Wikipedia:Reference desk/Archives/Science/2019 March 20

= March 20 =

Gold teeth vs. silver teeth
Is one preferred over another, apart from the obvious price difference? Anna Frodesiak (talk) 07:12, 20 March 2019 (UTC)


 * According to Crown (dentistry), gold (actually a gold alloy, as pure gold is too soft) causes less wear on real teeth than silver, and is easier to adjust later. Silver, on the other hand, being stronger, does not have to be as thick as gold. That might let you get away with grinding off less tooth. Someguy1221 (talk) 08:03, 20 March 2019 (UTC)


 * Gold is malleable, nearly immune to corrosion, and hard enough to form a biting surface that can be used for years. Gold was used before silver became available and has continued to be used for specialized purposes. Dental restorations are often made from a combination of precious metals. Gråbergs Gråa Sång (talk) 08:20, 20 March 2019 (UTC)


 * Interesting indeed Someguy1221 and Gråbergs Gråa Sång. Oh, we might need some redirects or such at Gold teeth. Do you think silver has a funny metal taste where gold doesn't? Anna Frodesiak (talk) 09:00, 20 March 2019 (UTC)


 * Possibly, but I'd worry that my silverteeth would blacken over time, or perhaps poison me. I remember King Rat mentions aluminum teeth. Gråbergs Gråa Sång (talk) 09:09, 20 March 2019 (UTC)

PAGE ]]) 21:16, 21 March 2019 (UTC)
 * Gold works. It's still one of the best materials for doing this, especially for longevity.
 * Also, one garlic or poached-egg based meal and your silver teeth will be black.
 * Thorium is an excellent dental alloy too and was used in the 1850s-1860s. However the radioactive aspects of it weren't understood at the time.  There are interesting studies done on Americal civil war graves, showing the effects of thorium on the bones after a few years.
 * One of my favourite dental alloy stories is about Stellite. In the mid 1940s, there was a problem of how to design turbocharger blades, which had to be strong, survive high temperatures and also be cast to precise shapes. The British engineer, and denture wearer, S.D. Heron suggested using Stellite. Although the characteristics of the material obviously suggested itself for making turbocharger blades, it was thought impossible to cast it to the precision needed. Heron took his dentures out and put them on the table in front of the meeting... Andy Dingley (talk) 11:40, 20 March 2019 (UTC)
 * There's also the question of the price difference not being that much. The lab fee for a gold crown (UK, this week) is £170. That's to cast a gold crown, supplying the gold, from models made by a dentist and to be fitted by the dentist. So the surgery fees are on top of that, and would generally be quite a bit more.
 * You can have a cheaper crown than a gold one, but you can't have a metal crown (same process) or ceramic crown that's much cheaper. The cost is mostly skilled labour, not just bullion.  It might be cheaper with some forms of resin crown, as these can be formed in place in one operation and can require less work. Andy Dingley (talk) 15:43, 20 March 2019 (UTC)
 * Try Googling George Washington's teeth I belive they were made of wood  — Preceding unsigned comment added by 81.131.40.58 (talk) 15:47, 20 March 2019 (UTC)
 * Wrong. See Please don't guess when answering refdesk questions. --Guy Macon (talk) 16:19, 20 March 2019 (UTC)
 * There's plenty of unattributed guesswork in that article too. The fable of the wooden teeth has been around a long time. One source I recall opined that the young Washington had "whittled them from cherrywood after his father punched his teeth out." ←Baseball Bugs What's up, Doc? carrots→ 17:48, 20 March 2019 (UTC)
 * By "There's plenty of unattributed guesswork in that article too" are you implying that Smithsonian Might be wrong on this?
 * George Washington's false teeth not wooden
 * Did George Washington have wooden teeth?
 * Contrary to popular mythology, George Washington's dentures were not made of wood
 * Drilling Holes in George Washington’s Wooden Teeth Myth
 * Did George Washington Have Wooden Teeth?
 * What Were George Washington's Teeth Made Of? (It's Not Wood)
 * George Washington's Dentures
 * Did George Washington Have Wooden Teeth?
 * The Funky History of George Washington's Fake Teeth
 * Did George Washington really have wooden teeth?
 * George Washington did not have wooden teeth.
 * --Guy Macon (talk) 18:16, 20 March 2019 (UTC)
 * It would have been nice if the NG writer had done as much research as you did. And beware of "arguing from authority". The fact that something appears in NG does not make it infallible. ←Baseball Bugs What's up, Doc? carrots→ 18:21, 20 March 2019 (UTC)
 * Although: "The first recorded wooden dentures in Japan appeared in 16th century and were used until beginning of 20th century". Luckily, GW didn't go to Japan for his gnashers.   Alansplodge (talk) 19:31, 21 March 2019 (UTC)
 * If you're checking with the Smithsonian, you might as well just hop across the Potomic River to Mount Vernon, where George Washington's actual dentures are on display in a glass case. --Ahecht ([[User talk:Ahecht|TALK

