The One With Ross's Teeth - S6-E8
Monica: What happened to your teeth?
Ross: I whitened them.
Chandler: Really?
Ross: Yeah, what... What do you think?
Monica: Well, uh, I think I shouldn't look directly at them.
Ross: Come on, seriously.
Monica: Ross, they're really, really, really white!
Chandler: Yeah, what was wrong with your old... Human teeth?
Ross: Well, I did leave the gel on a little longer than it said to.
Monica: How much longer?
Ross: Uh, uh... A day.
Monica: Ross, you know that tonight is your date with Hillary?
Ross: I know! That's why I did it! Come on, are they really that bad?
Chandler: No. No, no, no, you'll be fine. Hilary's blind, right?
Monica: She will be after tonight.
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.