First, you need to investigate whether it's the IMPLANT (supporting post in bone) or the CROWN (cap on top of the implant) that broke. If the crown broke off, that's easy to replace. The old crown is removed and a new cap is replaced. You will have to pay for the crown. On the other hand, if the implant itself broke, that's more complicated. This now means that the cap and implant have to be removed, most likely bone grafted int the socket and you will have to wait about 4-6 months for the ridge of the jaw to heal before re-implanting another implant post. Again, you will likely have to pay for the surgery although the companies that make the implants will warranty the parts for 10 PLUS years nowadays. That should save you a couple hundred dollars. Your dentist will receive a replacement implant and not charge you for the material cost. Let's face it, who can guarantee anything for 5 years of more? Understandably if the crown or implant broke off in the first couple years, I would say you should have the cost of re-doing it waived. But after five years of heavy wear and tearing, chewing and biting, it's reasonable to have to pay for re-treatment.