Biomedical Engineering Reference
In-Depth Information
platelets, and infl ammatory cell adhesion. These events constitute what is
regarded as the native response to the material and do not represent the
optimal behavior between a material and host tissue. The goal of several
current strategies is to provide enhanced osseous stability through nano-
and/or micro-surface mediated events acting as instructive micro- and
nanoenvironments that can improve the quality of the tissues regenerated
at the scaffold tissue interface. These strategies can be divided into those
that attempt to enhance the integration of new bone through changes in
surface topography, and strategies to use the implant as a vehicle for local
delivery of a bioactive coating that may achieve osteoinduction of new
bone differentiation along the bone/implant interface [129, 130].
Commercially pure titanium grade 4 and its alloys in the form of the
currently used titanium-aluminum-vanadium, or the future promising
titanium tin tantlum are used for the manufacturing of dental implants to
restore lost teeth and in the form of parts of the cranium to restore bone
lost as a result of tumor or trauma. Cranial implants can be custom made
using the titanium casting machines, ready made in the form of plates
and screws, and recently, precisely custom made using rapid prototyping
technology.
6.6.1
Biology of Osseointegration
Bone healing around implants is normally an infl ammatory reaction elic-
ited by the surgical trauma and modifi ed by the presence of the implant.
Various cell types, growth factors and cytokines are involved; a hematoma
is formed at the bone-implant interface and may play a role as a scaffold
for peri-implant bone healing.
The blood cells entrapped at the implant interface are activated and
release cytokines and other soluble, growth and differentiation factors.
The formed fi brin matrix acts as a scaffold (osteoconduction) for the
migration of osteogenic cells and eventual differentiation (osteoinduc-
tion) of these cells in the healing compartment. Osteoblasts and mesen-
chymal cells seem to migrate and attach to the implant surface from day
one after implantation, depositing bone-related proteins and creating a
noncollagenous matrix layer on the implant surface that regulates cell
adhesion and binding of minerals. This matrix is a calcifi ed afi brillar layer
on the implant surface, involving poorly mineralized osteoid similar to
the bone cement line that is rich in calcium, phosphorus, osteopontin and
bone sialoprotein.
A few days after implantation, osteoblasts in direct contact with the
implant surface begin to deposit collagen matrix directly on the early
formed cement line on the implant surface. Being completely envel-
oped by the mineralizing front of calcifying matrix; osteoblasts became
clustered as osteocytes in bone lacunae. The early deposition of newly
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