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ePaper created 2016-05-18, 11:28:18 | version 1.38.0
endodontic instrumentation opinion | 23 roots 2 2016 Keeping instruments centred in canals that are highly oval, anatomy that is more the rule than the exception, keeps the instruments intact at the ex- pense of compromised cleansing most often in the bucco-lingual plane. The new single file interrupted rotary systems are prone to instrument separation because they are still generating a minimum of 200 fullrotationsperminute,asasingleinstrumentthey arenowdoingthecompleteshapingafterglidepath creation and suffer from the same need to remain centeredwithintheconfinesofthecanaldespitethe presenceofsignificantbuccalandlingualextensions of pulpal tissue. By instrumenting the canal to smaller tapers, the rotary systems either continuous or interrupted re- move less tooth structure and are less prone to breakage.However,theyarestillconfinedtocantered preparations with little lateral brushing occurring leaving untouched buccal and lingual extensions of tissue. If we go back to an earlier time prior to the intro- duction of greater tapered rotary systems, we basi- cally relied on the use of K-files to shape the canals. Fromthestart,theseinstrumentsarepoorlydesigned to shape and cleanse canals. Their main defect in de- sign is the incorporation of 30 predominantly hori- zontal flutes aligned along the 16 mm of working length. Horizontal flutes can only shave dentin away with thepullstrokebecauseitisonlythenthatthecutting edges of the flutes are more or less at right angles to the plane of motion, a requirement for the removal ofdentin.Thissameflutealignmentunfortunatelyis designedtoimpactdentinatthetipoftheinstrument when it is directed apically. Losing length when using K-files is familiar to most dentists, especially when curves exist in the apical third. Rather than employing instruments with predominantly horizontal flute orientations as ourinitialtools,weshouldbeusinginstrumentswith predominantly vertical flute orientations, similar to the designs incorporated into most rotary systems. A predominantly vertical flute orientation will shave dentin from the canal walls with the first clockwise stroke. When the instrument is removed and reintroduced into the canal, the vertically ori- entedfluteswilltendtoglidepastanydebrispresent ratherthanimpactingitapically.Theseinstruments are defined as reamers. Essentially, we are using a watch-winding motion, similar to that used with K-files, but with far greater efficienciesandfarlesslikelihoodforapicalblockage. We further improve the mechanics by incorporating aflatalongthelengthofthereamersfurtherreducing engagement and creating an instrument that now has two columns of cutting chisels that work in both the clockwise and counter clockwise motion. A watch-winding motion eliminates the full rota- tions that lead to excessive torsional stress and cylic fatigue that produce the instrument separations we want to avoid. The hand fatigue associated with the useofK-filesiscompletelyeliminatedwhengenerat- ing the watch-winding motion in a 30- to 45-degree reciprocating handpiece. The speed of the procedure is significantly increased because the reciprocating handpiece has the added advantage of oscillating at 3,000 to 4,000 cycles per minute.5 ForthosedentistsusinggreatertaperedrotaryNiTi systems,thegoaloftheK-fileswaslimitedtocreating a glide path producing an 02 tapered centred space uptoatmosta20.Therelievedreamersalsohavethat function,butwiththepowerofareciprocatinghand- piece generating oscillations of 3,000-4,000 cycles perminute,theinstrumentshavetheaddedabilityto vigorously work the buccal and lingual extensions of highly oval, sheath-like pulpal anatomy. One need not be concerned about the reduced flexibility of stainless steel relieved reamers. In their smaller dimensions they are easily flexible enough to negotiate complex curved canals. As the thinner, highly flexible instruments faithfully enlarge the original canal anatomy free of distortions, they are defining a pathway that the somewhat larger and less flexible relieved reamers will then faithfully fol- low.Thegoalinmostsituationsistoproduceanapi- cal preparation of 30 applied to all the walls of the canals, be they round or not. Please realize that this goal will ultimately produce a larger version of the originalcanalanatomyratherthantheimpositionof a large conical shape that bears little relationship to the original anatomy. For the most part, we do not want to exceed a ta- perof04.Suchaconservativepreparationpreserves coronal dentin and in combination with the relieved reamers allows us to remove tissue from those thin extensions that are off limits to rotary NiTi instru- mentation.6 The system we are defining is based pri- marilyon02taperedstainlesssteelrelievedreamers (Fig. 1). After the glide path creation using the re- lieved reamers (SafeSiders), crown-down prepara- tionsarenolongernecessary.Ratherthefinalprepa- ration is a simple extension of instrumentation that widensthecanalfroma20/02preparationtoamax- imumof30/04inmostsituations(TangoEndo,Fig.2), a final result that requires only two more instru- mentsafterthe20/02preparationhasbeenachieved. 22016