international magazine of oral implantology

28 I implants1_2011 I special _ endo-implant algorithm Tulsa Dental Specialties), Continuous Wave Com- pactionTechnique(ElementsObturation,SybronEndo) and Thermoplastic Injection (Obtura III Max, Obtura Spartan). Resilon (RealSeal, SybronEndo), a high-perform- anceindustrialpolyurethane,wasdevelopedasanal- ternativetogutta-percha.Therearescatteredstudies that demonstrate that Resilon exhibits less microbial leakage42 and higher bond strength to root-canal dentine43, reduced peri-apical inflammation44 and enhanced 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 strength46 and low cohesive strength plus stiffness.47 In addition, Resilon did not achieve a completehermeticapicalseal.48 Theseresultsindicate thatamoreappropriatematerialforroot-canalobtu- ration still needs to be developed. There is still no ob- turation method or material that produces a leak- proof seal. A material that is bio-inductive and pro- motes regeneration, a smart nano-material that can adapttotheever-changingmicroenvironmentofthe canalsystemisessential,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 worldoftoday,thishasengenderedanincreaseinthe weightofthemassofobturatingmaterialandanim- provementinthebacterialseal.Thisappliestocarrier- based obturation techniques, Continuous Wave Compaction Technique and Obtura III obturation without cone placement. _Instrumentation The steps required for debridement and disin- fectionoftheroot-canalspacearesequentialandin- terdependent. Aberration of any node in the process 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 main- tained free of debris by recapitula- tion with a small file through the apical foramen.50 The most pre- dictable method is to use a desig- natedpatencyfileregularlythrough- out the cleaning and shaping proce- dure in conjunction with copious irriga- tion. A #0.08 K-file passively moved throughtheapicalterminuswithoutwidening itismosteffective;itwillrefreshtheNaOClattheter- minusastheactionofthefilegoingtothepointofpa- tency produces a fluid dynamic. Regrettably, loss of workinglengthremainsacommonadverseeventdur- ingendodontictherapy,especiallyamongstlessexpe- rienced 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,modifieddouble-flare); however,step-back52 andcrown-down53 arethemost universallyaccepted.Experiencehasshownacrown- down preparation will cause fewer procedural errors (apical transportation, elbow formation, ledging, strip perforation, instrument fracture). The prelimi- nary removal of coronal dentine (pre-enlargement— treating the apex last) minimises blockage and en- ables an increasing volume of irrigant penetration, thereby sustaining 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 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