Why bone goes missing
Alveolar bone exists to hold roots. When a root disappears, the bone that surrounded it loses its purpose and begins to resorb: fastest in the first year after extraction, and then more slowly for the rest of your life. Nobody does anything wrong to cause it; it simply happens.
Other causes stack on top: periodontal disease that had already destroyed bone before the tooth was lost, a long-standing infection, trauma, or the constant pressure of a full denture resting on the gum for years.
In the upper back jaw there is an anatomical factor as well. The maxillary sinus is an air cavity above the molars, and over time it tends to pneumatise — to expand downwards into the bone as it becomes free. That is why this region needs an additional procedure more often than any other.
The types of graft
A graft is not a block that gets screwed in. In most cases it is a particulate material acting as a scaffold for your own bone to grow through, protected by a membrane. The material varies:
- Autograft
- The patient's own bone, harvested from elsewhere in the mouth. It behaves best biologically, but it needs a second surgical site.
- Allograft
- Processed, sterilised human bank bone. It avoids the second surgery and is extensively documented.
- Xenograft
- Of animal origin, usually bovine, treated until only the mineral matrix remains. It resorbs very slowly, which helps hold the volume long term.
- Alloplast
- Synthetic material such as calcium phosphates. No biological origin, useful for patients who prefer to avoid one on principle or belief.
- Guided bone regeneration
- Not a material but a technique: covering the graft with a membrane so that soft tissue, which grows faster, cannot invade the space before bone does.
The sinus lift, specifically
When the height of bone beneath the maxillary sinus is insufficient for an implant, the membrane lining the sinus floor is lifted and the space gained is filled with graft material. There are two approaches.
The crestal approach works through the implant site itself, pushing the sinus floor up by a few millimetres. It is minimally invasive and suits small deficits. The lateral approach opens a window in the outer wall of the upper jaw, allows far more height to be gained, and is a more substantial operation.
Depending on how much bone remains, the implant goes in at the same time or waits for the graft to consolidate. That decision also depends on the stability achieved, and it too is made in theatre.
How long it takes
A graft has to consolidate before it can carry an implant, and that consolidation is measured in months, not weeks. The usual range runs from four to nine months depending on technique, material and how much volume was replaced; only then does the implant osseointegration period begin.
Added together, a case with an extensive graft can run nine to eighteen months from the first surgery to the definitive crown. That is why the first visit puts so much weight on whether a graft will be needed: it changes the calendar more than any other variable.
When the graft is small and done at the same time as the implant, it adds no appreciable time. Both extremes exist, which is why there is no single figure.
Risks, and when it can be avoided
The risks specific to grafting are infection of the material, exposure through the gum, more resorption than expected so the final volume falls short, and — in a sinus lift — perforation of the sinus membrane or subsequent sinusitis. A perforation noticed during surgery is repaired and generally does not change the outcome; an unnoticed one can.
It is also worth knowing that grafting is not always compulsory. There are alternatives that sometimes solve the same problem without replacing bone: shorter or narrower implants where the anatomy allows, tilted implants that seek out the bone that is there, or rethinking the prosthesis so it rests elsewhere. Which one applies depends entirely on what the CT scan shows.
And there are situations beyond what a general implant practice should treat, which are referred to maxillofacial surgery. Saying so in good time is part of the job.
This page is general patient information, written so that you arrive at the practice knowing what to ask. It is not a diagnosis or a treatment recommendation: those can only follow a clinical examination and the appropriate imaging.
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