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` Following the completion of adequate coronal
access preparation, the most critical act inassuring the success of endo dontic therapy is the
accurate determination of working length prior to
the radicular preparation.
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DEFINITION
` WL defined as ³the distance from a coronal
reference point to the point at which canal
preparation and obturation should
terminate´(Ingle)
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` Should not change
b/w appointments
` undermined cusps &
fillings, they should
be reduced considerably
before access preparation
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` Anatomic apex- is ³tip or end of root determinedmorphologically´
` Radiographic apex - is ³tip or end of rootdetermined radiographically´
` It is an artificial measurement which is
reproducible.
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Apical constriction ± [minor diameter = CDJ]
` Apical portion of root canal which has narrowestdiameter [simon 1993]
` coincides with CDJ [Kuttler 1955]
Apical foramen - is main apical opening of the rootcanal which may be located away from anatomic or radiographic apex
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` CDJ- is the region where cementum and dentin areunited
` Varies from tooth to tooth, root ± root, wall ± wall
` The point at which cemental surface terminates at or near the apex of tooth.
` It is not always coincide with apical constriction
` Location of CDJ ranges from 0.5-3mm short of anatomicapex
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` WL determines how far into canal ,
` It effects degree of pain & discomfort which pt willexperience
` If placed in correct limits, it plays an important role indetermining the su ccess of treatment
` Before determining a definite WL, there should bestraight line access for the canal orifice for unobstructed penetration of instrument into apicalconstriction
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` Apical perforation.
` Over instrumentation& over filling.
` Increased incidence of post operative pain.
` Prolonged healing time.
` Reduced success rate.
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` Incomplete instrumentation& under filling
` Ledge formation.
` Apical percolation into the unfilled ³dead space´ at theapex.
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R ADIOGR APHIC :
Ingle¶s method
Wein¶s method
Grossman's method
Radiovisiography
Xeroradiography
Tactile / apical periodontal sensitivity
Absorbent Paper point evaluation
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Electronic Methods ( Apex locators) : Resistance Type
Impedance Type
Frequency Type
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` 1) must be accurate
` 2)easily & readily performed
` 3) easily confirmed.
` Working knowledge of the average length of all
the teeth is foremost in order to prevent errors.
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maxillary mandibular ` Central 21.8 20.8
` Lateral 23.1 22.6
` Canine 26 25
` 1st premolar 21.5 21.9` 2nd premolar 21.6 22.3
` 1st molar 21.3 21.9
` 2nd molar 21.7 22.4
` 3rd molar 17.1 18.5
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Stop attachment
Endo-M-block
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` Clinician should develop the mental image of the position of the rubber stop on the instrument shaft ,
` Any movement from that position should be
immediately detected & corrected
` where it meets the reference point on the tooth
` Essential to record the reference point & WL of each instrument in the pt¶s chart
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Disadvantages of using rubber stops
`Not only is it time consuming, butrubber stops may move up or down the
shaft,
which may lead to preparations short or past the A. constriction
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` Instruments have been developed with millimeter marking rings etched or grooved into the shaft of theinstrument
` These act as a built-in a ruler with the markings placed
at 18,19,20,22 & 24 mm
` Marking rings ±best coronal reference point on thetooth is at the cavo-incisal or cavo-occlusal angle
` The marking rings are necessary when rotary Ni-Tiinstruments are used
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` Radiographic method of length determination
involves measurement of radiographic apex and
then subtracting a specific value from that length
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` Measure the tooth on the
preoperative radiograph
` Subtract at least 1.0mm ³safetyallowance´ for possible imagedistortion or magnification
Set the endodontic ruler & adjust the
stop on the instrument at that level
INGLE¶S METHOD
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` On radiograph,
measure thedifference b/w the
end of the instrument
& end of the root
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` From the adjusted length
of tooth, subtract 1.0 mm
³safety factor ́ ± to confirm
with the apical terminationof the root at apical constriction
` New corrected length
&readjust the stop on theexploring instrument
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` Because possibility of radiographic distortion, sharplycurving roots, & operator measuring error , aconfirmatory radiograph of the adjusted length is highlydesirable
` When the length of the tooth has been accuratelyconfirmed, reset the endodontic r u ler at this
measurement
` Record final WL and the coronal point of reference onthe pt¶s record
` Length of the tooth in a c u rved canal be reconfirmed after instrumentation is completed
` curved canal is straightened out by instrumentation
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` The magnification effect of the radiograph.` Magnification of 2 mm (d u e to divergence of
the central beam) is allowed for all teeth.
