Biomedical Engineering Reference
In-Depth Information
ties are obtained. Although the biocompatibility of this material has been
assessed (Garmendia et al., 2009), the biocompatibility of CNTs still
remains a controversial issue.
16.3.2 Dental implants
The oral environment presents extreme working conditions that include
humidity, acidic or basic pH, cyclic loading and peak loads that can reach
extremely high levels when hard objects are accidentally encountered during
mastication. The introduction of new materials and processing techniques
has led the technological evolution of ceramics for dental applications,
mostly in the last 30 years. New ceramic materials offer greater performance
in both strength and toughness, which has made it possible to expand the
range of indications to long-span fixed partial prostheses, implant
abutments and implants. The high level of crystallinity is responsible for
an improvement in mechanical properties through various mechanisms such
as crystalline reinforcement or stress-induced transformation.
Unfortunately, higher crystallinity is also associated with higher opacity,
which is not always desirable for dental ceramics. Other factors such as
crystal size and geometry, modulus of elasticity, phase transformation, and
thermal expansion mismatch between crystal and glassy phases play a
crucial role in determining the final mechanical response of the ceramic
(Denry and Holloway, 2010).
YTZP is a very interesting ceramic for dental implants due to its
outstanding mechanical and biocompatibility properties. Currently there is
a wide range of zirconia block suppliers in the dental implant market. These
blocks are used to manufacture posterior bridges using CAD/CAM. But
aging is still a problem, as dental implants are placed in a humid
environment. Furthermore, YTZP is also one of the most opaque of the
ceramic materials currently available (Spear and Holloway, 2008). There are
also other important features to be considered; these include: the effect of
sandblasting and heat treatment on the microstructure and strength;
bonding to veneering porcelains; bonding to cement; the visible light
translucency related to aesthetic restoration; X-ray opacity; and clinical
survival rates. Nanoscale zirconia-alumina composites are meant to further
improve these properties (Ban, 2008).
Philipp et al. (2010) examined the clinical performance of veneered ceria-
stabilized tetragonal zirconia-alumina nanocomposite frameworks for
dental prostheses. Their nanocomposite was found to be a reliable
framework material after 1 year of functioning. Nevarez-Rascon et al.
(2009) studied the performance of different ATZ and ZTA nanocomposites.
The reported sintered density, grain size, Vickers hardness and fracture
toughness values are in accordance with international standards applied to
