Boise, ID...June 4, 1994
Last Updated on Wednesday, January 14, 1998

Crown-Down Prep is easy with circumferential filing.

The function of circumferential filing is twofold, to enlarge a canal from small to large and to get it clean.

But there are certain circumstances where the canal is already larger than the largest file that you plan to use on it.

In this case the function of circumferential filing is simply to render the inside of the canal smooth and clean.

The typical case is the upper central incisor that is obviously larger than your largest file.

Once the apical length of the canal is measured you can simply start circumferentially filing with the largest file that will fit.

But instead of inserting the file to full depth and then starting to file, you insert just the tip of the file into the orifice and file.

Each time that you make one circumferential pass you go a little deeper until you have the depth you want.

In the case where you have misjudged the size of the canal, and the file will not go to depth, you can just stop and change to the next smaller file until you have reached full depth.

An interesting sidelight to this technique is that you can use this basic idea and use the tip of a file as an orifice opener.

The usual instrument of choice is a #30 sonic Fine-Cut File in the STS or in the Fine-Cut Endo Handpiece.

Immediately after making your access prep and flushing with water, insert just the tip of a #30 into the orifice and begin filing.

You can hardly go too deep with a #30 as the apex is rarely that large.

This will remove some of the overhanging dentin and make it easier to get the #15 into the apex for your measurement xray.

We are now recommending that this be the standard preparation method on opening the access.

One word of caution here.

If you do too much filing and flair the canal too much, and if you have to do much probing, you are then pushing a #15 into a canal that is wide enough for buckling to occur.

Buckling #15 that way is a pretty good way to break it, so don't overdo it.

If you have a canal that is already open to a #30 to start then it is going to be necessary to circumferentially file closer to the apex than otherwise just to get the apical 3mm clean.

The Chronic Asymptomatic Granuloma

A particularly important use for crown-down filing occurs when you have a chronic asymptomatic granuloma.

The uniqueness of the problem arises because the canal is probably contaminated with anaerobes but the apical granuloma is sterile.

The problem arises because in the normal measuring technique the first file pushes these anaerobes through the apex and can precipitate quite an infection.

One solution is to load the patient with antibiotics before you begin.

But there is another partial solution and that is to clean the bulk of the canal before measuring.

By 'guesstimating' the length of the canal and then subtracting about 20% to allow for xray distortion, you can do a crown-down prep with plenty of irrigation until you get to within 20% of the apex, then drop a file gently into the canal, take an xray and add 80% of the remaining distance to the apex and file to there, repeating this until you get to within one or two millimeters of the apex.

By this time you have cleaned the bulk of the canal without ever going to the apex.

At this point you can medicate the canal, close it up and wait a week to do the final dressing and filling.

Or you can irrigate gently with sodium hypochlorite ( Yes.

I know I warned you about using it.

So be careful. ) then go the rest of the way to the apex.

This would also be a justifiable use of a paraformaldehyde mixture, using the chemicals to kill the bugs.

Then rinse well before going to the apex.

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