Titanium properties

I recently had to endure a prolonged and difficult dental procedure (90 minutes) not by choice, it was a complicated root treatment carried out through the porcelain and metal reinforcement of a four tooth bridge. During the procedure my dentist was using very fine flexible needle like items to penetrate down through the the tooth to access the nerves, I enquired as to what these needle like items were, my dentist knows that I am interested in anything remotely connected to engineering, even if it is the gory aspects of dentistry. He explained that they were in fact tapered and had minute cutting edges on them and acted as a kind of reamer, he said that they were made of different materials, some were stainless steel and some titanium. The principle property required was that they should be flexible, he said the stainless ones although flexible were prone to breakage when inside the tooth, the titanium ones were also of the required flexibility but much less prone to breakage. The titanium items were heat treated to achieve a hardness so that they could cut in the tooth but were extremely flexible, he demonstrated by bending one through at least 90 degrees, can anyone explain how the titanium is treated to achieve a high degree of hardness for cutting and yet be very flexible, remember we are talking of an extremely narrow needle.

Dave W

Maybe you are thinking in th wrong direction about this. The thinner a rod becomes the less its surface is required to deform for a given radius. (a 3mm glass rod is stiff, a 3micron filiment is flexible). It's more about geometry than anything else. The minimum bend radius is going to be proportional to the diameter of the rod.

regards Martin

To be honest, Dave ... much of this is beyond me: **LINK**

https://www.nikhef.nl/pub/departments/mt/projects/KM3NeT/Referencedesigns/BEOC%20Break%20Out%20Electrical%20Optical%20Cables/Datasheets_information/AA5069_Heat%20Treating%20of%20Titanium%20and%20Titanium%20Alloys%20_%20KEY%20to%20METALS%20Article.pdf

but; it might point you in the right direction.

MichaelG.

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See also: https://en.m.wikipedia.org/wiki/Endodontic_files_and_reamers

Edited By Michael Gilligan on 14/12/2017 11:26:53

Many years ago I went to an open day at R-R Barnoldswick. At the time they had begun making RB211 front fan blades from Titanium, but they weren't letting on how they did it, beyond saying it involved heat and pressure. Nowadays, living in Sheffield, still the centre of the 'special steels' industry, I gather that many alloys, not just steel, now exist that simply did not, even 20 years ago.

Geoff

Looking at images of the nickel titanium tools they appear to be cut on opposite sides rather like collets thereby allowing some extra flexibility.

Michael, had quick skim through the link you gave, yes very technical, I will have to read it slowly and carefully to adsorb its content but I am sure that it does give the answer that I am seeking. It is a long time since I dealt with in depth technical information and my brain has tended to stagnate these past few years.

Geoff many moons ago when they were developing the RB 211 engine I remember being shown a video where they used powerful X-Ray's to observe how the titanium blades were deforming when the engine was run in the test house, my interest then was employed in Non Destructive Testing.

Martin, I should have remembered about the stiffness versus diameter, particularly with the glass example, I still wonder how the titanium alloy can have cutting edges yet still be flexing.

Dave W

Just a guess but it could be they're made of a fairly ordinary bendy Titanium alloy and the blade part is hardened with a thin coat of Titanium Nitride. TiN is that yellow stuff on twist drills and milling cutters; it's 3 or 4 times harder than HSS and I suppose it could take a good edge.

I know sword blades have a soft core for toughness and it's only the cutting edge that's very hard. Blades are both flexible and sharp; perhaps the titanium tools are similar.

Your 90 minute dental horror story will probably give me nightmares tonight. Reminded me of that scene in Marathon Man. Shudder.

Dave

This may be a little too much detail for those of a nervous disposition: **LINK**

https://www.nature.com/articles/4811738.pdf

but it includes some useful notes about endontic files and reamers

MichaelG.

Again thanks for responses,

Dave your explanation re cutting edges make sense, I was impressed how flexible the instrument was.

Michael thanks for the link, have not read all of it yet, need to concentrate well on it, but what I have read so far is very informative and explains a lot of the process that I was wondering about, particularly why a rubber sheet was stretched across my mouth, thought it was just to stop me making a meal of the instruments and the debris created but main function appears to exclude saliva and prevent infection in the work area.

Dave W

I think, the main reason for using titanium in dentistry is related to its biological inertness, eg immune system does not attack it.

So if some tiny chips/splinters of titanium are left inside your tooth there won't be inflammation. Main advantage of titanium is toughness comparable to steel at about half of density of the latter. It is also more stainless than stainless steel. Heat treatment of titanium would rather result in annealing, not hardening because nothing like martensite exists there. Hardness would be manipulated by other alloying components, surface coating and cold forming. Wires drawn at certain temperature regimens would be reasonably hard and flexible.

"why a rubber sheet was stretched across my mouth, thought it was just to stop me making a meal of the instruments and the debris created but main function appears to exclude saliva and prevent infection in the work area."

I wonder if your dentist have used female condom or something very similar to these ends. It serves comparable purpose, namely "prevents infection in the work area" and sometimes can also "exclude saliva".

Martin

Edited By Martin Dowing on 18/12/2017 09:32:49

Edited By Martin Dowing on 18/12/2017 09:45:17

I think those rubber sheets may be called "dental dams".

No experience of titanium myself but it sounds as if diffusion (surface) hardening is the way it is done. As with stainless steel, carbon and nitrogen react with it to form TiC and TiN (in this case) which are very hard.

Found an interesting PhD thesis that provides an overview of current processes (CVD, PVD etc)as well as a closer look at nitrogen diffusion hardening in particular.

I would expect that titanium-based tooling would use an alloy, rather than pure Ti. Aluminium seems to be one such alloying element.

Murray

PS - rather bizarrely, perhaps, there is an appendix to the thesis (pp223) relating to the "Non-linear Viscoelastic Properties" of the skin of the orange-footed sea cucumber. Not something you might expect to find in a work focused on surface treatment of Ti perhaps!

Try searching for dental dam for an explanation of the rubber sheet use.

Martin, "rubber sheet" was I think purpose made for dentistry, although never having seen a female condom couldn't be sure, have led a very sheltered life in some respects, wondering if you are in fact taking the piss?

Dave W

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... or even just look at the second page of the article that I linked at 19:11:49 on 14/12/2017 [which Samsaranda has already done].

MichaelG

Edited By Michael Gilligan on 18/12/2017 10:10:30

@Samsaranda,

No offense meant. Just your desription of virtues of working of discussed rubber item so much have matched workings of female condom that I couldn't resist noting it.

Martin