[crazygringo]

Bath/bathe and breath/breathe also change their vowels, so they wouldn't count.

But teeth/teethe is another good one! As for wreathe, that too... I didn't even know that was a word. :)

[pwinnski]

Off the top of my head, I think it's a verb form: to surround something. Smoke wreathed around the altar as the chime rang through the hall.

[dahart]

Ah, right. Wreathe: me neither.