Method of Preparing Nickel Titanium Alloy for Use in Manufacturing Instruments with Improved Fatigue Resistance

Abstract

A method of treating Nitinol to train the structure thereof to remain in the martensite state, including the steps of subjecting the Nitinol to a strain and while subjected to the strain, thermally cycling the Nitinol between a cold bath of about 0° C. to 10° C. and a hot bath of about 100° C. to 180° C. for a minimum of about five cycles.

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       12 . A flexible instrument comprising an elongated metallic element that is subject to lateral and torsional stress as used and in which the instrument is stabilized in an induced martensitic phase that persists under pre-determined working temperatures and exemplifies substantially improved fatigue resistance. 
   
   
       13 . A flexible instrument according to  claim 12  wherein said metallic element is formed of a nickel/titanium alloy. 
   
   
       14 . A flexible instrument according to  claim 13  wherein said nickel/titanium alloy is Nitinol. 
   
   
       15 . A flexible instrument according to  claim 12  in which the instrument is stabilized by being subjected to thermal cycling a plurality of times between cold and hot baths while under deformation. 
   
   
       16 . A flexible instrument according to  claim 15  in which the deformation is-provided by strain of between 1% and 10%. 
   
   
       17 . A flexible instrument according to  claim 15  in which said thermal cycling includes subjecting the instrument to temperature changes between a first temperature of about 0° C. to 10° C. and a second temperature of about 100° C. to 180° C. 
   
   
       18 . A flexible instrument comprising:
 an elongated metallic shaft having proximal and distal portions;   a handle portion of said proximal portion for facilitating mechanical or manual manipulation of said shaft;   wherein said shaft is formed of a shape memory alloy which has been subjected to thermal cycling while under deformation to induce said shaft to maintain the martensitic phase at a body temperature range in which said shaft demonstrates significantly improved longitudinal and torsional fatigue resistance.   
   
   
       19 . A flexible instrument according to  claim 18  wherein said metallic shaft is formed of a nickel/titanium alloy. 
   
   
       20 . A flexible instrument according to  claim 19  wherein said nickel/titanium alloy is Nitinol. 
   
   
       21 . A flexible instrument according to  claim 18  in which the instrument is stabilized by being subjected to thermal cycling a plurality of times between cold and hot baths while under deformation. 
   
   
       22 . A flexible instrument according to  claim 18  in which the deformation is provided by strain of between 1% and 10%. 
   
   
       23 . A flexible instrument according to  claim 21  in which said thermal cycling includes subjecting the instrument to temperature changes between a first temperature of about 0° C. to 10° C. and a second temperature of about 100° C. to 180° C. 
   
   
       24 . A medical/dental device for use in the human body, comprising:
 an elongated instrument formed of a binary superelastic metal alloy susceptible of different molecular phases that has been subjected to thermal cycling while under deformation to induce said instrument to maintain a selected phase at body temperatures in which said instrument demonstrates significantly improved longitudinal and torsional fatigue resistance.   
   
   
       25 . An elongated instrument according to  claim 24  wherein said metal alloy is formed of a nickel/titanium alloy. 
   
   
       26 . An elongated instrument according to  claim 25  wherein said nickel/titanium alloy is Nitinol. 
   
   
       27 . An elongated instrument according to  claim 24  in which the instrument is subjected to thermal cycling a plurality of times between cold and hot baths while under deformation. 
   
   
       28 . An elongated instrument according to  claim 24  in which the deformation is provided by strain of between 1% and 10%. 
   
   
       29 . An elongated instrument according to  claim 27  in which the instrument is subjected to thermal cycling between a first temperature of about 0° C. to 10° C. and a second temperature of about 100° C. to 180° C. 
   
   
       30 . An endodontic instrument that is flexible and resistant to torsional fatigue and that is adapted for use in performing root canal therapy on a tooth, comprising:
 a cylindrical elongate shank composed of an alloy comprising at least about 40% titanium and at least about 50% nickel, said elongate shank further having a proximal end and an opposite distal end so as to define a working length adjacent said distal end;   at least one ground flute extending helically around said shank working length and defining at least one cutting edge, a helical land positioned between axially adjacent flute segments; and   said shank being trained to remain in a trained molecular state at body temperature by having been subjected to strain of between about 1% and about 10% while being thermally cycled between hot and cold baths.