WORKING LENGTH DETERMINATION

Dr Emil Santhosh Mani

Dept. of Conservative Dentistry and Endodontics

Definitions

▶ Working length:

According to Cohen’s 6^th edition ,Every part of endodontic treatment is controlled by a measurement of the instrument's penetration depth into the canal. This length is typically determined in millimeters. It is measured from a point on the tooth's coronal surface that is within the clinician's field of view. It varies from the complete canal length to some arbitrarily determined point near the termination of the canal space.

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

History

▶ End of 18^th century: WL was calculated when file was placed in canal & patient experienced pain.

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▶ 1899 : Kells introduced X-rays in dentistry.

▶ 1929 : Collidge studied the anatomy of root apex in relation to treatment problems.

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▶ 1955 : Microscopically investigated the root apices.

▶ 1962 : Sunada – Found electrical resistance between periodontium and oral mucous membrane.

▶ 1969 : Inove significantly contributed to evolution of electronic apex locators.

SIGNIFICANCE OF WORKING LENGTH

into

canal,

▶ Working length determines how far

instruments can be placed and worked.

▶ It affects degree of pain and discomfort which patient will experience following appointment by virtue of over and under instrumentation.

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▶ If placed within correct limits, it plays an important

role in determining the success of treatment.

▶ Before determining a definite working length, there should be straight line access for the canal orifice for unobstructed penetration of instrument into apical constriction.

▶ Once apical stop is calculated, monitor the working length periodically because working length may change as curved canal is straightened.

Consequences of over extended working length:

▶ Perforation through apical constriction

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▶ Overinstrumentation

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▶ Overfilling of root canal

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▶ Increased incidence of postoperative pain

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▶ Prolonged healing period

▶ Lower success rate due to incomplete regeneration of cementum, periodontal ligament and alveolar bone.

Consequences of working short of actual working length:

▶ Incomplete cleaning and instrumentation of the canal

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▶ Persistent discomfort due to presence of pulpal remnants

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▶ Under filling of the root canal

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▶ Incomplete apical seal

▶ Apical leakage which supports existence of viable bacteria, this further leads to poor healing and periradicular lesion.

Causes of loss of working length:

▶ Presence of debris in apical ⅔ of canal

▶ Failure to maintain apical patency

▶ Skipping instrument sizes

▶ Ledge formation

▶ Inadequate irrigation

▶ Instrument separation

▶ Canal blockage

▶ Taper lock.

Definitions:

▶ Anatomic apex:

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It is the “tip or end of root determined morphologically .”

▶ Radiographic apex:

It is the “tip or end of root determined radio-graphically.”

▶ Apical foramen

It is main apical opening of the root canal which may

be located away from anatomic or radiographic apex.

▶ Apical constriction

It (minor apical diameter) is apical portion of root

canal having narrowest diameter. It is usually 0.5 to 1

mm short of apical foramen. The minor diameter widens apically to foramen, i.e. major diameter.

TOPOGRAPHY OF APICAL CONSTRICTION

According to “The position and topography of the apical canal constriction and apical foramen” by PAUL M. H. DUMMER et al. International Endodontic Journal - 1984

Definitions

▶ Reference point:

Reference point is that site on occlusal or the incisal surface from which measurements are made.

• It should be stable and easily visualized during preparation.
• Usually it is the highest point on incisal edge of anterior teeth and buccal cusp of posterior teeth.
• It should not change between the appointments. Therefore in case of teeth with undermined cusps and fillings, they should be reduced considerably before access preparation.

Conditions for Loss of Reference Point:

▶ Fractured tooth surface

▶ Carious tooth structure

▶ Undermined cusps

▶ Undermined Fillings

Definitions

▶ Cementodentinal junction

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It is the region where cementum and dentin are united, the point at

which cemental surface terminates at or near the apex of tooth.

• It is not always necessary that CDJ always coincide with apical constriction.

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• Location of CDJ ranges from 0.5 to 3 mm short of anatomic apex.

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Cementum changes with age. It increases with age, due to deposition,

however CDJ doesn’t change.

Working Width:

Working width is defined as “initial and post instrumentation horizontal dimensions of the root canal system at working length and other levels”.

The minimum initial working width corresponds to initial apical file size which binds at working length. The maximum final working width corresponds to the master apical file size.

Working width was described in “Endodontic working width: current concepts and techniques” by - Yi-Tai Jou et al in 2004 in DCNA.

Reasons for widening root canal:

• To remove microorganism from the canal mechanically.

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• To increase the area of root canal for better irrigation.

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• To completely remove the pulp tissue.
• To attain a sound apical stop so as to achieve a three- dimensional seal. The round shape conforms to the round cross sectional tip of gutta percha.

Guidelines sufficient for instrumentation:

1. Enlarge the root canal atleast three sizes beyond the first instrument that binds the canal.

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• Enlarge the canal until it is clean. It is indicated by white dentinal shavings on the instrument flutes.

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BUT THESE GUIDELINES ARE NOT SOLE CRITERIA IN ALL THE CASES.

Advantages of Narrow Apex

▶ Decreases risk of canal transportation.

▶ Avoids extrusion of debris and obturating material.

Disadvantages Of Narrow Apex

▶ Incomplete removal of infected dentin.

▶ Not ideal for lateral compaction.

▶ Irrigants may not reach the apical-third of canal.

Advantages of Wide Apex

▶ Complete removal of infected dentin.

▶ Better disinfection of canal at apical third.

Disadvantages Of Wide Apex

▶ Increased chances of extrusion of irrigants and obturating material.

▶ Not recommended for thermoplastic obturation.

▶ More chances of preparation errors.

