the canal

other term for coronal to apical

step down

crown down pressure less technique

double flare technique

coronal to apical

reaming motion

use of hand and rotary instruments (*enlarge coronal third first)

Involves preparation of the coronal two thirds of the canal first followed by middle and apical third of the canal.

advantages of coronal to apical

shaping is easier

minimizes debris extrusion

better penetration of irrigants because wide on coronal

elimination of the bulk of microorganisms , tissue, and debris from middle coronal third before shaping apical third

disadvantages of coronal to apical

gauging of the apical third is done as the last phase of the procedure

hybrid technique

use of hand and rotary

step back step down combination procedure

Involves combination crown down and step- back techniques. Starts preparing the coronal then apical then fuse the two creating a smooth taper.

coronal instrumentation with reaming motion and apical instrumentation with circumferential filing

method of hybrid technique

starts with coronal third → apical third → middle third

crown down then Step back

achieving patency with pre curved no.10 or smaller K file

passive pressureless placement of sequential sizes of #15, 20, and 25 K files to the point of canal binding

coronal pre-enlargement with GG drills, SX or K files in the sequence no. 3, 2, and 1 (Not beyond 3-4 mm of canal orifice)

establishing the working length

placement of 40 or smaller k file to the point of canal binding

enlarging working length from size 15 K-file to recommended master apical file sizes

canal preparation done with sequential use of progressively larger instruments placed successively short of working length

this step back is performed till middle third to obtain continuous taper preparation

advantages of hybrid technique

most commonly used today

optimizes the advantages of crown down and step back techniques

disadvantages of hybrid technique

since 1984, Middle third portion should be carefully prepared in order to prepare a continuous tapered preparation

phase I of step back preparation

apical preparation up to the file #25 (MAF) to full WL with recapitulation using prior size files

In this example, start with 10 (patency file) → recapitulation Before proceeding to the next, you go back

• MAF → 25mm

• IAF → 10mm

phase II of step back preparation (serial filing)

ideally its just 3 files bigger: 30 35, 40, 45

its objective is to create a tapering conical shape

stepping back procedure in 1mm increments (go 1 mm short - standard)

recapitulation with no. 25 file till full working length → as you go shorter, you have to increase the diameter of the canal

Now apical area is prepared and steps are produced

• master apical file (MAF)

• initial apical file (IAF) → first file being introduced in the canal (apically) aside from patency files depending on the size of the canal

• (6, 8, 10 files cannot be your IAF since they are only used to check if the canal is present)

phase II-A of step back preparation

refining phase

gates glidden #2,3,4 are used to create coronal and middle preparations

phase II-B of step back preparation

return to #25 last file (MAF)

short of working length to smooth the step back with vertical push-pull strokes (circumferential filing) H-files used

guttmann “final prep should be exact replica of original canal configuragtion'“

always smoothen the area using MAF with filing motion (push – pull motion) to scrape off the steps created

sign that the step is already scraped off

smooth, glassy surface

final preparation

final form with smooth taper

able to prepare the apical stop

advantages of final preparation

better tactile awareness

keeps apical preparation small in its original position-graudal taper

ability to prepare proper apical stop

avoids zipping

disadvantages of final preparation

chances of pushing debris into peri-radicular tissues

WL likely to change as canal curvatures are eliminated

advantages of coronal to apical preparation

better tactile awareness in negotiating the delicate apical third microanatomy

it reduces pressure

holds greater volume of irrigant → enhances cleaning

removal of dentin mud decreases post treatment problems

improves identifying the foramen

EPT more reliable

disdvantages of coronal to apical preparation

increased removal of tooth structure

step down preparation

first suggested by schilder in 1974

goerig 1982 named and described the technique in detail

principle → coronal aspect of the root canal is prepared and cleaned before the apical part

procedure of step down preparation

in this method, the access cavity is filled with sodium hypochlorite and the first instrument is introduced into the canal

start with exploration of the canal with a fine, stainless steel, .02 taper (#8, 10, 15, 20, determined by the canal width). it is important that the canal be patent to the apical constriction before cleaning and shaping begin

sometimes the chosen file will not reach the apical constriction, and one assumes that the file is binding at the apex. but more often than not, the file is binding in the coronal canal

in this case, one should start with a wider (0.04 or 0.06 taper) instrument or a gates-glidden drill to free up the canal so that a fine instrument may reach the mid- and apical canal

prepare the coronal portion of the canal to the depth of 16-18mm or to the beginning of the curve using files #15, 20, 25 in a circumferential filing motion

gates-glidden drills 1,2,3 are then used to refine the coronal preparation, the #3 drill extending 1-2mm into the canal orifice