` Thus: 26mm=length measured on radiograph.
` -1mm=difference between radiographic
apex and actual foramen.
` -2mm=magnification factor
23mm=estimated WL (acc to WALTON)
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A periradicular lesion will resorb bone
and apical root structure.
Bone resorption is apparent, probably there isalso root resorption, Even though it may notapparent radio graphically
If there is root resorption, the apical constriction isprobably destroyed ± hence the shorter moveback up the canal
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WL distance from the apex is determined
when radio graphically there is:
No bone or root resorption: 1 mm from apex
Bone but no root resorption: 1.5 mm from
apex
` Bone and root resorption: 2 mm from
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` After working to estimated WL with size
15 or 20 file a radiograph is taken.
Corrected
WLis determined bymeasuring the discrepancy between the
tip of the file and the radiographic apex.
` The file is then adjusted to 1 to 2 mmshort of the radiographic apex.
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` Buccal object rule basic concept is vertical or horizontalangulation of X-ray tube changes, the object buccal or
closest to tube head moves to opposite side of radiograph compared to the lingual object
` To separate the buccal & lingual roots to visualize the WL
tube head should be moved from a20
degreem
esialangulation
` Buccal root to the opposite or distal side of radiogrph & lingual root on mesial side (SLOB)
` Misinterpretation still possible
` This can be reduced by using different types of files (K,H)or different file sizes in different canals
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Actual lengthof the tooth =
GROSSMAN·S Method
Actual length of the instrument xapparent length of tooth in radiograph
apparent length of instrument in
radiograph
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` If the coronal portion of the canal is not constricted, an experiencedclinician may detect an increase in resistance as the file approachesthe apical 2-3mm
` Accuracy is 64%` Inexact` Ineffective with immature apex` Highly inaccurate if the canal i s constricted throughout its entire
length/ if the canal has excessive curvature` Considered as supplementary to high quality, carefully aligned,
parallel,WL radiographs or an apex locator ` Survey few general dentist & no endodontists trust` Even most experienced specialist would be prudent to use 2 or
more methods
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Limitations of tactile methods :-
When coronal portion is constricted ( i.e coronal 2/3rd )the clinician cannot discern the apical anatomy with
accuracy ,since contacts in the cervical regions that
interfere with and often mask contacts in the apical area.
This may be over come by coronal 2/3rd preparation (radicular access /step down ) to improve the quality of
tactile information .
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` When the entire length of canal is constricted.
` When the canal has excessive /unusual curvature
.` Ineffective in root canals with an immature apex
,root resorption .
` By itself this method is often inexact , hence canbe used as a supplementary to more precise
methods .
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` Based on pt response to pain, doesn¶t meet the idealmethod
` Therapy has gained a notorious reputation for being
painful,&
it is incumbent on dentists to avoidperpetuating the fear of endodontists by inserting anendodontic instrument & using the pt pain reaction todetermine WL
` Inflamed tissue, HP developed inside the canal may
cause moderate to severe, instantaneous pain
` Little useful information but considerable damage isdone to the pt¶s trust
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Supplementary method useful in
I mmat u re apex ( wide open ) ± reliable means of
working length estimation ,by gently passing the
blunt end of a paper point into the canal after profound anesthesia has been achieved
` Moisture or blood on the apical portion that
passes Beyond the apex may be an estimation
of WL or the junction between the root apex andthe bone.
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R esorption /perforation ±
` Cases where apical constriction has been lost (without free bleeding or suppuration ) the
moisture/ blood is estimate of amount of
overextended preparation .
