I don't know about safe implant materials. I'm sure there are many people here that can give you suggestions. I have to have a tooth extracted now and I'm in the process of trying to find a dentist who can do it properly. I'm not planning on having an implant, at least now. I can't afford an implant or a bridge and frankly I just want the tooth out! I believe there needs to be a healing process anyway after an extraction. My dentist who did my Amalgam replacement made a retainer for me so that I can wear it an hour a day and it is supposed to help prevent shifting of my other teeth. I'm going to get the tooth out and try to let my body do some healing before I decide what, if anything, I'm going to do about a replacement. I might just leave a gap. It's my molar so it's not something that can be seen anyway and I'm learning how to chew without it!
Good luck with your dental work. Your babies are lucky you breastfeed!