[smackfu]

I’d assume most people at least change it when they get a free one at their six month cleaning.

[vuln]

Looks like you're also assuming most people can afford cleanings twice a year...

[ghaff]

A dentist cleaning without dental insurance is $100 or less in the US. Yes, I realize there are people for whom that is a non-trivial expense. The overlap between that demographic and those getting some startup toothbrush service is, I would assume, nil.

[RightMillennial]

If you're a consumer of niche subscriptions, I don't think a dentist appointment every 6 months is going to be a financial burden.