Type : -
` Sterilized paper points (Pre-Sterile ),Color
coded ( IS
O size).` Newer Calibrated (mm markings
18,19,20,22and 26).
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All apex locators function by
using human body to complete
electric circuit.
One side of apex locators
circuits connected to an
endodontic instrument and other
connected to patients body
How does it work ?
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` Designed to determine canal length by
³reading´ when vital tissue has been
reached by the file tip at the apical
foramen.
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` Resistance apex locators, measure apposition tothe flow of direct current or resistance
` Sono-explorer was imported from Japan by
Amadent
` Today most of the 1st gen. Apex Location devicesare off the market
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RESISTANCE TYPE
` Measured the differencein resistance between thepulp and periodontalligament (6k)
` Uses direct current
` Requires dry field for accurate measurements
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` Advantages:
` Easy to operate
` Digital read out` Audible indication.
` Disadvantages:
` Requires dry field.
` can not be estimated beyond 2mm.` Requires calibration.
` Pt sensitivity.
` Requires lip clip with good contact.
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IMPEDANCE TYPE
` Based on impedance
measurements at same or different frequencies
` Uses alternating current
` Can be used in wet field.` Uses insulated probes.
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` Based on principle of impedance
` Impedance systems are based on the theory
that the root canal, a long hollow tube, develops
an electrical impedance, caused by transparentdentin deposition which exhibits a sharp
decrease at the cementodentinal junction which
can be measured electrically
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` Advantages:
` Operates in fluid environment
` Analoge meter ` No pt sensitivity
` No lip clip required.
` Disadvantages:
Difficult to operate.
No digital read out.
Requires coated probes.
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` Impedence Apex Locators, measure apposition to theflow of alternating current
` Sono explorer - developed by Inoue` Apex finder ` Endo analyzer ` Digipex` Digipex ± ll` Exact- A-Pex` Foramatron iv +` Dio
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` Flashing LED light and
a digital LED display
Small,Lightweight,
Inexpensive
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FREQUENCYDEPENDENT M u ltiple freq u ency type
` Uses multiple frequencies to determine theposition of the file in the canal
` Uses alternating current
` Difference method/ratio method
` Can be used in wet/dry fields
` Most accurate among the three
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` Measures the impedance difference between two
frequencies or the ratio of two electrical impedance to
define position of file.
Difference method : -
Works by comparing the difference in impedance using the
relative
value of two alternating currents at frequency of 1 and 5kHz .
As file moves towards the apex , the difference becomes
greater and
shows the greatest value at the apical constricture allowing for measurement of that location
For example - Endex
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` Ratio method : -
` Measures the impedance of 0.4 kHz and 8 khz at thesame time .
` Calculates the quotient of impedance and expressesthe quotient in terms of position of the file inside the
canalThis quotient values are not affected by the electrical
condition inside the canal
In addition it is unnecessary to calibrate this device each
time because the microprocessor automatically controls the
calculated quotient to the a relationship with the file
position and the digital read out .
For example- Root ZX
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` Frequency dependent, impedence of a given circuitmay be substantially influenced by the frequency of thecurrent flow
` Endex` Neosono ultimo Ez apex locator ` Mark v plus` JUSTWO orJUSTY II` APEX FINDER A.F. A.` Endo Analyzer 8005 ( AL& PT)` ROOT ZX` Tri Auto ZX
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` Advantages:
` Easy to operate.
` Operates in fluid environment.
` Analoge read-out, audible indication
` Rechargeable.
`
Disadvantages:
` Can be short circuted.
` Requires a lip clip with good lip contact.
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` Uses dual- frequency &comparative impedence
principlesMeasures 2-impedences
at 2- frequencies (8 and 0.4 kHz)
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FREQUENCY DEPENDENT
T wo frequency type
Eg:Elements diagnostic system
(sybron endo )
P ropex -iv
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MULTI FREQUENCY
DEPENDENT
A pex locator with built
in pulp tester
Eg:
Mini apex loator
Neosono Co- pilot
.
i - pex
Root - pi
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`
Tri A
uto ZX` Endy ZX
` Sofy ZX
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` Combination of Apex Locator & Endodontic Handpiece
` Cordless, automatic endodontichandpiece with a built in root ZXapex locator
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SOLF Y ZX` Combination of an Ultrasonic
hand piece and a Root ZX
` Designed to preventoverinstrumentation bystopping the ultrasonicvibration when files reachesthe required location.
