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.
Nikos MattheosClinical Associate Professor in Implant Dentistry
