DTUK1410

May 24-30, 201020 Clinical United Kingdom Edition plug. Therefore, establishing api- cal patency is recommended even during treatment of canals with vital pulps (51) . Historically, numerous tech- niques have been advocated for canal preparation (balanced force, anti-curvature, double- flare, modified double-flare); however, step-back (52) and crown-down (53) are the most universally accepted. Experi- ence has shown that a crown- down preparation will cause fewer procedural errors (apical transportation, elbow formation, ledging, strip perforation, instru- ment fracture). The preliminary removal of coronal dentin (pre- enlargement – treating the apex last) minimises blockage and enables an increasing volume of irrigant penetration thereby sus- taining working length through- out the procedure (54) . The balanced force shap- ing philosophy is integral to the crown-down approach. Its premise is that instruments are guided by the canal structure when rotational/anti-rotation- al motion (watch-winding) is used. Changing the direction of rotation controls the probability that instruments will become overstressed and thus ensures that the cutting of structure oc- curs most efficiently (55) . Endo- dontists have long appreciated what the science reported, that the balanced-force hand instru- mentation technique produced a cleaner apical portion of the ca- nal than other techniques (Fig 15) (56, 57) . As will be discussed shortly, this author remains committed to hand filing in or- der to refine apical third shap- ing and creating an enhanced apical control sone taper. Two distinct phases are re- quired for the preparation of ca- nals with nickel titanium (NiTi) rotary files. It is essential, that no matter the protocol used, a res- ervoir of NaOCl must be main- tained and replenished repeat- edly in the strategically extended access preparation. The coronal portion of the canal space is ex- plored with small sized K-files to establish a glide path for the rotaries to follow. The taper of NiTi files, regardless of manu- facturer induces a crown-down effect in the straight portion of the canal. After the coronal and middle third segments are opened and repeatedly irrigated with NaOCl, a sequence of small K-files can progress apically, ul- timately defining patency, con- firming the topography of the accessible canal space and its degree of curvature. A second “wave” with the NiTi rotaries is then used to ef- fect deep shape approximating the working length and depend- ing upon the configuration 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 and modifica- tions to the process are always necessary as a function of the tooth morphology and type be- ing treated. The apical control zone is de- fined as a matrix like region cre- ated at the terminus of the apical third of the root canal space. The sone demonstrates an exagger- ated taper from the spatial posi- tion determined by an electronic foramenal locator to be the mi- nor apical diameter. Whether this is linear or a point determi- nation is a function of histopa- thology. The enhanced taper at the terminus creates a resistance form against the condensation pressures of obturation and acts to prevent excessive extrusion of filling material during thermo- labile vertical compaction. All NiTi systems are mod- eled upon a single or multiple taper ratio per millimeter of file length. Fig 16a demonstrates the metrics of the F1, F2, F3 fin- ishing files of the ProTaper Uni- versal system (author’s prefer- ence). These files demonstrate a common taper in the last four mm of the file, which in the vast majority of situations corre- sponds to the length of the api- cal third of the root canal space. As shown, the .07 taper of the F1 (.20 tip), the .08 taper of the F2 (.25 tip) and the .09 taper of the F3 (.30 tip) produce the corre- sponding diametral dimension indicated each millimeter 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 page 19DTß page 22DTà ESTETICA E80 Rise above the rest with KaVo. • Outstanding ergonomics and attractive, highly functional designs. • Innovation at its best. • State of the art technology reliability and functionality at amazingly low prices. From as little as £286* per month excl VAT KaVo Dental Limited · Raans Road, Amersham, Bucks HP6 6JL Tel. 01494 733000 · Fax 01494 431168 · mail: sales@kavo.com · www.kavo.com Contact your local KaVo or Gendex supplier for more details! *Finance is subject to status and for business purposes only. KaVo – Dental Excellence Estetica A4 SELECTED:Layout 1 25/2/09 13:42 Page 1