Dental Tribune United Kingdom Edition

Thursday 22nd, Friday 23rd and Saturday 24th November 2012 Manchester Central, Petersfield, Manchester M2 3GX “Cosmetic Interfaces: Bringing It All Together” The British Academy of Cosmetic Dentistry Ninth Annual Conference 2012 Featuring Dr Rafi Romano, Dr David Garber & Dr Maurice Salama October 22 - 28, 201222 Clinical United Kingdom Edition 1 instruments were tested using a patented reciprocating motion while Group 2 instruments were used in continuous rotation for control. For all group speed was set at 800 rpm. The cyclic fatigue testing de- vice used in the present study has been used for studies on cyclic fatigue resistance previously. The device consists of a mainframe to which a mobile plastic sup- port is connected for the electric handpiece and a stainless steel block containing the artificial ca- nals. The electric handpiece were mounted on a mobile device to allow precise and reproducible placement of each instrument inside the artificial canal. This ensured three-dimensional align- ment and positioning of the in- struments to the same depth. The artificial canal was manufactured by reproducing an instrument’s size and taper, thus providing the instrument with a suitable trajec- tory that respects the parameters of the curvature chosen. A simu- lated root canal with a 60° angle of curvature and five millimetre ra- dius of curvature was constructed for instrument type. The centre of the curvature was five millimetre from the tip of the instrument, and the curved segment of the canal was approximately five millime- tre in length. All instruments were rotated or reciprocated until frac- ture occurs. The time to fracture was recorded visually with a 1/100 second chronometer. Mean and standard deviation were calculat- ed.Alldatawererecordedandsub- jected to statistical evaluation with analysis of variance test. Statistical significance was set at P < .05. Results Results indicated that reciprocat- ing motion showed a significant increase (p<0,05) in the time to failure when compared to con- tinuous rotation. Mean time to failure was 195 sec for group 1, Mean time to failure of continu- ous rotation group control group was 86 secs. Discussion Although multiple factors con- tribute to file separation, cyclic fatigue has been shown as one of the leading causes (Shen et al. 2006). Fatigue failure usually oc- curs by the formation of a micro- crack at the surface of the file that starts from surface irregularities. During each loading cycle the mi- cro-cracks develop, getting deep- er in material, until complete sep- aration of the file (Christ 2008). All endodontic files show some irregularities on the surface, and inner defect, as a consequence of the manufacturing process, and distribution of these defects influ- ence fracture strength of the en- dodontic instruments (Anderson et al 2007, Wei et al. 2007). The advancement in TF tech- nology and manufacturing pro- cess allowed the production of a new generation of NiTi instru- ments, with better flexibility and more resistance to cyclic fatigue. On the contrary, little is known abouttheeffectofreciprocationon the lifespan of TF endodontic in- struments. Literature shows that reciprocating motion can extend cyclic fatigue life when compared to continuous rotation Therefore the term reciprocating motion includes several possible move- ments and angles, each of which may influence performance and strength of the NiTi instruments. The original Giromatic handpiece (Micro Mega, Besançon, France), and the more recent M4 motor (Sybron Endo, Orange, CA), have the same angles in CW and CCW, while Tecnika motor (ATR, Pis- toia, Italy), used by Yared (2008) with the single file F2 ProTaper technique, had a reciprocating movement with CW angle > than CCW. For the newer Reciproc (VDW, Munich, Germany) and Wave One (Dentsply Maillefer, Ballaigues, Switzerland) the ac- tual movements and angles are not clearly disclosed by manu- facturers, but all studies seem to show an increased lifespan of the instruments. Movement kinematic is among the factors which could affect lifespan of NiTi instrument because it determines stress dis- tribution, which instruments ac- cumulate during time. It seems sensible that reciprocating motion determines a better distribution of stresses during time than con- tinuous rotation. This study com- pared cyclic fatigue resistance of TF instruments used with a new patented reciprocating mo- tion and in continuous rotation on a static metal block. The results of thepresentstudyclearlyshowthat reciprocating motion can extend cyclic fatigue life of TF when com- pared with continuous rotation. DT page 21DTß