Instrumentation Technique Lecture 10 PDF

DR OSAMA MOHAMED 01001333356 Instrumentation technique Step-Back or Step-Down? Lecture 10  Two approaches to débride and shape th...

DR OSAMA MOHAMED 01001333356 Instrumentation technique Step-Back or Step-Down? Lecture 10  Two approaches to débride and shape the canal emerged:  Either starting at the apex with fine instruments and working one’s way back up (or down) the canal with progressively larger instruments—the “step-back” or serial technique  Orthe opposite, starting at the cervical orifice with larger instruments and gradually progressing toward the apex with smaller and smaller instruments—the “step-down” technique, also called “crown- down” filing.  Any one of these methods of preparing the root canal will ensure staying within the confines of the canal and delivering a continuously tapered preparation. And, eliminate blocking, “apical ledging, transportation, ripping, zipping and perforation”.Buchanan LS. 1989  Step-Back Preparation and Curved Canals. This method of preparation has been well described by Mullaney (telescopic or serial root canal preparation) It is divided into two phases:  Phase I : is the apical preparation starting at the apical constriction.  Phase II : is the preparation of the remainder of the canal, gradually stepping back while increasing in size.  The completion of the preparation is the Refining Phase IIA and IIB to produce the continuing taper from apex to cervical DR OSAMA MOHAMED 01001333356  Although the step-back technique was designed to avoid zipping the apical area in curved canals, it applies as well to straight canal preparation.  As Buchanan noted, “all root canals have some curvature. Even apparently straight canals are usually curved to some degree”.  Canals that appear to curve in one direction often curve in other directions as well  Prior to the introduction of nickel- titanium files, one of the first axioms of endodontics has been to  “always use a curved instrument in a curved canal”.  The degree and direction of the curve are determined by the canal shadow in the radiograph.  Buchanan has made an art of properly curving instruments to match the canal silhouette in the film Step-Back, Step-by-Step—Hand Instrumentation. Phase I  First the canal must be explored with a fine pathfinder or instrument and the working length established—that is, the apical constriction identified.  The first active instrument to be inserted should be a fine (No. 08, 10, or 15) 0.02, tapered, stainless steel file, curved and coated with a lubricant, such as Gly-Oxide, R.C. Prep, File- Eze, Glyde, K-Y Jelly, or liquid soap.  The motion of the instrument is “watch winding,” two or three quarter-turns clockwise- counterclockwise and then retraction.  On removal, the instrument is wiped clean, recurved, relubricated, and repositioned.  “Watch winding” is then repeated. Remember that the instrument must be to full depth when the cutting action is made.  This procedure is repeated until the instrument is loose in position.  Then the next size K file is used—length established, precurved, lubricated, and positioned.  Again, the watch-winding action and retraction are repeated. Very short (1.0 mm) filing strokes can also be used at the apex.  It is most important that, a lubricant be used in this area,  As it is often fibrous pulp stumps, compacted into the constricture, that cause apical blockage. In very fine canals, the irrigant that will reach this area will be insufficient to dissolve tissue.  Lubrication, emulsifies tissue, allowing instrument tips to macerate and remove this tissue.  It is only later in canal filing that dentin chips pack apically, blocking the constriction.  DR OSAMA MOHAMED 01001333356  By then the apical area has been enlarged enough that sodium hypochlorite can reach the debris to douche it clear.  By the time a size 25 K file has been used to full working length, Phase I is complete.  The 1.0 to 2.0 mm space back from the apical constriction should be clean of debris unless this area of the canal was large to begin with, as in a youngster. Then, of course, larger instruments are used to start with.  Apical limitations of instrumentation should be at the apical constriction , which is about 0.5 to 1.0 mm from the anatomic ( radiographic ) end of the root. NB:  Using a number 25 file here as an example is not to imply that all canals should be shaped at the apical restriction only to size 25.  Many, in fact most, canals should be enlarged beyond size 25 at the apical constriction in order to round out the preparation at this point and remove as much of the extraneous tissue, debris, and lateral canals as possible.  