CEREC Q1 | 2015 - page 20

18 | CERECDOCTORS.COM | QUARTER 1 | 2015
C L I N I C A L S T U D Y | | | B Y D E N N I S J . FA S B I N D E R , D . D . S . , A . B . G . D .
the concern and debate about margin fit and internal adaptation of CEREC CAD/CAM restorations has been
ongoing since the first milled restoration was tried in a cavity preparation. There are many purported benefits of a good
margin fit for a restoration: preventing microleakage and recurrent caries; ensuring periodontal health; and supporting clinical
longevity of the restoration, among others.1,2
The Impact of Margin Fit
on CEREC Restorations
How Good Is Good?
Margin fit is one of the primary clinical concerns doctors have
when they are trying to decide if they should invest in the CEREC
system. And many CEREC Specialists spend considerable time
trying to explain the fit and internal adaptation of CEREC restora-
tions and the resulting clinical outcome.
One of the initial confounding issues is that doctors are used to
evaluating finished, laboratory-fabricated ceramic restorations on
model dies returned from the laboratory. The restorations have
been finished on the dies, often with the use of a microscope, and
have a final glazed and polished surface. Doctors are not used to
evaluating milled ceramic restorations as they are removed from
the mill before they have been finished and polished. The desired
positive margin upon initial try-in is often considered evidence of
a less-than-optimal fit to the untrained CEREC doctor.
In order to enter into the debate on margin fit, one must first
consider the question: what is a “clinically acceptable” margin fit
for a restoration? In general, this means finding out at what quan-
titative margin fit the restoration can be delivered. Or conversely,
at what quantitative margin gap must it be remade. Early research
focused on doctors’ ability to detect margin deficiencies. Labo-
ratory studies were done using steel bars with varying sizes of
grooves cut in them simulating margin gaps. Dentists were blind-
folded and asked to detect the various size grooves with a sharp
explorer. It was found that a sharp explorer was a reliable means
to detect margin discrepancies as small as 36 µm.3 Other labora-
tory studies found that the mean detectable discrepancy was actu-
ally somewhat larger, reported at 80 µm4 and 93 µm.5
It is well established that dentists’ tactile skills and training
allow them to detect relatively small margin discrepancies.
However, the actual problem is not in detecting margin gaps but
deciding what to do once they are detected. This is where the
range of what is clinically acceptable becomes somewhat conten-
tious. What would the vast majority of well-trained dentists do
with a specific margin fit? Is it well-fitting and can be delivered, or
is it not well-fitting and should be remade? One study determined
the mean acceptable margin gap to be 119 µm, with margins as
small as 26 µm being rejected by some of the dentists. The author
concluded that the subjects of the study were not able to evaluate
the marginal openings consistently.6 Another study reported that
104 µm was the minimum average value below which marginal
openings were acceptable.5
Experienced dentists had a range of 32-230 µm for horizontally
openmargins and 43-196 µm for vertically openmargins. The author
concluded thatwhenevaluating themargindiscrepancyof nonvisible
marginswithanexplorer, experienceddentistshad little consensus in
their ratings. In spite of the inconsistency and wide ranges reported
in many studies, the general consensus is that a margin discrepancy
below 120 µm is considered clinically acceptable.7-11
The preceding studies illustrate the wide range of margin
discrepancies dentists find acceptable, and this often clouds the
discussion of whether a CEREC margin is clinically acceptable.
However, in view of the general consensus that 120 µm is clinically
acceptable, just how well do CEREC restorations fit?
A very good systematic review of CAD/CAM restorationmargin
fit included more than 230 studies published between January
2000 and October 2012 with 26 different CAD/CAM systems.12
Ninety of the studies were selected for data analysis. Eleven of the
studies combined for an average margin fit of 76.9 µm for CEREC
inlays and onlays. Nine of the studies combined for an average
margin fit of 65.3 µm for CEREC crowns. These average margin
fits were based on restorations from CEREC 2, CEREC 3 and
CEREC 3-D studies.
The values reported in the systematic review were also consis-
tent with a study comparing the fit of CEREC 3 crowns to several
types of laboratory-fabricated crowns, including Empress 2,
Procera, and InCeram.13 There was no significant difference in the