I've heard the story that at higher outputs (250,000 watts and up) than the traditional 50,000-watt "clear channel" stations, dental fillings became receivers. Here's someone who reports experiencing such an occurrence:
Your wifi, your cellphone, your Bluetooth, all have antennas buried in
them. But at 800 or 1850 or 1900 or 2450 Mhz, their wavelengths are
VERY short, a few cm of a metal strip against the plastic case under
your hand. HF antennas at much lower frequencies must be longer, much
longer. Here's a proper HF transmitting antenna:
It's about 400M high for reference, but we can't fit it on the boat!
It radiated to Europe for 50 years American propaganda, mostly for
Russians. The transmitter was from 250,000 to 1,000,000 watts. I've
been there when it was on the air. Your tooth fillings talk to you...
Here's the antenna in question:
Maybe he's exaggerating, maybe not. Here's more testimony from the Geophysical Institute at the University of Alaska:
According to Robert Hunsucker, a professor emeritus at the Geophysical Institute with the University of Alaska Fairbanks, my phone isn't that complicated, and neither is a receiver circuit. A receiver is so simple, Hunsucker said, that anything from a phone to a person's mouth can act as one ... Hunsucker said the problem can sometimes be cured with a radio-frequency filter that can be attached to the phone line. He also said that if the radio signal is very strong, a filter might not be enough.
Such is the extremely rare case when a person's mouth acts as a receiver. The electrical conductivity of the human body can act as an antenna. A metallic filling in a tooth, reacting just so with saliva, can act as a semiconductor to detect the audio signal. The speaker in this case could be anything that vibrates within the mouth enough to produce noise, such as bridgework or maybe a loose filling. [Emphasis added.]
He says it's extremely rare, but he also describes how it could happen. Failure to reproduce the case by Mythbusters shouldn't hold any water in that case. A thing may be rare and difficult to reproduce, yet still happen.
Edit to add a further account from a seemingly credible source:
It's real. I attended a Field Day setup a few years ago, staged by the Westside Amateur Radio Club in Los Angeles. They had one of their stations inside a trailer, and the radio had an automatic antenna tuner. Well, SOMEBODY didn't ground the thing right. I was inside the shack about 5' from the radio when the op said, "Well, 15 meters is dead; let's tune it up on 20." He changed bands and hit the deadly little "Automatic Tune" button. The radio began buzzing as the tuner went to work. Also, I let out a scream as one of my teeth with a nice filling in it suddenly felt like a dentist was drilling in it with NO anesthetic! I RAN from that trailer uttering obscenities and the pain vanished as soon as I got clear of the thing. Needless to say I didn't hang around that particular shack much during the rest of the contest.
I am persuaded by the proximity argument. Since electromagnetic radiation diminishes proportional to the square of the distance, it is credible that running away would decrease the effect. If he was standing five feet away from the transmitter to start, ten feet would reduce the effect to 25%, 20 feet to 6.25%, etc.