Q & A Regarding Apex Locators

                                             APEX LOCATORS

QUES    Disadvantages of 2^nd generation EAL?

ANS      Disadvantages are:-

·         Requires calibration

·         Requires coated probes

·         No digital read-out

·         Difficult to operate

QUES   Meachanism for 3^rd, 4^th and 5^th generation EAL?

ANS    

3^rd generation

·         They are frequency dependant apex locators

·         Based on the fact that different sites in canal give difference in impedance between high (8 KHz) and low (400 Hz) frequencies

·         Difference in impedance is least in the coronal part of canal. As the probe goes deeper in the canal, difference increases

 

4^th generation & 5^th generation

·         Measure resistance and capacitance separately rather than the resultant impedance value.

·         There can be different combination of values of capacitance and resistance that provide the same impedance, thus the same foraminal reading.

·         4^th generation EAL need to perform in relatively dry or partially dry canals whereas 5^th generation EAL perform well in the presence of blood and exudates

QUES   Examples of all generation EAL?

ANS    

1^st generation:- Endodontic Meter

   Endodontic Meter S II

2^nd generation:- Sonoexplorer

    Digipex

    Digipex II

    Endoanalyzer

    Formation IV

3^rd generation:- Endex

   Root ZX

   Propex

   EZ apex locator

   Mark V Plus

   Exact-A-Pex

4^th generation:- Raypex 4

   Elements apex locator

5^th generation:- Propex II

QUES   What generation is Propex and Propex II EAL?

ANS     Propex – 3^rd generation

 Propex II – 5^th generation

QUES   Histologically where is minor diameter located?

ANS    CDJ does not always coincide with apical constriction and is located 0.5-3mm short of anatomical apex (Grossman 12^th ed).

QUES   Which EAL is ideal for all situations?

ANS     5^th generation EAL perform well in the presence of blood and exudates but they experience considerable difficulties while operating in dry canals.Therefore, additional insertion of liquids in the canal is exerted almost always. Low toxicity of measurement in dry canals, as well as the need to insert extra liquid still predetermine the preferences in favour of 4^th generation devices

QUES   What is resistance, impedance, capacitance?

ANS     Impedance: Electrical impedance is the measure of the opposition that a circuit presents to the passage of alternating current when a voltage is applied

·         The electrical resistance of an electrical element is the opposition to the passage of direct electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes.

·         Capacitance is the ability of a body to store an electrical charge. Any body or structure that is capable of being charged, either with static electricity or by an electric current exhibits capacitance.

Que-  Histologically minor diameter is known as?

Ans-

  Minor diameter(Apical constriction) is the narrowest portion at the terminal end of the

pulp space. It is approximately 0.5 mm. short of the apical foramen.

 Taylor pointed out that narrower spot at the apical level which he believed to correspond histologically to the Cementodentinal Junction (CDJ).

IEJ, 1998, 31, 384-93

Que-  At what stage is working length taken?

Ans- Before determining a definitive working length, the coronal access to the pulp chamber must provide a straight line pathway into the canal orifice.

Que- How is the circuit completed by Apex Locators?

Ans- All EALs function by using the human body to complete an electrical circuit. One side of the apex locator’s circuitry subsequently is connected to the oral mucosa through a lip clip and the other side to a file. When the file is placed into the root canal and advanced apically until it is tip touches periodontal tissue at the apex, the electrical circuit is completed. The electrical resistance of the EAL and the resistance between the file and oral mucosa are now equal, which results in the device indicating that the apex has been reached.

Que- Which method of taking radiographs is preferred in Endodontics and why?

Ans

ü  Ideally, radiographs should be taken with a paralleling technique rather than the bisecting technique as it produces more geometrically accurate images (Vande Voorde & Bjorndahl 1969, Forsberg & Halse 1994).

ü  The paralleling technique is used for both periapical and bite-wing radiographs and is the most accurate technique for taking these projections.

ü  For film or digital radiographs, the receptor should be placed vertically and horizontally parallel with the teeth that are being radiographed. The X-ray beam should be directed at right angles to the teeth and receptor.

ü  In the case of periapical radiographs, the film or digital receptor should be placed parallel to the full length of the crown and root of the teeth being imaged.

ü  The paralleling technique for bite-wing radiographs is simpler as the radiograph is more easily placed in the patient’s mouth even if the palate is shallow or the patient gags easily.

ü  A series of investigations by Forsberg (1987) concluded that the paralleling technique was more accurate than the bisecting angle technique for accurately and consistently reproducing apical anatomy.           

ü  The paralleling technique results in good quality x-rays with a minimum of distortion.