Working length determination /certified fixed orthodontic courses by Indian dental academy

WORKING LENGTH
DETERMINATION

INDIAN DENTAL ACADEMY
Leader in Continuing Dental Education
www.indiandentalacademy.com

Definition
 Working length is defined in the
endodontic Glossary as “the distance
from a coronal reference point to the
point at which canal preparation and
obturation should terminate”.
 The explicit location of the physiological
apex of root canal is a prerequisite for a
successful endodontic therapy.


 The anatomic apex is the tip or
the end of the root determined
morphologically, whereas the
radiographic apex is the tip or
end of the root determined
radiographically.
 Root morphology and
radiographic distortion may
cause the location of the
radiographic apex to vary from
the anatomic apex.

 The apical foramen is the
main apical opening of the root
canal. It is frequently
eccentrically located away from
the anatomic or radiographic
apex.


 An accessory foramen is an orifice
on the surface of the root
communicating with a lateral or
accessory.
 The apical constriction (minor
apical diameter) is the apical portion
of the root canal having the
narrowest diameter. This position
may vary but is usually 0.5 to 1.0
mm short of the center of the apical
foramen.
 The cementodentinal junction is
the region where the dentin and
cementum are united, the point at
which the cemental surface
terminates at or near the apex of a
tooth - histologic landmark.
 The location of the
cementinodentinal junction also
ranges from 0.5 to 3.0 mm short of
the anatomic apex.


MINOR DIAMETER
 The apical constriction is the narrowest part of the canal
with the smallest diameter of blood supply, thus creating
the smallest wound site and best healing condition.
 This anatomical landmark can be called the minor diameter
of the canal.
 The minor diameter represents the transition between the
pulpal and the periodontal tissue, located in the range of
0.5 to 1.0 mm from the external foramen or major
diameter on the root surface.


Significance
 It determines how far into the canal the instruments
are placed and worked,
 It limits the depth to which the canal filling may be
placed,
 It affects the pain & discomfort for the patient,
 It determines the success of the treatment.


Methods
 Radiographic methods,
• Ingle’s,
• Grossman’s
• Digital radiography/Xeroradiography
 Non-radiographic methods,
• Digital tactile sense,
• Apical Periodontal sensitivity,
• Paper Point measurement,
• Apex Locators
 Others.


Apex Locators
 In 1918, Custer was the first to report the use of electric current to
determine working length.
 The scientific basis for apex locators originated with research conducted by
Suzuki in 1942.
 in vivo research on dogs using direct current discovered that the electrical
resistance between the periodontal ligament and the oral mucosa was a
constant value of 6.5 kilo-ohms.


 Sunada adopted the principle reported by Suzuki and was the first
to describe the detail of a simple clinical device to measure
working length in patients.
 He used a simple direct current ohmmeter to measure a constant
resistance of 6.5 kiloohms between oral mucous membrane and
the periodontium regardless of the size or shape of the teeth.
 The device used by Sunada in his research became the basis for
most apex locators.


First-Generation Apex Locators.
 First-generation apex location devices, also known as
resistance apex locators, 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).


Second-Generation Apex Locators.
 Second-generation apex locators, also known as impedance
apex locators.
 The major disadvantage of second-generation apex locators
is that the root canal has to be reasonably free of
electroconductive materials to obtain accurate readings.
 The presence of tissue and electroconductive irrigants in
the canal changes the electrical characteristics and leads to
inaccurate, usually shorter measurements.


Third-Generation Apex Locators
 The principle on which “third-generation” apex locators are based
frequency of the electric current.
 In biologic settings, the reactive component facilitates the flow of
alternating current, more for higher than for lower frequencies.
 Thus, a tissue through which two alternating currents of differing
frequencies are flowing will impede the lower-frequency current
more than the higher-frequency current.


 The reactive component of the circuit may change, for example,
as the position of a file changes in a canal.
 When this occurs, the impedances offered by the circuit to
currents of differing frequencies will change relative to each other.
 This is the principle on which the operation of the “third-
generation” apex locators is based


Working length determination /certified fixed orthodontic courses by Indian dental academy

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Working length determination /certified fixed orthodontic courses by Indian dental academy