Inlay augmentation is a
technique used in bone re-building operations, in which the height of
the alveolar ridge remains unchanged.
In the animation you can see how after tooth loss, lack of sufficient
pressure causes bone to recede. Our body is very economical, use it – or
lose it! After a while there is no longer enough bone for an implant,
and the implant would stick out into the maxillary sinus (shown by the
blinking light).
The missing bone is replaced using inlay surgery, in which bone material
is inserted between a patient’s own bone and the maxillary membrane –
this technique is also known as a sinus lift operation. After a few
weeks the bone heals and it is possible to insert an implant.
Another technique is onlay augmentation, in the animation you can see
how the missing bone is replaced using onlay surgery, meaning that the
bone used (coming either from a donor or the patient’s own body, for
example the chin) is screwed onto the desired spot, and the maxillary
ridge is raised. After some weeks the replacement bone has healed and
become attached to the bone and an implant is then possible.
This is the main difference between inlay- and onlay surgery. In inlay
surgery, the height of the alveolar ridge is not changed, in the case of
onlay surgery it is. If there are still teeth left and there is only
some bone and a few teeth missing in the back, then in general it is
better to perform onlay surgery, since this leads to more aesthetically
pleasing results. If there are no more teeth left and the alveolar bones
have receded evenly, then inlay surgery of the sinus lift type is
usually the way to go. Sometimes these two techniques are combined.
As you can see, nowadays there are many different surgical techniques
which can be used to build up jaw-bones. The material used to replace
bone can be either human bone or bone from animals such as cattle or it
can be synthetic.
Human bone heals best, while synthetic materials heal worst. With human
bone, it is possible to use either purified bone from donors – or else
one’s own – by means of a bone transplant.
When using a patient’s own bones, care should be taken to ensure that
the transplanted chunk does not exceed a certain size. The reason for
this is that the transplanted bone contains various cells. Once the
block is removed, the cells in it are cut off from the supply of
nutrients. If a chunk is small, then after transplantation the cells are
once again supplied with nutrients from the side by the process of
diffusion. If the chunk of bone is too big, then diffusion is not
enough, it takes days for new blood vessels to reach the interior. For
the cells inside the chunk this takes too long – the cells die. This
triggers an immune reaction, in which the immune system removes the dead
cells, which in turn leads to bone absorption. This is why larger chunks
of bone are transplanted using the microvascular method, meaning that
the bone is removed along with the supplying vessel which is then
connected to another vessel in the area to which it is transplanted,
which ensures the supply of nutrients to the inside of the transplant.
Microvascular transplants are not usually necessary in dentistry, small
chunks of bone are usually enough – which is also why it is pointless to
spend a lot of money on growing bone chunks using cells in test tubes
under the right conditions, because the moment that the bone is removed
from this „optimum“ incubator – and transferred to a human body, it
already begins to „melt away“ for the above-mentioned reasons. This
method is very interesting and sounds very nice, but it’s also expensive
and pointless.