This month's EndoFiles Fax is an adaptation of an article ("The Heartache of Separation" by Dr. Richard Mounce in Apr/03 Dentistry Today) Here are some suggestions that should help prevent the breakage when using Nickel-Titanium Rotary (Ni-Ti) Instruments (regardless of the make) for endodontic treatment.
(1) Do NOT initially consider using NiTi unless you have an appropriate, torque controlled electric handpiece. Attempting to use them in a "geared down" or "slowly turning" standard air driven slow speed handpiece is a recipe for breakage. Do make the necessary investment in equipment to use them properly. It is foolish to spend money on these files and then use them with a conventional engine where torque levels are dangerously inconsistent.
(2) The advantage of using NiTis is that they are less fatiguing on the hands. NiTis do not always result in shorter instrumentation times. This occurs because a proper glide path MUST BE ESTABLISHED in order for them to be used correctly. Hand instruments are still necessary and it can often take quite a while before it is safe to place NiTis to full working length. Spend the extra time to get a proper "glide path" with hand files and you will find NiTis work efficiently.
(3) Broach canals first to initially remove as much pulp tissue as possible. Small, well lubricated hand files should then be used to "dissect" the remaining pulp (if present) as they ware worked down the canals and allow deeper penetration of irrigants. Once a glide path is achieved with #8 and 10 files, they would be worked up to approximately size #20 before any NiTis are taken to full working length. NiTi files should never be used to "pathfind" a canal.
(4) Use a Crown-Down method for canal preparation. This ensures that the apical curves can be negotiated safely because the body and coronal aspects of the canal have been cleared of obstructive dentin. Taking a NiTi files to the apical third without properly instrumenting the upper two-thirds risks fracture. It also reduces the chances of blocked canals.
(5) Recent research has shown that the accumulation of debris in manufactured microfractures is one of the unseen contributing factors to broken rotary files. Frequent cleaning of the flutes can lessen the chances that this debris will enter the microfracture and enlarge the space, resulting in propagation of the original fracture and eventual separation. Cleaning of the flutes also reduces the frictional forces on the file and makes cutting more efficient.
(6) Do not force a file that does not want to go more deeply into the canal. The motion in entering a file into the canal should be smooth, deliberate, and in approximately 1- to 2- mm deep increments relative to the last instrument. Separation can occur in a fraction of a second if the file is used forcefully. ProTaper files (in particular) are best used with a more "lateral" stroke, emphasizing lateral rather than vertical pressure. Go back a hand file if you have problems getting to the apex.
(7) Never use these files without adequate lubrication. I use a combination of EDTA and sodium hypochlorite in the canal when instrumenting with these files. Do not instrument dry. Instrumenting dry can create a plug of apical dentin mud and increase the risk of transportation or fracture.
(8) Many clinicians are opposed to the idea of the disposable instrument, for financial reasons. If you do choose to use these files on more than one tooth, consider only using them a second time if the previous case had "easy" canals. If the case was difficult or tight, check the files carefully and consider immediate disposal rather than reuse. If a file is bent, stretched, or has a shiny spot, discard it immediately.
(9) Do take RNT files to the true working length, but only in canals where the RNT file will easily go to length. S shaped canals, longer canals with multiple curves, sharp apical curves or posterior accesses that make direct access into the orifice difficult, (MBs of upper molars!) can place stresses on instruments that surpass the breaking torque value. For those kinds of canals, it may be necessary to instrument the apical portions by hand. Tulsa has brand new handles that fit over the Ni-Ti shanks and allow you to use these instruments in your fingers. This can allow you to use the same instruments in a safer manner.