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I 29 opinion _ GTX rotary system I roots2_2010 Atatimeinwhichcanal shapes are moving in the direction of more con- servative coronal diam- eters, the GTX 1mm maximum flute diame- terpreservestoothstruc- ture in this region of the canal. The most important areaofthetoothwithregard to vertical root fracture is the 1mmregionbelowandabovethe crestal bone. This 2mm zone is where the GTX 1mm maximum flute diameter is mostbeneficial,whichisthereasonthatIfeelitissuch an important feature. Since implants are the comparative treatment against which endodontic treatment is now meas- ured, the bar for endodontic treatment is much higherthanitoncewas,andconservingtoothstruc- ture and preserving the structural integrity of the tooth are critical for long-term success—not only long-term success for the treated tooth, but also long-term success for endodontics. If I look back at the canal shapes I was creating ten years ago, I see a significant improvement in the amount of dentine I am saving apical to the pulpal floor. The 1mm maxi- mum flute diameter of the GTX system automatically preserves canal dentine in the area most critical for maintaining the structural integrity of the tooth. _M-Wire NiTi GTX files are the first rotary instruments to use a new type of NiTi wire known as M-Wire. M-Wire NiTi, the raw material used to manufacture GTX files, was developed by Dr Ben Johnson of Tulsa in Oklahoma. M-Wire is manufactured using a proprietary wire- drawing method, which produces a more favourable molecular arrangement of the NiTi alloy matrix. MultiplestudiesdemonstratethatM-Wireissuperior to traditional NiTi 508 in both flexibility and cyclic fatigue resistance. Increased flexibility means there are fewer lateral cutting forces applied to the canal in areas of curvature, which results in less lateral transportation of the canal. Cyclic fatigue resistance means the instrument is less likely to separate in areas of canal curvature. M-Wire is the most signifi- cant improvement to endodontic instrumentation since NiTi was introduced over two decades ago. _Increased flute space and reduced core diameter When you first look at a GTX file, you notice that the flutes are spaced farther apart and there are fewer spirals on the instrument. This feature is the helical angle. The helical angle for GTX is greatly reduced compared to original GT files. The re- ducedhelicalanglepro- duces a more stretched out fluting geometry. The space between flutes is increased, thereby pro- viding more space for den- tine shavings to accumulate duringuse.Thisfeatureallowsfor GTX files to be used in the canal for more revolutions before the flutes fill with debris. Along with increasing the flute space, the reducedhelicalanglecreatesamoreefficientcutting angle for the rotating blade edges to engage the dentine. This is the same reason reamers are more efficient in rotary action than files. In order to increase flexibility further, the new GTXsystemhasareducedcorediameter.Thereduced core diameter is partly a consequence of the reduced helicalangleandincreasedflutespace.Corediameter is the single most important factor affecting ins- trument flexibility. The reduced core diameter of the GTX instruments offers a flexibility advantage over the original GT system. _End result The advances in instrument flute geometry and metallurgy incorporated into the new GTX system have created a superior cutting instrument, while maintaining the inherent safety and system-based approach of the original GT system. From a clinical standpoint, fewer files are needed to produce the final canal shape. At a time in which cutting speed is what many clinicians desire, it is refreshing to see DrBuchananandDentsplytakeadeliberateapproach to maintaining the safety level for which the original GT file system is known. Holding true to radial lands and a safe-ended tip design are what distinguish the GT brand from all the others._ Fig. 2_File cross-sectional view showing a non-radial landed cutting edge design: in this design, only the cutting edge contacts the radial arc. Dr Chris J.Lampert received his certificate in Endodontics from Boston University and is a full-time practicing Endodontist in Portland,Oregon.Dr Lampert is a Specialist Member of the AmericanAssociation of Endodontists,theAmerican Dental Association and the Oregon DentalAssociation.He can be contacted at lampertendo@gmail.com. _about the author roots Fig. 2

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