Interesting thread.
I remember as a child my mother giving me lemon juice, salt and bicarb - eek!
Costco sell kits for tooth whitening (Smile brand?), but having checked the reviews discovered that the ingredients do your teeth no favours, so stayed clear.
Following over a year of dental work - implants, replacing split fillings etc - I have recently invested in having moulds made by my dentist, and was given 4 syringes of 16% Carbamide Peroxide gel (there are weaker formulations especially for those with sensitive teeth).
The brand is White Dental Beauty, Novon enhanced formula (whatever that means).
Instructions were to floss and clean teeth then apply the gel in amounts no bigger than a grain of rice at the bottom of the mould.
Any more than this will spill over onto gums and sting, so a cotton bud is needed to clean up. I quickly learned that less is better; plus you can just target the teeth that need most attention.
Wear for at least 2 hrs. I tend to pop the moulds in last thing at night then on waking, I clean my teeth and the moulds, job done for a month. I used it for two weeks initially and was amazed at the control it offered - I did not end up with artificially white teeth, but just fresher and cleaner.
Easy peasy!
It did a super job of lifting the tea stains ( I drink Matcha and green tea) and although it wasn't supposed to, cleaned up the veneers too.
I do have sensitive teeth but was advised to keep using the one recommended for me by the dentist, Biomin - which has been a game changer. It is so effective I would never go back to anything else.