Would brushing with baking soda make silver teeth untarnished again? Anna Frodesiak (talk) 23:39, 20 March 2019 (UTC)
 * Hmm. Removing silver tarnish with baking soda, the sites I find showing how to do it all suggest boiling water. This is for silverware and jewelry, obviously, and not teeth. Someguy1221 (talk) 00:16, 21 March 2019 (UTC)


 * Zirconium dioxide aka Zirconia has taken over the dental implants including crowns and bridges for most parts since 1980. Amalgam (dentistry) (Gold, Silver) contains mercury, which unfortunately slowly dissolves from any dental application parts in very small dosage and can cause Mercury poisoning.
 * Zirconium dioxide aka Zirconia has taken over the dental implants including crowns and bridges for most parts since 1980. Amalgam (dentistry) (Gold, Silver) contains mercury, which unfortunately slowly dissolves from any dental application parts in very small dosage and can cause Mercury poisoning.


 * The only common alternative is Titanium, which some persons can become allergic to (bad situation if you notice after your 10'th new Titanium-Implants). Zirconia is biocompatible and hypoallergenic but Implants are still very expensive. --Kharon (talk) 00:25, 21 March 2019 (UTC)


 * Zirconium dioxide, eh? I always thought that looked like glass. If I ever need crowns, that sounds like the right stuff (...either that or californium). Anna Frodesiak (talk) 00:39, 21 March 2019 (UTC)
 * Zirconia is white, and looks like most other ceramics. Only cubic zirconia is glass-transparent, and that requires chemical doping (a trick from the semiconductor electronics industry) to give it the right crystal structure.
 * Zirconia ceramics are good for veneers on teeth, but on the biting surfaces they're a bit too brittle. Gold will last longer (a lifetime, with some very gradual wear) whilst ceramics are often a decade or two. Sometimes they can fail within a year.
 * As to zirconia for dental implants, then it all depends on the dentist. At least in the UK, the only way to find a good dentist is to ask another dentist. They, and the GDC, are dreadful at communicating to the public anything about what good dentistry should be able to offer and what it ought to cost. Generally the most expensive dentist is far from the best one (they're just the one in the most fashionable part of town) and the really good dentists are the much more modest ones, whom the other dentists know about, but the public never really hear about. Implants are a specialisation beyond this, and only a few dentists are really good with them, and even fewer can do zirconia implants really well. Andy Dingley (talk) 01:29, 21 March 2019 (UTC)
 * You know, Andy, there is probably a tiny fraction of people who think of zirconia and do not think cubic zirconia. It was news to me. Now when someone talks about it, I can be the smarty-pants. Thank you. Anna Frodesiak (talk) 02:55, 21 March 2019 (UTC)
 * Titanium isn't a problem for allergies, but vanadium, an alloying element in most engineering alloys of titanium, is. This hasn't been an issue in medical applications of titanium for decades. Andy Dingley (talk) 01:31, 21 March 2019 (UTC)

George Washington's teeth
Looking at all those links above, I'm wondering if there is enough for an article, or at least an expansion of the George Washington article.

