Working Length

CONTENTS Introduction Definition and significance Reference points – coronal and apical Anatomic considerations and terminology Failure to accurately determine working length Calculation of working length

• Use of radiography apex as termination point

• Specific distances short of radiographic apex Methods of determining working length

• Requirements for ideal method

• Radiographic method

o Conventional method

o Xeroradiography

o Digital radiography

• Apical periodontal sensitivity

• Paperpoint measurement

• Electronic method with apex locators

o History

o How does they work ?

o Classification and accuracy

o Uses

o Contraindications

o Future

Clinical considerations

References

Conclusion

Working length is defined in endodontic glossary as “the distance from a coronal reference point to point at which canal preparation and obturation should terminate.

Significance :

1) Determines how far into canal the instruments are placed and worked.

2) Limits depth to which canal filling may be placed.

3) Will affect degree of pain and discomfort.

4) It calculated with in correct limits, plays on important role in determining success of treatment.

• Anatomic apex v/s Radiographic apex

Note : Root morphology and radiogrpahic distortion cause the location to vary

• Apical foramen

• Accessory foramen

ANATOMICAL CONSIDERATIONS AND TERMINOLOGY

APICAL CONSTRICTION-Apical portion of RC having narrowest diameter.

Dummer classification

1) Typical single constriction

2) Tapering constriction with narrowest portion near actual apex.

3) Several constrictions / multiconstricted

4) Constriction followed by a narrow, parallel canal.

5) Complete blockage of apical canal by 20 dentin.

Apical perforation Increased postoperative pain

Incomplete instrumentation

Underfilling

Remannts of pulp

Ledge formation

Apical percolation

Prolonged healing

Over filling

Increased failure due to incomplete regeneration

of cementum, pdl alv bone

CEMENTODENTINE JUNCTION

• It is a histological landmark, cant be seen clinically / radiographically.

• 0.5-3mm short of apical apex.

REFERENCE POINTS

1) Coronal reference point

2) Apical reference point

Coronal reference point :

• It may be cusp tip of canal being measured

• Same cusp tip for all canals.

• Cavosurface margin

• Ledge

Common method of marking instruments

• Stops

o Silicone

o Metal

o Plastic

Note :Silicone stops should be

perpendicular and not oblique.

Devices to assist in dispensing the stops

• Endobloc, filemate

• As an alternate to R-stops, instruments have been developed with mm marking rings etched or grooved in to shaft of instruments. These act as built-in-ruler with markings placed.

APICAL REFERENCE POINT

Where should working length terminate ?

• In 1916 the pulp tissue extends through apical foramen.

• Later Groove stated that tissue in apical foramen is periodontal tissue.

• Groove was challenged by several authors stating that CDJ is not definable point, histological land mark.

• In 1955 extensive investigation on root apex by Kuttler had lead to more details.

IN RESORPTIVE WHERE ?

Weine recommendations in such cases are

1) If no root / bone resorption is evident, preparation should terminate 1mm from apical foramen.

2) If bone resorption is apparent but no root resorption shorten the length by 1.5mm.

3) If bone and root resorption are apparent, shorten the length by 2mm.

RADIOGRAPHIC APEX AS TERMINATION POINT

• Those who use this concept state that it is impossible to locate the CDJ clinically and radiographic apex is reproducible.

Radiographic apex reproducible ?

Advantages :

• Impossible to locate CDJ

• Does not want to eliminate unwanted possibly diseased materials.

• Less chances of under obturation.

Disadvantages :

in success

• Post operative pain.

• Studies shown that canal exits eccentrically short of root.

in healing.

SPECIFIC DISTANCES SHORT OF RADIOGRAPHIC APEX

Short of apex ?

According to studies of Kutler,

Minor diameter :

Major diameter :

Distance between major diameter and minor diameter

= 0.524 (18-25yrs).

= 0.659 mm (55 yr)

The narrows diameter of canal is not at the site of exiting of canal from the tooth, but usually occurs with in dentin

Diameter of canal at the site of exiting of canal is twice as wide as minor diameter.

• Rapid location of apical constriction

• Easy measurement

• Rapid periodic monitoring

• Patient and clinician comfort

• Minimal radiation to patient

• Ease of use in special patients

• Cost effective

METHODS OF DETERMINING WORKING METHODS OF DETERMINING WORKING LENGTHLENGTH

METHODS OF DETERMINING WORKING METHODS OF DETERMINING WORKING LENGTHLENGTH

• Most commonly used method

Requirements :

• An undistorted periapical radiograph with parallel technique.

• Adequate coronal access to all canals

• An endodontic mm ruler

• Knowledge of average length of all teeth

RADIOGRAPHIC METHOD

INGLE’S METHOD

Grossman’s method :

Actual length of tooth =Actual length of instrument X radiographic length of tooth

Radiographic length of instrument

Bregmen’s method :

CRD =CRI x CAD

CAI

CRD – Real tooth length

CRI – Real instrument length

CAD – Apparent tooth length

CAI – Apparent instrument length

Variations :

Accuracy ?

• Depends on radiographic technique used

• Forsberg demonstrates that paralleling technique was significantly more reliable than bisecting angle technique. they found it was 82-89% accurate.

DIFFERENCES BETWEEN PARALLEL & BISECTING ANGLE TECHNIQUES

Parallel Bisecting

Greater geometric accuracy

Reproducibility

Fewer retake’s

Lower radiation dose

Superimages of upper molar roots

Superior image of bone margins

Quick and easy with rubber dam in place

Comfortable for all patients

NEW TECHNOLOGY

Xeroradiography :

Advantages :

• Fine detail

• Pronounced edge enhancement

• High image contrast

• Low exposure

• Shows end of instruments and apex

Disadvantages :

• Electrocurrent – discomfort

• Process of development – 15 min

Advantages :

time between exposure and interpretation.

radiation dose

• Digital image enhancement

• Patients can more easily, view and appreciate

• Patients acceptance

Disadvantages :

• Cost

• Small sensor cant capture

• Image storage

DIRECT DIGITAL RADIOGRAPHY

LIMITATIONS OF RADIOGRAPHY

1. Apical formamen may exit in buccal or lingual direction so

becomes difficult to view.