APEX LOCATOR WITHULTRA SONIC HANDPIECE
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APEX LOC ATOR WITH
BUILT IN PULP TESTER
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` Provide objective infor mation with high degree of accuracy
` Useful in conditions where apical portion i s obsr u cted by anatomicstructures such as zygomatic arch, tori, exostoses etc.
` Useful in patients with gag reflex
` Pregnant patients
` Root perforations, resorptions, root fracture
` RCT of teeth with incomplete root formation
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` Accurate
` Objective measurements
` Easy & fast
` Reduction of exposure to radiation
` Perforations can be detected
` Can measure pulp space exactly to the constriction
` Can detect resorption & root fracture
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RADIO VISIO
GRAPHY
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` A rigid chargedcoupled device (CCD)connected by a cableto computer, monitor & printer.
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` The ³Radio´ component x ray unit: Consists of a
hypersensitive intra oral sensor and a
conventional x-ray unit
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` The ³³ VISIO VISIO´́ portion: Consists of a video monitor
and display processing unit
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` Is a high resolution video printer that instantly
provides a hard copy of the screen image using
the same video signal.
The ³³GRAPHY GRAPHY ́́ component:
DIRECT DIGITAL RADIOGRAPHY
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Advantages :
q time between exposure andinterpretation.
q radiation dose
Digital image enhancement
Patients can more easily, view andappreciate
Patients acceptance
Disadvantages :
Cost
Small sensor cant capture
Image storage
Faded image
DIR ECT DIGIT AL RADIOGRAPHY
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` Determination of working length
U SES IN ENDODONTICS
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` Amethod of obtaining a digital image in which an
existing radiograph is scanned & converted in to a
digital form using a CCD.
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1. Improved disease detection
2. Quantification of disease change over time
3. 2D/3D reconstruction of the following.
4. Improved patient education.5. Remote electronic consultation
(tele dentistry)
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` Xerographic copying process
` Both soft and hard tissues
` Equipment :
electrostatically charged aluminium plate
Selective discharge on selenium
Latent image pattern
Spraying toner Hard copyHard copy
X ray photons
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XeroradiographyXeroradiography
Advantages :Advantages :
Fine detail
Pronounced edge enhancement
High image contrast
Low exposure
Disadvantages :Disadvantages :
Electro current ± discomfort
Process of development ± 15 min
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` There is no statistically significant difference in WL
estimation accuracy
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` Straight line access, modifications required to permit the
instrument to penetrate, unimpeded, to the apicalconstriction
` Loss of working length during cleaning & shaping can befrustating procedural error
` Monitor the working length periodically, working length maychange as a curved canal is straightened
` Loss may also related to be the accumulation of dentinal &pulpal dedris in the apical 2-3mm of the canal or
` Failing to maintain foramen patency, skipping instrumentsizes, or f ailing to irrigate the apical 1/3rd adequately
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` Occationally, WL is lost owing to ledge formation or to
instrument separation and blockage of the canal
` Apical constriction:- not only narrowest part of the canal buta morphologic landmark that can help to improve the apical seal when the canal is obturated
` Failure to accurately determine & maintain WL- length beingtoo long & may lead to perforation through the A. constriction
` Destruction of constriction may lead to overf illing / overextension & an increased incident of post operative pain
` Prolonged healing period & lower success rate owing toincomplete regeneration of cementum, PDL & A.bone
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` Failure to determine & maintain WL accurately cleaning &
shaping short of the apical constriction
` Incomplete cleaning & underfilling may cause persistentdiscomfort, often associated with an incomplete apical seal
` A. leakage may occur into the uncleaned & unfilled spaceshort of A. constriction leakage supports the continued existence of viable bacteria- contributes to a continuedperiradicular lesion & lowered rate of success
` Measurement should be made from a secure ref erence pointon the crown, in close proximity to the straight-line path of the instrument, a point that can be identif ied & monitoredaccurately
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Definition of the working width
`
MinlWW(N)- M
inimal initial horizontal dimension Nmm short of working length.
