Page 30 - CEREC Q4 | 2014

28 | CERECDOCTORS.COM | QUARTER 4 | 2014
comparison to full-glass ceramics. The
patient is instructed to close lightly, and
by using a 20-micron diamond to adjust,
valuable time is saved in re-adjustments
and re-finishing.
Refinements were completed, and the
restoration was then polished. There
is no firing step or glazing necessary
for this material; extra-oral polishing
is all that is necessary to achieve its
final finish. This was performed with
a diamond polishing paste and a soft
applicator (either a goat-hair brush or
a muslin wheel) at 7,000 to 8,000 rpm
using a light, intermittent touch.
All-glass ceramic materials require
etchingwithhydrochloric acid formicro-
mechanical retention and silanization
for chemical bond.6 Lava Ultimate must
be silanated, but mechanical retention is
gained in a different manner. Lava Ulti-
mate is composed of engineered 4-10 µm
zirconia and 20 µm silica glass particles
bound in larger aggregated clusters. As
a result of these extremely small particle
sizes, interstitial spacing is greatly
reduced, providing a much harder and
wear-resistant surface than resin alone
— similar to glass ceramics and with very
near neutral antagonist wear.
This resin-reinforced matrix has a
unique chemical composition that differs
from any light/self-cure composite due
to proprietary processing resulting in
the lack of an air-inhibited layer or any
unreacted methacrylates due to near-
complete cross-polymerization. Because
of this, hydrofluoric acid has no effect on
the intaglio surface. Therefore, the inta-
glio must be mechanically air abraded to
roughen its surface tomake it receptive to
the adhesive process. This is performed
using 50 micron aluminum oxide at 2-3
bar pressure (approximately 30-42 psi).
Alternatively, it can be mechanically
roughened with 3MESPE CoJet Sand.
The 30-micron aluminum oxide
particles are coated with silica serving
to simultaneously roughen the intaglio
| | | P O T I C N Y
Surface priming was next done using
a high-performance system, Scotchbond
UniversalAdhesive. This adhesivebonds
to all surfaces and has silane incorpo-
rated into its chemistry in a stable solu-
tion with a two-year shelf life at room
temperature.8 Silane degrades rapidly in
the presence of air, and this, combined
chemistry, eliminates the need for addi-
tional bottles (and the guesswork often
associated with its use).
Scotchbond Universal Adhesive allows
for the use of any of three etch modes:
total etch, selective etch with phos-
phoric acid, or self-etch with no phos-
phoric acid relying on the acid primers in
Scotchbond Universal chemistry for this
purpose. Self-etch mode is very effec-
tive with this product and comparable
to results obtained with phosphoric acid
etch for dentin.9 Therefore, with rela-
tively little enamel present, self-etch was
chosen for this case.
The dental assistant dispensed one-to-
two drops of the material into a dappen
well with two micro-applicators nearby.
The applicators were wetted with the
ScotchbondUniversal Adhesive andsimul-
taneous application was begun by the
dentist (tooth) and assistant (restoration).
It isoptional but recommendedto light
cure the adhesive on the tooth surface at
this stage; however, light curing should
NOT be done on the intaglio. Improp-
erly thinned adhesive on the prep can
lead to a pooling effect once light cured,
which could prevent the restoration
from seating. So it is very important to
thin the material adequately if light-
curing will be performed.
After application of the primer-adhe-
sive system, RelyXUltimate cement was
dispensed into the crown. This material
is optimized for use with Scotchbond
Universal adhesive and includes an
auto-cure initiator, enabling dual-cure
functionality.
While the assistant dispensed the
RelyX Ultimate cement into the crown,
the dentist also applied a small amount of
cement onto the surface of the tooth. This
step, as well as the flow of the material,
can help prevent entrapment of air, and
is a good way to ensure that the restora-
tion seats fully. RelyX Ultimate cement is
very convenient to use with a self-mixing
dual-barrel syringe supplied with three
different styles of applicator tips for any
procedure including endodontic posts
and veneers. Transparent cement is used
Fig. 8: Sandblasting
the intaglio
Fig. 9: The primed
tooth surface
prior to adhesive
cementation
of the restoration while silicatizing the
surface. This roughened, silica-coated
surface will now be maximally receptive
to the silanization step required for these
materials, enabling the strongest bond
possible (Fig. 8).7 Properly performed,
the intaglio will exhibit a uniform matte
appearance indicating proper mechan-
ical surface treatment prior to surface
chemical priming with silane.
The adhesivewas scrubbed vigorously into
both surfaces for 20 seconds, completely
wetting tooth substrate. Once this was
completed, the material was air-thinned
on both surfaces until no movement of
the adhesive was observed and the solvent
was thoroughly evaporated (approxi-
mately five-15 seconds). Figure 9 shows the
appearance of the preparation following
this step (note the uniformgloss).
8 9