I have it as well and at this point used the same head for 5 months. There's no visible deterioration and I exceed the recommended brushing time by doing 5 instead of 3 minutes. Why exactly is the head only good for 3 months?

Brushing your teeth for too long can have bad effects on your dental health[1][2]. The heads loose their strength over time and if you replace that with pushing harder, you might also overbrush.

[1]: https://www.colgate.com/en-us/oral-health/brushing-and-floss... [2]: https://riverrundentalspa.com/brush-teeth-too-long/

You probably don't brush correctly: you need to apply sufficient pressure on your teeth so the bristles can scrub the enamel well enough. Or else there is no way your head has no visible deterioration after 5 months at 5 min per brushing.

The toothbrush has an integrated pressure sensor and starts vibrating when you apply too much

Then I don't believe you have no visible deterioration.

The brushes have this sensor for a reason. Too much pressure may harm your gum. The article talks about a ultrasound brush, no pressure required.

It's not only a matter of aesthetics but bacteria etc. Your brush head collects a sh*tload of food waste (which you don't see with your eyes) and remains a bit wet after usage. Perfect substrate for some living organisms. If you have a microscope, feel free to have a closer look.

If you reset it, it's as good as new, right?