I believe there several reasons such as not using antibiotics to flush out the infection before and after procedure, bad choice of drilling and alignment, using too big of a crown causing occlusion problems. I could give you even more reasons but the problem is that the dentist who referredthe periodontist sticks up for him like he is a saint and says that these things do happen you know.
I think alot would have to do with WHY the implant failed.
Do you know why your implant failed?
Gellia