When converting characters, make sure that there are no hidden morphs enabled. I found that almost any character using Teen Josie head morphs will f'-up the teeth. You can get around this, if Teen Josie is really necessary, by creating a new morph of the G3 then converting your new morph to G8. It is more work, but it works. There are turorials all over the place in how to create a morph. One caveat, it must be a single slider complete morph, not a control morph that moves a bunch of dials at once. This is only to fix up f'ed-up teeth. Other issues with conversions require other solutions.