CEREC Q1 | 2015 - page 21

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margin fit of any of the CEREC crowns or laboratory-fabricated
crowns with a range of 63 to 83 µm, all of them well below the
clinically acceptable level of 120 µm (Table #1).
One of the common criticisms of studies dealing with the margin
fit of CERECrestorations is that they areusuallydone bywell-trained
clinicians with the skill and ability to create a good margin fit. One
study reported on the fit of CEREC crowns designed and milled
by doctors with less than two years of experience with the CEREC
system and dental assistants with no experience other than a basic
training program.14 The CEREC crowns were compared to the fit of
Empress crowns fabricated by Empress-certified dental laboratory
technicians. All the crownsweremade on replicas of the samemaster
preparation to remove the influence of the preparation design as a
variable. There was no significant difference in the margin fit of any
of the crowns withmargin fits between 60 µmand 70 µm (Table #2).
Another study compared the margin fit and internal adaptation
of CEREC crowns using the Redcam and Bluecam.15 There was no
significant difference in the margin fit of the crowns based on the
type of camera used for the case, with the CEREC AC having an
equivalent margin fit to CEREC 3 (Table #3).
The preceding evidence supports the fact that the CEREC
system can consistently produce margins well below what is
considered clinically acceptable. This should satisfy a doctor’s
early concerns about how well CEREC restorations fit. But once
a doctor has invested in the CEREC system, the focus shifts to
ensuring the longevity of the restoration.
So, does margin fit actually influence restoration longevity? This
is a little more difficult to answer since most clinical research does
not include a quantitative measure of the margin fit as part of the
clinical evaluation of the restorations as they return for the yearly
recall evaluations.
Most published research reveals that the CEREC 1 system fabri-
catedmargins with greatermargin discrepancies compared tomore
current CEREC systems. One clinical study measured margin gaps
of 51 CEREC 1–generated inlays after five years of clinical service.16
The mean horizontal margin gap was 373 ± 147 µm, and the mean
vertical margin depth was 111 ± 67 µm. There was no significant
difference in margin fit between molars and premolars. Only three
inlays failed due to fracture after five years of clinical service.
Vita Mark II onlays were adhesively placed in 496 patients
between 1993 and 1997 using CEREC 1 andCEREC 2 units with two
different versions of the software.17 Twenty-five restorations were
randomly selected from each of the three fabrication groups and
recalled for examination after 3.2 to 4.6 years. Replicas were made
of the restorations and a scanning electron microscope was used to
measure marginal interfacial width. Interfacial margin width of the
CEREC 1 (308 ± 95 µm) onlays was significantly larger than those of
CEREC 2 onlay groups (243 ± 48 µmand 207 ± 63 µm). One restora-
tion was reported fractured for the CEREC 1 group with no recur-
rent caries noted on any of the measured onlays.
Another clinical study reported on 2,328 inlays and onlays
placed in a private practice for 794 patients that were fabricated
with CEREC 1 and CEREC 2 units.18 The margin gap of 44 restor-
ations selected at randomwas measured to be 236.1 ± 96.8 µm. The
study reported a total of 35 failures over nine years. The Kaplan-
Meier survival probability was 97.4 percent at five years and
95.5 percent at nine years.
In the three clinical studies mentioned, the margin fit was
reported to be at least twice as great as what would be considered
clinically acceptable, with no significant impact on the failure rate
TABLE 1
Mean values in microns + standard deviation. Groups that are significantly different
are indicated by letters (p<0.05).
Microns Margin Axial Wall Occlusal
ProCAD/C3 65.5 ± 24.7 a 61.8 ± 21.3 a 120.3 ± 29.7 a
Paradigm/C3 66.0 ± 14.1 a 68.8 ± 21.4 a 124.5 ± 15.7 a
Empress 2 75.5 ± 29.8 a 43.8 ± 15.3 a 88.5 ± 29.9 a
Procera 63.3 ± 24.1 a 126.8 ± 35.4 b 142.3 ± 42.8 a
InCeram 83.0 ± 18.0 a 75.0 ± 39.2 a 125.3 ± 32.0 a
CEREC InLab 64.3 ± 22.5 a 77.5 ± 25.6 a 130.8 ± 18.1 a
TABLE 2
Operator Margin Axial Wall Occlusal Wall
Dentist 61.8 ± 27.9 a 86.6 ± 20.9 b 263.1 ± 38.2 b
Assistant 60.8 ± 20.5 a 88.2 ± 19.1 b 271.2 ± 41.3 b
Lab Tech 69.1 ± 26.9 a 125.4 ± 29.9 a 183.4 ± 61.2 a
TABLE 3
Operator Margin Axial Wall Occlusal Wall
RedCam/powder 58.60 ± 6.34 74.11 ± 11.12 189.03 ± 24.86
BlueCam/powder 61.07 ± 10.0 70.19 ± 12.23 184.65 ± 45.44
BlueCam/Optispray 64.61 ± 7.71 76.25 ± 5.96 188.34 ± 43.75
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?