You mean interdentals? They exist in Mapudungun, a language in South America, but I'm assuming the reason they're so rare is because they're scarcely distinguishable from dentals.

No, I mean bidentals. Clasp your teeth and aspirate.

You know, bidentals are kind of easy and the sound like sfh.

Yeah. That's what I mean. Why are they not used in natural languages?

Because they sound stupid.

Lol. That sounds really linguistical (hint of sarcasm).

Alright, the real reason is probably because they don't contrast well with other sounds. But I'm not a phonologist so this is just an informed guess.

Do find bidentals easy to say right before a vowel? I can't do it at will without keeping my teeth clasped. I find it quite a bit of work, as opposed to a more simple sound, like [t].

Hmm, I never found them that hard, only a little awkward. I put them in my auxlang thinking they were fine, but…

I heard somewhere that there was some sort of bidental in a NW Caucasian language...

Can anybody clarify?