Dental amalgam?

Recently a member of my family broke a tooth, and the previous filling, where it had been teased out neatly by the dentist, left a very sharp point which was cutting into the tongue. I tried to file it down, without success and then tried a couple of my whetstones which merely got scored *****
So, this begs the question as to whether a supply of dental amalgam could be used to produce our own ceramic cutting inserts?
***** Finally had to snap it off with a pair of electronic side-cutters.

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I'm sure this suggestion was made tongue-in-cheek (or tongue-in-broken-tooth) but...
Given that dental amalgam contains mercury, it's probably not a great idea, even if it proved to be hard and robust enough. Although the mercury is very strongly bonded by the other metal in the mixture, and does not leach out at normal temperatures (it would not be safe to use otherwise) I suspect it might be released at the very high temperatures experienced when doing heavy cutting. Mercury vapour is * extremely* toxic.
David

On Wed, 31 Oct 2012 01:14:39 +0000, David Littlewood
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It is. I'm surprised that dentists are still using amalgam - nasty to prepare/use and nasty to remove, potentially nasty for the recipient, and (in my experience at least) the modern composites are way more durable. When I moved to Manchester (~20 years ago) theer were no dentists nearby signing on NHS patients so I went private - over a period of a couple of years the dentist removed all of my amalgam fillings & relpaced them with composite and a couple of crowns. With the old fillings I usually expected a couple of them to need replacing at each visit; since the amalgam fillings were removed I have had maybe 2 composite fillings repaired/replaced in ~20 years. Doesn't say much for the resilience of amalgam as a potential machining material to me.
As others have suggested, sounds like the hard/sharp bit was a peg of some kind.
Regards, Tony

On 31/10/2012 18:30, Tony Jeffree wrote:
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I too have had a problem with this, it's ok to put mercury in our body, but not landfill.
The reason is simple. It's down to the dental profession having a state sponsored pricing strategy.

Mike Perkins wrote:
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Amalgam of mercury and silver is non-toxic under normal conditions.

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Mercury vapour is quite toxic, but mercury liquid is not absorbed to any great extent. The amount in a set of fillings isn't going to do you a lot of harm. As to the longevity of amalgam fillings, I will admit that I finally had to have one partially ground out and replaced this year. Damn thing had barely lasted 41 years :-(. I suspect that a lot of the replacement of amalgam and most of the replacement by composite is driven by the per unit pricing model of dentistry. I'm _so_ glad we're back on the NHS. I got really sick of paying £200/year to get my teeth cleaned!
Mark Rand RTFM

writes
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No, quite serious, one of those times when armchair musings might just advance the art of machinig.
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Actually, amalgam was probably the wrong word, as I do not think that mercury is involved. Whatever is the compound, some form of ceramic or maybe epoxy, ISTR the he sets if off using UV light.

On Wed, 31 Oct 2012 20:05:36 -0000, "gareth"
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Sounds like a composite filling material in that case...from Wiki:
"As with other composite materials, a dental composite typically consists of a resin-based oligomer matrix, such as a bisphenol A-glycidyl methacrylate (BISGMA) or urethane dimethacrylate (UDMA), and an inorganic filler such as silicon dioxide (silica). Compositions vary widely, with proprietary mixes of resins forming the matrix, as well as engineered filler glasses and glass ceramics. The filler gives the composite wear resistance and translucency. A coupling agent such as silane is used to enhance the bond between these two components. An initiator package (such as: camphorquinone (CQ), phenylpropanedione (PPD) or lucirin (TPO)) begins the polymerization reaction of the resins when external energy (light/heat, etc.) is applied. A catalyst package can control its speed."
So it is basically a resin with a powdered mineral/glass/ceramic filler.
Regards, Tony

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So, it's back to square one, and can we obtain / use it for synthesizing our own ceramic inserts?

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Well I suppose you could do if you are prepared to invest the months or even years required to develop a material of sufficient hardness and strength to cut steel, and then form it very accurately to the shape required; but I wonder why you would want to given the widespread availability and relative cheapness of commercial inserts.
Cliff Coggin.

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But doing things for ourselves is what it is all about.

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True enough, but it is so easy to get side tracked into making a tool to make a tool to make a tool, that we don't get anything done. At it's worst one can end up re-inventing the wheel!
Cliff.

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Which is exactly where I am at the moment. I only need a couple of anti-backlash gears and some gear rack for a radio project, and I'm sidetracked into a gera-hobbing machine!
To paraphrase you, from an industrial saying, "When you are up to your arse in alligators, it is easy to forget that you came to drain the swamp" :-)

On 01/11/12 22:20, gareth wrote:
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Actually in a sense it's more the other way round, but close enough (the filler is nano-scale, and joins itself up, kinda, a bit like PVA-and-water glue).
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No, composite filling materials are softer than eg amalgam, and nowhere near as hard as eg HSS, never mind ceramic insert materials which are orders of magnitide harder and more wear resistant.
We tend to think of filling materials as being hard and strong and wear-resistant, as compared to the rest of our bodies they are; but compared to engineering materials they aren't really - eg gold alloy is often considered the best structurally, and that isn't in the same class as the better engineering alloys.
As for engineering insert materials, they are much stronger and harder and more wear resistant still.
Also the organic portion (the methacrylate bit) of a composite filling wouldn't withstand more than a couple hundred degrees centigrade, whereas an insert is required to withstand many hundreds, a thousand, or more.
-- Peter Fairbrother

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I wonder what the cost of TiN coated TC crowns would be :-)
"gold teeth" that could bite through a coin. (or at least, strip wire without cracking)
Mark Rand RTFM

On Fri, 02 Nov 2012 19:08:45 +0000, Mark Rand
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Presumably that was what "Jaws" used in the Bond movies...
Regards, Tony

Mark Rand wrote:
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I often strip wire with my teeth.
Ooops! There goes another one!

Peter Fairbrother wrote:
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AIUI, it's pure gold (leaf), compressed into the cavity and burnished.

On Tue, 30 Oct 2012 23:51:12 -0000, "gareth"
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The only dental amalgam I'm familiar is one made with approximately 50% mercury, 327% silver, tin and copper. This amalgam is not particularly hard. I imagine what you encountered is either a ceramic or a resin that is maybe filled with some type of ceramic. Ask the dentist what is used, I'm curious. Eric

snipped-for-privacy@whidbey.com on Tue, 30 Oct 2012 18:48:46 -0700 typed in uk.rec.models.engineering the following:
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    less see, half mercury and the other "three hundred twenty seven percent" is silver tin and copper. Collapsed to fit the spec, no doubt. B-)
    What did they use to say "Ninety percent of this game is half mental."
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tschus pyotr
Yes, I am sure it was a typo. A one in a million chance, which works out in reality to nine out of ten times. -- pyotr filipivich Most journalists these days couldn't investigate a missing chocolate cake at a pre-school without a Democrat office holder telling them what to look for, where, and why it is Geroge Bush's fault.