Endodontic files: parameters for selection and reuse
Eugenio Pedullà, who was involved in development of a new endodontic files system, suggests giving preference to flexible, pre-bendable instruments and provides guidance for the possible reuse of the files
Overthelastfewyears,increasingnumbersofcanalpreparationinstrumentshavebeenintroducedonthe marketandworkingoutthemostappropriateinstrumenttousedependingontheclinicalcasesinquestion isnotassimpleasitseems."Clearly,notallendodonticfilesarethesame,"explained Eugenio Pedullà,an Associate ProfessoratCatania University in Italy,who wasinvolvedincomingup witha newsystemfor ColteneHyFlexEDMendodonticfiles."Wehavenowreachedtheseventhgenerationofendodonticshaping instrumentsmadefromtitanium,asreportedinarecentreviewonthissubjectintheofficialjournalofthe European Society of Endodontology. It is essential for dentists to have an awareness of the various possibilitiesofferedbythesefiles,oratleastthemainones,inordertomakethebestandcorrectuseofthe propertiesoftheinstrumentthatyouhavedecidedtouse."
Professor Pedullà, what parameters should be used to guide the choice of endodontic files?
There are many parameters that influence the characteristics, and especiallythemechanicalcharacteristics,ofnickel-titaniumendodontic instruments.Thetwomostimportantcharacteristicsarethedimensions of the instrument, and particularly the taper and the heat treatment applied to the NiTi alloy. These two parameters do in fact have a significantinfluenceontheflexibilityofendodonticinstruments. A heat-treated instrument has greater flexibility than an identical instrument made from traditional NiTi. This increased flexibility will, however,begreaterinthecaseofsomeheattreatmentsthanothers.As widely reported in the literature, CM (controlled memory) heat treatmentistheonethatprovidesthegreatestflexibility.
Asfarasthedimensionsareconcerned,justbearinmindthatthesmaller the files are, the greater their flexibility, given the smaller amount of metalpresent.Ofthetwomainparametersrelatingtothedimensionsof endodonticinstruments,thetipdiameterandthetaper,thelatteristhe one that has the greatest influence on the characteristics of the instruments,asitinfluencesthesizeofthewholeworkingpartofthefile andnotjustitstip.Thus,a 30.04instrumentwillbemoreflexiblethan onethatisidenticalbut25.06.
What materials were used in the past?
For a very long time, root canal preparation was carried out using instrumentsmade fromsteel,averyrigidmetalwhichhasahardtime following the often curved anatomy of root canals, frequently causing transportation. From the 1990s, the introduction of NiTi provided instruments with larger dimensions but which retained a high level of flexibility, with better adaptation to the original anatomy and, at the same time, made it possible to achieve appropriate dimensional preparation with a smaller number of instruments, speeding up endodontictherapy.
The introduction around 2007 of heat treatments applied to NiTi subsequently improved the flexibility of endodontic instruments and consequentlyprovidedbetteradaptationtotheanatomy.
PARAMETERS FOR SELECTING ENDODONTIC FILES
• Preferably use flexible or pre-bendable instruments for cases involving curved anatomical features, and an instrument that is a bit less flexible as well as at least one that is at least slightly pre-bendable for narrower canals.
• Always have pre-bended instruments available in any case, even if only to enable easy insertion in cases where access is too complicated for anatomical reasons, or the patient has limited mouth opening.
• Always perform early crown lengthening (in the correct manner, i.e. without lengthening it beyond the first 5 mm and obtaining a slightly smaller opening size than you will achieve by the end of the preparation) and create a glide path before carrying out the actual canal shaping using larger NiTi instruments.
• Seek to perform conservative shaping using a .04 taper file but complete the preparation to at least 30 as the tip diameter.
Furthermore, using a CM heat-treated instrument with a .04 taper enables smoother, more comfortable apical shaping
• Where possible, reuse the files in an endodontic system; while this depends on multiple variables, I generally recommend reusing files (check for integrity and any deformation beforehand) for two molars at most (approximately 6 root canals) and sometimes only one (3-4 root canals), especially in the case of smaller instruments such as glide path files.
Interview Prof Eugenio Pedullà, Dental Journal Italia, 01 July 2024
(File endodontici, parametri per la scelta e per il riutilizzo (dentaljournal.it)
What are the main characteristics of the alloys used today for producing instruments and what advantages have they provided?
Themaincharacteristiciscertainlyflexibilityandtheabilitytobepre-bended Greaterflexibilityenablesgreaterresistancetoinstrumentfracturingwhencurvedrootcanalpreparations arecarriedout,inadditiontocloseradaptationtotheoriginalendodonticanatomy(Fig.1);theabilityto pre-bendinstrumentsprovideseasieraccesstorootcanalsthankstothereducedlengthoftheinstrument andtheangleofthetipwheninsertedintotherootcanal.
