It is the
instrument used in dentistry to determine the working length of root canal in
root canal treatment as an adjunct to radiography. They are basically used to
locate apical foramen by determining the apical constriction or cement-dentinal
junction.
The basic
principle of apex locator is based on electrical resistance and apex of the
root of the canal has a specific resistance to electrical current ad this is
measured using a pair of electrodes typically hooked into the lip and attached
to an endodontic file. These are divided into 4 types based on the way the apex
is located.
1st
generation is also called resistance apex locator. They are based on the
principle that resistance offered by periodontal ligament and the oral mucous
membrane is the same the is 6.5 k ohms. They measure the opposition to the flow
of direct current that is resistance. This locator gives a false reading in the
presence of blood, pus, irrigants , a chelating agent. The main advantage of
using this apex locator are using operated digital readout,can be used wit6h
k-file, may incorporate pulp tester and disadvantages are require dry field,
patient sensitivity and cannot estimate beyond 2mm.
2nd
generation apex locator works on the principle of impedance,hence they are
called impedance apex locator. They work by measuring opposition to flow of
alternating current. The major disadvantage of second-generation apex locator
is that root canal has to be free of electroconductive materials to obtain
accurate readings.presence of electro-conductive irrigants changes the electric
characteristic and lead to inaccurate readings. The main disadvantage of using
these type of apex locator is that they do not require lip clip, no patient
sensitivity, analogue method and disadvantages are no digital readout, difficult
to operate, the canal should be free of electro-conductive irrigants and tissue
fluids.
The 3rd
generation is also called frequency-dependent apex locator.It works on the
principle of frequency or comparative impedance.they are based on the fact that
different sites in the canal give a difference in impedance between high and
low frequencies. The difference in impedance is least in the coronal part of
the canal and as the probe goes deeper into canal difference increases and it
is greatest at a cement-dentinal junction. The main advantage of using this
apex locator is easy to operate, uses k-file, an audible indication,can operate
in presence of fluids, analogue readout and disadvantages are they require lip
clip and chances of short circuit.
4th
generation measures the resistance and capacitance separately rather than the
resultant impedance value. By using 4th generation apex locator the capacitance
and resistance broken down into primary components and measures separately for
better accuracy and thus fewer chances of occurrence of errors.
Evolution in
endodontics is at their fast pace and now the market is going toward the 5th or
6th generation. Reference is taken from journals issued in dentist junior and
NCBI.
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