2. Dense bone and Anatomic structures can make visualization

of R-C files impossible by obscuring the apex.

3. Super imposition of zygomatic buttress has been shown to

interfere radiograph in maxillary molar apices.

4. Depositing 20 dentin and cementum can move A.construction.

5. Provides and the dimensional image of 3 dimensional

structure.

6. Technique sensitive in both its exposure and interpretation.

DIGITAL TACTILE SENSE

Accuracy ?

Seidberg – 64% accuracy

Invivo – 25% accuracy

Preflared canals – 75% accuracy

• Clinicians should be aware of this and this should be in

conjunction with other methods.

Disadvantages :

1) Ineffective in root canal with immature apex.

2) In accurate if canal is constricted throughout its length or it

curvature is present.

APICAL PDL SENSITIVITY

• Always working length determinants should be painless.

• If an instrument is advanced in the canal toward inflamed tissue,

hydrostatic pressure developed inside the canal may cause

moderate to severe instantaneous pain. at the onset of pain, the

tip may still be several mm short of apical constriction.

• When pain is afflicted in this manner, little useful information is

gained by clinician, and considerable damage is done to patients

trust.

• Canal contents totally necrotic – mild awareness or no reaction

Indications :

• Root canal with immature apex

• Cases in which apical constriction

has been lost.

New dimension, to paper point

evaluation by addition of mm

markings 18, 19, 20, 22, 24mm

from tip and can be used to

estimate working length.

PAPER POINT MEASUREMENT

• Increased visibility.

• Good illumination.

• Better depth of focus.

• Reliability, reproducibility.

• Saves time.

• Greater comfort.

History :

In 1918, Custer was first to report the use of electric current to

determine working length.

Suzuki in 1942 stated that E. resistance between pdl and oral

mucosa was a constant value of 6.5 k.

Sunada adopted the Suzuki principle and done his research.

Inoue made significant contributions lead to the evaluation of

sono-explorer.

ELECTRONIC METHOD WITH APEX LOCATORSELECTRONIC METHOD WITH APEX LOCATORS

• 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 ?

Ist GENERATION APEX LOCATORS

Measure opposition to flow of direct current / resistance

Root canal meter (1969) – 150 Hz

Endodontic meter

Dento meter

IInd GENERATION APEX LOCATORS

Sono explorer Sono explorer MK III

Endocater : contains sheath over probe

Apex finder : visual digital LED indicator

Endo analyzer : A. locator + pulp tester

Digiapex I, II, III : A. locator + pulp tester

Exact-A-pex : LED bar graphs

Foramatron IV

Note : Root canal as to be reasonably free of electro conductive materials to obtain accurate readings.

III GENERATION APEX LOCATORS

Endex :

• Uses very low current and two

frequencies of 5 & 1 kHz

• Accurate when fill with electrolyte

Neosono ultima Ez & copilot

Justy II : 500 & 2000 Hz

Apex finder AFA : Wet / dry

Root ZX : 8 & 0.4 kHz

Microprocessor

TriAuto ZX

IV GENERATION APEX LOCATORS

Bingo 1020 / Raypex 4

• Frequencies of 400 Hz and 8 kHz

• Easier for beginner to use in preflared canals

V GENERATION APEX LOCATORS

Raypex 5

Has a unique feature of apex zoom

4 blue – Beginning of apical region.

3 green – Apical constriction region

4 yellow – Adjacent to apical foramen

1 red – Reached apical foramen

&

Red dot – Apex has been passed.

OTHER USES OF APICAL LOCATORS

• To detect and locate root perforations

• Diagnosis of external and internal resorption.

• Prepared pin holes can be checked.

• Horizontal or vertical root fracture

• Can be used even in deciduous teeth

• Number of radiographic can be reduced

Contraindications :

Patients with cardiac pacemakers ??

1. Biological phenomenon such as inflammation can still have effect on accuracy?

2. Intact vital tissue, inflammatory exudate and blood can conduct electric current and cause inaccurate readings.

3. Other conductors that cause short circuiting are metallic restorations, caries, saliva and instruments in 2nd canal

4. Lack of patency, calcifications can also effect.

COMMON PROBLEMS ASSOCIATED WITH APEX LOCATORS

COMMON PROBLEMS ASSOCIATED WITH APEX LOCATORS

CLINICAL CONSIDERATIONS

Failure to accurately determine and maintain

working length may result in

Length being too long

Lead to perforation

Over filling or over extension

Increased incidence of post operative pain

Prolonged healing period

lower success rate

Short of apical constriction

Persistent discomfort associated with

incomplete apical seal

Apical leakage

Bacterial entry

Failure.

Invitro evaluation of accuracy of three electronic apex locators.

JOE, Vol 30, No. 4, 2004: 231-233

Safety of electronic apex locators and pulp testers with implanted cardiac pacemakers / cardio venter / defibrilator.

JOE, Vol 2, No. 12, 2003: 103-106

REFERENCES REFERENCES

Morphological measurement of anatomical landmarks in human maxillary and mandibular molars pulp chamber.

JOE, Vol 30, No. 6, 2004

Use of microscopes in endodontics: A report based on questionaire.

JOE, Vol 25, No. 11, 1999: 755-58

CONCLUSIONCONCLUSION