Your toothbrush is worn-out!
Why Hacker News recommends it
HN commenters link it for electron micrographs of fresh versus worn bristles when toothbrush wear comes up.
What it is
Ben Krasnow of Applied Science uses a scanning electron microscope to compare new and worn toothbrush bristles. He shows how the microscopic texturing wears down with use.
Recommended by 1 HN commenters across 1 different months, 2023 to 2025.
What Hacker News said
Recommends error503 · 2023-05 · on “Hacking a Philips Sonicare Toothbrush”
Probably depends on which body you are using. In mine it both flashes a tiny LED and does an extra little buzz-buzz buzz-buzz signal with the ultrasonics when you turn it on (or off, can't recall which) when the head has 'expired'. Continues to work fine, though. You might be interested in this YouTube video from Applied Science with electron micrographs of 'new' and 'worn' toothbrush bristles - there is a very marked invisible change that happens: [this video]
Cites mrob · 2024-08 · on “Toothpaste Null-Terminator”
I use an even simpler and more reliable system to avoid running out of toothpaste: brushing with plain water. Evidence suggests that brushing with toothpaste (called "dentifrice" in scientific papers) does not remove any more plaque than brushing without it. Here's a systematic review from 2016: >Does dentifrice use help to remove plaque? A systematic review [LINK] "The cumulative evidence for this systematic review demonstrates that there is moderate certainty that toothbrushing with a dentifrice does not provide an added effect for the mechanical removal of dental plaque." However, plaque removal is not the only purported function of toothpaste. It can also serve as a fluoride delivery sys
Cites plausibility · 2024-11 · on “Ask HN: Life-changing purchases since 2020? (Under $100 and under $1000)”
The usual problem with toothbrush bristles is they become microscopically worn down, so they don't scrape off plaque as effectively. Even if you can't see the problem, it might not be working as well as a fresh head will. You can find electron microscope scans of fresh toothbrushes and worn ones in this[0] Applied Science YouTube video. [0]: [this video]
Cites mrob · 2025-04 · on “Toothpaste widely contaminated with lead and other metals, US research finds”
Something else you could send: >Does dentifrice use help to remove plaque? A systematic review [LINK] "The cumulative evidence for this systematic review demonstrates that there is moderate certainty that toothbrushing with a dentifrice does not provide an added effect for the mechanical removal of dental plaque." I also don't use toothpaste. However, I do replace my toothbrush regularly (every 3 months, which I believe most dentists recommend). Toothbrushes have microscopic texturing to help them clean, which wears out with use. Here's a video showing it under an electron microscope: [this video] A fresh toothbrush cleans noticeably better than a worn one. I think this is much more important tha