ROEN0110

I 17 special _ endo-implant algorithm I roots1_2010 apical third shaping and creating an enhanced apical control zone taper. Two distinct phases are required for the prepara- tion of canals with NiTi rotary files. It is essential that, no matter the protocol used, a reservoir of NaOCl be maintained and replenished repeatedly in the stra- tegically extended access preparation. The coronal portionofthecanalspaceisexploredwithsmall-sized K-files to establish a glide path for the rotaries to fol- low.ThetaperofNiTifiles,regardlessofmanufacturer, inducesacrown-downeffectinthestraightportionof thecanal.Afterthecoronalandmiddlethirdsegments have been opened and repeatedly irrigated with NaOCl, a sequence of small K-files can progress api- cally, ultimately defining patency, confirming the to- pography of the accessible canal space and its degree of curvature. A second ‘wave’ with the NiTi rotaries is then used to effect deep shape, approximating the working length, and depending upon the configura- tion of the apical third, to enlarge the terminus to the gauged apical size and initiate the taper of the apical control zone.58 This is a basic concept. It is inherent in all templated protocols that each tooth is different, andmodificationstotheprocessarealwaysnecessary as a function of the tooth morphology. The apical control zone is defined as a matrix-like regioncreatedattheterminusoftheapicalthirdofthe root-canalspace.Thezonedemonstratesanexagger- ated taper from the spatial position determined by an electronic foraminal locator to be the minor apical diameter. Whether this is linear or a point determi- nation is a function of histopathology. The enhanced taperattheterminuscreatesaresistanceformagainst the condensation pressures of obturation and acts to prevent 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 millimetre back from the apical terminus, if the crown-down protocol built into this multiple taper file system is adhered to. If the shape of the internal micro-morphology of the root complex were epide- miologically similar, then imprinting of the canal preparation would be logical. Unfortunately, such is not the case.59 Figure 16b demonstrates that the use of hand files in the apical third can alter the preliminary shape cre- 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 0.2mm or 20% taper with no undue disruption of thenativeanatomy.Schilder’s precept for shaping was to keep the apical foramen as small as practically possible. Whatever file approximates the minor apical diameter, in conjunctionwithhandfiling, the apical control zone cre- ated will enhance the api- cal seal, as the rheological vectors of compaction and condensation have a greater lateral volume of displace- mentattheterminus. 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.

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