Zipping requires repetitive filing near the apex, around a curve with large files. The only files that go near the apex using our handpiece and filing system are #15.

Since these files cut only on the way out, they do not create ledges and this allows us a technique trick that is unavailable to others, namely to do the bulk of our filing, keeping the tip of the file a few millimeters from the apex, and then going back to finish the apex at our leizure.

This method is the epitome of "crown-down filing" because of the incapability of the system causing ledges i.e. the coronal portion of the prep can be done first, the middle next and the apex at the end.

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