@goatsarah my dentist's advice was (paraphrased) that my gums and jaw are crap, and I'd lose implants like the several teeth I've lost. (Teeth themselves are good, no fillings ever, but that doesn't really help.) The remaining ones seem more secure though, gums have improved a lot.
@armb there are things they can do about the bone. I needed bone regeneration because it was 4 years since the tooth was pulled. My surgeon specialises in it, and the X-rays when he put the implant in (covered over with gum) and then 4 months later, were quite different. The first showed an implant protruding into the soft tissue between the jaw and sinus, barely held in place. The second showed the same implant utterly surrounded by brand new bone.
It might be worth talking to someone who specialises in it. We get a lot of dental tourism here in the Algarve because it’s cheaper but you’re still getting top notch EU trained doctors and surgeons (mine studied in London and spent the start of his career doing surgery for the NHS before returning home to Portugal and a decent climate).