The Neck is the smallest diameter of the canal and is immediately adjacent to the periodontal ligament.

The neck can theoretically be any length but for consistency of the filling technique placing the needle tip one millimeter from the apex seems to be about right.

Cement of the thickness we mix it has difficulty going through any tube smaller than the bore of a 30 gauge needle which is 0.15mm which is the size of the tip of a size 15 file. Most apices are at least size 15 and to get them clean it is necessary to enlarge them somewhat.

Since we don't want the needle to extend beyond the apex and a needle has an outside diameter of 0.30mm the largest size we would deliberately make an apex is size 30.

Since the smaller the canal the better it is for control the best size is about a size 20 unless it has to be made bigger for purposes of getting it clean.

The neck constricts the flow of cement and thus forces the cement exiting the needle to expand to adapt to the walls of the canal above the neck.

The Flare is the "V" shaped or hyperboloid section of the canal made by circumferential filing.

It is prepared with circumferential filing with the Fine-Cut Endo Handpiece using Fine-Cut SPeed files. Generally "V"-filing is used.

Flaring is done for access to the apex and for purposes of cleaning the canal.

Theoretically you can prepare any canal to any size with any size file that will fit initially. Thus theoretically you could use ONLY one size, namely a size 15(the smallest SPeed File available.)

But practically any size will do as long as it fits and is stiff enough to maintain contact with the side walls of the canal during circumferential filing. Which, by the way, is why we recommend that stainless steel files be used for circumferential filing. Nickel Titanium files are good for other things but they are too flexible for circumferential filing.

The term 'parabola' was chosen simply to give us something to call this portion of the prep and it is generally paraboloid. It is the area above the neck and below the flare in which cement can be extruded without danger of flow through the apex.

The Parabola is usually made to the diameter of the tip of a size 50 file or about 0.50mm. This is to ensure that there is room around the sides of a 30 gauge needle(0.30mm) to allow cement to flow coronally rather than apically.

A hand size 50 can be used with push-pull filing to enlarge the bottom of the flare or it can be drilled out with a size 50 LightSpeed file. Since the largest Fine-Cut SPeed file is a size 40, a 40 can also be used in some cases in the Fine-Cut Endo Handpiece.

If we want the needle (minimum size 30 gauge, i.e. 0.29mm outside diameter to fit within one millimeter of the apex then the canal must be made slightly larger than that at the 1 mm point.

This area is called the Mc Combs prep in honor of Rey Mc Combs who was the first to suggest it.

32.5mm

This can be done by making that area conical with a hand file with a minimum diameter of 0.31( actually closer to 0.32 is better) or we can drill out that portion with a LightSpeed size 32.5. But a more elegant solution is to use one of the new Fine-Cut "infiNiTi"� nickel titanium files in the handpiece.