Dental Implants are designed to last a lifetime. Grade A Implants should be manufactured from 100% titanium. Titanium is very strong and the body accepts this material in almost all cases. More information about the History of Dental Implants can be found here: http://www.dentalcentreturkey.com/history-of-the-dental-implant/
In some cases Implant manufacturers are giving a lifetime guarantee and any high quality Implant manufacture will give a 10-20 year guarantee. The guarantee is for the Implant itself. There is a chance that after 30-40 years in the body the Implant may need to be replaced if the patient has severe bone loss the Implant may be lost or if the patient has severe gum disease. The overall oral health of the patient is very important.
Make no mistake, Implants are a long term solution. Dental Bridges that are cemented to teeth either side of the gap are expected to last 10-15 years. Dental Implants are a solution that will last the longest period of time and if oral hygiene is good they will last you a lifetime.