QUARTER 4
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2014
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CERECDOCTORS.COM
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dentition. Partial coverage restorations
suchas inlays or onlays typicallyperform
as well as, if not better than, their full-
coverage counterparts. Less invasive
partial coverage restorations have
demonstrated equivalent fracture resis-
tance and failure risks to full ceramic
coverage of compromised cusps, for
example.
16
Some research indicates that
partial coverage restorations, such as
ceramic inlays prepared with a minimal
preparation design, may demonstrate a
higher fracture strength compared to
traditionally prepared teeth.
17
Coupled with adhesive protocols
and techniques, conservative treat-
ments such as indirect inlays and onlays
can be performed where otherwise
more aggressive restorations, such as
full-coverage crowns, may have been
used. These restorations can be placed
securely for long-term function through
chemical, adhesive retention, rather
than relying on the mechanical, prepa-
ration-driven retention.
To maximize the benefits of partial-
coverage restorations, material selection
has been shown to influence fracture
resistance and failure risks of partial
coverage restorations, particularly in the
posterior region.
18
Restorative materials
used should have sufficient strength to
support occlusal forces and, should frac-
ture occur, protect the remaining tooth
structure.
18
Materials such as leucite-
reinforced glass ceramics (e.g., IPS
Empress) provide clinicians with such
assurances as longevity and strength.
For example, after four years, the
overall failure rate of IPS Empress inlays
was only 4 percent;
19
another study
demonstrated a low failure rate of only
10 percent after eight years.
20
Addition-
ally, Stappert et al
21
found the survival
rate of IPS e.max posterior partial
coverage restorations to be 100 percent,
indicating its successful clinical perfor-
mance for patients who desired highly
esthetic and long-lasting restorations.
TODAY’S MATERIAL CAPABILITIES
While the leucite - reinforced glass
ceramics of the 1990s laid the foundation
for restorative success with inlays and
onlays
2
, scientific advancements have led
to the development of stronger, metal-
free materials such as lithium disilicate
(e.g., IPS e.max), which can be placed
anywhere in themouth,making it a viable
alternative to traditional restorative
options.
22
Lithium disilicate is a glass-
ceramic consisting of lithium dioxide,
phosphor oxide, potassium oxide,
alumina and quartz powders, which are
melted and heated together until a glassy
matrix composed of 70 percent needle-
like crystals is formed.
22,23,24
While lithium disilicate can be used
to fabricate high-strength, full-coverage
restorations, it also provides the option
of fabricating partial-coverage restora-
tions that require minimal tooth prepara-
tion with conservative designs for highly
esthetic, predictable outcomes.
22
More-
over, the characteristics of this material
enable its processing with more than one
technique or fabrication method; lithium
disilicate can be used with CAD/CAM
technology todirectlydesignand fabricate
restorations in offices or laboratories.
23
The load-bearing property of mini-
mally invasive lithium disilicate occlusal
onlays (i.e., 0.6-1.4-mm thick) can exceed
70percent of zirconia.
25
Additionally, since
there is a relatively weak dependence on
fracture load on restoration thickness,
a 1.2-mm thin lithium disilicate onlay is
as fracture-resistant as a 1.6 mm onlay,
allowing clinicians to place thinner resto-
rations with less preparation, but without
the risk of potential fractures.
25
Other
studies have shown that volume of partial
coverage restorations such as all-ceramic
inlays are not influenced by volume,
suggesting that volume-reduced, all-
ceramic inlays may not have an increased
fracture risk
26
, allowing clinicians to place
even more conservative restorations as
clinical indications dictate.
EFFICIENT TREATMENTS
THROUGH TECHNOLOGY
Digital technology provides exceptional
benefits for clinicians and patients. The
use of CAD/CAM has become pervasive
throughout areas of dentistry over the
past 25 years, and partial coverage resto-
rations such as inlays and onlays are no
exception.
26
In fact, the materials devel-
oped for this technology and their excep-
tional properties encourage the use of this
technology and these restorative proto-
cols in everyday dental practice.
27
Use of such technologies for already
conservative procedures only augments
their benefits. A low rate of restora-
tion fracture and long-term clinical
survivability
of
CEREC-designed
partial-coverage restorations has been
well documented.
28
In-office CAD/
CAM fabrication of all-ceramic partial
coverage restorations allows clinicians
to design the restoration, correct and
alter it on screen, and mill the restora-
tion in the office while the patient waits,
eliminating the need for provisional
restorations. This saves the patient
time, money and risk of negative conse-
quences associated with provisional
restorations. Using a chairside CEREC
system to fabricate inlays has been
shown to reduce the risk of enamel
cracks and marginal enamel chipping by
omitting temporary restorations.
29
CLINICAL APPLICATIONS
Using an advanced material such as IPS
e.max for partial-coverage restorations
is a viable solution to a full-coverage
crown. These restortions are predictable,
reliable, esthetic and conservative and,
when paired with a universal adhesive
cement (e.g., Multilink Automix, Ivoclar-
Vivadent), patients receive the benefits of
truly conservative dentistry.
For example,multiple teethwithfailing
amalgam restorations can be treated in
a single visit in a conservative manner
with partial coverage restorations, even
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