You are delusional my friend. Guess what Einstein? Ive had a bone graft and implants already and they both failed. Are you seriously naive enough to think back to back 17 year bridges is a good average?? Boy are you ever in for a rude awakening. The average lifespan of one bridge is 10 years, not 17. I had a bridge for 20 years and it was in tatters at the end. My second bridge lasted 4 years before it failed. You will be lucky if you get 7 years out of the second bridge because your roots will not be able to handle the stress of another bridge, let alone a bone graft and implants. I assume this is in the front of your mouth which means even further complications. There are no guarantees about anything, but I can promise you after 25 years of fixed bridges, bone grafts and implants you are going to develop multiple root conditions. Nevermind the astronomical costs and very high likelihood of problems. A partial denture is in your future whether you choose to accept it or not. DESTROYING YOUR NATURAL TEETH IS NEVER A GOOD OPTION!