international magazine of oral implantology

30 I implants1_2011 I special _ endo-implant algorithm other techniques (Fig. 15).56, 57 As discussed below, I remaincommittedtohandfilinginordertorefineapi- cal third shaping and creating an enhanced apical controlzonetaper.Twodistinctphasesarerequiredfor thepreparationofcanalswithNiTirotaryfiles.Itises- sentialthat,nomattertheprotocolused,areservoirof NaOCl be maintained and replenished repeatedly in the strategically extended access preparation. The coronal portion of the canal space is explored with small-sizedK-filestoestablishaglidepathforthero- taries to follow. The taper of NiTi files, regardless of manufacturer, induces a crown-down effect in the straight portion of the canal. After the coronal and middlethirdsegmentshavebeenopenedandrepeat- edly irrigated with NaOCl, a sequence of small K-files can progress apically, ultimately defining patency, confirming the topography of the accessible canal spaceanditsdegreeofcurvature.Asecond‘wave’with theNiTirotariesisthenusedtoeffectdeepshape,ap- proximatingtheworkinglength,anddependingupon the configuration of the apical third, to enlarge the terminustothegaugedapicalsizeandinitiatetheta- peroftheapicalcontrolzone.58 Thisisabasicconcept. Itisinherentinalltemplatedprotocolsthateachtooth is different, and modifications to the process are al- waysnecessaryasafunctionofthetoothmorphology. The apical control zone is defined as a matrix-like re- gioncreatedattheterminus of the apical third of the root-canal space. The zone demonstrates an exagger- ated taper from the spatial position determined by an electronic foraminal locator to be the minor apical diam- eter.Whetherthisislinearor a point determination is a function of histopathology. The enhanced taper at the terminus creates a resistance form against the con- densationpressuresofobturationandactstoprevent excessive extrusion of filling material during thermo- labile vertical compaction. AllNiTisystemsaremodelleduponasingleormul- tipletaperratiopermillimetreoffilelength.Figure16a demonstrates the metrics of the F1, F2, F3 finishing filesoftheProTaperUniversalSystem(mypreference). These files demonstrate a common taper in the last 4mm of the file, which in the vast majority of situ- ations corresponds to the length of the apical third of the root-canal space. As shown, the 0.07 taper of the F1 (0.20 tip), the 0.08 taper of the F2 (0.25 tip) and the 0.09 taper of the F3 (0.30 tip) produce the corresponding diametral dimension indicated each millimetrebackfromtheapicalterminus,ifthecrown- downprotocolbuiltintothismultipletaperfilesystem is adhered to. If the shape of the internal micro-mor- phology of the root complex were epidemiologically similar, then imprinting of the canal preparation wouldbelogical.Unfortunately,suchisnotthecase.59 Figure16bdemonstratesthattheuseofhandfiles intheapicalthirdcanalterthepreliminaryshapecre- atedbytheNiTifiles.Handfileshavea0.02taper(along theshaftofthefile,thediameterincreasesby0.02mm per mm of length—a 0.20 file with 16mm of flutes would be measure 0.52 mm at the coronal end of the flutes). In the example shown, a #20 file is positioned at the minor apical diameter. Careful positioning of a series of file within the last millimetre can produce a 0.2mmor20%taperwithnounduedisruptionofthe native anatomy. Schilder’s precept for shaping was to keep the apical foramen as small as practically possi- ble. Whatever file approximates the minor apical di- ameter, in conjunction with hand filing, the apical control zone created will enhance the apical seal, as therheologicalvectorsofcompactionandcondensa- tion have a greater lateral volume of displacement at the terminus. Fig. 15_Rheology is a science that addresses the deformation and flow of matter. The biochemistry of filling material, its viscosity gradient, the lubricating effect of sealer and optimal thermal application are only aseffectiveastheflowcharacteristics oftheshapecreatedanditsdegree ofcleanliness. Fig. 14b Fig. 15 Fig. 14b_The volume of irrigant necessary to prevent apical blockage is indeterminate. While NiTi rotary instrumentation has minimised this to a significant degree, a slurry of dentine mud is always a risk factor to be monitored.