When a tooth has to be removed and an implant is planned in that position then preservation of the socket is a must. The extraction must be done as gently as possible to preserve the bone, and steps must be taken to ensure maximum bone regeneration.
Socket preservation is usually done if there was an active infection of the lost tooth, or if the lost tooth had multiple roots. Allowing the bone to fill in the socket will allow for the infection to be cleared away, and prevent any unwanted deflection of the implant during placement.
When a tooth is extracted (removed) it leaves a socket.
Under normal circumstances, bone (yellow) will fill in that socket from below. However, soft tissue (red) can also dive down into that same socket. Soft tissue grows faster than bone, and thus limits the amount of bone healing in the socket. If there is insufficient bone you may not be a candidate for implants.
When preserving a site for implants, a membrane (green) is placed at the time of extraction over the socket.
A membrane acts like a shield, or an umbrella over the socket thereby preventing soft tissue from entering the socket. This will allow the bodies own natural regenerative ability to re-grow the bone in the socket.
Generally, in 4 months there has been sufficient healing and you can return for placement of your implant.
If there was damage to the socket, such as from a large infection or damage during the extraction, then bone graft material may need to be used. Since the body need to turn-over this bone graft, the socket must heal for an 8 month period before implants can be placed.