Biomedical Engineering Reference
In-Depth Information
volume. Originally, these approaches were
highly dependent upon the methodologies of
GBR, that is, membrane placement with a sub-
merged implant and bone grafting. Recently,
more reliance has been placed on natural bone
healing in the tooth extraction site. The use of
barrier membranes has been questioned, and
grafting into residual defects to overcome
dimensional differences between the implant
and tooth socket has been shown unnecessary,
if the defects are
this does not mean that progress should not
continue toward a more natural result. Such a
result might involve an attachment that pro-
vides a more natural feel and that is able to
adapt better to occlusal forces. One can also
envisage an attachment that better accom-
modates the scalloped architecture of the
gingival tissues and recreates the gingival pap-
illary tissue, thus leading to better long-term
results.
One of the most studied molecules related to
the therapeutics of bone growth is BMP-
2
mm or less (see clinical view
in Fig.
). Howe ve r, it i s s t i l l u nc e r t a i n w he t he r
placement of a dental implant alters the normal
healing pattern. Early studies have indicated
that healing in the tooth socket is not signifi -
cantly affected by implant placement [
9
.
5
2
, one
of over
structurally similar proteins that
make up the transforming growth factor
40
β
(TGF-
is one of several
members of the BMP family that are true dif-
ferentiation factors, capable of triggering the
differentiation of mesenchymal stem cells
(MSCs) into an osteoblastic lineage that leads
to bone formation. The therapeutic effects of
BMP-
β
) superfamily. BMP-
2
].
A second therapeutic approach that has dra-
matically altered current use of dental implant
therapy is maxillary sinus grafting. This pro-
cedure relies on GBR techniques to promote
bone regeneration in the inferior region of the
maxillary sinus. After tooth extraction in the
posterior maxilla, sinus pneumatization fre-
quently extends inferiorly as the alveolar ridge
resorbs superiorly. As a result, the volume of
bone that remains is minimal. This may
severely limit the use of implant therapy. To
correct these defi ciencies in the posterior
maxilla, the sinus is augmented with the aid of
bone grafting. Sinus augmentation for implant
therapy seems to be as successful as implant
placement in native alveolar bone [
2
are concentration-dependent. As cur-
rently used, concentrations of BMP-
2
far exceed
physiologic levels. To maintain high concentra-
tions locally, a carrier is needed and may also
be important to promote regeneration in the
extracellular environment. This ECM may also
provide an appropriate environment for the
response of the progenitor cells to the BMPs.
The need for high concentrations may be
related, in part, to signals or interactions with
other components of the microenvironment.
BMP-
2
]. However,
the specifi c approach taken by the clinician
makes an important difference. For example, a
particulate bone graft provides greater implant
success than does block grafting. Also, implants
with a roughened surface at the osseous inter-
face assure much greater clinical success, as
does the use of a barrier membrane to occlude
the osteotomy.
Functional support becomes truly critical
for tooth replacement in the posterior maxilla
and mandible. Whereas previously there were
clear limitations regarding the use of dental
implants in the maxillary posterior because of
the poor bone quality attributed to maxillary
sinus pneumatization, current technology
makes implant therapy in these regions of the
mouth highly successful and has shortened the
time of healing for osseointegration to
70
2
was used in maxillary sinus grafting
in
patients whose healing response was eval-
uated over a period of
12
]. Bone height
after grafting was assessed by tomography. The
study found a mean gain in bone height of
8
4
months [
7
mm, suffi cient to allow for implant place-
ment in
.
5
11
of the
12
patients, a clearly promis-
ing result.
As discussed earlier, remodeling of the alve-
olar bone following tooth extraction can often
compromise or complicate dental implant
therapy. A recent study of the use of BMP-
2
in
extraction sites found that BMP-
signifi cantly
increased alveolar bone volume following tooth
extraction and that the ability to place dental
endosseous implants was greatly enhanced
[
2
]. BMPs have been utilized in GBR proce-
dures to augment alveolar bone in order to
allow for direct placement of implants into the
dental surface [
28
8
weeks, periods previously thought impossible
[
6
to
].
Carriers that can support the soft tissues
more rigidly are still being sought, usually
to be combined with some type of growth
25
,
34
,
37
,
40
,
50
].
Current therapeutic approaches can create
very nice esthetic and functional results, but
4
,
17
