Page 13 - CEREC Q1 | 2014
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QUARTER 1
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2014
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CERECDOCTORS.COM
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It turns out, the glazes are the culprits.
Glazes used on both e.maxCAD and BruxZir are proving
to be short-lived andmore abrasive, andwearing to opposing
dentition than the underlying lithium disilicate and zirconia
body materials.
The following three issues with glazes have been observed
and documented:
• Glaze roughening with increased abrasivity over the entire
surface of the restoration (Fig. 1). This type of defect is prob-
ably due to problems in glaze application or firing, or both.
• Glazebreakdownandexcessiverougheningatocclusal contact
areas (Figs. 2-3). This is the most common glaze problem, but
not all cases have this problem because some crowns were
milled deliberately out of occlusion, and have remained out of
occlusion thus far during their three years of service. This is an
interesting point, since most authorities believe that restora-
tions designed purposely out of occlusion quickly erupt in to
contact. This work shows this is not necessarily so.
• Glaze removal and severe roughening due to occlusal adjust-
ment (Fig. 4).
In light of the above described issues, the relevant question
is: why are we glazing? There are two main reasons to glaze:
(1) to preserve the characterization staining and, (2) to form a
smooth, shiny surface.
Since we now know the current glazes are more abrasive and
wearing to opposing dentition than the body materials they
cover, should polishing be considered in place of glazing? (If so,
we need abrasives and instruments that produce a fast, smooth
high shine with minimum separate steps.) Or, should glazing
of only non-occlusal contact surfaces be considered? Or,
4a
4b
Fig. 4: SEM images of a BruxZir restoration after
occlusal adjustment with a coarse diamond:
(a) The three circles indicate areas where the glaze was
stripped off the underlying body material.
(b) The 115x magnification of the area within the left circle
shows the diamond furrows on the roughened glaze
(see RG) and the smooth exposed zirconia body
material (see Z).
should the glazes be improved to prevent the rough build-up
around the edges as they wear at occlusal contacts? Although
it is apparent that change is necessary, the exact nature of the
change has yet to be identified.
At TRAC Research, we prefer polishing to glazing – with
glazing only on facial surfaces of anterior restorations where
characterization stains are often necessary for esthetic
purposes. But, each clinician will decide for him/herself. The
purpose of this informal report is to make clinicians aware of
the issue so all can begin working on possible best solutions.
Since the materials milled by the CEREC system are
performing exceptionally well in vivo, it is not unreasonable
to simply eliminate the problematic glaze materials. Users
are encouraged to consider modifying their esthetic enhance-
ments to prevent the more rapid wear of opposing dentition by
glazes roughened during their degradation.
If you have an interest in participating in a similar study
on newest CEREC materials, contact Dr. Christensen at
All materials necessary, plus step-by-
step directions, are provided and patients are paid for both their
time and fuel (and in appreciation) for yearly recalls.
