Teeth whitening strips honestly feels like a cheat code to me. Do u know other "frugal" tips?

I have ADHD and BPD and because of that I often neglected my body, including my teeth. They were always yellowish and had this dental plaque/tartar(I am not a native speaker, in my language we use the same word for it) on them. I used to clean this dental plaque every time when I went to the dentist and had my teeth professionally whitened at the dentist office once, when I was a teenager.

Of course it was ridiculously expensive and everyone told me, I won't make a huge difference myself(I think we all had this episode in our life, when we tried banana peel for it). So i bought it, without much expectations. And what do u mean, my dental plaque is gone and they are already whiter after just 7 days? I spent just above 10 euros for it, while dentists easily took hundreds for similar effect. I am so fricking happy.