Electronic Apex Locators Flashcards
According to Nekoofar et al 2006, what regards to EAL-What are the resistors in the root canal?
Dentine
Cementum
Tissue within root canal
According to Nekoofar et al 2006, as the file approaches the minor apical foramen, what happens to the resistance between the file and AF?
Decreases
According to Nekoofar et al 2006, Which tissues with regards to root canal anatomy have capacitive abilities?
Tissue fluid
Periodontal ligament
According to Nekoofar et al 2006, what are the methods by which EAL work?
- Measure of resistance
- Measure impedance
- Voltage gradient methods
According to Nekoofar et al 2006, what is the shape of the apical foramen?
Inverted cone
According to Nekoofar et al 2006, where is the base of the inverted cone located, major or minor AF?
Major AF
According to Nekoofar et al 2006, what other anatomical landmark is at the minor apical foramen?
Apical constriction
According to Nekoofar et al 2006, what junction is seen near or at the minor apical foramen?
CDJ
According to Nekoofar et al 2006, in what tissue is the Major AF located within?
Cementum
According to Nekoofar et al 2006, list some reasons as to why the position of the Major AF may chance location
- Physiolgical e.g. Age
- Pathological e.g. resorption
According to Nekoofar et al 2006, in the ideal situation where would root canal preparation terminate?
- At the CDJ, this is because the root canal is narrowest here and likely to create the smallest wound
- where pulp tissue becomes periodontal
According to Nekoofar et al 2006, what is the problem with locating CDJ?
This is a histological site
-Location of CDJ can vary in person to person (to is not very reproducible)
According to Nekoofar et al 2006, what is the problem with using the radiographic apex as canal terminus?
the apical construction can be 0.5-1mm short of this
According to Nekoofar et al 2006, what is the basis of function for how EAL work?
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
What resistance value did Sunanda 1962 find was between the file and PDL at apical foramen?
6.5 kilo ohms
also the same in perforations
According to Nekoofar et al 2006, what is the disadvantage of using DC current?
- small electric shock felt by patient
- do not work well if electrolyte are preset
What is the importance of accurate measurements during RCT?
Ensure bacteria have been eliminated from
Within the canal system
Define working length
Distance from coronal reference point to point at which root canal prep and obturation should terminate
Why is the CDJ not used for length determination
- It is a histological site
2. Not a constant feature clinically therefore hard to determine
When were electronic apex locators first developed ?
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
On what basis do modern day apex locator work on?
Common resistance between oral mucosa and PDL is 6.5 kHz
How do apex locators work?
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
How are apex locators classified
McDonald classification: current flow
Generation
What type of current flow exist?
DC or AC
What type of AC EAL are there ?
Resistance
Impedance
Frequency
What type of frequency EAL exist?
Subtraction type
Ratio type
First generation apex locators were what type and what were the downfalls
Resistance based
Needed dry environment, patient could feel a shock, had to be calibrated
What were the second generation EAL based on and their downfalls
Measured Impedance and was able to detect sudden change in impedance at the apex
- they were difficult to operate and need dry canal
What generation is propex 2?
Fifth generation: measures multiple
frequencies to determine canal length
Multi frequency
How accurate is the propex 2?
86%
Radiographs are 75%
Vinyak et al 2013
What is the function of EAL based upon?
Electrical conductivity of tissues surrounding the root apex is greater than tissues inside the root canal (provided it is a a non conductive state)
What did Sunada 1962 find?
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
How do multifrequency apex locators work?
Detects canal terminus by determining a sudden change in the resistance or capacitive features
