working length determination in endodont

1. WORKING LENGTH
DETERMINATION

2.  WORKING LENGTH:
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”

3.  REFERENCE POINT: is
that site on occlusal or the
incisal surface from which
measurements are made.
 ANATOMIC APEX: tip or
end of root determined
morphologically

4.  RADIOGRAPHIC APEX: tip or end
of root determined
radiographically.
 APICAL FORAMEN (major
diameter): is main apical opening
of the root canal. It is frequently
eccentrically located away from the
anatomic or radiographic apex.
 APICAL CONSTRICTION (minor
diameter): is apical portion of root
canal having narrowest diameter. It
is usually 0.5 to 1 mm short of apical
foramen.

5.  CEMENTODENTINAL JUNCTION: the region where
cementum and dentin are united, the point at which
cemental surface terminates at or near the apex of tooth.
 Location of CDJ ranges from 0.5-3mm short of anatomic
apex.

6.  Determines how far into canal, instruments can be placed
and worked.
 Consequences Of Over ExtendedWorking Length:
 Perforation through apical constriction.
 Overinstrumentation
 Overfilling of root canal
 Increased incidence of postoperative pain.
 Prolonged healing period
 Lower success rate (because of incomplete regeneration
of cementum, periodontal ligament and alveolar bone

7.  Consequences Of Working Short of actual working Length
 Incomplete cleaning & instrumentation of canal.
 Persistent discomfort due to presence of pulpal remnants
 Under filling of the root canal.
 Incomplete apical seal.
 Apical leakage which supports existence of viable bacteria
and contributes to poor healing and periradicular lesion

8. Causes of loss of working length:
 Presence of debris in apical 2/3rd of canal
 Failure to maintain apical patency
 Skipping instrument sizes
 Ledge formation
 Inadequate irrigation
 Instrument separation
 canal blockage

9.  Definition: Working width is defined as “initial and
postinstrumentation horizontal dimensions of the root canal
system at working length and other levels”
 the minimum initial working width= initial apical file size
which binds at working length and other levels
 The maximum final working width corresponds to the
master apical file size

10.  Reasons for widening root canal:
 To remove microorganism from the canal mechanically
 To increase the area of root canal for better irrigation
 To completely remove the pulp tissue
 To attain a sound apical stop so as to achieve a 3
dimensional seal.The round shape confirms to the round
cross sectional tip of gutta percha

11.  2 guidelines for instrumentation:
 Enlarge the root canal atleast 3 sizes beyond the first
instrument that binds the canal
 Enlarge the canal until it is clean. It is indicated by white
dentinal shavings on the instrument flutes
 The main aim should be to remove the canal irregularities of
dentin to make the canal walls smooth

12.  Factors affecting size of working width
 Whether root canal is vital/non-vital
 Presence of periapical pathology
 Presence or absence of root resorption
 Canal configurations like C-shaped canal, bayonet canals,
etc
 Presence or absence of isthmus

13.  Advantages of narrow apex:
 Decrease 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 oobturating
material
 Not recommended for thermoplastic obturation
 More chances of preparation errors

14.  Average root length from anatomic studies
 Radiographs
 Matematical method
 Tactile sensation
 Bleeding on paper point
 Apical periodontal sensitivity
 Electronic apex locator

15. RADIOGRAPHIC METHODS
•GROSSMAN FORMULA
•INGLE’S METHOD
•WEIN’S METHOD
•KUTTLER’S METHOD
OTHER METHODS
•BEST’S METHOD
•BREGMAN’S METHOD
•BRAMANTE’S METHOD
•RADIOGRAPHIC GRID
•ENDOMETRIC PROBE
•DIRECT DIGITAL RADIOGRAPHY
•XERORADIOGRAPHY
•SUBTRACTION RADIOGRAPHY

16.  Two schools of thought are there:
 Cementodentinal junction is impossible to locate clinically
and the radiographic apex is the only reproducible site
available for length determination.
 Those who don’t follow this concept say that radiogrpahic
apex is not reproducible. Its position depends on number
of factors like angulation of tooth, position of ilmm, film
holder etc.
 Two techniques used: Paralelling technique (superior) and
bisecting angle technique

17.  Before access opening, fractured cusps, weakened cusps are
reduced to avoid fracture of weakened enamel during the
treatment.This will avoid the loss of initial reference pont
and thus the working length.

18.  Pre-op radiograph is used to calculate the working length.
 Measure estimated working length from preoperative
periapical radiograph
 It can be confirmed by placing an endodontic instrument
(with stopper adjusted) into the canal and taking a second
radiograph.
 Instrument inserted should be large enough not to be loose
in the canal because it can move while taking radiograph and
this may result in errors in determining its working length.

