Depends why their teeth are ugly.

You betta be a mix of zac efron liam payne justin bieber frank ocean because...........

super janky teeth would probs turn me off tbh
but if they are reasonable i can probably over look it, as far as structure is concerned...colour is different. Yellow filmy teeth *shivers*

I don't think i've ever really encountered a potential partner with really messed up teeth though

I put years of work into having perfect teeth so I have very high expectations of others.

if there's one or two crooked teeth and they're not super white then it'd be fine, but if they're missing teeth, have an extreme over-bite, or yellow teeth than its a deal breaker