Biomedical Engineering Reference
In-Depth Information
(
), combined with an interfacial
bone modulus of
1500
to
3000
µε
Despite the limitation, the overall results
suggest that mechanically driven osseointegra-
tion adaptation is possible. The results support
the hypothesis that long-term bone distribu-
tion in the implant interface is related to the
local interface tissue strain state. Thus,
mechanical adaptation for long-term osseoin-
tegration of porous coated implants seems to
occur at a local level of micromotion.
GPa, the Frost theory
can best predict bone ingrowth corresponding
to actual experimental ingrowth (
r
0
.
5
and
1
).
This local strain-ingrowth relation has not
been previously described for osseointegration
with the use of either isolated local models [
≈
0
.
8
71
,
93
]. Our data
showed that such a local correlation depends
upon the synergy between global boundary
conditions and local bone properties. If off-
axis loading occurs or if bone is either too com-
pliant or too stiff (for example outside of the
physiological range), the strain-ingrowth rela-
tion, even with use of the same MES, becomes
statistically weaker. A vertical load yields the
best association for the strain-ingrowth rela-
tion. The effect of the other anterior-posterior
loading components on the strain-ingrowth
relation was poor, confi rming previous fi nd-
ings that a vertical load is the dominant mode
of motion on the canine tibia [
] or global models [
3
,
15
,
54
,
55
8.4.2 Dental Implants
Endosteal implants have been among the most
signifi cant developments in dentistry over the
past
]. The use of implants
for edentulous patients and for single tooth
replacement has grown exponentially. Previ-
ously we found that alveolar ridges, which
contain distinct porosity with active synthesis of
trabecular bone (intramembrane ossifi cation
[
20
years [
5
,
29
,
85
,
94
]), may respond to mechanical stimuli
differently than long bone. This difference re-
lates implant osseointegration to alveolar crest
bone adaptation and emphasizes the impor-
tance of early loading on a mandibular micro-
environment. This fi nding is particularly acute
in dental clinical practice where immediate
functional loading, i.e. no waiting or healing
period, is preferred for newly inserted implants.
Dental implants have a specifi c thread design
to lock into the jawbone, minimizing interfacial
motion. In addition, various adjuvant treat-
ments, such as food selection and implant
splinting (connecting implants together), can
be applied to reduce bite forces and minimize
interfacial movements. It has been shown that
with careful clinical designation, early loading
does not cause excessive relative movement that
would result in failure of osseointegration
between the implant and bone. For these reasons,
dental implants have started a trial in immedi-
ately loading in the past two decades [
61
,
107
], and that other
loading conditions in an optimization simula-
tion were not signifi cantly correlated with the
actual ingrowth.
In the study described above, the binary rule
that was used to relate strain state to the amount
of bone is limited to two hypothetical strain
regions for bone adaptation: below MES (a
single value) for resorption and above MES for
maintenance. However, according to Frost's
theory, MES is a physiological strain window
(
8
), not a single value, within
which bone retains its mineral (maintenance).
Bone resorbs if strain is below the window. If
the strain is above the window, the bone will
either deposit more mass (formation) to
strengthen the structure or undergo tissue
damage or necrotic resorption. Our binary rule
simplifi es interfacial bone remodeling to two
functions, resorption (
200
to
2500
µε
<
MES) and maintenance
(
MES) only, by seeking a strain threshold for
the lower bound of the strain window. The pre-
dicted areas of bone ingrowth (strain
≥
].
We tested alveolar bone regeneration adapta-
tion using an animal model [
111
MES)
from the rule eventually include homeostasis of
maintenance, formation, and resorption.
Potential necrotic resorption was not separated
in the present study, because only a small
portion (
≥
]. In this
study, Sinclair mini-pigs (Sinclair Research
Center, Columbia, MO) and in vivo controlled
loads were used. Titanium threaded dental
implants (Walter Lorenz Co., Jacksonville, FL)
and intraoral hydraulic devices were placed
unilaterally in the premolar alveolar ridges of
mandibles. Both the implant and the device
were protected from any bite forces. A con-
trolled load consisting of daily loading for a
68
,
71
%) of the tissue area was predicted
to be under a high-strain condition (
<
4
).
Further studies are needed to include the upper
bound of the strain window for more accurate
predictions of the amount of bone growth that
can be achieved.
>
4000
µε
-
month period was administered to the implant
5
