Biomedical Engineering Reference
In-Depth Information
obtain suitable bonding between dental implant and metal substrate
[4-7]
. A few factors may lead
to a decrease in the bonding strength, e.g., high affinity of titanium for oxygen
[3,8-10]
and mis-
match of the coefficients of thermal expansion between titanium and porcelain
[10-13]
. Insufficient
bonding leads to device failure, reduces durability and functionality of the system, and poses clinical
and aesthetic problems. Recently, suitable bonding of dental implants and metal substrates has been
obtained using various methods of modification of the metal substrate surface
[3,4,6,14-19]
.
These surface modified metal substrates should address the following problems: (1) incompatibil-
ity between the artificial implant and the natural and (2) metallic dental implants material can release
metallic ions which could become toxic or detrimental to the host. Moreover, metallic surfaces are
not generally bioactive, and surface treatment is usually needed to enhance the bioactivity. To over-
come these problems, coating the metallic implant with other materials were explored in previous
studies, such as glass-ceramics
[20]
, SiO
2
-CaO
[21]
, hydroxyapatite (HA)
[22,23]
, TiO
2
nanoparti-
cles
[24]
, SiO
2
and SiO
2
-TiO
2
[25]
. By these methods, the mechanical properties of metallic implant
are not only complemented with biocompatible and bioactive features using different coatings, but
also reduce the release of metallic ions to the biological environment.
In this chapter, various different coatings on titanium and Ti6Al4V alloys and their potential in
improving bioactivity when applied as dental materials are briefly reviewed. Subsequently, some
conventional characterization techniques that are employed to evaluate the behaviors of titanium and
Ti6Al4V alloy with different coatings will be also addressed.
9.1.1
SiO
2
-CaO Coatings on Ti6Al4V Alloys
Sol-gel technology is a common method to create surface layers; the required equipment is quite sim-
ple and the thermal treatments are not too aggressive. Most importantly, the sol-gel process allows
control of the microstructure, thickness and composition of the surface coating, ensuring high levels
of purity and homogeneity
[26]
. However, the coating process of a metal by a bioactive ceramic or
glass is somewhat complex. The expected clinical success depends greatly on this process, since the
quality and durability of the interfacial bond between prosthesis and host tissue is closely related to
several parameters of the coating—chemical composition, purity, particle size, thickness—and also
to the surface quality of the metallic substrate
[27]
. Recently,
in-vitro
assays of binary glasses in
the SiO
2
-CaO system have shown promising bioactivity; glass pieces soaked in fluids mimicking the
composition of human plasma grew a hydroxycarbonate apatite (HCA) surface layer similar to the
mineral component of natural bone tissue
[28,29]
. Also, various coatings of SiO
2
CaO on Ti6Al4V
alloy substrates by sol-gel method revealed that the porosity and roughness of the coatings were
determined by the precursor solutions used in the coating procedures
[30,31]
.
9.1.2
SiO
2
and SiO
2
-TiO
2
Intermediate Coatings on Titanium and Ti6Al4V Alloy
The bond strength of titanium-porcelain systems can be increased by intermediate coatings of
SiO
2
and SiO
2
-TiO
2
, produced by sol-gel between the metal substrate and ceramics. The coatings
obtained using the sol-gel process are characterized by low thickness, high homogeneity, satisfac-
tory mechanical and chemical stability, good bonding to the substrate, high biocompatibility, and
corrosion resistance
[32-35]
. Moreover, the process of manufacturing sol-gel coatings runs at low
temperatures and there is also the possibility of obtaining both mono- and multicomponents
[36]
,
which can be multilayered, and also the possibility of producing coatings for implants with complex
