Somewhere in the United States patent record sits a blueprint for a fake tooth with a power plant inside it.

Two engineers at the headset maker Plantronics, Thomas Trumbull and Timothy Johnston, filed Jaw powered electric generator in May 2012 and had it granted three years later. Their design splits an artificial tooth into two pieces. One is anchored to the jaw, the other is free to shift by a fraction of a millimetre, and a piezoelectric element sits in the gap between them. Biting squeezes the element, and that pressure becomes current, tidied by a rectifier circuit and stored in a tiny battery.

Plantronics built Bluetooth headsets, so the motive barely needs explaining. Gadgets keep shrinking and keep needing a plug, and the patent’s own background section grumbles about people hauling spare batteries and adapters. A tooth that quietly banks energy at lunch solves that in the most literal way available.

How pressure turns into power

Piezoelectricity takes its name from the Greek for pressing. Certain ceramics and crystals have lopsided internal structures that shift when squashed, pushing positive charge to one face and negative to the other. Ease off and it reverses. Same trick as the click in a barbecue igniter.

A jaw is a promising place to try this. It closes hundreds of times during a meal, with real force behind it, and none of that effort currently does anything except break down food.

Why the numbers disappoint

“The power level we achieved is hardly sufficient,” Aidin Delnavaz, who co-built the closest thing to a working version, told New Atlas. He and Jérémie Voix of Montreal’s École de technologie supérieure wired piezoelectric fibre composite into a helmet chin strap and had volunteers chew gum, a method detailed in a paper published in Smart Materials and Structures. Their rig produced around 10 microwatts in normal use and 18 at its absolute best.

Set that against the ceiling. Average mechanical power available from chewing runs to roughly seven milliwatts, so the strap was capturing a fraction of a percent of what a working jaw puts out.

Eighteen microwatts will not charge a phone, or a watch, or anything with a screen.

Delnavaz’s own fix, in comments released by IOP Publishing, was brute force: stack 20 layers of the composite, six millimetres thick, enough to run a 200-microwatt hearing protector.

The version that made it into a lab

Chew power works better once the ambition shrinks to something that never leaves the mouth. Geelsu Hwang at the University of Pennsylvania School of Dental Medicine has been building a crown out of dental resin loaded with barium titanate nanoparticles, work outlined by Penn Today. Chewing and toothbrushing flex the particles, and the charge feeds a ring of near-infrared micro-LEDs at the base of the crown. That light treats the gum tissue that so often turns inflamed and costs patients their implant.

Hwang picked up a $2.6 million grant from the National Institutes of Health to test the antibacterial side of it and move toward implants in minipigs.

A tooth that reports back

Clamp down with one of these implants, and the tooth feels it too. Researchers at Huazhong University of Science and Technology 3D-printed an implant with a piezoelectric core of barium calcium zirconate under a ceramic crown, turning biting force into an electrical signal the jaw nerves carry to the brain. Conventional implants feel nothing, which is why people wearing them tend to bite too hard and wreck the teeth on either side.

Twenty-three volunteers at the university hospital tried it. As reported by Advanced Science News, about 90 percent said their chewing sensation had returned. That is one small trial from one team, published this year in Advanced Science, not a settled result.

What happened to the patent

Trumbull and Johnston’s jaw generator is now listed as expired for unpaid maintenance fees. Nobody thought it worth the renewal cheque, which sounds like failure and reads more like a correction. Bite energy was never going to escape the mouth and charge the things in your pocket. It stays where it is generated, keeping a light on under the gum line, or telling a brain how hard it just crunched an almond.