Can serous otitis cause teeth pain?

Otitis: No, however an infection and being "run down" can allow another infection to surface acutely, like a tooth abscess. Most likely a bad coincidence.

Yes: And infected teeth may cause ear pain too.

Not likely: The external part of your ear is innervated by auriculo temporal cranial nerve v which shares the same ganglion as the nerve that innervate your teeth (v2 and v3), but the inner pat of the ear does not share the same nerve pathway. However, if you have some offshoots from ear that travel with v2 or v3, potentially the tooth can hurt when your ear hurts.