Electronic Apex Locators

Question 1

According to Nekoofar et al 2006, what regards to EAL-What are the resistors in the root canal?

Answer 1

Dentine
Cementum
Tissue within root canal

Question 2

According to Nekoofar et al 2006, as the file approaches the minor apical foramen, what happens to the resistance between the file and AF?

Answer 2

Decreases

Question 3

According to Nekoofar et al 2006, Which tissues with regards to root canal anatomy have capacitive abilities?

Answer 3

Tissue fluid

Periodontal ligament

Question 4

According to Nekoofar et al 2006, what are the methods by which EAL work?

Answer 4

• Measure of resistance
• Measure impedance
• Voltage gradient methods

Question 5

According to Nekoofar et al 2006, what is the shape of the apical foramen?

Answer 5

Inverted cone

Question 6

According to Nekoofar et al 2006, where is the base of the inverted cone located, major or minor AF?

Answer 6

Major AF

Question 7

According to Nekoofar et al 2006, what other anatomical landmark is at the minor apical foramen?

Answer 7

Apical constriction

Question 8

According to Nekoofar et al 2006, what junction is seen near or at the minor apical foramen?

Answer 8

CDJ

Question 9

According to Nekoofar et al 2006, in what tissue is the Major AF located within?

Answer 9

Cementum

Question 10

According to Nekoofar et al 2006, list some reasons as to why the position of the Major AF may chance location

Answer 10

• Physiolgical e.g. Age

- Pathological e.g. resorption

Question 11

According to Nekoofar et al 2006, in the ideal situation where would root canal preparation terminate?

Answer 11

• At the CDJ, this is because the root canal is narrowest here and likely to create the smallest wound
• where pulp tissue becomes periodontal

Question 12

According to Nekoofar et al 2006, what is the problem with locating CDJ?

Answer 12

This is a histological site

-Location of CDJ can vary in person to person (to is not very reproducible)

Question 13

According to Nekoofar et al 2006, what is the problem with using the radiographic apex as canal terminus?

Answer 13

the apical construction can be 0.5-1mm short of this

Question 14

According to Nekoofar et al 2006, what is the basis of function for how EAL work?

Answer 14

The electrical conductivity inside the root canal system is less than the tissues surrounding it
NB providing the canal is either dry or not filled with conductive fluid

Question 15

What resistance value did Sunanda 1962 find was between the file and PDL at apical foramen?

Answer 15

6.5 kilo ohms

also the same in perforations

Question 16

According to Nekoofar et al 2006, what is the disadvantage of using DC current?

Answer 16

• small electric shock felt by patient

- do not work well if electrolyte are preset

Question 17

What is the importance of accurate measurements during RCT?

Answer 17

Ensure bacteria have been eliminated from

Within the canal system

Question 18

Define working length

Answer 18

Distance from coronal reference point to point at which root canal prep and obturation should terminate

Question 19

Why is the CDJ not used for length determination

Answer 19

1. It is a histological site

2. Not a constant feature clinically therefore hard to determine

Question 20

When were electronic apex locators first developed ?

Answer 20

Custer 1918
Revisited by Suzuki 1942 - used dogs teeth to study current flow finding a constant resistance between oral mucosa and canal
Sunada 1962 developed first device

Question 21

On what basis do modern day apex locator work on?

Answer 21

Common resistance between oral mucosa and PDL is 6.5 kHz

Question 22

How do apex locators work?

Answer 22

Use human body to complete the circuit
Lip electrode and file in canal
The apex locator beeps when the resistance between file and oral mucosa is same value as EAL

Question 23

How are apex locators classified

Answer 23

McDonald classification: current flow

Generation

Question 24

What type of current flow exist?

Answer 24

DC or AC

Question 25

What type of AC EAL are there ?

Answer 25

Resistance
Impedance
Frequency

Question 26

What type of frequency EAL exist?

Answer 26

Subtraction type

Ratio type

Question 27

First generation apex locators were what type and what were the downfalls

Answer 27

Resistance based

Needed dry environment, patient could feel a shock, had to be calibrated

Question 28

What were the second generation EAL based on and their downfalls

Answer 28

Measured Impedance and was able to detect sudden change in impedance at the apex
- they were difficult to operate and need dry canal

Question 29

What generation is propex 2?

Answer 29

Fifth generation: measures multiple
frequencies to determine canal length
Multi frequency

Question 30

How accurate is the propex 2?

Answer 30

86%
Radiographs are 75%
Vinyak et al 2013

Question 31

What is the function of EAL based upon?

Answer 31

Electrical conductivity of tissues surrounding the root apex is greater than tissues inside the root canal (provided it is a a non conductive state)

Question 32

What did Sunada 1962 find?

Answer 32

When the tip of a file reached the PDL through the apical foramen the electrical resistance between instrument and oral muscles was a constant value

Question 33

How do multifrequency apex locators work?

Answer 33

Detects canal terminus by determining a sudden change in the resistance or capacitive features