Biomedical Engineering Reference
In-Depth Information
(4) surface texturing and porous/foamed structure, including texturing
process [NASA, 1997; Banks, 1997], macroporous Ti structure formation
[Fujibayashi et al., 2004], and
(5) tissue engineering and scaffold structures and materials, including fi lm
and 3-D structure [Li and Chang, 2004; Taira et al., 2005; Burgess, 2005;
Lee et al., 2005; Walboomers et al., 2005; Ni et al., 2006; Wu et al., 2006],
and elecrospinning [Hohman et al., 2001; Li et al., 2005; Buttafoco et al.,
2006 ].
With the aforementioned supportive technologies, surfaces of dental and
orthopaedic implants have been remarkably advanced. These applications can
include not only ordinal implant system but also miniaturized implants, as well
as customized implants.
There were two ways of implant anchorage or retention: mechanical and
bioactive [De Putter et al., 1986; Albrektsson et al., 2004]. Mechanical retention
basically refers to the metallic substrate systems such as titanium materials. The
retention is based on undercut forms such as vents, slots, dimples, screws, and so
on, and involves direct contact between bone and implant with no chemical
bonding. The osseointegration depends on biomechanical bonding. The poten-
tially negative aspect with biomechanical bonding is that it is time consuming.
Bioactive retention is achieved with bioactive materials such as HA or bioglass,
which bond directly to bone, similar to ankylosis of natural teeth. The bioactivity
is the characteristic of an important material which allows it to form a bond with
living tissues. It is important to understand that bioactive implants may, in addi-
tion to chemical bonding, show biomechanical anchorage; hence a given implant
may be anchored through both mechanisms. Bone matrix is deposited on the HA
layer because of some type of physiochemical interaction between bone collagen
and the HA crystals of the implant [Denissen et al., 1986]. Recent research has
further redefi ned the retention means of dental implants into the terminology of
osseointegration versus biointegration. When examining the interface at a higher
magnifi cation level, Sundgren et al. [Sundgren et al., 1986] showed that unim-
planted Ti surfaces have a surface oxide (TiO
2
) with a thickness of about 35 nm.
During an implantation period of eight years, the thickness of this layer was
reported to increase by a factor of ten. Furthermore, calcium, phosphorous, and
carbon were identifi ed as components of the oxide layer, with the phosphorous
strongly bound to oxygen, indicating the presence of phosphorous groups in the
metal oxide layer. Many retrospective studies on retrieved implants, as well as
clinical reports, confi rm the aforementioned important evidence that surface
titanium oxide fi lm grows during the implantation period, and that calcium,
phosphorous, carbon, hydroxyl ions, proteins, and so on, are incorporated in an
ever-growing surface oxide even inside the human biological environments
[Ellingsen, 1991; Albrektsson et al., 2004].
Numerous
in vitro
studies on treated or untreated titanium surfaces were
covered and to some extent were incorporated with Ca and P ions when such
surfaces were immersed in SBF (simulated body fl uid). Additionally, since bone
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