Dear friends, in the next few minutes
we will discuss some implications of implant dentistry
in the posterior maxilla.
As we have seen previously, the extraction of teeth
is a catalyst to a chain reaction that leads to
compromise of the alveolar bone and the soft tissues.
In the case of the posterior maxilla, we have two different phenomena
which together can significantly
reduce the availability of bone for dental implants.
The first, is the reduction of the height and width
of the alveolar ridge which occurs normally
after every extraction.
The second, is what we call the pneumatisation of the sinus.
Is there a balloon in the sinus?
Not really, but then again I like the idea!
Let's try to imagine a bit of the anatomy.
Sinus is lined with a very thin membrane,
the sinus mucosa or Schneiderian membrane.
And just like a balloon this membrane
has only one opening at the highest point, the Ostium,
where it communicates with the nose.
If you think about it, the sinus is
under mild but constant pressure changes as long as you live.
Every breath you take in,
creates negative pressure in the sinus cavity
and every time you breathe out,
the pressure becomes positive.
If the sinus membrane wasn't firmly attached on the bone
what we could see with every breath
would resemble the idea of the balloon.
And if you prefer the real thing to the animations,
take a look at this clip.
The membrane detached from the sinus walls
during augmentation surgery
as it moves following the breathing of the patient.
This is actually an elderly patient
with a thick fibrous membrane.
Sometimes the move can be much more spectacular,
especially in younger patients
with thinner and more sensitive membranes, as in this case.
So maybe the balloon metaphor
might be not so far from the reality after all!
The dynamics of the anatomy might give you a good idea
of the complexity of this area
when it comes to implant surgery.
The constant pressure changes
transferred to the mechanosensitive bone
through the sinus membrane
might contribute to the gradual expansion
of the sinus after teeth are lost.
Regardless of the cause,
a recent radiographic study estimated that
approximately 60% of the bone loss height
is attributed to the marginal alveolar ridge reduction,
while about 35% is due to the sinus pneumatisation.
This means that we often have to augment
both the sinus as well as the alveolar ridge,
in order to place the implants
in the proper prosthetic position.
Does the extent of the pneumatisation correlate with the amount of the missing teeth?
A clear answer to this is not easy
based on the existing research.
In one of our three dimensional radiographic studies
we found that the bucco-lingual width
of the residual alveolar ridge was related
to the presence or absence of adjacent teeth,
but not the height.
A good predictor of reduced bone height
appeared to be periodontal bone loss at the existing teeth
and evidence of abnormal lining of the sinus membrane.
Often, we will see that the presence of a single posterior tooth
appears to prevent major sinus expansion,
but other times,
even the loss of one single tooth
can provoke a significant downgrowth of the sinus.
What appears to be significant predictive factor
is the relation of the roots of the posterior teeth
to the actual floor of the sinus
and this is something that is not easy to evaluate
on the basis of two-dimensional radiographs.
Very often, the apical portion of the roots of the molars
are in very close proximity
or even intermingled with the sinus floor.
In such cases, extraction of the teeth
can actually lead to much faster pneumatisation of the sinus.
Consequently, in order to address
the challenges of this compromised anatomy,
sinus floor elevation and sinus augmentation procedures have been proposed
with the most established being
the Transalveolar or Osteotome technique
and the Lateral window sinus floor elevation.
Each of these approaches will have many modifications
and also specific indications and contraindications.
In general, 8 mm or more of bone height should be enough
for the placement of an implant without engaging the sinus.
Cases where we have 6 to 7 mm
combined with a flat sinus floor are well indicated
for the Osteotome technique.
Similarly, we can treat cases with 4 to 5 mm
and a flat sinus floor with osteotome,
only here, often a grafting material is recommended.
Cases with an oblique sinus floor
or with less than 4 mm of residual bone height
are typically treated with the lateral window approach.
In the case of the lateral window,
implants can be placed simultaneously with the sinus elevation
if the residual bone height is enough
to offer primary stability.
Otherwise, a two-stage procedure is followed
and implants are placed six to nine months
after the sinus augmentation.