Fatigue-resistant Nitinol instrument

Patent metadata

Field	Value
Publication number	US-9878366-B2
Application number	US-201414269968-A
Country	US
Kind code	B2
Filing date	May 5, 2014
Priority date	Nov 17, 2009
Publication date	Jan 30, 2018
Grant date	Jan 30, 2018

Abstract

A fatigue-resistant Nitinol instrument has a working portion in the deformed monoclinic martensitic state and an austenite finish temperature in the range of 40° to 60° C. Because the operating environment of the instrument is about 37° C., the working portion remains in the monoclinic martensitic state during its use. The relatively high austenite finish temperature and fatigue resistance is achieved by subjecting the nickel-titanium alloy to a final thermal heat treat in a temperature range of about 410° to 440° C. while the nickel-titanium alloy is under constant strain of about 3 to 15 kg. Further, the high austenite finish temperature is achieved without subjecting the alloy to thermal cycling to produce shape memory. Additionally, there are no intermediate processing steps occurring between obtaining a finished diameter of the wire or blank through cold working and the final thermal heat treat under constant strain.

First claim

What is claimed is:

1. An endodontic instrument comprising:
a working portion composed of a nickel-titanium alloy and configured for use in the human body, the working portion having cutting surfaces, an austenite finish temperature in the range of 40° to 60° C., and a shape memory restoration such that, after a 90° bend and release, the working portion when released returns less than 88°;

the working portion having been subjected to a first heat treat while under constant strain before the cutting surfaces are formed and subjected to a second heat treat after the cutting surfaces have been formed.

2. An endodontic instrument according to claim 1 further comprising the first heat treat is at a different temperature than the second heat treat.

3. An endodontic instrument according to claim 1 wherein the first heat treat is in a temperature range of 410 to 440° C.

4. An endodontic instrument according to claim 1 wherein the second heat treat is in a range of 248 to 500° C.

5. An endodontic instrument according to claim 4 wherein the second heat treat is in a range of 300 to 450° C.

6. An endodontic instrument according to claim 1 wherein the working portion when released returns no more than 75°.

7. An endodontic instrument according to claim 6 wherein the working portion returns to no more than 60°.

8. A method of manufacturing an endodontic instrument from a nickel-titanium blank to obtain improved fatigue failure characteristics, the method comprising the steps of:
(i) applying an elongational strain deformation to the blank within its reversible strain limit at a first heat treat temperature;
(ii) after step (i), forming an instrument from the blank by performing machining operations; and
(iii) after step (ii), heat treating the instrument at a second heat treat temperature.

9. A method according to claim 8 further comprising the first heat treat is at a different temperature than the second heat treat.

10. A method instrument according to claim 9 wherein the first heat treat is in a temperature range of 410 to 440° C.

11. A method instrument according to claim 9 wherein the second heat treat is in a range of 248 to 500° C.

12. A method according to claim 11 wherein the second heat treat is in a range of 300 to 450° C.

13. An method according to claim 8 wherein after step (iii) the endodontic instrument has an austenite finish temperature in a range of 40 to 60° C.

14. A method according to claim 8 wherein after step (iii) the endodontic instrument has a shape memory restoration such that, after a 90° bend and release, the working portion when released returns less than 88°.

15. An endodontic instrument according to claim 14 wherein the working portion when released returns no more than 75°.

16. An endodontic instrument according to claim 15 wherein the working portion returns to no more than 60°.

Assignees

• Dentsply Sirona Inc
• Dentsply Sirona Inc

Inventors

• Johnson William B

Classifications

• C22F1/10

  of nickel or cobalt or alloys based thereon · CPC title

• A61C5/42

  Files for root canals; Handgrips or guiding means therefor · CPC title

• C21D1/26 Primary

  Methods of annealing · CPC title

• C21D2211/001

  Austenite · CPC title

• C22F1/006

  Resulting in heat recoverable alloys with a memory effect · CPC title