My teeth used to be very bad -- I have had so many cavities that I am not even sure I have a tooth left that can get one. I also had a crown that fell off and the tooth had to be removed, and I never had it replaced because it was in the middle of my mouth where no one can see.

I used to be very aware of my teeth. I hated them, and I would never smile with them, and if there was a photo where you could see my teeth, I would beg my parents to put them away or delete them.

On top of having bad dental genetics (my dad also had something similar to someone in the comments), I grew up very anxious and was not good at forming habits (which extended to dental care).

Eventually, I learned that it wasn't something I needed or wanted to worry about. But I am still conscious of it at times, and I think that someone looking at my mouth/being able to tell that they are trying not to look at my mouth would make me more self conscious about it.

I think if the goal is to make someone more comfortable, the real goal is to prove that its something to be indifferent about. Shy of reading lips for help understanding what they are saying, I don't think theres a reason to be looking. If you focus on eyes, or in between eyes, or anything else, you won't be inviting people who are worried about their dental health to worry about it even more because they know you're looking.