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ePaper created 2015-03-10, 11:16:47 | version 1.33.01
58 — issue 1/2015 Endodontics Article INFLUENCE OF BRUSHING ACTION — on torsional and fatigue resistance of TF Adaptive instruments — Professor Dr. Gianluca Gambarini, Professor of Endodontics at the Sapienza University of Rome’s dental school, in Italy. He is an international lecturer and researcher, and actively collaborates with a number of manufacturers all over the world to develop new technologies, operative procedures and materials for root canal treatment. Professor Dr. Gambarini also works in a private endodontics practice in Rome. Nickel-titanium (NiTi) alloy was intro- duced in endodontics more than 20 years ago, to make shaping procedures easier, more rapid and predictable. Since 1993, manufacturers have mainly changed cross-sectional designs and geometrical traitsofinstrumentstoimproveintracanal resistance to fracture. In 2007, another strategy to achieve this goal was pro- posed: the use of new manufacturing processes to optimize the microstructure of NiTi through innovative thermome- chanicalprocessing.NiTiinstrumentspro- duced with these technologies (M-Wire, CM wire, Twisted Files, etc.) showed bet- terpropertiesforendodonticuse,interms of flexibility and resistance to mechanical stress, compared with the traditional NiTi alloy and processing. Morerecently,athirdfactor(theuseof reciprocating motion instead of continu- ous rotation) has become very important in this search for safer instrumentation techniques. Current literature data show that reciprocating motion can extend both torsional and cyclic fatigue resist- ance of NiTi instruments compared with continuous motion, mainly because it re- duces instrumentation stress. In fact, in onemovementofrotation,theinstrument cuts and is engaged into the canal, while in the other (usually with a smaller angle), the instrument is disengaged and stresses are reduced. Following these concepts, new motors with specific reciprocating movements were developed, and single- file techniques were proposed for clinical use. Despite this improvement, however, the accumulation of all instrumentation stress on one single file was still felt to be dangerous; consequently, a new recipro- cating motion was developed to be used according to a sequence to optimize per- formance and safety. Released in 2013, TF Adaptive (TFA; Axis|SybronEndo) uses an innovative mo- tion,differentfromanyothermotionpre- viously used in endodontics, that com- bines the advantages of both continuous rotation and reciprocation. When theTFA instrumentisnot(orverylightly)stressed, the movement can be described as an in- terrupted continuous rotation, allowing optimal cutting efficiency and removal of debris, since the cross-sectional and flute designsaremeanttoperformattheirbest in a clockwise motion. In contrast, while negotiating the canal, owing to increased instrumentation stress and metal fatigue, themotionoftheTFAinstrumentchanges into reciprocation, with specifically de- signed clockwise and counterclockwise angles. Moreover, these angles are not constant, but vary depending on the anatomical complexities and the intra- canalstress.Thisadaptivemotionisthere- foremeanttoreducetheriskofintracanal failure without affecting performance, by theElementsMotorautomaticallyselect- ing the best movement for each clinical situation (Fig. 1). Other clinical factors can significantly affecttheclinicalresistanceofNiTiinstru- ments:the anatomical challenges,the use of torque control motors, the applied pressure,andthedifferencesinuseamong variouscliniciansintermsofsequence,the creation of a glide path, and the amount ofbrushingaction(forcoronalflaring).All thesedifferencesareverydifficulttoeval- uate, since they are mostly related to in- dividual skills, sensitivity and operative choice. It would be interesting to assess the extent to which fatigue resistance is affected by different clinical usage, such as performing or not performing a brush- ingaction.Thebrushingaction(orcircum- ferential filing) is meant to increase coro- nal flaring and, consequently, make apical progression of the next instrument in the sequence easier with less stress placed on it. Therefore, the goal of this study was to compare the torsional and cyclic fatigue resistanceofTFAinstrumentsafterclinical use,inordertoevaluatetheclinicaladvan- tages of brushing action, if any. Methodology Twenty packages of TFA small (SM) files were selected for this study (Fig. 2) and randomly divided into two groups of ten each. Each instrument was used once in sequence to prepare a mandibular molar with three canals (Fig. 3). Following the manufacturer’s guidelines fortheTFA SM sequence,amanualglidepathuptoanISO size 15 was established using the K-file stainless-steel instruments contained in thepackage.Accordingtothetrafficlight concept, it was decided to stop at yellow and use only the first two instruments in the sequence: the SM1 (green, #20.04) followed bythe SM2 ( yellow, #25.06). All instruments were used with the patented TFAElementsMotor,whichautomatically selects the best kinematics (continuous rotationorreciprocation)accordingtoin- tracanal stress. All instruments reached working length in incremental steps (1 mm), without being forced apically and with flutes being cleaned after each 1mm apical progression. Irrigation with sodium hypochlorite was performed with the use of each instrument. Inthefirstgroup(A),nobrushingaction was performed. In the second group (B, withbrushingaction),oncetheSM1instru- ments had reached working length, cir-