An implant-supported denture is used when a person doesn't have any teeth in the jaw, but has enough bone in the jaw to support implants. An implant-supported denture has special attachments that snap onto attachments on the implants.
Implant-supported dentures usually are made for the lower jaw because regular dentures tend to be less stable there. Usually, a regular denture made to fit an upper jaw is quite stable on its own and doesn't need the extra support offered by implants. However, you can receive an implant-supported denture in either the upper or lower jaw.
You should remove an implant-supported denture daily to clean the denture and gum area. Just as with regular dentures, you should not sleep with the implant-supported dentures at night. Some people prefer to have fixed (permanent) crown and bridgework in their mouths that can't be removed. Your dentist will consider your particular needs and preferences when suggesting fixed or removable options.