Biomedical Engineering Reference
In-Depth Information
GBR developed out of earlier attempts to
regenerate the supporting tissues of the peri-
odontium, that is, guided tissue regeneration
(GTR) [
A second limitation is their tendency to be
easily deformed, which may lead to collapse
of the membrane into the wound space. To
minimize this problem, the space under these
membranes is maintained with the use of bone-
grafting materials.
Bone-grafting materials in GBR include
autogenous bone, which is considered the gold
standard, as well as allogenic, xenogenic, and
alloplastic grafting materials. These materials
not only support the barrier membrane, but
also provide osteogenic cells for autogenous
grafting and osteoinductive molecules such as
BMPs. They also constitute an osteoconductive
scaffold that supports the growth of osseous
tissue within the wound space [
]. Both approaches typically
use membrane barriers to control the cellular
repopulation of a maintained wound space [
23
,
24
,
61
6
,
41
]. Cells that repopulate the wound space
control the resulting tissues. In the case of GBR,
the objective is to develop new bone tissue [
,
46
39
,
54
]. Early studies demonstrated that the
osseous healing that occurs in conjunction
with GBR techniques paralleled the healing
within a tooth socket following extraction [
,
55
].
The initial clot that is formed is followed by
granulation tissue with vascular ingrowth,
osteoid tissue formation, and mineralization
that begins on the edges of the wound surface.
For GBR to be successful, clots must be stabi-
lized and the wound space preserved to allow for
cellular and vascular ingrowth and for selective
repopulation by osteogenic cells. Each of these
objectives is addressed by the use of barrier
membranes that serve to defi ne the borders of
the osseous defect, restrict fi brotic tissue forma-
tion, and provide stability for the ensuing clot.
Available biocompatible membranes are either
nonresorbable or resorbable, each condition
having advantages and disadvantages.
Nonresorbable membranes have proven
quite effective at limiting cellular ingrowth but
may require a second surgical procedure for
removal. An additional limitation of nonre-
sorbable membranes is the increased likeli-
hood that soft-tissue complications will arise
during the healing period [
55
].
The use of GBR techniques to augment alveo-
lar bone has proven more successful in lateral
ridge than in vertical ridge augmentation pro-
cedures. The increased intraoral functional
demands on the vertical ridge augmentation
procedures are thought to make it more diffi -
cult to maintain the wound space necessary for
regeneration of the crestal bone [
60
,
68
].
Given these limitations, an alternative tech-
nique that has found increased intraoral appli-
cation is distraction osteogenesis [
63
,
64
]. The
development of intraoral fi xation devices has
made it possible to use distraction osteogenesis
as an alternative to gain vertical ridge height in
the anterior mandible [
14
,
67
]. However, this
procedure is often accompanied by clinical
complications that limit its use [
51
,
52
26
].
]. Typically, GBR
techniques aim to retain the barrier membrane
for at least
63
9.5 Current Trends and
Future Applications
months to allow for optimal
bone growth. Premature loss or degradation of
the membrane may compromise bone forma-
tion or cause loss of the wound space [
4
to
6
]. Non-
resorbable membranes have been modifi ed by
reinforcement with titanium. Titanium rein-
forcement prevents soft-tissue collapse and
thus improves maintenance of the desired
wound space [
65
The application of bone biology to dental
therapy is probably best typifi ed by extending
implant therapy to the treatment of recent
tooth extractions. Often implants can be placed
during the same patient visit at which tooth
extraction was carried out. This is termed
“immediate implant placement.” Although the
advantages, disadvantages, and specifi c meth-
odologies are still under debate, the attempt to
use implant therapy to improve patient care
will undoubtedly lead to greater utilization of
these approaches.
Immediate implant placement developed
directly from GBR techniques to augment bone
].
The decreased likelihood of soft-tissue com-
plications during the healing process is a major
reason for the increased use of resorbable
membranes. These membranes are usually
made from copolymers of polylactide and poly-
glycolide or from collagen. A major concern in
using these membranes is that the barrier
membranes may be resorbed prematurely,
thereby diminishing osseous regeneration [
35
72
].
