Now that we are shipping Fine-Cut Endo ContraAngles again we have a new group using the handpiece for the first time so I thought it appropriate to review some does and don'ts.
The new FCECA(Fine-Cut Endo Contra Angle) has a new system for returning the file to its "down" position. We have returned to the concept of powered up and powered down strokes. This makes it much quieter and smoother running. It makes it possible to run the handpiece with much lower air pressure than before.
After several years of experience, we find that most dentists really don't need the file to move up and down more than about 1000-2000 strokes per minute. Since most air motors do not have a speed indicator on them, we suggest that you start at a speed that is adequate to get the up and down motion started and then reduce it until it seems smooth. Even at the slowest speed, the FCECA can open a canal from size 15 to 50 in about 60 seconds.
Lubrication: There are five miniature ball bearings they must be lubricated two on the main drive shaft, one that operates the eccentric cam and two on the rocker arm.
Before each use we recommend removing the FCECA from the motor and flooding it with oil from the back until it runs out the front. This will lubricate first the two main bearings, then flow into the cam bearing and then into the rocker arm bearings. Wipe off the excess before use.
It takes a lot of energy to translate rotary motion into an up and down motion that starts and stops 1000 times a minute and the handpiece might run a little warm. Unless the motor is run at excessively high speeds this is, most of the time, not objectionable. It may however indicate a need for lubrication.
Although it is theoretically possible to do crown-down-orifice-opening with any size file, until you get comfortable with the FCECA I'd suggest that you start with a size 25 or 30, spiraling down until the file sticks. Using a smaller size can get you into trouble because the canal may be big enough to accept it but be curved enough to cause the file to bind.
As you gain experience you will be better able to detect when the file is repeatedly getting stuck and cutting itself free. The smaller files will flex around curves that will stop a larger one.
If you feel that the file is "pulling itself in" this is diagnostic of a curve. If a file is in a straight canal smaller than the file, it can't bind. If it is in a canal smaller than itself that is straight it simply gets stuck and stops cutting.
In a canal that is big enough for the file but curved, on the in-stroke the file flexes around the curve but on the out stroke, the back-action cutting flutes prevent it from coming back out without tugging on it. The natural tendency is to relax outward pressure and thus the file SEEMS to pull itself in.
Actually Push-Pull probing "can" be done but it requires the development of a feel for it that might come slowly with experience. You have to push down hard enough for the file to get stuck and then pull upward with enough force to help the file chisel away the dentin. This requires skill.
Again, be sure that the dental assistant is adding water to the prep at all times.
The up and down motion of the file is about 1.5mm minus any play of the file in the file holder.
This is limited to allow better control of the circumferential filing motion and better depth control on your part.
Here's a startling fact of life. It is easier to break a file in a large canal than a small one. The only way a file can break with this contra-angle is for it to buckle on the way in, get caught and then forcefully straighten out on the way out. Since in a canal that is near the same size as the file, the file cannot buckle, it can't break.
Where this may be a problem is after doing crown-down-orifice-opening with a size 30, you probe to the apex by hand and then go back in to circumferentially enlarge the portion of the prep between the depth of the #30 and the three millimeter point.
In many canals there are fins, irregularities, lateral canals and bifurcations which the tip of the file can bump into and the canal being larger allows the file to buckle.
There is a technique that can make life easier for you in these cases.
Start with the motor off and insert the file to the maximum depth, turn the motor on and spiral up and out of the canal. This will eliminate any possibility of hitting anything with the tip on the way in. It will also make a nice transition from the curve at the apical end and the straighter part at the coronal end.
OK. That's all I can think of immediately. If I think of anything else, I'll add it later. Keep watch on this spot.