I’m not the guy, but I’d like to challange my English by talking about this topic.

I vibe with that. I’ve been trying to learn a new language as well, so let me try and provide you with the kind of direct feedback that I wish more people would give me. Overall your writing is good enough that I would believe you were a native speaker, albeit a sloppy one. To take your writing to the next level, here’s what I’d change:

I brush my teeth on a “when I remember to” or “when it’s really dirty”. so like twice weekly probably.

This can be rephrased slightly into a more natural expression:

I brush my teeth on a “when I remember”/“when it’s really dirty” basis, so like twice weekly probably

Why: Saying that you do something “on a X basis” is a very common pattern for this type of expression. I switched to using “/” instead of “or” here to because this particular pattern is so strongly fixed that we can’t add extra words to it without sounding unnatural. I also combined the sentences together because one single compound sentence is generally more pleasing than two simple ones.

except of a bit of tartar (hopefully correct word, the hard stuff that acumilates and sticks to your teeth)

Yup, that’s exactly the right word. It would have also been acceptable for you to say “gunk”, since “tartar” is a specialized word that not everyone will know.

The scary part is thst the dentists I’ve been to did not say anything about it, which leaves me to think they didn’t even see it, that leaves me again to, what else didn’t they notice?

You’ve made excellent use of the trailing question mark! This is exactly the right tone for what I believe you were going for here, though your verb tenses are a little mixed up. Here’s what I’d change to bring the tenses back into alignment:

The scary part is that the dentists I’ve seen haven’t said anything about it, which leaves me to think they didn’t even see it. It makes me wonder what else they didn’t notice?

Why Part 1: You’ve combined “I’ve been to” (present perfect tense) with “did not say” (past tense) inside of the same clause. Mismatches like this sound quite bad because native speakers have a strong intuition for tense construction. Here the issue is fixed by simply changing the entire clause into the past tense, though we could have just as easily done the opposite and made the whole clause present perfect (i.e.: “the dentists I’ve been to won’t say anything about it”).

Why Part 2: It gets difficult to read sentences when they become this long, so I broke it into two. Note the much shortened second sentence. I did this because English speakers tend to favor a kind of long/short/long/short rythm in speech and writing. Less grammar on “down beats” feels better. It’s a pretty cool trick to use once you get the hang of it, don’t you agree?

The thing that I notice and hints that I should brush is the frequent canker sores (again, let’s hope the right word, little annoying ass white spots that, apears, hurts than dips)

This sentence is actually a really good learning opportunity because it reveals something about English-speaking culture: we hate attributing actions to passive objects. Yes… it’s not technically wrong to say “the things that hint I should brush are canker sores”, but it still feels wrong unless you’re writing poetically. Here’s how I’d write it instead:

When I get frequent canker sores it’s a hint that I should brush.

Why: Canker sores no longer do the hinting. It’s you who gets the canker sores and they merely exist as hints. Alternatively, you could even phrase it like this: “Increasingly frequent canker sores tell me that I should brush”. If we anthropomorphize “canker sores” as actively intelligent beings, we’re allowed to attribute actions to them without falling into the “passive object action” trap. Yes… this stupid language really works like that. We will go so far as to pretend that canker sores are sentient if it means we can blame stuff on them. I am sorry 🙏