May 24-30, 2010United Kingdom Edition ism - marketing is inexorably di- recting science. However, gutta- percha in combination with a myriad of sealers and solvents remains the primary endodontic obturating material. The domi- nant systems remain carrier- based obturation (Thermafil – Tulsa Dental Specialties, Tulsa OK), Continuous Wave Compac- tion Technique (Elements Ob- turation – Sybron Endo, Orange CA and Thermoplastic Injection (Obtura III Max – Obtura Spar- tan, Earth City MO). Resilon (RealSeal - Sybro- nEndo Corp., Orange, CA), a high-performance industrial polyurethane was developed as an alternative to gutta-percha. There are scattered studies that show Resilon exhibits less micro- bial leakage (42) and higher bond strength to root canal dentin (43) , reduced periapical inflammation (44) and enhanced fracture resist- ance of endodontically treated teeth when compared with gutta- percha (45) (Fig 13). Other studies have reported undesirable prop- erties associated with Resilon including low push-out bond strength (46) and low cohesive strength plus stiffness (47) . In ad- dition, Resilon could not achieve a complete hermetic apical seal (48) . These results indicate that a more appropriate material for root canal obturation still needs to be developed. There is still no obturation method or material that produces a leakproof seal. A material that is bio-inductive and promotes regeneration, a “smart” nano-material that can adapt to the ever-changing mi- croenvironment of the canal system is essential, but to date, remains elusive. All polymers demonstrate melt temperature and flow rate. Both gutta-percha and Resi- lon demonstrate a viscoelastic gradient that manifests as a dy- namic rheological birefringence in the molded state. Dependent upon the molecular weight of the source material (without the opacifiers, waxes and modifiers), gravimetric measurements of the time-temperature-transfor- mation diagram of any molding compound can be constructed. In the thermoplastic world of to- day, this has engendered an in- crease in the weight of the mass of obturating material and an im- provement in the bacterial seal. This applies to carrier based ob- turation techniques, Continuous Wave Compaction Technique and Obtura III obturation with- out cone placement. Instrumentation The steps required for debride- ment and disinfection of the root canal space are sequential and interdependent. Aberration of any node in the process impacts upon the others, leading to ia- trogenic damage and potentially treatment outcome failure. The most common distortion of na- tive anatomy is ledging; canal curvature exceeding 20o was shown to produce ledging of mandibular molars in a cohort of undergraduate students 56 per cent of the time (49) . Dentin chips pushed apically by instrumenta- tion incorporated with fragments of pulp tissue will compact into the apical third and the forame- nal area causing blockage, alter- ing the working length due to the loss of patency (Figs 14a, 14b). Apical patency is a technique in which the minor apical diame- ter of the canal is maintained free of debris by recapitulation with a small file through the apical fo- ramen (50) . The most predictable method is to regularly use a des- ignated patency file throughout the cleaning and shaping proce- dure in conjunction with copious irrigation. A #.08 K-file passively moved through the apical termi- nus without widening it is most effective; it will refresh the NaOCl at the terminus as the action of the file going to the point of patiency produces a fluid dynamic. Regret- tably, loss of working length re- mains a common adverse event during endodontic therapy, es- pecially among less experienced clinicians. Its major cause is the formation of an apical dentin Fig 14a – 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 ellipticization of the foramen. Fig 14b – The volume of irrigant necessary to prevent apical blockage is indeterminant. While NiTi rotary instrumentation has minimized this procedural problem to a significant degree, nonetheless, a slurry of dentin mud is always a risk factor to be monitored. 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 as effective as the flow characteristics of the shape created and its degree of cleanliness. page 20DTà FenderMate® is a trademark registered by Directa AB. Registered Design and Patent pending. Form Contact Point Flexible wing exerts pressure for maintained separation and cervical adaption Inserts like a wedge Tight cervical marginal adaptation prevents overhangs World’s Fastest Composite Matrix? 3108-1001©DirectaAB Matrix Distributed in the UK by Trycare, Tel. 01274-88 10 44 More Designs by Dentists www.directadental.com FenderMate tryKit for only £ 9.00* (value £ 26.00) *Redeemable against your next purchase of FenderMate. Promotion code DP02 to be mentioned on order.

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