8
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CERECDOCTORS.COM
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QUARTER 3
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2015
Multilink Sprint was removed from the market due to generally
poor results unrelated to this study. One crown fractured between
two and three years. Analysis of the crown revealed it was actually
0.9 mm at the point of fracture rather than the recommended 1.5
mm thick. The reported success rate of 96.3 percent at 4.6 years
is at least as good if not better than the reported success rates for
PFM or zirconia veneered crowns.
Another clinical study that included full contour e.max CAD
crowns reported on 235 lithium disilicate crowns in 76 patients
placed by a single dentist in private practice (Cortellini & Canale
2012). The purpose of the study was to evaluate the clinical effec-
tiveness of feather-edgemargins for lithiumdisilicate crowns. The
rationale for the clinical study was based on previous in vitro work
indicating that the fracture resistance of feather edge lithium
disilicate crowns was not significantly different from chamfer
or shoulder margin designs (Cortellini, et al, 2014). The use of
a feather-edge margin was proposed to be a more conservative
tooth preparation design allowing for more enamel at the margins
for adhesive bonding of the ceramic. One-hundred-and-thirty-six
crowns were located in the anterior area, and 99 posterior crowns
included 59 premolars and 40 molars.
The crown preparation included a minimum space of 0.3 mm
at the margin, 0.5 mm along the axial walls and 1 to 1.5 mm on
the occlusal surface. These dimensions are significantly reduced
compared to the recommended dimensions of 1.2 axially and a
minimum of 1.5 mm occlusally. All the crowns were monolithic
and fabricated by a laboratory technician using either full-contour
CAD-CAM (23 crowns, e.max CAD, Ivoclar) or a pressed tech-
nology (212 crowns, e.max Press, Ivoclar), andwere individualized
with a surface staining technique.
Crowns were adhesively bonded using Scotchbond (3M ESPE)
and Variolink Veneer (Ivoclar) for crowns with equigingival or
supragingival margins. Crowns were adhesively bonded using
Multilink Automix (Ivoclar) for crowns with subgingival margins.
The study reported a single lithium disilicate molar crown frac-
ture after three years of clinical service. The author suggested that
the strength of the crowns was ensured by both by an adequate
occlusal thickness and by a reinforcement of the marginal area by
means of a slight enlargement of the emergence profile through a
thin increment of ceramic material simulating the CEJ.
All the crowns were adhesively bonded to the preparation
providing maximum strength to the crowns; however, the stated
occlusal reduction was only 1 mm to 1.5 mm that would result in
crowns with occlusal thickness less than the 1.5 mm recommended
by the manufacturer. There were no debonded crowns and no
biological complications. No differenceswere reported between the
CAD/CAM-manufactured and press-fit lithium disilicate crowns.
However, only about 10 percent of the total crowns were fabri-
cated with a CAD/CAM technique. Although some crowns were in
clinical service for up to four years, the mean follow-up was only 18
months — which is a relatively short clinical period to determine
definitive outcomes on ceramic restorations as the results of fatigue
failure may not be seen until three years of clinical service.
Another prospective clinical study placed 100 IPS e.max CAD
crowns (Fasbinder, et al, 2015). The preparation had shoulder
margins with a rounded internal line angle, a minimum of 1.5 mm
occlusal and 1.2 mm axial reduction. Each crown was fabricated
and delivered chairside in one appointment. A CEREC 3/Bluecam
(Sirona Dental) was used to fabricate the monolithic crowns. The
crown preparations followed the manufacturer’s recommended
dimensions of 1.2 axial reduction with a minimum of 1.5 mm
occlusal reduction.
The first 23 crowns were cemented with a self-etching bonding
agent and resin cement (ML= Multilink-Automix; Ivoclar). The
second 39 crowns were cemented with an experimental self-
adhesive resin cement (EC = Experimental Cement; Ivoclar). The
remaining 38 crowns were cemented with a self-adhesive, light-
cured resin cement (SP = SpeedCEM; Ivoclar).
Tooth sensitivity was evaluated by report to cold stimulus. Mild
sensitivity was reported on 15 percent of the teeth at one week,
with all sensitivity resolved by four weeks. The crowns were eval-
uated by two examiners using a modified USPHS rating at each
annual recall. There was no difference in the gingival and plaque
indexes between the IPS e.max CAD crowns and control teeth.
Four crowns debonded during the study; three of the crowns that
were cemented with the experimental cement debonded at 13,
20 and 36 months, and were re-cemented with Multilink with no
further problems identified. One crown debonded at 36 months
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FA S B I N D E R
TABLE 2:
LITHIUM DISILICATE CROWNS RECALL
Year crown
No. of
Follow-up
Follow-up
placed
crowns
range (months) mean (months)
2007
22
36-48
42.59
2008
39
35-24
31.2
2009
77
23-12
17.49
2010
97
11-6
8.12
Total
235
6-48
18.04
