Biomedical Engineering Reference
In-Depth Information
demonstrated in many different applications.
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The spontaneous formation
of a dense oxide film on the surface of titanium provides high biocompatibility,
but it also poses as a disadvantage because its spontaneity can result in poor
aesthetics. The grayish color results from exposure caused by soft tissue reces-
sion or thin gingival biotype especially in anterior sites in the mouth. Zirconia
implants have been introduced that might offer a better alternative to titanium.
Unlike titanium implants that can give the gingiva an unnatural bluish/gray
appearance, zirconia has an opacity that resembles natural teeth and its bright
white color may provide satisfactory aesthetics.
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The increased adhesion of bone-forming cells, osteoblast, on nanostructured
materials was reported in 1999
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using alumina with grain sizes between 49 and
67 nm and titania with grain sizes between 32 and 56 nm. These nanomaterials
were reported to promote osteoblast adhesion compared with their respective
micrograined materials. Additional studies of these nanostructured ceramics
(such as alumina, titania, and HA) exhibited in vitro osteoblast proliferation.
Their long-term functions as measured by intracellular and ECM protein syn-
thesis such as collagen and alkaline phosphatase, as well as calcium-containing
mineral deposition, were superior on ceramics with less than 100-nm grain or
fiber sizes.
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Two, three, and four times the amount of calcium deposition
was observed on nanostructured materials compared with the conventional
HA, titania, and alumina when osteoblasts were cultured for up to 28 days. In
addition, osteoblast functions such as viable cell adhesion, proliferation, and
calcium deposition were further increased on nanofiber materials compared
with nanospherical structures of alumina. This was believed to result from the
nanofibers having more closely approximate the shape of HA crystals and col-
lagen fibers in bone compared with nanospherical geometries.
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The surface
chemistry and/or crystal structures of the conventional ceramics tested in these
reports were similar to their respective nanophase materials except the degree of
nanometer surface features that was altered.
Stadlinger
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performed animal studies to investigate and compare the
osseointegration of 14 zirconia and 7 titanium dental implants in minip-
igs. At the end of a healing period of 4weeks, a histological analysis of the
soft and hard tissue and a histomorphometric analysis of the bone-implant
contact (BIC) and relative peri-implant bone-volume density (rBVD) was
performed. Submerged zirconia and titanium implants surface showed
an intimate connection to the neighboring bone, both achieving a BIC of
53%. The nonsubmerged zirconia implants showed some crestal epithe-
lial downgrowth with a BIC of 48%. Zirconia exhibited the highest rBVD
values (80%), followed by titanium (74%) and nonsubmerged zirconia
(63%). These in vivo studies suggest that unloaded zirconia and titanium
implants osseointegrate similarly within the 4-week healing period studied.
Figure 6.4
shows a comparison between nanoscale and conventional
microscale titania
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which is the oxide that forms on the widely implanted
titanium (Ti).
