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HISTORICAL REVIEW
ž 1918 Custer- use of electric current for working
length
ž 1942 Suzuki- conducted scientific study of apex
locator
ž 1960 Sunada- found electrical resistance between
periodontium & oral mucous membrane
ž 1969 Inove- significant contribution in evolution of
EAL with his reports on Sono-Explorer
ž 1996 McDonald & Pratten- done experiments in
cadaver
CLASSIFICATION OF ELECTRONIC APEX LOCATOR
ž By McDonald- depends on:
₋
Type
of current flow
₋
Opposition
to current flow
₋
Number
of frequencies involved
·
Ist
generation apex locator
·
IInd
generation apex locator
·
IIIrd
generation apex locator
·
IVrth
generation apex locator
Ist GENERATION APEX LOCATOR
ž Known as Resistance apex locator
ž Measure opposition to flow of direct current or
resistance
ž Based on the principle that resistance offered by
periodontal ligament & oral mucous membrane is the same i.e. 6.5k ohm
TECHNIQUE
ž Turn on the device & attach the lip clip near the
arch being treated
ž Hold 15 no. file & insert it 0.5mm into sulcus of
tooth
ž Adjust the control knob until the reference needle is
centred on the meter scale & produces audible beep
ž Note this reading
ž Prepare the access cavity & apply rubber dam
ž Using preoperative radiograph estimate the working
canal width
ž Insert the file into canal
ž Take the radiograph with file in place at the length
indicated by apex locator
ADVANTAGE
ž Objective information with accuracy
ž Used where radiograph cannot be used accurately
1.Maxillary molar (due to
zygomatic process)
2.Mandibular molar (due to
mandibular tori)
ž Patients with gag reflux
DISADVANTAGE
ž Wrong readings due to:
1. low battery
2. wet canal
3. tissue present in canal
4. too narrow canal
IInd GENERATION APEX LOCATOR
ž Known as impedance locator
ž Measure opposition to alternating current or impedance
ž Various apex locators are
Sono-Explorer
Apex finder
Endo analyser
Digipex
Formatron IV
DISADVANTAGE
ž Root canal has to be free of elecroconductive material
to obtain accurate readings
ž Presence of tissue & electroconductive irrigants
lead to inaccurate measurements
ž Pilot & Pitts reported that:
· 5.25% sod. Hypochlorite solution
· 14.45% EDTA
solution
· normal saline solution are
conductive
ž This creates a “catch 22” situation
ž Not all apex locators have the degree of
sophostication in electronic circuitry that adjust its sensitivity to
compensate for intracanal environment
IIIrd GENERATION APEX
LOCATOR
ž Frequency dependent apex locator.
ž Based on the fact that different site in canal give
difference in impedance between high (8khz) & low(400hz) frequences.
ž Difference in impedance is least in the coronal part
of the canal.
ž As the probe goes deeper difference increases.
ž Also known as “comparative impedance” because they
measure relative magnitudes of impedance which are converted into “length”
information.
VARIOUS IIIrd GENERATION
APEX LOCATORS
1.Endexby Yamaoka
ž The original IIIrd generation apex locator
ž It measures impedance between two currents
ž Operates most accurately when the canal is filled with
electrolyte: sod. hypochlorite
2. Neosono ultima apex locator
ž Works best in
the presence of sod. Hypochlorite
ž It is attached
with pulp tester, it is called Co-pilot.
3.APEX FINDER
ž Uses multiple frequencies & comparative impedance
principles
ž Accurate regardless of irrigants or fluid in the canal
ž It has a LCD panel that indicates the distance of the
instrument tip from the apical foramen in 0.1mm increments
ž The display has a ‘canal condition indicator’ that
reflects canal wetness/dryness & allow the user to improve canal
conditions
ROOT ZX
ž Uses dual frequency & comparative impedance
principle
ž Simultaneously measures two impedances at two
frequencies inside the canal
ž A microprocessor in the device calculates the ratio of
the two impedances
ž The quotient of impedance is displayed on LCD panel
& represents the position of the instrument tip inside the canal
ADVANTAGE
ž Requires no adjustment or calliberation
ž Can be used when the canal is either empty or moist
ž Easy to read LCD
ž Allows shaping & cleaning of the root canal with
simultaneous of the working length
ž Iv-th generation apex locators
ž They measure resistance & capacitance separately
rather than the resultant impedance value.
ž There can be different combination of values of
capacitance & resistance that provides same impedance,resulting in same
reading.
ž The IV- generation apex locators broken this to
primary components & measures seperately for better accuracy & less chance
for occurance of errors.
COMBINATION OF APEX LOCATOR
& ENDODONTIC HANDPIECE
Tri Auto ZX
ž Cordless electric endodontic handpiece with a built in
Root ZX apex locator
ž Handpiece uses Ni-Ti rotory instruments that rotate at
280-320 rpm
ž It has 3 automatic safety mechanisms
1. Auto - start – stop mechanism:-
ž handpiece
starts rotation when the instrument enters the canal & stops when it is
removed
2. Auto – torque – reverse
mechanism:-
ž handpiece
automatically stops & reverses rotation when the torque threshold (30gm/cm)
is exceed
Sofy ZX
ž Monitor the location of file tip during all
instrumentation
ž Minimizes the danger of over instrumentation
ENDY 7000
ž Reverses the rotation when the tip reaches apical constriction.
ž Basic condition of
accuracy of electronic apex
locators
ž Canal should be free from debris & tissue
ž Apex locators works best in a relatively dry
environment but extremely dry canal may lead to low readings
ž Excess fluids must be removed from the chamber
ž If residual fluid is present in the canal it should be
of low conductivity value
ž Descending order of conductivity of irrigating
solutions5.25% NaOCl >17% EDTA> saline
ž Proper contact of file with canal wall & peri apex
ž No blockage & calcification in the canal
Uses of apex locator
ž Provide objective information with high degree of
accuracy
ž Useful in conditions where apical portion is
obstructed by anatomical structures like tori, exostoses
ž In patients with gag reflex
ž Pregnant patients
ž Root perforation, resorption, root fracture
ž Pulp vitality
ž RCT of teeth with incomplete root formation
Advantages
ž Accurate
ž Objective measurements
ž Easy & fast
ž Reduction of exposure to radiation
ž Can detect resorption & root fracture
ž Perforations can be detected
Contraindication
ž Patients with cardiac pace maker
ž Teeth with necrotic pulp
Conclusion
ž Working length can be accurately measured by
combination of various technique such as tactile sense, radiography etc
ž Electronic apex locator provide accurate readings and
serve as an important diagnostic tool
References
ž Text book of endodontics-Ingle
ž Text book of endodontics-Nisha Garg
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