This question is very frequently asked, and it is difficult to answer. The guarantees assumed are a little misleading, so please read carefully!
Dental implants come with a manufacturers guarantee of 5 years, 10 years, and lifetime guarantee. Does this mean that that implant is likely to function for 5 or 10 years? It does not.
The manufacturers guarantee simply means that the dental implant will be guaranteed against structural failures resulting from manufacturing errors. It is basically saying that if any structural errors are in the dental implant, they should become apparent within 5 or 10 years, or never. This does not, for instance, mean that if you have been using your dental implants to chew up rocks, that the manufacturer will refund your dental implant for 5 years, as any problems you may experience chewing rocks is not a result from any structural inequity on the part of the dental implant. Also, if you only brush your teeth once a week, and you get an infection and the implant does not integrate and the implantation site rejects the implant, the manufacturer will not refund your dental implant or send you a new one, as this constitutes a problem that is not with the dental implant.
As for the actual life of a dental implant, they usually last for the rest of your life. If implanted properly, the dental implant should be snug and air free inside of your bone, which forms a layer around it, and as such, nothing will really touch it, and the dental implant should stay intact.