Length Determination

7/28/2019 Length Determination

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ByBy

Ahmed LabibAhmed Labib


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Working length: is the length to which the root

canal preparation and obturation will terminate.


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So the working length of a tooth: is the lengthbetween an external reference point on the crown

of the tooth, and the cemento-dentinal junction of

the root.


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CDJ: (the apical foramen) the anatomical

apex is 0.5 mm to 1 mm shorter than the

radiographic apex.


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The optimum length is at the apical constriction.


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Biological rationale for working length:

-Establishing a good working length of the

tooth is the most important step in cleaning

and shaping of the root canal.

-I

t greatly facilitates accurate instrumentationand filling of the root canal.


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Obtur.


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Over instrumentation

Over instrumentation results in perforation of the

apical foramen with the following results:

1-The periapical tissue might become traumatized by

the instrumentation to post treatment

inflammation, pain, and swelling.


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2-Necrotic material might be forced into the periapical region

with subsequent acute inflammation.

3-The irrigation solutions and intracanal medicaments may

leak out through the apical foramen with subsequent

irritation of the periapical area.

4-The apical foramen might be enlarged by the perforating

instrument so that the subsequent filling material may be

extruded from the foramen and irritate the periapical tissue.

N.B.: Instrumentation to the radiographic apex is consideredover instrumentation.


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Under instrumentation

Instrumentation shorter than the

cemento-dentinal junction may result in::


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2-Any bacteria or necrotic material left in

the canal beyond this point of shelfingmight result in case failure.

3-E

ven if there is no pulp tissue beyondthe ledge (when ledge is formed after

complete cleaning) one cant fill this area,

with subsequent microleakage, which may

lead to case failure.

1-Shelfing the canal, (a ledge in a root

canal formed during instrumentation )

which will catch the instrument.


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Methods of Working Length

Determination

Methods of Working Length

Determination


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Methods of working length determination:

1-Radiographic.

2-Electronic apex locator.

3-Tactile sensation.

4-Paper point.

5-Apical Periodontal sensitivity.


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1.Radiographic method:

a) Average length of the tooth.

b) Preoperative radiograph.

c) Tactile sensation.

A properly angulated, developed and fixed X-

ray film with an instrument inside the root

canal, is still the most accurate method for

length determination , which can bedetermined by:


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Radiographic Apex Location:

The following items are essential to perform thisprocedure:

1. Good, undistorted,preoperative radiographs showing the

total length and all roots of the involved tooth.

2. An endodontic millimeterruler.

3. Knowledge of the average length of all teeth.

4.Adequate coronal access to all canals.

5.A definite, repeatable plane of reference to an anatomiclandmark on the tooth, a fact that should be noted on the

patients record.


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Preoperative radiograph should be examined

to reveal the following:

1-The number, size, shape, curvature and angulationsof the root(s).

2-Presence of any periapical pathosis and degree of

bone and root resorption if present.

3-Presence of vertical or horizontal roots fracture.

4-Root obstructions by pulp stone or obliteration of the

root by secondary dentin.

5-Old root canal treatment if present.

6-Estimation of the tooth working length.


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.

-The estimated length is the length to which

the initial file will be inserted into the canal, and

then confirmed by another radiograph.

-If the estimated length is 21 mm. the stopper

must be adjusted on the initial file shaft to be21 mm away from the file tip, then the file is

inserted into the canal and a confirmatory

radiograph is taken.


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Radiographic estimation of working length:

- Measure the tooth length on the preoperative radiograph

from cusp tip or incisal edge to the radiographic apexto

get an estimation of the actual working length of the tooth.

-Subtract1 mm from this length to get the position ofthe

anatomical apex or the cemento-dentinal junction.


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1-N

oB

one orR

oot resorption (normal case):the difference is 1mm. from the apex.

2-Bone resorption butNo Root resorption:

the difference is 1.5 mm. from the apex.

3-Bone and root resorption: the difference is

2 mm. from the apex.


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Important considerations for estimated tooth

length:

1-Tactile perception: sense of feel or tactile sense

Feeling the constriction of the cemento-dentinal junction with the

measuring instrument can assist in estimating the working length of the

tooth.

2-Average length of tooth:

The knowledge of different average teeth lengths can be of great value in

estimating working length.


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Selection of the external reference point:

1-In anterior teeth incisal edge.

2-In posterior teeth cusp tip for each canal.

-In case of more than one-reference point for canals of posteroir

teeth, this must be registered in the patient chart.

