Page 32 - CEREC Q2 | 2014

30 | CERECDOCTORS.COM | QUARTER 2 | 2014
our professional belief system is
a complex mix between scientifically
provenfactsandemotionallybasedbeliefs.
Composite placement is not exempt
from this combination. We all know (or
should know) that the fourth genera-
tion of adhesives (multi-bottle systems)
perform better than simplified adhesive
systems (one bottle). However, sales of
simple adhesive systems overtook the
sales ofmulti-bottle systems several years
ago. On the basis of scientific evidence,
we also know (or should know) that the
more layers of composite we place and
cure with the least possible intensity
in a maximum period of time (within a
certain range of time and intensity) while
avoiding excess and following the cusp’s
slope, the better the result should be.
Nevertheless, most dentists place
composites in bulk with lots of excess,
cure them as fast as possible and remove
the excess with burs. Why? Because it’s
less time-consuming. What still remains
unclear in evidence-baseddentistry is the
question of how many steps are needed
in the layering procedure, and howmany
curing cycles should be carried out if
we would like to be efficient while also
doing a good job. Therefore, a composite
that can be placed in bulk, has reduced
shrinkage stress, and allows good adapta-
tion and enough curing depth in order to
save time is a material eagerly awaited.
There are already many materials avail-
able now that attempt to achieve this goal.
These materials mainly try to replace
dentin with a bulk fill of a
flowable composite that
needs to be covered with a
universal composite layer in
Fillings in One Step:
Are They Already a Reality?
Composite Restorations for the CEREC Dentist
C A S E S T U D Y | | | B Y E D U A R D O M A H N , D . D . S . , D . M . D .
outcome. Ideally, new initiators or a
combination of them should be used in
order to “boost” the curing process.
The working time seems to be diamet-
rically opposed to the curing depth, but it
is not. By adding some reaction retarders,
it is possible to increase the “insensitivity”
to light, making the working time longer,
without affecting the curing depth.
The third and last factor to be overcome
is the polymerization stress. As mentioned
before, a flowable material cannot fulfil
these requirements because of its inherent
higher volumetric shrinkage compared toa
universal composite. It is widely accepted
thatavolumetricshrinkagebelow2percent
should be the standard. Flowablematerials
cannot come to values below 3 percent or
3.5 percent, even if they incorporate very
large fillers (used to reduce shrinkage, with
the disadvantage of surface roughness and
wear, asmentioned before).
Thebest candidate for abulkfillmaterial
is a universal composite, with an already
reduced shrinkage. This is the case for
Tetric EvoCeram Bulk Fill. The depth of
cure was enhanced not only by increasing
the translucency but also by adding a new
initiator in the blue light spectrum. This
initiator acts as a polymerization booster.
In addition, the working time has been
extended by incorporating a “light sensi-
tivity inhibitor.” Finally, the volumetric
shrinkage has been reduced to be below
2 percent and the shrinkage stress is
controlled by a stress reliever, making this
newcomposite a real bulk-fillmaterial.
Another relevant issue is the diameter
of the light probe of the curing light.With
a diameter of 10mm, the tip of bluephase
style allows even large MOD cavities
a subsequent step. Most of thesematerials
cannot be appliedwithout a covering layer
because they incorporate large fillers;
fillers that limit their polish-ability, and
increase their wear and surface rough-
ness to clinically unacceptable levels.
Other systems are too translucent, which
improves light penetration but alsomakes
them appear too greyish. The challenges
in developing an appropriate material
are many; only recently was it possible to
overcomemost of them.
If we contemplate the characteristics
of conventional composites and curing
lights, we realize that the following
aspects were in need of improvement:
• The depth of cure and light penetra-
tion should be at least 4 mm, instead
of the standard 2 mm, to allow the
placement of a real bulk fill
• Working time should be longer in
order to enable the clinician to adapt
the composite properly to the cavity
walls, avoiding excess
• Polymerization shrinkage (especially
shrinkage stress) should be consider-
ably reduced, because the amount of
composite cured in one step is larger
• Fast and easy accessibility to all surfaces
to be cured should be ensured — espe-
cially in pediatric patients and patients
with reduced mouth opening or TMJ
problems — and one-step curing should
be possible even in large cavities
The increase of the depth of cure
should not be achieved only by making
the composite extremely translucent
(less opacity, better light penetra-
tion), because too-high translucency
will be detrimental to the final esthetic