Biomedical Engineering Reference
In-Depth Information
One investigation found no benefi t of immedi-
ate implant placement in the extraction site.
The levels of bone resorption were not altered
by the presence of the dental implant [
The formation of all three tissues is impor-
tant, because the connective tissue fi bers of the
periodontal ligament insert into both the
cementum and the bone tissue. Regeneration
must therefore include tissue formation that is
coordinated and involves all components of the
periodontium. Two signifi cant complicating
factors are that tissue formation must occur in
the presence of tooth mobility and the constant
challenge from plaque bacteria, since plaque
formation is both instant and continuous. Sali-
vary proteins are deposited rapidly on the
cleaned surfaces, and bacteria immediately
adhere to what is called the acquired pellicle.
With continued growth of the microbial fl ora,
plaque is formed.
The tissues of the periodontium (bone, peri-
odontal ligament, cementum, and gingiva)
grow at different rates. This can complicate
periodontal regeneration, because coordinated
growth is required. In fact, the expected
outcome for surgical procedures where only
scaling and root planing are performed is the
formation of a so-called long junctional epithe-
lium, where the epithelium from the gingiva
proliferates along the diseased root surface,
and no bone, periodontal ligament, or cemen-
tum is formed. For this reason, therapies have
been devised to inhibit the epithelial prolifera-
tion and to favor the formation of the bone,
periodontal ligament, and cementum. Because
the growth of some tissues is favored over that
of other tissues, the term applied to these strat-
egies is “guided tissue regeneration” (GTR), a
term reserved for the formation of new peri-
odontal tissue.
In the past, some type of barrier membrane
was used to promote preferential growth of
selected tissues [
]. In
contrast, the use of xenogenic grafting of the
extraction site may to some extent limit
the dimensional changes associated with the
osseous healing [
2
]. Both of these approaches
are recent, and experience with them is limited.
It is hoped that the limitations and benefi ts of
these approaches will become known.
In summary, bone loss around teeth or bone
loss after teeth have been removed can present
major challenges for dental rehabilitation. Peri-
odontists have focused on restoring the bone
around the teeth, and virtually all dentists are
involved with dental implants (either in the
surgical placement of the endosseous screw or
in the tooth replacement on top of the screw).
In what follows we will focus on the techniques
and strategies that enhance bone formation
around teeth and in areas where teeth are
missing and on bone formation prior to and at
the time of dental implant placement.
12
9.2 Bone Formation
Around Teeth
Periodontal disease results in the loss of peri-
odontal ligament and bone adjacent to the
tooth. Dental plaque adheres to the side of the
tooth, and if the connective tissue attachment
to the tooth is lost, a periodontal pocket forms.
The bacteria associated with these periodontal
pockets change from a largely aerobic to a
largely anaerobic fl ora, one considered to be
pathogenic. Over time, the plaque becomes cal-
cifi ed and is termed calculus. Calculus forms
along the root surface deep into the pocket and
periodontal tissues. Bone loss associated with
periodontal pocket formation may involve only
the tooth with the pocket and result in vertical
bone loss adjacent to the affected tooth. Alter-
natively, bone loss can also involve the adjacent
tooth and lead to horizontal bone loss between
teeth. In either case, the optimum choice of
treatment would be to remove the plaque and
calculus on the surface of the tooth root and
regenerate the lost bone, the periodontal liga-
ment, and the cementum on the affected tooth
root surface.
]. The rationale is that if the
epithelium is excluded, the slower-growing
periodontal ligament cells and the bone and
cementum cells will fi ll the defect and regener-
ate the periodontium (Fig.
44
). This was fi rst
demonstrated with a membrane fi lter placed
around a mandibular anterior tooth. A nonre-
sorbable expanded polytetrafl uoroethylene
membrane was manufactured and used as GTR
procedures gained popularity. However, in
9
.
2
40
%
to
% of the procedures, the gingival tissues
over the top of the membrane receded, and the
membrane became exposed to the oral cavity
and contaminated with bacteria. As a result,
tissue regeneration was compromised. This,
and the fact that a second surgical procedure
60