As stainless steel instruments become larger, theybecome stiffer.  Metal “memory” plus stress on the instrument startsits straightening.  It will no longer stay curved and starts to dig, to zip the outside (convex) wall of the canal.  It must be emphasized here that irrigation between each instrument use is now in order, as well as recapitulation with the previous smaller instrument carried to full depth and watch wound:  This breaks up the apical debris so that it may be washed away by the sodium hypochlorite.  All of these maneuvers (curved instruments, lubrication, cleaning debris from the used instrument, copious irrigation, and recapitulation) will ensure patency of the canal to the apical constriction  NB : file 25 ( red color ) is the last size of files can use in curved canal but above file 25 the files become stiffer and can’t use in curved canals > From files 30 is very stiff files and can’t use in curved canals.  DR OSAMA MOHAMED 01001333356 Phase II  In a fine canal (and in this example), the step-back process begins with a No. 30 K-style file. Its working length is set 1 mm short of the full working length.  It is precurved, lubricated, carried down the canal to the new shortened depth, watch wound, and retracted.  The same process is repeated until the No. 30 is loose at this adjusted length.  Recapitulation to full length with a No. 25 file follows to ensure patency to the constriction.  This is followed by copious irrigation before the next curved instrument is introduced.  In this case, it is a No. 35, again shortened by 1.0 mm from the No. 30 (2.0 mm from the apical No. 25.)  It is curved, lubricated, inserted, watch wound, and retracted followed by recapitulation and irrigation.  Thus, the preparation steps back up the canal 1 mm and one larger instrument at a time.  When that portion of the canal is reached, usually the straight mid canal, where the instruments no longer fit tightly, then circumferential / perimeter filing may begin, along with plenty of irrigation.  It is at this point that Hedstroem files are most effective. They are much more aggressive rasps than the K files.  The canal is shaped into the continuous taper so conducive to optimum obturation.  Care must be taken to recapitulate between each instrument with the original No. 25 file along with ample irrigation DR OSAMA MOHAMED 01001333356 Phase IIA preparation:  Gates-Glidden drills must be used with great care because they tend to “screw” themselves into the canal, binding and then breaking.  The midcanal area is the region where reshaping can also be done with power-driven instruments:  Gates-Glidden drills, starting with the smaller drills (Nos. 1 and 2) and gradually increasing in size to No. 4, 5, or 6.  Proper continuing taper is developed to finish Phase IIA preparation.  Gates-Glidden drills must be used with great care because they tend to “screw” themselves into the canal, binding and then breaking. To avoid this, it has been recommended that the larger sizes be run in reverse. But, unfortunately, they do not cut as well when reversed.  A better suggestion is to lubricate the drill heavily with RC- Prep or Glyde, which “will prevent binding and the rapid advance problem”.  Lubrication also suspends the chips and allows for a better “feel” of the cutting as well as the first canal curvature.  Used Gates-Glidden drills are also less aggressive than new ones.  Newer instruments with various tapers from 0.04 to 0.08 mm/mm of taper are now available for this purpose as well and can be used as power-driven or hand instruments.  With any of the power-driven instruments, using them in a passive pecking motion will decrease the chances of binding or screwing into the canal Refining Phase IIB  is a return to a size No. 25 (or the last apical instrument used), smoothing all around the walls with vertical push-pull strokes, to perfect the taper from the apical constriction to the cervical canal orifice.  In this case, a safe-ended, noncutting-tip Hedstroem file is the most efficient.  It produces a good deal of dentin chips, however, that must be broken up at the apex with a cutting-tip K file and then flushed out with abundant sodium hypochlorite.  At this point, it is recommended that sodium hypochlorite be left in place to the apex for 5 to 10 minutes.  This is the only way in which the auxiliary canals can be cleaned. “final preparation should be an exact replica of the original canal configuration— shape, taper, and flow, only larger  Hand-powered Gates-Glidden drills (Handy Gates) or LIGHTSPEED instruments may be used for this final finish, as well as the Orifice Openers or Gates-Glidden drills.  “Coke-bottle” preparations should be avoided at all cost?