3-R

eference point should be easily checked duringinstrumentation.

4-It should be selected in sound tooth structure to avoid

breakage of the restoration or undermined enamel between

visits.)

5-Avoid inclined planes as a reference point.

6-The file stopper must be rested in a straight position on the

reference point to prevent length discrepancies during

instrumentation and filling of the root canal.


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Placing the stopper


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Initial radiograph with file in the canal:

Three possibilities may be faced at this step:

1-The file tip is just on the cemento-dentinal

junction (1mm shorter than the radiograph apex),

so this is ourworking length to which allinstrumentation and filling procedure will be confined.


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2-The file tip is at the radiographic apex or longer

than it, so we subtract the length of the file beyond theradiographic apex + 1mm. (The distance between the

radiographic apex and the cemento-dentinal junction).

And another confirmatory X-ray must be taken to get sure

that we got the accurate working length of the tooth.

Over estimated length


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3-The file tip is shorter than the radiographic

apex by more than one mm. In this case we add thelength difference between the file tip and the radiographic

apex and then subtract one mm. to get the accurateworking length. Again, anotherConfirmatory X-raymust

be taken to be sure that we reach the accurate working

length.

Under estimated length


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Confirming working length of tooth:

1. Reset the stopper to the new estimated length.

2. Reinsert the file into the canal as done before to its new

estimated length.

3. Take a new radiograph to confirm the length.

4. Examine the new radiograph to determine if the correct

working length of tooth has been reached (just to the

cemento-dentinal junction). If this length has been

reached that is it, and this length should be recorded in

the patient chart.

5. If the working length of tooth has not yet been reached,

additional adjustment of the length must be done, until

working length of tooth is reached and confirmed.


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Summary


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Disadvantages of the radiographic method :1. Health hazards.

2. The film reveals only two dimensional picture for athree dimensional object(Tooth)

So the third dimension of the tooth structure

does not appearin the radiographic film.

This may lead to superimposition of root canals over

each other in the radiograph, which may lead to

inaccurate working length determination.

Hence there was a need to develop a radiographic

technique that can overcome this disadvantage which

is called the BuccalObjective Rule (Changing the

Horizontal Angulation ) or(T

ube-S

hift ).


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Stand. Standard

Mesial shift

Distal shift


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Tube-Shift Localization (Clark)

SLOBRule

Same Lingual Opposite Buccal

TheSLOB rule is used to identify the buccal orlingual location of objects (impacted teeth, rootcanals, etc.) in relation to a reference object (usually

a tooth). If the image of an object moves mesially

when the tube head is moved mesially (Samedirection), the object is located on the Lingual. If theimage of the object moves distallywhen the tube

head moves mesially (Opposite direction), the object

is located on theBuccal.

INGLEs Rule ( M - B - D , M - L - M )


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When using the SLOB rule, the directionof the beam must be opposite to the way

the tube head is moved.

Horizontal Tube Shift: When thetube head is moved mesially, the beam is

directed more distally (from the mesial).

If the tube head is moved distally, the

direction of the beam is more towardsthe mesial (from the distal).


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The buccal (yellow) and lingual

(red) objects are superimposed

on each other because the beam is

directed perpendicular to both of

them and they are in the same

relative position mesiodistally.

mesial

distal

mesialdistal

Horizontal movement


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B

When the tube head is moved

mesially ( the beam is directed

distally ). The buccalobject(yellow) moves distally

(Opposite to tube head

movement) and the lingualobject (red) moves mesially

(Same direction as tubehead) in relation to the second

molar.

mesial

distal

mesial distal

Horizontal movement

Mesial Shift

P


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B

When the tube head is moved

distally ( the beam is directed

mesially). The buccalobject(yellow) moves mesially

(Opposite to tube head

movement) and the lingualobject (red) moves distally( Same direction as tubehead) in relation to the second

molar.

mesial distal

mesial

distal

Horizontal movement

Distal Shift

P


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Are devices developed to:

1-facilitate the determination of the working length.

2- Avoid the hazards of exposure to multiple X-ray

doses.

2- ElectronicMethod:( Electronic apex locators )


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Theprinciple idea of electronic apexlocatoris based on electrical resistance

when the file (which is attached to thedevice) come closer to the apex; the device

will recognize the impulses in the periapical

area; this will indicate the accurate length.


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Classification and Accuracy

of Apex Locators.

This classification is based on:

1. the type of current flow.2.the opposition to the current flow.

3.the number of frequencies involved.