A → #3 GG drill, B → #2 GG drill, C → #1 GG drill

estimated working length

steps

• Pre-operative Radiograph

  • Measure crown length + refer to tables of tooth length

  • Estimate root length and entire working length

  • Take radiograph before prepping

  • Measure crown length radiographically or use average tooth length table

• Apical Patency Radiograph

  • Insert patency file until preliminary working length (PWL)

  • Take x-ray

  • Use 27 mm file (IWL/PWL)

  • 0.7 mm extrusion observed

  • Subtract 1 mm → adjust to 26 mm

  • Check if file goes beyond apex (nilapas) and if canals are present

  • Adjust if nilapas

• Working Length Determination (Crown Down)

  • Root length = EWL – Crown length

  • Divide root length into thirds:

    • Coronal third

    • Middle third

    • Apical third

  • Look for a file that binds at:

    • Crown length

    • Coronal third

    • Middle third

  • From file that binds at middle third:

    • Choose 3 larger files

    • Go 1 mm shorter as file size increases

• IAF Selection and Radiograph

  • Insert file that binds at apical third

  • Take radiograph to verify EWL

  • Working length using IAF = IWL

  • Look for file that binds at 26 mm

  • Example:

    • File #30 (IAF)

    • Next: #35, #40

• Serial Filing / Apical Preparation

  • From chosen IAF:

    • Choose 3 larger files

    • Maintain IWL for all

  • Serial files:

    • #30 – IAF

    • #35

    • #40 – MAF

• MAF Selection and Radiograph

  • Insert last file used (MAF)

  • Take radiograph

  • Check preparation up to apical third

• Step Back

  • From chosen MAF:

    • Choose 3 larger files

    • Go 1 mm shorter as file size increases

  • From 26 mm:

    • #45 – 25 mm

    • #50 – 24 mm

    • #55 – 23 mm

mishaps during cleaning and shaping

loss of working length

blockage of the canal system

ledging

breakage of instruments in the canal

zipping

stripping or lateral wall perforation

overinstrumentation

overpreparation / underpreparation

cause of loss of working length

due to rapid increases in file size and accumulation of dentinal debris in the apical 1/3 of the canal

malpositioned instrument stops

preventive measures of loss of working length

frequent irrigation with NaOCl

recapitulation

periodic radiographic verification of working length

proper use of instruments stops

use of directional stops in curved canals

cause of blockage of the canal system

packing of:

• dentin chips

• paper points

• tissue debris

• cotton pellets

• restorative materials

• fractured instrument in the canal

ledging

an artifically created irregularity on the surface of the root canal wall that prevents the placement of instruments to the apex of an otherwise patent canal

causes of ledging

attempt to prepare calcified canals

failure to pre-curve SS instruments

inadequate access cavity preparation

false estimation of pulp space direction

attempt to retrieve separated instruments

failure to use instruments in a sequential manner

causes of breakage of instruments in the canal

flexural fatigue

torsional fatigue 

management of breakage of instruments in the canal

Bypass 

Retrieval

prevention of breakage of instruments in the canal

Knowledge of the physical characteristics of the instrument 

Flaws, such as shiny areas or unwinding are detected on the flütes

Instrument bending or crimping occurs due to excessive use 

The file kinks instead of curving 

Corrosion is noted on the instrument

zipping

Refers to transportation of the apical portion of the canal

It is characterized by a normally curved canal which has been straightened, especially in the apical third

causes of zipping

Failure to pre-curve files

Rotation of instruments in Curved canals

The use of large, stiff Instruments to bore out a curved canal

stripping or lateral wall perforation

Refers to thinning of the lateral root wall with eventual perforation

causes of stripping or lateral wall perforation

Overzealous instrumentation in the mid-root areas of certain teal usuall molars

prevention of stripping or lateral wall perforation

Use of anti-curvature filing

Clean & shape the canals us files extravagantly & in a sequential manner

Avoid using large diameter instruments as instrument

overinstrumentation

Violates the periodontal ligament and alveolar bone

Loss of apical constriction creates: 

• An open apex 

• Lack of an adequate apical seal

• Pain & discomfort to the patient

overpreparation / underpreparation

It is the failure to remove pulp tissue, dentinal debris, and micro-organisms from the root canal system.

 treatment: "retreatment"

Underprepared canals are best managed by:

Proper length determination 

Canal cleaning & shaping

Recapitulation