WEBVTT - Why can biting on aluminum foil be painful?

0:00:00.520 --> 0:00:03.840
<v Speaker 1>Welcome to Brainstuff from house stuff works dot com where

0:00:03.840 --> 0:00:15.240
<v Speaker 1>smart Happens. Hi Am Marshall Brain with today's question, why

0:00:15.440 --> 0:00:19.040
<v Speaker 1>is it that biting on aluminum foil can be painful?

0:00:19.760 --> 0:00:23.040
<v Speaker 1>Biting on aluminum foil can be painful, and it's usually

0:00:23.120 --> 0:00:26.000
<v Speaker 1>noticed if you have metal in your mouth from things

0:00:26.079 --> 0:00:30.280
<v Speaker 1>like fillings or crowns. Basically, when you bite on foil,

0:00:30.600 --> 0:00:32.879
<v Speaker 1>you set up a battery in your mouth and the

0:00:32.920 --> 0:00:39.199
<v Speaker 1>electrical current stimulates nerve endings in your tooth that generates pain. Specifically,

0:00:39.240 --> 0:00:42.959
<v Speaker 1>here's what happens. First of all, the pressure from biting

0:00:43.159 --> 0:00:47.199
<v Speaker 1>brings two different metals, in this case aluminum foil and

0:00:47.360 --> 0:00:50.720
<v Speaker 1>mercury in your fillings or gold in your crowns, in

0:00:50.920 --> 0:00:54.680
<v Speaker 1>contact with each other in a moist salty environment. The

0:00:54.760 --> 0:00:58.840
<v Speaker 1>salty environment is provided by your saliva. The two metals

0:00:59.120 --> 0:01:02.600
<v Speaker 1>have an electric chemical potential difference between them, or a

0:01:02.760 --> 0:01:06.800
<v Speaker 1>voltage that gets generated because they're coming into contact with

0:01:06.840 --> 0:01:11.360
<v Speaker 1>each other. The electrons flow from the foil into the tooth,

0:01:11.760 --> 0:01:14.440
<v Speaker 1>so you have this electrical current created by this little

0:01:14.440 --> 0:01:18.080
<v Speaker 1>battery flowing into your tooth. The current gets conducted into

0:01:18.120 --> 0:01:21.360
<v Speaker 1>the tooth's root, usually by the filling or crown, and

0:01:21.400 --> 0:01:24.800
<v Speaker 1>the current sets off nerve impulses in the roots nerve.

0:01:25.400 --> 0:01:28.399
<v Speaker 1>Those nerve impulses go to your brain, and then finally,

0:01:28.440 --> 0:01:32.679
<v Speaker 1>the brain interprets those impulses as pain. The production of

0:01:32.680 --> 0:01:36.640
<v Speaker 1>the electric current between two dissimilar metals like this is

0:01:36.680 --> 0:01:41.640
<v Speaker 1>called the Voltaic effect after Alessandro Volta, who discovered it

0:01:42.280 --> 0:01:45.520
<v Speaker 1>long ago when he was creating early batteries. He made

0:01:45.560 --> 0:01:50.520
<v Speaker 1>them by stacking dissimilar metal discs with blotterer paper soaked

0:01:50.560 --> 0:01:54.080
<v Speaker 1>in salt water between them. This was called a voltaic pile,

0:01:54.640 --> 0:01:57.840
<v Speaker 1>and it was an easy way to create a simple

0:01:57.920 --> 0:02:01.760
<v Speaker 1>and very low power battery. If you have no metal

0:02:01.880 --> 0:02:04.360
<v Speaker 1>dental work in your mouth, you're not going to feel

0:02:04.360 --> 0:02:07.480
<v Speaker 1>this effect. You've got to have these two dissimilar metals

0:02:07.480 --> 0:02:10.320
<v Speaker 1>coming together for you to feel the pain that aluminum

0:02:10.360 --> 0:02:15.680
<v Speaker 1>foil causes. Be sure to check out our new video podcast,

0:02:15.880 --> 0:02:18.760
<v Speaker 1>Stuff from the Future. Join How Staff Work Staff as

0:02:18.800 --> 0:02:22.520
<v Speaker 1>we explore the most promising and perplexing possibilities of tomorrow.

0:02:23.960 --> 0:02:26.680
<v Speaker 1>The How Stuff Works iPhone app has arrived. Download it

0:02:26.720 --> 0:02:28.040
<v Speaker 1>today on iTunes