Tobias K. Boehm, DDS, PhD, MBA, PC (7/13/2024)
“I had a bone graft done. Why do I need another one?” This is a question that often comes up during my consultations with patients who wish to have dental implants placed. Generally, what happens is that they had a tooth removed some time ago, the area has healed and now they want a tooth replaced with a dental implant. However, during the exam I point out that the tissue in this area has diminished in width and x-ray images show bone loss as shown below.
Lost ridge width after extraction
(https://commons.wikimedia.org/wiki/File:Basicimplant_preop_ridge.jpg, Coronation Dental Group, CC 3.0 license)
I then typically recommend a bone graft to regain the lost tissues, and it is then when patients typically tell me that they had a bone graft placed when the tooth was removed. Patients often are questioning me then why they need another bone graft if they already had one done, and sometimes they are upset because they have been told that the original bone graft would prevent needing a bone graft in the future.
So what happened?
There are several reasons why a bone graft may be needed despite already having had a bone graft placed:
Ridge preservation bone grafts reduce, but not prevent bone loss after tooth removal
Generally, some bone loss and tissue loss occurs during normal healing after tooth removal regardless of grafting (1). The mouth is adapted to heal quickly after injury, and that means that healing processes after tooth removal are aimed at closing the wound and not preserving bone. The fastest way for the body to heal a tooth socket after tooth removal is to destroy some bone at the tip of the tooth socket, and let the soft tissue collapse and grow into the socket for fastest closure.
Bone grafting done for the purpose of ridge preservation on average just reduces the amount of bone loss after tooth removal. Presence of graft materials prevents soft tissue from growing into the tooth socket and allow the slower growing bone tissue to fill the socket instead. Dentists generally recommend bone grafting at the time of tooth removal for ridge preservation as this on average results in about 0.5-1 mm of preserved bone height and 1-2mm of preserved bone width compared to basic tooth removal (1). While small, this preserved bone can mean the difference between needing additional bone grafting, or being able to place an implant at all.
Some sites have narrow bone to begin with
Generally, bone supporting front teeth is very thin towards the lips, sometimes no thicker than a sheet of paper or absent altogether. This type of bone can be broken off easily during tooth removal. Thin bone also lacks its own blood supply and may die off when it exposed during surgery. Since it is thin, it is also easily removed by bone-resorbing cells (osteoclasts) during normal healing. All of these factors favor severe bone loss during healing regardless of grafting, and often result in a site that is too narrow for implant placement. Yet, bone grafting may still be beneficial and a skilled surgeon may be able to prevent severe bone loss in these cases.
Thin bone overlying upper front teeth (Dr. Boehm, 2020)
Severely damaged bone is unlikely to grow back
Sometimes, severe gum disease, root canal infections, mouth injury and damage during tooth removal result in damaged tissue and a tooth socket shape that is unlikely to support regrowth of bone. Severe infections can result in scarred bone lacking blood vessels and bone progenitor cells that can support growth of new bone.
The shape of the socket after tooth removal matters as well. A healthy, normal tooth socket after tooth removal is similar to a box, with four walls and a deep floor to hold in materials. Gum disease and root canal infections destroy bone around teeth, which is like removing the sides of a box. The more sides of the box are missing, the less it can hold. For a tooth socket, that means that a socket with missing bone walls is less likely to hold bone graft materials and support regrowth of tissue.
Bone level x-ray images before and after tooth removal (Dr. Boehm)
Ridge preservation does not address pre-existing bone defects
Sometimes, jaw bone may have grown in a way to be thinner than average, or there are concavities in the jaw bone just outside of the tooth-supporting bone. Teeth may be shorter than average, resulting in shorter tooth-supporting bone and smaller jaws. Unusually curved teeth or tooth shapes may come with reduced jaw bone. Maxillary sinuses may be unusually large and envelop the root tips of upper molars and premolars. In all those circumstances, removing teeth may result in shorter than usual bone or bone concavities.
Since ridge preservation only places bone graft materials into the tooth socket, it usually does not address the before-mentioned bone defects.
Since implants and teeth have different requirements on the amount of supporting bone, all these circumstances may require additional bone grafting in the form of ridge augmentation or sinus augmentation.
A similar problem can occur with individuals who had strongly inclined teeth, tooth crowding or a very convex facial profile. In these cases, the jaw bone may have pronounced concavities or the jaw bone shape may not align with the position where implants need to be.
Long term bone loss after tooth removal
The only purpose of tooth-bearing jawbone is to support teeth, and after teeth are lost, the body will slowly remove jawbone as it is not being used. This happens regardless of bone grafting, and if bone grafting was done long time ago, this gradual bone loss may be significant enough to require additional bone grafting or even prevent implant placement. In my experience, this amount of bone loss tends to become a problem for therapy if implant therapy is delayed for at least five years after tooth removal. While this is bothersome for anyone who had a bone graft placed after tooth removal, the bone loss is likely worse for people who simply had teeth removed without ridge preservation bone grafts.
References
(1) Pickert FN, Spalthoff S, Gellrich NC, Blaya Tárraga JA. Cone-beam computed tomographic evaluation of dimensional hard tissue changes following alveolar ridge preservation techniques of different bone substitutes: a systematic review and meta-analysis. J Periodontal Implant Sci. 2022 Feb;52(1):3-27. doi: 10.5051/jpis.2007100355. PMID: 35187870; PMCID: PMC8860760.