` MinlWW0 - Minimal initial horizontal dimension at
working length.` MinlWW1 - Minimal initial horizontal dimension 1
mm short of working length
` MinlWW2 - Minimal initial horizontal dimension 2mm short of working length.
` MinFWW(N) - Minimal final horizontal dimension N
h f ki l h
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mm short of working length.
` MinFWW0 - Minimal final horizontal dimension atworking length.
` MinFWW1 - Minimal final horizontal dimension 1
mm short of working length.
` MinFWW2 - Minimal final horizontal dimension 2
mm short of working length.
` MaxFWW(N) Maximal final horizontal dimension N
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` MaxFWW(N) - Maximal final horizontal dimension N
mm short of working length.
` MaxFWW0 - Maximal final horizontal dimension at
working length.
` MaxFWW1 - Maximal final horizontal dimension1mm short of working length
` MaxFWW2 - Maximal final horizontal dimension
2mm short of working length
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` Round (circular) : max I WW equals min IWW .
` Oval : maxiww is greater than miniww (upto 2 timesmore).
` Long oval : max i ww is two or more times greater thanmin I WW ( up to 4 times more).
` Flattened (flat , ribbon ) : Max I WW is four or moretimes greater than Min IWW.
` Irregular : cannot be defined by 1- 4.
Determination of initial working width at working length
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Determination of initial working width at working length(initial apical file determination ± estimation of initialcanal diameter):-
` Three critical parameters should be taken intoconsideration in the course of cleaning and shaping theroot canal system.
1) length of the canal.
2) taper of the preparation.
3) horizontal dimension of the preparation
l l th
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` canal length :
when using an instrument to gauge working length, the longer
the canal, greater the frictional resistance which may affectthe clinician¶s tactile sense.
If the coronal flare is too conservative then the shaft of theinstrument may engage the canal wall giving premature or false conclusion as to the WW.
` canal taper
Any tapering discrepancy between the gauging instrument andcanal may lead to an early instrument engagement causing afalse sensation of apical binding .
The last 3- 5 mm of the canal can have parallel walls makingcorrect determination of IWW difficult.
` canal curvature :
Th t f th t l b
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The curvature of the root canal can becategorized into two dimensional, three dimensional,small radius . large radius and double curvature (s-
shaped , bayonet shaped ).
Each of these curvatures or their combination can causedeflection of gauging instrument.
` canal content:
The content of the root canal may be fibrousor calcified in the nature. The mixed canal contents cancreate different degrees of functional resistance against thegauging instrument affecting tactile sense.
` Canal wall irregularities:
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g
Like attached pulp stones ,denticles reparative
dentin , resorption can create convexities or concavities
on the canal wall surface.
` instrument for determining initial working width:
The rigidity, flexibility and tapering of the
instrument used for determining IWW can affect theaccuracy.
` Eliminating or minimizing the influence of affecting
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factors.
By being aware of the existence of the affecting factors
in IWW determination.
Early coronal flaring and additional canal flaring to
ensure effective irrigation and to minimize anyinterference with tactile sensation.
Careful selection of the adequate instrument having
maximal flexibility and minimal taper may avoid
interference.
Root canal preparation should follow the exact outline of
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the horizontal dimension of root canal especially for long
oval and flattened root canal.
`Reaming action may result in key hole or dumb bell
demonstrating unprepared parts of root canal.
Circumferential instrumentation can confirm to outline of
horizontal dimension of the root canal at different level of canal
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` Accurate determination of working length is
essential to endodontic & restorative success.` Depends on proper knowledge of root canal
anatomy, direct visualization and access to theroot canal system, accurate radiographic
technique, interpretation, exact measuringtechniques.
` Effectively using various combinations of thesetechniques will lead to significant mastery of
even most difficult root canal system.