See:
 * George Washington's teeth article history (now a redirect to the man)
 * Redirects for discussion/Log/2014 June 10
 * Images at commons
 * George Washington (not much there)

Anna Frodesiak (talk) 21:31, 21 March 2019 (UTC)

Okay, George Washington's teeth is now an article. Anna Frodesiak (talk) 09:21, 22 March 2019 (UTC)
 * Excellent! Keep this discussion in mind the next time someone claims that the ref desks serve no purpose. ←Baseball Bugs What's up, Doc? carrots→ 12:52, 22 March 2019 (UTC)

sine rms
is there a simple formula for the rms of a "cut" sinusoid as a function of the phase x (0..$$\pi$$)? It's just that I was playing with the stuff in LTSpice and found out that the relationship between the average voltage and phase is nonlinear. So I thought it must be proportional to the area under the sinusoid (because, what else is there), which I figured must be $$\textstyle \int_{x}^{\pi}\sin(t)dt$$ and which is apparently the same as $$\cos(x)+1$$. Now when I plot the voltage vs the inverse of that ($$\arccos(y-1)$$), the average (i.e. the average of the (absolute) values assumed by the sinusoid) is super-linear just as I wanted but the rms still is not, but I'm reading it's the rms that has physical significance Aecho6Ee (talk) 23:36, 20 March 2019 (UTC)


 * Using only the positive swing of the sinusoid i.e. 0≥t≥pi the average voltage of the sinusoid cut at x is Vav = cos(x) + 1 which is the deflection of a moving-coil voltmeter. However the heating power of the wave, see Joule heating, is V2 = ( cos(x) + 1)2.

|             |              2         x   |  cos(x) + 1  |  (cos(x) + 1) ________________________________________________        π   |      0       |        0 .9 π |   .049.. |    0.0024..        .5 π |      1       |        1 .1 π |   1.951.. |    3.807..         0   |      2       |        4

For alternating electric current, RMS (Root mean square) is equal to the value of the direct current that would produce the same average heating in a resistive load. DroneB (talk) 12:15, 21 March 2019 (UTC)
 * I'm using the inverse $$\textstyle x(v)=\arccos(\sqrt{v}-1)$$ to find out at what point in the sinusoid half-cycle to turn the voltage on to get a certain Vrms out. I'm stepping $$v$$ from 0 to 4 linearly, pass it to the arccos, then set the phase of the switch from that (appropriately scaled, i.e. 0 to 10ms - the length of a half-cycle at 50Hz), then measure the Vrms. It's decidedly non-linear. What am I doing wrong? I found out if I do $$\textstyle \pi-arccos...$$ it's much much better but there are still small kinks at both extreme ends Aecho6Ee (talk) 11:07, 22 March 2019 (UTC)

Safely holding a huge piece of uranium
How is it that he can hold this without things flying off it, through the gloves, and giving him hand cancer? Anna Frodesiak (talk) 23:45, 20 March 2019 (UTC)


 * I just thought I'd point out that you can buy uranium on Amazon. Not all radioactive material is so dangerous that it would hurt you by holding it just for a short period of time. Or even longer period if it's less radioactive. There are a couple things that I can think of off the top of my head which have radioactivity but can safely be handled. † dismas †|(talk) 23:50, 20 March 2019 (UTC)


 * Pure uranium is only slightly radioactive, and so can be handled (at least for short periods of time) with no risk to the handler's health. (Not so with plutonium -- that stuff is more radioactive, so requires special precautions during any kind of handling.) 2601:646:8A00:A0B3:51E3:EF9C:2B98:7660 (talk) 00:08, 21 March 2019 (UTC)
 * Even with plutonium, it's spontaneously an alpha emitter and so rubber gloves would be adequate shielding. In a neutron flux it's a different matter, as you might see enough fission (and thus more neutron flux) that this would now be a real hazard. That's what is happening inside a reactor. Plutonium (unlike uranium) does have enough spontaneous fission that it's a moderate hazard, but this depends a lot on which Pu isotopes are present. See Pu-240 for the wartime problems this caused with the production of the first atom bomb. Even now, plutonium for weapons on ships and submarines, where someone might be bunking next to it, has to be of supergrade plutonium which has a reduced level of the spontaneously fissile isotope, just to keep this background fission level (and also gamma radiation) safe. For land-based missiles they just stand well back, behind some concrete. Andy Dingley (talk) 01:17, 21 March 2019 (UTC)

I see. Okay. I always wondered that. Thank you. :) Anna Frodesiak (talk) 00:13, 21 March 2019 (UTC)


 * It is the decay products which create most of the radiation, not the uranium itself. 2601:646:8A00:A0B3:51E3:EF9C:2B98:7660 (talk) 00:16, 21 March 2019 (UTC)


