ROEN0110

16 I I special _ endo-implant algorithm Wave Compaction Technique (Elements Obturation, SybronEndo) and Thermoplastic Injection (Obtura III Max, Obtura Spartan). Resilon (RealSeal, SybronEndo), a high-perform- ance industrial polyurethane, was developed as an al- ternative to gutta-percha. There are scattered studies that demonstrate that Resilon exhibits less microbial leakage42 and higher bond strength to root-canal dentine43, reduced peri-apical inflammation44 and en- hanced fracture resistance of endodontically treated teeth when compared with gutta-percha45 (Fig. 13). Other studies have reported undesirable properties associated with Resilon, including low push-out bond strength46andlowcohesivestrengthplusstiffness.47In addition, Resilon did not achieve a complete hermetic apical seal.48 These results indicate that a more appro- priate material for root-canal obturation still needs to be developed. There is still no obturation method or material that produces a leak-proof seal. A material that is bio-inductive and promotes regeneration, a smart nano-material that can adapt to the ever- changing microenvironment of the canal system is essential,buttodate,remainselusive. All polymers demonstrate melt temperature and flow rate. Both gutta-percha and Resilon demon- strate a viscoelastic gradient that manifests as a dy- namicrheologicalbirefringenceinthemouldedstate. Dependent upon the molecular weight of the source material (without the opacifiers, waxes and modi- fiers), gravimetric measurements of the time-tem- perature-transformation diagram of any moulding compound can be constructed. In the thermoplastic world of today, this has engendered an increase in the weight of the mass of obturating material and an improvementinthebacterialseal.Thisappliestocar- rier-based obturation techniques, Continuous Wave Compaction Technique and Obtura III obturation without cone placement. _Instrumentation The steps required for debridement and disin- fection of the root-canal space are sequential and interdependent.Aberrationofanynodeintheprocess affects the others, leading to iatrogenic damage and potentially, treatment outcome failure. The most common distortion of native anatomy is ledging; canal curvature exceeding 20 degrees was shown to produce ledging of mandibular molars 56% of the timeinacohortofundergraduatestudents.49 Dentine chips pushed apically by instrumentation incorpo- ratedwithfragmentsofpulptissuewillcompactinto theapicalthirdandtheforaminalareacausingblock- age, altering the working length due to the loss of patency (Figs. 14a & b). Apical patency is a technique in which the minor apical diameter of the canal is maintained free of debris by recapitulation with a small file through the apical foramen.50 The most predictable method is to useadesignatedpatencyfileregu- larly throughout the cleaning and shaping procedure in conjunction with copious irrigation. A #0.08 K-file passively moved through the apical ter- minus without widening it is most effec- tive; it will refresh the NaOCl at the terminus as the action of the file going to the point of patency produces a fluid dynamic. Regrettably, loss of work- ing length remains a common adverse event during endodontic therapy, especially amongst less experi- enced clinicians. Its major cause is the formation of an apical dentine plug. Therefore, establishing apical patency is recommended even during treatment of canals with vital pulp.51 Historically, numerous techniques have been- advocated for canal preparation (balanced force, anti-curvature, double-flare, modified double-flare); however,step-back52 andcrown-down53 arethemost universally accepted. Experience has shown a crown- down preparation will cause fewer procedural errors (apicaltransportation,elbowformation,ledging,strip perforation, instrument fracture). The preliminary re- movalofcoronaldentine(pre-enlargement—treating the apex last) minimises blockage and enables an in- creasing volume of irrigant penetration, thereby sus- taining working length throughout the procedure.54 Thebalanced-forceshapingphilosophyisintegral to the crown-down approach. Its premise is that instruments are guided by the canal structure when rotational/anti-rotational motion (watch winding) is used. Changing the direction of rotation controls the probability that instruments will become over- stressed and thus ensures that the cutting of struc- tureoccursmostefficiently.55 Endodontistshavelong appreciated what the science reported, that the balanced-force hand instrumentation technique produced a cleaner apical portion of the canal than other techniques (Fig. 15).56,57 As discussed below, I remain committed to hand filing in order to refine roots1_2010 Fig. 14a_On left, the working length has two reference points, coronal and apical. Failure to maintain patency at the minor apical diameter will cause loss of the apical reference point as a result of blockage, or ellipticisation of the foramen. Fig. 14a