Biomedical Engineering Reference
In-Depth Information
increase blood fl ow [
] and oxygen levels in
bone, as well as activate osteoclasts, a process
that will stimulate cell signaling, differentia-
tion, and, subsequently, remodeling and new
bone formation. Conventionally, tooth move-
ment is used to align tooth position by remod-
eling the bone surrounding the roots of the
teeth. More recently, these principles have been
used to regenerate large amounts of bone for
replacement of periodontal defects and atro-
phied ridges [
65
Fibrous Tissue
+
Fibrous Cartilage
0
31
].
-
Osseous Tissue
8.3.3 Growth Modification
Dental functional appliances (e.g., the Herbst
appliance) have been used as bite-jumping
devices to modify the growth of the jaw bones.
The movement of the jaw, which is guided by
these devices, modifi es the stress/strain fi elds
of the mandibular condyle and glenoid fossa.
As a result, the growth of the mandible and the
maxilla can be redirected to correct abnormal
bite patterns of individuals. The theory of
growth relativity states that bone growth mod-
ifi cations occur relative to retrodiscal tissues,
which are temporomandibular ligaments, and
the transduction of the nonmuscular forces
[
Ca
2+
, PO
4
3-
Collagen
Figure 8.5.
Phase diagram showing three tissue phases
associated with tissue composition and stress received in a
given tissue.
8.3.2 Tooth Movement
]. The retrodiscal tissues are stretched
like a large elastic band between the fossa and
the displaced condyle. The transduction of
these nonmuscular forces has been shown to
be effective at a signifi cant distance from the
actual physical soft-tissue attachments. In a
simplifi ed two-dimensional fi nite element
analysis, we found that tensile strains of
64
,
117
Some of the aforementioned principles are
being practiced by a large percentage of ortho-
dontists today. Moving a tooth on the tensile
side of its alveolar socket can regenerate bone
[
]. In theory, tooth movement is
equivalent to “distraction”. The periodontal
ligament is composed of fi brous tissue, and the
cells of the periodontal ligament serve as an
interzone tissue analogous to the osteotomized
gap in distraction osteogenesis. The continu-
ous forces generated during the orthodontic
treatment, in general, are reactivated every
74
,
75
,
95
,
113
1700
to
could be created by the temporo-
mandibular ligament. This yielded a biome-
chanical effect on condylar growth. These
values were estimated on the basis of a
3000
µε
-mm
forward movement of the mandible. This
model did not include muscular system and
occlusal forces; future modeling will include
more detailed anatomy and three-dimensional
dental-muscular structures. Nevertheless, the
tensile strain vectors ran posteriorly and
matched with the posterior growth direction
observed in animal studies [
1
1
to
2
months by the use of a metallic wire. Within
this
-month (nonadjustment) period, the dis-
traction and consolidation phases occur. At the
beginning of loading (in this case, a new adjust-
ment made by adjusting an orthodontic wire),
the periodontal ligament is stretched for
approximately
2
mm within a day and then
left to consolidate for the rest of the nonadjust-
ment period. The tensile strain level applied to
the periodontal tissue in a central incisor is
estimated to be
0
.
3
].
Our preliminary data support the growth rela-
tivity concept, which suggests that tensile
strains and stresses due to the constraint of
mandibular movement are related to modifi ca-
tion of osteogenesis within the mandibular
condyle.
64
,
117
,
118
500
to
1000
µε
for the periodon-
tal ligament and
for the lamella dura. It
has been postulated that these strains can
10
µε
