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April 1-7, 201318 Endo Tribune United Kingdom Edition I n endodontic treatments, Nickel-Titanium instruments in continuous rotation1 opti- mise root canal shaping. Gener- ally, rectilinear and barely curved root canals with a round or oval section does not cause difficulties and can be prepared by using all standard techniques. I n endodontic treatments, Nickel-Titanium instru- ments in continuous rota- tion1 optimise root canal shap- ing. Generally, rectilinear and barely curved root canals with a round or oval section does not cause difficulties and can be prepared by using all stand- ard techniques. However, par- ticularly thin and moderately or strongly curved canals with a laminar section are more diffi- cult to shape and involve a con- siderable risk of failure. Despite its super elastic quali- ties, Nickel-Titanium alloy has one important inconvenience, namely its low resistance in case of repeated use which results in instrument separation. Instrument fracture can occur either through material fatigue caused by a significant number of compression-tension cycles or through torsion due to obstruc- tion of the instrument’s tip in the canal 2, 4 . A certain number of factors such as the pressure exercised on the contra-angle head 5 , the speed ofrotationandthenumberofclin- ical applications favour the occur- rence of instrument separation. In addition to these procedur- al mistakes, instrument diameter, taper, profile6, 7 and machining as well as canal curvature are cru- cial for the occurrence (or not) of instrument fracture 8 . Continuous rotation versus reciprocating technique In recent years, we have seen sev- eral alternating movement sys- tems (clockwise – counter-clock- wise rotation) come forward, destined to limit instrument sepa- ration, for example M4® (Sybron Endo), Endo-Eze AET® (Ul- tradent), EndoExpress® (Essen- tial Dental System), WaveOne® (Dentsply) and Reciproc® (VDW). The alternative movement technique varies between 30° and 90°, being thus either symmetric or asymmetric, depending on the manufacturer. The kinetics of re- ciprocation reproduces the man- ual movement of the intra-canal file, restricts the risk of instru- ment fracture and facilitates the penetration into calcified canals 9 . The systems with a 90° al- ternative and symmetric move- ment require a large instru- mental sequence whereas the systems limited to a 30° move- ment have a restricted cut- ting capacity and a tendency to extrude dentine and pulp de- bris towards the periapex 10 . The latest generation systems with an asymmetric range do not require any pressure being exer- cised on the contra-angle head. Although an evolution of the GIROMATIC® technology seemed to be possible, the new One Shape® instrument is used in continuous rotation. The ac- knowledged benefits of this rota- tional dynamic are an excellent tactile sensation and a remark- able cutting efficiency. The difficulty in the instru- ment’s development lies in its One single instrument for safe root canal preparation Dr Jérome Elias, Dr Jean-Jacques (J-J) Bonnin