Directional Stop Attachments

attachments can be made up of metal, plastic or silicon rubber.

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▶ Stop attachments are available in tear drop or round

shapes.

▶ Most commonly

instruments are

used stoppers for endodontic

silicon rubber stops, though stop

perpendicular to the instrument not at any

▶ Irrespective of shape, the stop should be placed

other

direction (oblique) so as to avoid variation in working

length.

▶ Advantage of using tear shaped stopper is that in curved canal, it can be used to indicate the canal curvature by placing its tear shape towards the direction of curve.

Different Methods Of Working Length Determination

Radiographic Method of Length Determination(Ingle’s Method)

▶ Before access opening, fractured cusps, cusps weakened by caries or restorations are reduced to avoid fracture of weakened enamel during the treatment. This will avoid the loss of initial reference point and thus the working length.

▶ Measure the estimated working length from

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preoperative periapical radiograph.

▶ Adjust stopper of instrument to this estimated working length and place it in the canal up to the adjusted stopper.

▶ Take the radiograph.

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▶ On the radiograph, measure the difference between the tip of the instrument and root apex. Add or subtract this length to the estimated working length to get the new working length.

calculated by

▶ Correct working length is finally subtracting 1 mm from this new length.

Weine’s Modification:

Modification in the length subtraction

▶ • No resorption - subtract 1 mm

▶ • Periapical bone resorption - subtract 1.5 mm

▶ • Periapical bone + root apex resorption - subtract 2 mm

Radiographic methods of working length determination: ADVANTAGES:

• One can see the anatomy of the tooth

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• One can find out curvature of the root canal
• We can see the relationship between the adjacent teeth and anatomic structures.

DISADVANTAGES

• Varies with different observers.

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• Superimposition of anatomical structures.
• Two-dimensional view of three-dimensional object.
• Cannot interpret if apical foramen has buccal or lingual exit.

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• Risk of radiation exposure.

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• Time consuming.

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• Limited accuracy.

GROSSMAN METHOD/MATHEMATICAL METHOD OF WORKING LENGTH DETERMINATION

▶ It is based on simple mathematical formulations to calculate the working length. In this, an instrument is inserted into the canal, stopper is fixed to the reference point and radiograph is taken. The formula to calculate actual length of the tooth is as follows:

Disadvantages

Wrong readings can occur because of:

• Variations in angles of radiograph
• Curved roots
• S-shaped, double curvature roots

Kuttler’s Method

▶ According to Kuttler, canal preparation should terminate at apical constriction, i.e. minor diameter.

▶ Technique:

• Locate minor and major diameter on preoperative radiograph

• Estimate length of roots from preoperative radiograph

• Estimate canal width on radiograph. If canal is narrow, use 10 or 15 size instrument. If it is of average width, use 20 or 25 size instruments. If canal is wide, use 30 or 35 size instrument

Insert the selected file in the canal upto the estimated canal length and take a radiograph

• If file is too long or short by more than 1 mm from minor diameter, readjust the file and take second radiograph.

o If file reaches major diameter, subtract 0.5 mm from it for younger patients and 0.67 for older patients.

Advantages

• Minimal errors
• Has shown many successful cases.

Disadvantages

• Time consuming and complicated
• Requires excellent quality radiographs.

Non-radiographic Methods

Digital Tactile Sense

In this clinician may see an increase in resistance as

file reaches the apical 2 to 3 mm.

Advantages

• Time saving
• No radiation exposure.

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Disadvantages

• Does not always provide the accurate readings
• In case of narrow canals, one may feel increased resistance as file approaches apical 2 to 3 mm
• In case of teeth with immature apex, instrument can go periapically.

Periodontal Sensitivity Test

Method is based on patient’s response to pain.

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• does not always provide the accurate readings
• For example in case of narrow canals, instrument may feel increased resistance as file approaches apical 2 to 3 mm and in case of teeth with immature apex instrument can go beyond apex
• In cases of canal with necrotic pulp, instrument can pass beyond apical constriction and in case of vital or inflamed pulp, pain may occur several mm before periapex is crossed by the instrument.

Paper Point Measurement Method

In this method, paper point is gently passed in the root canal to estimate the working length

• It is most reliable in cases of open apex where apical constriction is lost because of perforation or resorption
• Moisture of blood present on apical part of paper point indicates that paper point has passed beyond estimated working length
• It is used as supplementary method.

Apex locators

SUMMARY

▶ minor diameter is a practical and anatomic termination point for the preparation and obturation of the root canal – and this cannot be determined radiographicaly.

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▶ Modern apex locators can determine this position with accuracies greater than 90% but with some limitations.

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• No individual method is truly satisfactory in determining endodontic working length.

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▶ Therefore, combination of methods should be used to assess the accurate working length determination

BIBLIOGRAPHY

▶ Endodontic practices and principles – 11^th ed

Grossman

▶ Endodontics Book – 6^th ed Ingle

▶ Pathways of Pulp – 10^th ed Stephen Cohen

▶ Textbook of Endodontics - Nisha Garg

▶ Bramante CM, Berbert A. ‘Critical evaluation of methods of determining working length.’ Oral Surg. 1974;37:463.

▶ Cluster LE, ‘Exact methods of locating the apical foramen.’ J Nat Dent Assoc. 1918;5:815.

▶ Kuttler Y. ‘Microscopic investigation of root apexes.’ J Am Dent Assoc. 1955;50:544-52.

▶ Endodontic working width: current concepts and techniques Yi-Tai Jou, DDS, DMD*, Bekir Karabucak, DMD, MS, Jeffrey Levin, DMD, Donald Liu