Question:
In performing a root canal on my tooth, my dentist used an "apex
finder" to determine how deep to go. He was unable to explain how it
worked. Does someone out there know?
Answer:
The other lead is the periodontal ligament which communicates with the
apex of the root.
*Apparently*, as the probe goes down the canal, the electrical resistance
changes as it reaches the apex, and when it's above a certain treshold, it
beeps.
You attach a ground to the lip, then attach the other lead to the file. As you
move down the canal, the density changes, and therefore the impedance changes.
When the impedance reaches a certain level, you are at the apex.
Basically, what happens is once the file is placed at a certain point, an
electrical circuit is completed, and the apex locator beeps to let you know
that you should stop where you are !
It is a function of electrical impedance, which sort of similar to
resistance but different. The low voltage electric circuit gets different
amounts of signal back from the ground plate relative to how close the tip
of the file is to the end of the root. I the patient is close to normal in
physiologic impedance, bone density. tissue wetness, tooth position, root
width, etc. you get reliable results.
