Water flosser.

I told my dentist how much I liked my water flosser, and he immediately said "that's fine but it's not very effective, you still need to use regular floss too".

Came to post this. These things are frigging amazing and like $20. Absolutely everyone should have one. Really you can floss and brush and it still gets stuff. I wish they existed when I was younger! Buy one! Thank me later!

On the 'dentists don't really know what they're doing' front, my kid's orthodontist ($$$$) describes himself as a "fencing contractor". Conversely, I got the water flosser tip from an Indonesian dentist who I hired opportunistically on holiday for a clean; he turned up in flip-flops but decanted to bare feet during operating and gave the most sage advice I've ever had in 40+ years of dentists: BUY A WATER FLOSSER. Terimakasih, Doktor!