It's one of the more complicated questions to answer to be honest.
Inbreeding won't introduce bad genes - but it will increase the chance of expressing any that are there already.
So a single generation of line breeding is possibly going to be ok but you have to be on the lookout for signs that it wasn't. That's the most important point to bear in mind with thinking about extending it to yet another generation. The safest route would to be exchange bloodlines with another breeder if possible. Killer pieds are not so rare as to make that a hard task and ( if done at the start of the process ) it may even save you a few years on the way to your dream clutch.
del