Bone grafting is a procedure where the dentist place and add bone graft or bone-like material to the jaw bone so that it will grow and fuse with the existing jaw bone within few months.
After tooth extraction, the bone undergo absorption which leads to loss of the bone height. Dental implants must have enough bone to support them in order to hold implant for long period of time.
If the bone wasn't long enough, wide enough or hard enough you will need procedure to add bone to your jaw.