 * Indeed! The common uranium isotopes decay by alpha emission, which is relatively harmless if it's outside your body, as it can be blocked by skin. But many of the decay products are beta emitters, see Decay chain. But even then, in the case of uranium ore, the isotopes are so long lived that it does not wind up being very many beta particles. The short term health concern is chemical toxicity, not radioactivity. Someguy1221 (talk) 00:22, 21 March 2019 (UTC)


 * Used nuclear reactor fuel might be where the idea of uranium being really bad comes from. Sagittarian Milky Way (talk) 04:32, 21 March 2019 (UTC)


 * The alpha particles given off by uranium are stopped by the upper, dead layers of skin and so would be safe to hold in your hand. The person in the picture is probably wearing gloves for at least 2 reasons.  The first is that you don't want to accidentally ingest or inhale particles that were left on your bare hands.  While uranium in the hand is quite safe, uranium particles in your lungs, mouth, stomach, etc are very, very much not safe.  Because you don't have a protective layer of dead skin cells inside your body, the alpha particles collide with living cells and cause problems.  When you convert from counts of radioactive decay to the statistical health effects alpha particles have about 20 x as much damaging potential as other forms of ionizing radiation.  So, in summary, on the outside = no damage, while on the inside = 20x damage!  The second reason for wearing gloves is that some of the daughter products of uranium include beta emitters.  Beta particles will penetrate skin, but can be stopped by a thin layer of metal, or a slightly thicker layer of rubber.Tobyc75 (talk) 17:10, 21 March 2019 (UTC)


 * Reputable and reliable sources who document best-practices for dealing with uranium will all say pretty much the same thing: if you don't need to hold the uranium, don't hold the uranium. The technical term for this is to keep your exposure as low as reasonably practical (ALARP).
 * Even if a particular level of exposure is "safe," according to some particular metric, it is almost certainly more safe to not expose anyone to it.
 * Here's a free online website, the Radiation Safety Manual, for Stanford University. I'm not certain if anyone there uses uranium, but there are surely examples of research and clinical use of ionizing radiation.  And here are several radiation safety training handbooks from the Department of Energy, where some employees surely do work with uranium.
 * I'd also like to point out one of the more non-obvious problems of working with uranium, which is the potential for creation and accumulation of radon. This is described in greater detail in the resources that I just linked.  If you're working with radiological sources, or if you're buying them on the internet for the fun and cool factor (!), make sure you're well-informed about all the hazards; and per the "ALARP" principle, ... maybe just ... don't?
 * Nimur (talk) 17:30, 21 March 2019 (UTC)

Most of this is above my mental pay grade, but thank you for the info that I do understand. It is certainly interesting. Anna Frodesiak (talk) 20:04, 21 March 2019 (UTC)
 * In a nutshell: there are different types of ionizing radiation. They are often all lumped together under the catch-all term "radiation". Sometimes this is defensible, but unfortunately this often misleads people, and when coupled with poor education on the subject leads to widespread radiophobia, as well as confusion between ionizing and non-ionizing radiation (microwaves, radio waves, and light). Neutrons, x-rays, and gamma rays are the scary "stay far away or be behind shielding" stuff, since they penetrate matter easily. But, a lot of radioisotopes don't produce these. The other problems with radioisotopes are inhalation and ingestion: if they get into your body, they can do damage.
 * Some radiation exposure is "natural" and part of everyday life. Uranium is present in low concentrations in a lot of soil and rock: granite contains a fair amount of it. As others have mentioned, uranium decay produces radon. This can accumulate in buildings in some places to dangerous levels: radon is a radioactive gas, which makes it dangerous since you can breathe it in. Everyone's body contains radioisotopes, the most prevalent of which is potassium-40. This has enough radioactivity that a big enough quantity of potassium can set off radiation detectors. The idea of a banana equivalent dose is humorously used to inform people about the level of naturally occurring radiation in common things. At the extreme end of "things that are radioactive but not concerning", bismuth is now known to be technically radioactive, but its half-life is so enormous that it can be treated as non-radioactive, so don't worry about taking pink bismuth for an upset stomach. The chemical toxicity of heavy metals like lead and uranium should concern people more than any radioactivity. Lead causes irreversible brain damage at fairly low blood concentrations. Bismuth has remarkably low toxicity in contrast, and many of the same desirable properties, so it is seeing more use as a substitute for things like lead: here, substitution of something technically radioactive actually makes you safer. --47.146.63.87 (talk) 23:13, 21 March 2019 (UTC)