60 09.2017 |
ZIRCONIA: EVOLUTION OF A UNIQUE UNIVERSAL RESTORATIVE
Zirconia framework-based restorations,
when veneered with an appropriate ceramic
layering system designed for zirconia, can
result in exceptional esthetics and can
achieve an imperceptible match to the surrounding dentition. The talented technician
may develop appropriate color and optical
properties of the restoration within the veneering ceramics. However, the past decade
of investigation has revealed that chipping
within the veneering ceramic or at the
framework/veneer interface frustrates
higher clinical success and survival of these
restorations. Veneer chipping, not framework fracture, appears to be the weak link
in zirconia-based restorations.
of tooth and implant-supported restorations.
9 The formation of
biofilm on dental prostheses—either natural tooth- or implant-supported—is material-related. A recent investigation measured the
colonization of dental implant abutments.
10 DNA checkerboard
analysis revealed that, compared to zirconia abutment materials,
higher total bacterial counts were greater on cast or machined titanium disks after 24 hours. This confirms the work of Bremer et al.
who showed that biofilm was lowest and thinnest on zirconia compared to lithium disilicate restorations.
11 The clinical impressions of
low biofilm formation and limited inflammation of zirconia restorations are supported by in vitro and in vivo studies. Bacterial adhesion
has proven to be slightly better than titanium. Scarano et al. reported
a degree of coverage by bacteria of 12.1% for zirconia as compared
to 19.3% on titanium.
12 Rimondini et al. confirmed these results with
an in vivo study where ceramic material made of tetragonal zirconia
polycrystals stabilized with yttrium (Y-TZP) accumulated fewer
bacteria than commercially pure grade 2 titanium (Ti) in terms of
total numbers of bacteria and presence of potential pathogens, such as rods.
13 It may be
concluded that zirconia materials offer advantages of biocompatibility for use as endosseous
biomaterials and oral biomaterials due both to
their remarkable strength and durability as well
as the surface properties of the materials.
Zirconia offers an excellent
option for the restoration of dental
implant cases. With digital design
and precision milling, screw-retained
monolithic zirconia (with or without
facial layering) restorations can be
Research regarding zirconia as biomaterial
began in the late 1960s. Helmer and Driskell
published the first paper in 1969.7 In 1988,
Christel et al. offered the use of zirconia as
an alternative to other materials used at the
time to manufacture the ball heads for total
8 Zirconia is still used in
this application and other medical prosthet-
ics to this day. Implied was acceptable bio-
compatibility. Clark showed that zirconia
was found to be better than other ceramic
biomaterials in use circa 1990 because it
possessed higher strength and hardness.
The interaction of zirconia with oral soft
tissues may be central to the performance
The next evolution of
zirconia offers high strength and
better translucency, but it still
requires ceramic layering on the
facial to achieve high esthetics.