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First-Generation Apex Locator:

( resistance apex locators)

It measure opposition to the flow of direct current

or resistance.

When the tip of the reamer reaches the apex in the

canal,the resistance value is 6.5 kilo-ohms (current

40 mA).

It had some problems.

Today, most first-generation apex location devices

are off the market.

Second Generation Ape Locators


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2.The Digipexhas a visual LED digital indicator and an audibleindicator.

3.The DigipexIIis a combination apex locator and pulp vitalitytester.

4.The Exact-A-

Pexhas an L

EDbar graph display and an audioindicator.

5.The Foramatron IVhas a flashing LED light and a digital LEDdisplay.

6.The ApexFinderhas a visual digital LED indicator.

7.The Endo Analyzeris a combined apex locator and pulp tester.

Second-Generation Apex Locators:(impedance apex locators)

They measure opposition to the flow of alternating current or

impedance.

1.Sono-Explorer, one of the earliest of the second generation apexlocators.

IMPROVEMENTSOFSONO-EXPLORER:


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Formatron IV


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Disadvantage of second generation apex

locators is that:1.The root canal has to be free ofElectroconductivematerials to obtain accurate readings.

2.T

he presence of tissue and electro-conductiveirrigants changes the electrical characteristics and

leads to inaccurate, (usually shorter

measurements).

3.This created a Question : Should canals be cleaned

and dried to measure working length, or should

working length be measured to clean and dry the

canals?


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Third-Generation Apex Locators.

They depend on the Frequency of current flow.

These devices have been called frequency

dependent

More advanced and more accurate.

work in wet canals (in the presence ofelectrolyte). eg: Saline or NaOCL.


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Endex (aka APIT), the original third-generation

apex locator. It measures the impedance betweentwo currents and works in a Wet canal with

sodium hypochlorite.


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The ApexFinderA.F.A. (All Fluids Allowed)Third generation apex locator. It functions best

with an electrolyte present and displays, on an

LCD panel, the distance of the file tip from theapex in 0.1 mm increments.


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Root ZX third-generation apex locatorThe Root ZX microprocessor calculates the ratio of two

impedances and displays a files approach to the apexon a liquid crystal display (LCD).

It functions in both a dry or wet canals .


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Tri-auto ZX :has 3 automatic safety mechanism1.Auto start stop.

2.Auto torque reverse.3.Auto apical reverse.

Combination of Apex Locator & Endodontic Handpiece

with a built-in Root apex locator.


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3 T til S ti th d


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3-Tactile Sensation method: If the coronal portion of the canal is not

constricted; an experienced clinician may detect anincrease in resistance as the file approaches the

apical 2 to 3 mm.

This detection is by Tactile sense.

Constriction and Course change apply pressure to the file

which give the sensation to the operator that the working

length is reached.

Two facts make tactile sensation possible:

Canals commonly constrict before the end of the root.

Canals frequently change its course in the last 2-3 mm.

It is a supplementary method

.

4 P P i t M th d


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4-PaperPointMethod: Can be used In a root canal with an immature

(wide open) apex.After profound anesthesia has been achieved.

Gently pass the blunt end of a paper point into

the canal.

The moisture or blood on the portion of the paper point


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The moisture or blood on the portion of the paper point

that passes beyond the apex may be an estimation of

working length or the junction between the root apex

and the bone.

In cases in which the apical constriction has been lost

owing to resorption or perforation,( and in which there isno free bleeding or suppuration into the canal), the

moisture or blood on the paper point is an estimate of

the amount the preparation is overextended.

This paper point method is a supplementary one.

5 A i l P i d t l iti it th d


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5-ApicalPeriodontal sensitivity method:

Any method of working length determination, based

on the patients response to pain, does not meet the

ideal method of determining working length. Working

length determination should be painless.

If an instrument is advanced in the canal toward

inflamed tissue, the hydrostatic pressure developed

inside the canal may cause moderate to severe,

instantaneous pain. At the onset of the pain, theinstrument tip may still be several millimeters short

of the apical constriction.


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When the canal contents are totally

necrotic, however, the passage of aninstrument past the apical constriction

may evoke a mildorpossibly a flare-

up reaction.


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Vital pulp tissue with nerves and vessels

may remain in the most apical part of the maincanal even in the presence of a large

periapical

lesion.

This suggests that a painful response may

be obtained inside the canal even though the

canal contents are necrotic and there is aperiapical lesion.


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Thank you

Documents

Length Determination