19.  The new working length is
calculated by adding or
subtracting the distance
between the instrument
tip and desired apical
termination of the root.
 Correct working length is
finally calculated by
subtracting 1mm from this
new length.

20.  Can see the anatomy of the tooth
 Can find out curvature of the root canal.
 Can see the realationship between the adjacent teeth and
anatomic structures.

21.  Varies with different observers.
 Superimposition of anatomical structures.
 Two- dimensional view of three-dimensional object.
 Cannot interpret if apical foramen has buccal or lingual exit.
 Risk of radiation exposure.
 Time consuming
 Limited accuracy

22.  Weine’s recommendations for determining the working length
based on radiographic evidence of root or bone resorption
 If no root or bone resorption: preparation should terminate 1.0
mm short of the apical foramen (shorten the length by 1 mm)
 Bone resorption is present but no root resorption: shorten the
working length by 1.5 mm
 Both root & bone resorption is present: shorten the length by
2.0mm

23. Canal preparation should terminate at apical constriction
(MINOR DIAMETER)
 Locate major & minor diameter on preoperative radiograph.
 Estimate length of roots
 Estimate canal width
 Select the appropriate file and insert into the canal and take
a radiograph.
 If file reaches major diameter, subtract 0.5 mm from it for
younger patients and 0.67 for older patients.

24.  Advantages:
 Minimal errors
 Has shown many successful cases
 Disadvantages:
 Time consuming and complicated
 Requires excellent quality radiographs

25.  An instrument is inserted into the canal, stopper is fixed to
the reference point and radiograph is taken
 Actual length of the tooth = ( apparent length of
tooth in radiograph/apparent length of instrument in
radiograph) × actual length of the instrument.
 Disadvantages: wrong readings due to-
 Variations in angles of radiograph
 Curved roots
 S-shaped, double curvature roots.

26.  By Everett & Fixott in 1963
 A millimeter grid is superimposed on the radiograph.
 Advantages:
 Overcomes the need for calculation
 Disadvantages:
 Not good method if radiograph is bent during exposure.

27.  Uses the graduations on diagnostic file which are visible on
radiograph.
 Disadvantage: smallest file size to be used is number 25.

28.  Digital image is formed
 2 types:
 Radiovisiography
 Phosphor imaging system

29.  New method
 Without film, image is recorded on an aluminium plate
coated with selenium particles.
Advantages:
 Offers edge enhancement and good detail.
 The ability to have both positive and negative prints
together .
 Improves visualization of files and canals.
 It is two times more sensitive than conventional D-speed
films
 More sensitive

30.  Disadvantages
 Since saliva may act as a medium for flow of current, the
electric charge over the film may cause discomfort to the
patient.
 Exposure time varies according to thickness of the plate.
 Process of development cannot be delayed beyond 15
min.

31.  Clinician may see an increase in resistance as file reaches the
apical 2 to 3mm.
 Advantages:
 Time saving
 No radiation exposure
 Disadvantages:
 Inaccurate readings
 Narrow canals, one may feel increased resistance as file
reaches apical 2 to 3mm.
 Teeth with immature apex, instrument can go periapically.

32.  Based on patient’s response to pain.
 Don’t always provide accurate readings
 In case of narrow canals , instruments may feel increased
resistance as file approaches apical 2-3mm
 In case of teeth with immature apex, instrument can go
beyond the apex
 In apical periodontal sensitivity test,
 In case of necrotic pulp: instrument can pass beyond apical
constriction
 In case of vital or inflamed pulp: pain may occur several mm
before periapex is crossed by the instrument

33.  Paperpoint is gently passed in the root canal to estimate the
working length.
 Most reliable: open apex cases
 Moisture of blood present on apical part of paper point
indicates that paper point working has passed beyond
estimated working length.
 Used as supplementary method.

34.  Used as an adjunct to radiography
 Used to locate the apical constriction or cementodentinal
junction or apical foramenand not the radiographic apex.

35.  APICAL CONTROL ZONE: is the mechanical alteration of the
apical terminus of the root canal space which provides resistance
and retention form to the obturating material against the
condensation pressure of obturation.
 The ability to distinguish between minor and major diameter is
most important for the creation of apical control zone

36.  Apex locators function by using human body to compete an
electrical circuit.
 One side of apex locator circuit is connected to endontic instrument
and other side is connected to patient’s body.
 Circuit is completed when endodontic instrument is advanced into
root canal until it touches the periodontal tissues

37.  Lip clip
 File clip
 Electronic device
 Cord which connects above three parts

38.  Provide objective information with high degree of accuracy
 Easy and fast
 Redction of exposure to radiation
 Perforation can be detected
 Can measure pulp space exactly to the constriction
 Can detect resorption and root fracture

39.  Can provide inaccurate readings in following cases.
 Presence of pulp tissue in canal
 Too wet or too dry canal
 Use of narrow file
 Blockage of canal
 Incomplete circuit & low battery
 Chances of over estimation
 Immature apex
 Incorrect readings in teeth with periapical radiolucenies, and
necrotic pulp associated with root resorption, etc.

