In the USA in the 1800s, a number of patients went to see their dentists with an unusual complaint: their teeth had exploded in their mouths.
Now not to go too layperson on you, but generally speaking, teeth are not known for their explosive capabilities. No country to date, we'd be willing to bet, has ever bombed another using teeth. Yet, in 1817, a reverend in Mercer County, Pennsylvania, began to experience the worst toothache of his life, that "set him wild".
"During his agonies he ran about here and there, in the vain endeavor to obtain some respite; at one time boring his head on the ground like an enraged animal, at another poking it under the corner of the fence, and again going to the spring and plunging his head to the bottom in the cold water; which so alarmed his family that they led him to the cabin and did all in their power to compose him," dentist WH Atkinson wrote in a report in the Dental Cosmos in 1860.
"But all proved unavailing, till, at nine o’clock the next morning, as he was walking the floor in wild delirium, all at once a sharp crack, like a pistol shot, bursting his tooth to fragments, gave him instant relief. At this moment he turned to his wife, and said, 'My pain is all gone.' He went to bed, and slept soundly all that day and most of the succeeding night; after which he was rational and well."
Two other cases were described by the dentist, one in 1830 and another in 1855. Like the reverend, they had a build-up of pain, followed by a sudden sharp pain, an exploded tooth, and instant relief. In one case, the tooth is noted to have "crumbled into pieces".
These were not isolated reports from one dentist who happened to keep his filling material a little too close to his jar of napalm – several other reports from other dentists suggest the phenomenon, though strange, was a real one.
"Just before the explosion took place, the tooth was aching dreadfully, disturbing the harmonical equanimity of every part of her organism to the extent that she at moments was labouring under slight aberrations of mind," dentist J. Phelps Hibler wrote of a patient in 1874.
"All at once without any symptom other than the previous severe aching, the tooth, a right lower first molar, bursted with a concussion and report, that well nigh knocked her over; splitting the tooth directly from the lingual to the buccal surface, and very much shattering the organ otherwise; at the same moment having a horrid sensation traversing the Eustachian tubes, which ended in rendering her quite deaf for a considerable length of time. The whole thing did not occupy but a moment, and the tooth ceased aching at once."
So, what's going on? Were people's teeth just more volatile back then? As the cases dried up around the 1920s, we can't study them directly. However, dentists have proposed theories throughout the years. One early theory was that gas built up within a decaying tooth, before this caused it to explode. Though gas buildup in teeth can happen – e.g. through an incomplete root canal – this would not cause enough pressure to make people's teeth explode in their mouth as described.
A more likely explanation than natural gas buildup due to decay is one proposed by Andrea Sella, Professor of Inorganic Chemistry at University College London. According to Sella, the explosive tooth phenomenon could have been caused by old-fashioned chemicals used to make fillings. In the 1800s, a variety of metals were used to fill cavities, from the inadvisable tin to the even more inadvisable lead. If two different metals were used in the same mouth, it could essentially turn their mouth into a battery.
“Because of the mixture of metals you have in the mouth, there might be spontaneous electrolysis," Sella told the BBC in 2016. "My favored explanation is that if a filling were badly done so that part of the cavity remained, that would mean the possibility of build-up of hydrogen within a tooth.”
The tooth could then either explode due to pressure (still unlikely) or be ignited, say when smoking a cigarette. Unfortunately, we still don't know the exact explanation, as there's no evidence these patients had fillings. Though, as the cases stopped happening, it is presumably to do with an old dental practice, and you don't have to worry about your teeth sitting there in your mouth like time bombs.