Island,
The tooth part is really just like a Crown with a threaded insert (There may be different attachment styles now). This (tooth) piece can be replaced. It is subject to chipping and cracking just like a conventional porcelain crown, so Lifetime may or may not be accurate.
And hopefully in 20 years they'll be able to "grow" teeth for restoration. I heard they were pretty close to this...who knows. Just like an innoculation for preventing cavities.
Oh, I think the cracking was my jaw bone.
