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roots - international magazine of endodontology No. 3, 2016

| technique canal shaping 16 roots 3 2016 rotary motion, but more recently a new approach to the use of NiTi instruments in a reciprocating move- ment had been introduced by Yared.11 The clockwise (CW) and the counterclockwise (CCW) rotations used by Yared were four-tenths and two-tenths of a circle respectively and the rotational speed utilised was 400 rpm.TheconceptofusingasingleNiTiinstrument to prepare the entire root canal was made possible duetothefactthatareciprocatingmotionisthought to reduce instrumentation stress. Recent literature data shows that a reciprocating motion can extend cyclic fatigue resistance of NiTi instruments when compared to continuous rota- tion,27, 28 mainly because it reduces instrument stress. Astheinstrumentrotatesinonedirection(usuallythe larger angle) it cuts and becomes engaged into the canal then it disengages in the opposite direction (usually with the smaller angle) and the stresses are therefore reduced. Following these concepts new instruments have been recently commercialised; Reciproc (VDW) and WaveOne (DENTSPLY Maillefer), which uses specifically developed motors that pro- duce a specific reciprocating movement (using ap- proximately 150 to 30°angles). This reduction of instrumentation stress (both tor- sional and bending stress) is the main advantage of reciprocating movements. It has been shown that a lotofdifferentreciprocatingmovementscanbeused, each one affecting the performance and the safety of the NiTi instruments. Therefore, when discussing the advantages and disadvantages of reciprocation, the exact motion should also be mentioned, since theactualangleofreciprocationcanhavesubstantial influence on both the clinical and experimental be- haviour of NiTi instruments.15 Anotherpossibleadvantageofreciprocationcould be better maintenance of original canal trajectory, mainly related to lower instrumentation stress and consequently its elastic return. However, it must be underlined that reciprocation does not affect the in- herent rigidity of the instruments. If a quite rigid Niti instrument of greater taper is slightly forced into a curved canal, it will create more canal transportation thanamoreflexibleone,duetoitsinherenttendency to straighten. Moreover, tip design could strongly in- fluence canal transportation, with a cutting tip being more dangerous that a non-cutting pilot tip. WhilereciprocationwithNiTiinstrumentshavebe- come very popular in recent years, with a significant number of published articles, some of these studies haveshownthatthereisalsoinherentdisadvantages in the reciprocating movements. It is well known that a small inadvertent extrusion of debris and irrigants into the periapical tissues is a frequent complication during the cleaning and shaping procedures, both with manual stainless steel and nickel-titanium rotary instrumentation Fig.4:The motion ofTFTM Adaptive instrument changes from rotary into reciprocation mode,with specifically designed CW and CCW angles which may vary from 600–0° to 370–50°. Fig.5: File size reference chart. Fig.4 Fig.5 32016

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