How does the taper of endodontic files influence their use?
The taperofthe fileshasasignificant influence on the flexibilityof the instruments and on their apical shaping forward movement capacity. This is because the greater the taper, the lower the flexibilitywillbeandthegreaterthefrictionontherootcanalwalls, whichmakesforwardmovementtowardstheapexlesseasy.
Some files are designed to be reused, but with use, and particularly after sterilisation in an autoclave, they may undergo alterations, even early on. What should be assessed after each use and how?
Fig.1:Necrotictooth14.A)Pre-opx-ray showinginitialevidenceofperi-apical radiolucencyoftooth14; B)X-rayafterfillingtooth14,whereyoucansee themaintenanceoftheoriginalanatomy,the dentinconservation,andthecenteringofthe preparationfinishedusingOGSFFinisher (30.04),appliedtotheapexinthepalatinecanal andatthepointwhereitmergeswiththe vestibularcanal
It is possible to reuse endodontic instruments made from NiTi, especially in the case of instruments used in sequence such as, for example,HyFlexEDMfiles.However,thenumberoftimesitispossible toreuseinstrumentsiscurrentlystillapointofdebateanddependson somanyvariables(suchastheanatomyencounteredandthetypeof fileused),thatitisnotpossibletoprovidepreciseguidance. Therefore,beforeanyreuse,itisalwaysworthwhilechecking,perhaps evenundermagnification,fordeformationsintheirspirals.Inparticular,shouldCM-treatedinstrumentsbe deformed,ifsubjectedtoheating(suchaswhentheyareautoclaved),theymayrecovertheiroriginalshape andbereused.If,ontheotherhand,inspiteofheating,theinstrumentdoesnotrecoverfromdeformation, thiswouldmeanthatithasalreadyundergoneplasticdeformationandisthereforesusceptibletofracturing andshouldbediscarded.
Thispossibilityofdistinguishingbetweenarecoverabledeformationandanunrecoverableoneisagreat advantageofCMalloys,giventhattraditionalNiTi,whichalwaysrecoversitsoriginalshape,doesnotenable anyinternaldeformationsthathavealreadyweakenedtheinstrumenttobeidentified,andtheinstrument maythenseparateunexpectedlywhileitisinarootcanal.
What problems can be overcome by the new HyFlex EDM endodontic files system you worked on?
Thissystemoffersmanyadvantages,startingfromasinglesequenceforanytypeofcanal; indeed,itwas conceivedtobeabletofunctioneveninparticularlydifficultanatomicalsituations(curves,doublecurves, narrowcanals,etc.).Inaddition,thedimensionsofthefilesweredesignedsothereisagradualdimensional shiftfromonefilesizetothenext,therebyenablingshaping withafewdabbingmovements,withoutthe needtore-enterseveraltimesthecanalbeforeachievingtheworkinglength.Inparticular,afteranopener (dimensions18.11)which will be appliedtotooth 5 - 6mmfromthe rootcanal opening,a glider will be used to create a 15.03 mechanical glide path down to the working length. Once the glide path has been achieved, shaping will be carried out with a shaper (18.045) which, thanks to its specific tip and taper dimensions,enableseasyshapingafterglideruseandalsoeasyworkingforthefollowinginstrument,the finisher,whichwillcompletetheshapingandrefinishingatthesametime,applyingadimensionof30.04. This is a system that enables minimally invasive preparation which closely follows the original anatomy thanks to the high flexibility of the CM heat treatment and the slim taper. It also benefits from all the advantagesprovidedbyCMalloy,suchasthepossibilityofhavingpre-bendedandbentfiles,highstrength withincurvedcanals,andahighcapacitytoremaincentredwithincanals. Consequently, the new HyFlex EDM files make it possible to overcome the problem of having to decide which instrument to use depending on the clinical cases in question, as well as the need to carry out reentryseveraltimeswiththesameinstrument,inadditiontoenablingdirectpreparationtobeachievedwith a diameter of 30, which is more suitable than a dimension of 25 for optimal mechanical and chemical disinfectionoftheapicalthird,andinparticulartheyoffereasyapicalshapingwhichmakestheendodontic preparationmorecomfortable,fasterandthereforemoreefficient.
Interview Prof Eugenio Pedullà, Dental Journal Italia, 01 July 2024
(File endodontici, parametri per la scelta e per il riutilizzo (dentaljournal.it)
Renato Torlaschi