Biomedical Engineering Reference
In-Depth Information
enhance MSCs numbers and peri-implant tissue healing surface. Moreover, the plasma clot in con-
tact with implant surface represents a three-dimensional microporous structure that allows diffusion of
regulatory factors
[54,55]
and is involved in the migration, proliferation, and differentiation of MSCs.
After MSCs recruitment in the injured site, cells adhere on the local extracellular matrix as well as on
the implant surface beginning an extensive proliferation in order to build up new tissue. Again, surface
modifications of implants in the nanometer range condition the biological responses.
5.4.3
Differentiation
In the microenvironment, MSCs are stimulated by some specific factors to differentiate into the ade-
quate cell line. Under the influence of these factors, MSCs switch to osteoblastic cells in contact to
bone tissue while they differentiate into fibroblastic lineage in the gingival tissue region. These two
differentiation pathways are in concurrence around dental implants. In some cases, implants are
encapsulated by fibrous tissue due to the proliferation and differentiation of MSCs into fibroblastic
cells. In response to cytokine, fibroblasts migrate and generate a capsule of collagen, the first step
in generation of gingival tissue or rejection on contact to bone. This fibrous capsule prevents bond-
ing between implant surface and juxtaposed bone and caused a failure of the implant
[56]
. On the
other hand, both the differentiation of MSCs into fibroblastic lineage and the fibroblastic adhesion
are desired in the gingival upper part of dental implants. Fibroblasts adhesion has been shown to be
lower on nanoscale surface compared to conventional surfaces
[57]
. Moreover, nanometer-sized fea-
tures have been shown to decrease fibroblast adhesion and proliferation
[58,59]
. The micro- and nano-
scale surface properties of metal implant including chemistry, roughness, wettability, could affect bone
formation
[60]
. Numerous treatment such as machining, grit-blasting, Ti/HA plasma spray, chemical
etching, anodization are available to modify the implant surface. Research has specifically demon-
strated that nanorough Ti
[61]
and nanostructured Ti can enhance osteoblast adhesion and differen-
tiation compared to their nano-smooth control
[62]
. Furthermore, surface with micro- and nanopores
have shown to enhance greatly osseointegration
[63,64]
. Surface properties may control the steps of
adhesion, proliferation, and differentiation of MSCs and thus, condition tissue integration.
5.5
TISSUE INTEGRATION
Brånemark et al.
[65]
described the osseointegration as a direct structural and functional bone to
implant contact under load. As previously discussed, the biological events occurring at the tissue-
implant interface are influenced by the chemistry, topography, and wettability of dental implant sur-
faces. The challenge in developing new implant surface consist in increasing the clinical success rate as
well as decreasing the tissue healing time for immediate loading of implants, particularly in aesthetic
situations
[66-68]
. One of the objectives is to develop implant surface having predictable, controlled,
and guided tissue healing. For instance, surfaces that promote contact osteogenesis rather than dis-
tance osteogenesis would be desired in bony site while intimate fibrous tissue healing in gingival tissue
(
Figure 5.1
). In order to enhance this intimate contact between tissues and implant, surface treatments
at the nanometer scale have been performed on metal implants and tested in various animal models.
Implant surface with various roughness have been used to increase the total area available for osteo-
apposition. Kubo et al.
[66]
observed a substantial increase by 3.1 times in bone-titanium interfacial