40.  Provide objective information with high
degree of accuracy
 When apical portion of canal system is
obstructed.
 In patients who cannot tolerate X-ray
film placement because of gag reflex
 Pregnant patients
 Detecting site of root perforations
 Children, disabled patients, patients
who are heavily sedated.
 RCT of teeth with incomplete root
formation.

41.  Patients who have cardiac pacemaker

42. Based on type of current flow and opposition to current flow
and number of frequencies involved
 First generation apex locator( resistance apex locator)
 Second generation apex locators (impedence apex locators)
 Third genertion apex locators
 Fourth generation apex locators
 Combination apex locators and endodontic handpiece

44.  Measures opposition to flow of direct current. i.e. resistance
 Principle: resistance offered by periodontal ligament and
oral mucous membrane is the same. i.e. 6.5K ohms.
 Not used nowadays: blood, pus, chelating agents etc used
within the canals can give false readings
Technique
1. Turn on the device and attach the lip clip near the arch
being treated.
2. Hold a 15 number file and insert it approx 0.5mm into sulcus
of tooth. Adjust the control knob until the reference needle
is centred on the metre scale and produces audible beeps.
Note this reading

45. 4. Prepare the access cavity and apply rubber dam and remove
pulp, debris etc.
5. Using preoperative radiograph estimate the working canal
width.
6. Insert the file into canal unless the reference needle moves
from extreme left to centre of scale and alarm beeps sound.
Reset the stop at reference point and record the lengths.
7. Take the radiographs with file in place at the length indicated
by apex locator. If length is longer or shorter, it is possible that
preoperative film can be elongated or apex locator is
inaccurate

47.  Easily operated
 Possible to get objective information with high degree of
accuracy
 Used when radiographs cannot be used accurately like
 Maxillary molars due to zygomatic process)
 Mandibular molars (obstruction due to mandibular tori)
 Patient with gag reflex
 Digital read out
 Audible indication
 Detect perforation

48.  Requires a dry field
 Many factors can lead to wrong reading like low battery,
tissue present in canal, wet canal, too narrow canal or canal
with blockage and problems of lip clip
 Patient sensitivity
 Requires calibration
 Cannot estimate beyond 2mm
 File should not contact metal restorations

49.  Low frequency
 Introduced by Inoue
 Measures opposition to flow of alternating current or
impedance.
 Indicates the apex when two impedance values approach
each other.

50.  Does not require lip clip.
 No patient sensitivity.
 Analog meter
 Detects perforations

51.  No digital read out.
 Difficult to operate
 Canal should be free of electroconductive materials to obtain
accurate readings.
 Requires coated probes
 Cannot use files

52.  High frequency
 Based on the fact that different sites in canal give difference
in impedance between high (8KHz) and low (400Hz)
frequencies
 Is least in coronal part of canal
 As the probe goes deeper into canal, difference increases
 Greatest at cementodentinal junction
 These should be termed as ‘comparative impedence”
because they measure relative magnitudes of impedence
which are converted into length information.

53.  There can be different combination of values of capacitance
and resistance that provides the same impedence.
 But te fourth generation apex locators measures resistance
and capacitance separately rather than the resultant
impedance value
 They are:
 AFA apex finder
 Elements diagnostic unit

54.  Tri Auto ZX is cordless electric endodontic handpiece with
builtin root ZX apex locator
 It has three safety mechanisms:
 Autostart stop mechanism: handpiece starts rotation
when instrument enters the canal and stops when it is
removed.
 Autotorque reverse mechanism: handpiece automatically
stops and reverses rotation when torque threshold
(30gm/cm) is exceed. Prevents instrument breakage.

55.  Autoapical –reverse mechanism
 It stops and reverses rotation when instrument tip reaches
a distance from apical constriction taken for working
length
 Prevents apical perforation

56.  Canal should be free from most of the
tissue and debris
 Canal should be relatively dry
 No cervical leakage
 If residual fluid is present, it should be of
low conductivity (5.25%NaOCl >
17%EDTA > saline)
 Proper adaptation of file to canal walls
and periapex
 No blockages or calcifications in canals
 Battery of apex locator and other
connections should be proper

57.  TEXTBOOK OF ENDODONTICS- NISHA
GARG & AMIT GARG