CEREC doctors.com - Q1 2017 - page 7

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the milling process. After dry-firing, having gone through this self-
healing stage, as the material cools to room temperature, it hardens
back to its optimal high strength.
SPEAKING OF MATERIAL STRENGTH, HAVE THERE BEEN ANY STUDIES TO
VALIDATE THE VARIOUS MECHANICAL PROPERTIES OF CELTRA DUO (ZLS)?
Yes, an in-vitro study was conducted by the Department of Restor-
ative Dentistry at the University of Toronto to determine the fracture
toughness of five different CERECmaterials used for crown fabrica-
tion. Fracture toughness (known as KIC) is an intrinsicmaterial prop-
erty that determines a material’s ability to resist crack propagation. A
restorativematerialwithhigh fracture toughness (KIC) shows abetter
resistance and longevity in service as compared to materials with
lower fracture toughness. For restorative materials, fracture tough-
ness is one of themost significantmechanical propertiesmeasured to
determine a material’s strength, durability, and longevity. The results
of this test demonstrated that when heat fired, Celtra Duo (ZLS)
achieved amean fracture toughness value of 2.65 KIC which is closest
to the fracture toughness of natural dentin (~3.0 KIC). Without heat
firing, Celtra Duo (ZLS) reported a KIC value of 1.01. With results in
this range for both the unfired and fired specimens, Celtra Duo can
be usedwith clinical confidence in both its fired and unfired states.
Another study was conducted by the Division of Biomaterials
at the University of Alabama at Birmingham School of Dentistry
to measure the various mechanical properties of several CEREC
materials, including wear, strength, and modulus of hardness. The
results demonstrated that Celtra Duo was generally stronger, stiffer,
and harder than the other materials tested. It was also reported that,
although we already knew this, the increase in strength seen with a
firing cycle of Celtra Duo was not due to additional crystallization as
nodifferenceincrystallinemicrostructurewasnotedinanSEMtaken
of fired Celtra Duo. The study reported what we knew of the mate-
rial’s unique behavior: the firing cycle improved Celtra’s strength by
healing any defects createdduring themilling process. The study also
reported that polishing has also been shown to improve the strength
of glass ceramics such as Celtra Duo by removing a zone of deforma-
tion surrounding surface defects. Therefore, polishing unfired Celtra
Duo after milling improves its strength as well.
AS A MATERIAL THAT OFFERS TWO DISTINCT PROCESSING PATHWAYS
— MILL & FIRE OR MILL & POLISH — CELTRA IS UNIQUE IN TERMS OF
PROCESSING. HAVE THERE BEEN ANY HURDLES TO OVERCOME, IN TERMS
OF CLINICAL USAGE AND PRACTICAL APPLICATION IN THE OPERATORY,
AND IF SO, IN WHAT WAYS HAVE THOSE DIFFICULTIES BEEN ADDRESSED
AND CORRECTED?
Like other materials, Celtra has its own unique firing schedule and
handling properties, and to ensure success, this schedulemust first
be programmed into the furnace before firing Celtra for the first
I recently had the opportunity to interview Dr. Markus Voll-
mann, Dentsply Sirona’s Director of Development and Applica-
tion Technologies, who was responsible for creating the block and
bringing it to market.
WHAT IS YOUR ASSESSMENT OF HOW CELTRA DUO (ZLS) HAS BEEN
ACCEPTED AND EMBRACED BY CEREC DENTISTS?
Overall, I’m very pleased with Celtra Duo’s reception among
CEREC dentists worldwide. Thematerial was officially launched in
the United States at the CEREC 30-year anniversary celebration in
September 2015, and after the rollout we realized a strong demand
for it. Our salesforce reports that when a dentist tries Celtra Duo,
they fully appreciate all the material has to offer in terms of work-
flow flexibility, processing options, polishability, and speed.
REGARDING DENTISTS WHO HAVE USED CELTRA AND LOVE IT:
WHAT DO THEY SAY THEY APPRECIATE MOST ABOUT THE MATERIAL?
ItreallycomesdowntoCeltra’suniqueprocessingpathways,itswork-
flowflexibility, and its simplicity of processing. It’s these characteris-
tics that set CeltraDuo apartmost, since no other block gives CEREC
dentists a choice in how to process the material and that an oven and
glaze are optional. The dentists I’ve spoken with who’ve used Celtra
Duo tellme it’s theworkflowflexibility that they appreciatemost, and
the freedomandcontrol that it affords them. That’sbeenacorepart of
theCERECphilosophy since thebeginning, though, so itmakes sense
to have a block that gives the dentist just as much processing control
as theCERECsystemitself does. CeltraDuo is thefirst andonly block
that’s in syncwith that philosophy. They also appreciate the esthetics,
many saying they simplypolishandplacewithout having to add char-
acterization and it looks great just like that. Of course all of this is a
direct result of the workflowflexibility.
THE CAPABILITY OF PROCESSING CELTRA DUO (ZLS) VIA DIFFERENT
PATHWAYS IS A DIRECT RESULT OF THE MATERIAL’S UNIQUE COMPOSITION,
CORRECT? CAN YOU ELABORATE ON THIS?
Yes, the high content of ultra-fine glass matrix in Celtra Duo (ZLS)
not only gives the material its excellent light-optical and mechanical
properties, it provides the added benefit of self-healing when fired.
Keep in mind that Celtra Duo is a fully crystallized, high-strength
block right out of the box — it does not require firing but can simply
be milled as is, polished, and seated. Celtra Duo does not require a
crystallization firing. However, dentists have the option to fire resto-
rations if they wish to increase the strength even further to a full
370 MPa. This is commonly referred to as a “dry firing.” When a
Celtra Duo restoration is dry-fired, the glass transition temperature
is reached, turning the material in a small part on the surface into a
highly viscous “liquid,” but not viscous enough as to lose the shape
of the restoration. Rather, the viscous glass fills any flaws caused by