Group Title: BMC Oral Health
Title: Use of zinc phosphate cement as a luting agent for Denzirâ„¢ copings: an in vitro study
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Title: Use of zinc phosphate cement as a luting agent for Denzirâ„¢ copings: an in vitro study
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Language: English
Creator: Soderholm, Karl-Johan
Mondragon, Eduardo
Garcea, Ileana
Publisher: BMC Oral Health
Publication Date: 2003
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Abstract: BACKGROUND:The clinical success rate with zinc phosphate cemented Procera crowns is high. The objective with this study was to determine whether CADCAM processed and zinc phosphate cemented Denzir copings would perform as well as zinc phosphate cemented Procera copings when tested in vitro in tension.METHODS:Twelve Procera copings and twenty-four Denzir copings were made. After the copings had been made, twelve of the Denzir copings were sandblasted on their internal surfaces. All copings were then cemented with zinc phosphate cement to carbon steel dies and transferred to water or artificial saliva. Two weeks after cementation, half of the samples were tested. The remaining samples were tested after one year in the storage medium. All tests were done in tension and evaluated with an ANOVA.RESULTS:Sandblasted and un-sandblasted Denzir copings performed as well as Procera copings. Storage in water or artificial saliva up to one year did not decrease the force needed to dislodge any of the coping groups. Three copings fractured during testing and one coping developed a crack during testing. The three complete fractures occurred in Procera copings, while the partly cracked coping was a Denzir coping.CONCLUSION:No significant differences existed between the different material groups, and the retentive force increased rather than decreased with time. Fewer fractures occurred in Denzir copings, explained by the higher fracture toughness of the Denzir material. Based on good clinical results with zinc phosphate cemented Procera crowns, we foresee that zinc phosphate cement luted Denzir copings are likely to perform well clinically.
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BMC Oral Health


B
Biol.l Central


Research article

Use of zinc phosphate cement as a luting agent for DenzirTM
copings: an in vitro study
Karl-Johan M Soderholm*, Eduardo Mondragon and Ileana Garcea


Address: Department of Dental Biomaterials, College of Dentistry, University of Florida, Gainesville, USA
Email: Karl-Johan M S6derholm* ksoderholm@dental.ufl.edu; Eduardo Mondragon emondragon@dental.ufl.edu;
Ileana Garcea igarcea@dental.ufl.edu
* Corresponding author


Published: 7 February 2003
BMC Oral Health 2003, 3:1


Received: 22 October 2002
Accepted: 7 February 2003


This article is available from: http://www.biomedcentral.com/1472-6831/3/1
2003 Soderholm et al; licensee BioMed Central Ltd. This is an Open Access article: verbatim copying and redistribution of this article are permitted in
all media for any purpose, provided this notice is preserved along with the article's original URL.


Abstract
Background: The clinical success rate with zinc phosphate cemented Procera crowns is high. The
objective with this study was to determine whether CADCAM processed and zinc phosphate
cemented Denzir copings would perform as well as zinc phosphate cemented Procera copings
when tested in vitro in tension.
Methods: Twelve Procera copings and twenty-four Denzir copings were made. After the copings
had been made, twelve of the Denzir copings were sandblasted on their internal surfaces. All
copings were then cemented with zinc phosphate cement to carbon steel dies and transferred to
water or artificial saliva. Two weeks after cementation, half of the samples were tested. The
remaining samples were tested after one year in the storage medium. All tests were done in tension
and evaluated with an ANOVA.
Results: Sandblasted and un-sandblasted Denzir copings performed as well as Procera copings.
Storage in water or artificial saliva up to one year did not decrease the force needed to dislodge
any of the coping groups. Three copings fractured during testing and one coping developed a crack
during testing. The three complete fractures occurred in Procera copings, while the partly cracked
coping was a Denzir coping.
Conclusion: No significant differences existed between the different material groups, and the
retentive force increased rather than decreased with time. Fewer fractures occurred in Denzir
copings, explained by the higher fracture toughness of the Denzir material. Based on good clinical
results with zinc phosphate cemented Procera crowns, we foresee that zinc phosphate cement
luted Denzir copings are likely to perform well clinically.


Background
CADCAM technologies have found increased use in den-
tistry during the past 15 years. Cerec, a system invented by
Mormann and Brandistini [1,2], was the first commercial-
ly available CADCAM system. Cerec was designed for
making ceramic inlays and veneers, and these should be
etched and bonded to the tooth with resin based luting
agents [3,41. Resin bonding was promoted because it im-


proved retention and sealed gaps around Cerec restora-
tions. Such gaps were often wider around the early Cerec
restorations than they were around cast restorations. In
addition, clinical experience evolving at that time suggest-
ed that the fracture rate of ceramic restorations decreased
if they were resin bonded rather than cemented with tra-
ditional zinc phosphate or glass ionomer cements [5].
However, because of high equipment cost and a not yet


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optimised technology, the Cerec system did not capture a
big market share. Instead, it was Procera, a system origi-
nally developed for industrial production of titanium
crowns that become the CADCAM system of choice dur-
ing the late 80th and the early 90th [6,7]. Procera did not
become popular because of its titanium crowns but rather
for its all-ceramic crowns [8]. These crowns consisted of
Al203 copings [8] with good fit and high strength on
which dental ceramics were fired to produce strong and
aesthetically appealing all-ceramic crowns. In contrast to
Cerec, Procera did not rely on an intraoral camera to make
an "electronic impression." Instead, Procera relied on tra-
ditional impressions and gypsum dies. The x, y, z-coordi-
nates of the dies were recorded at a dental laboratory by
use of an electronic stylus [9] and transferred electronical-
ly to the Procera laboratory where the Al203 coping was
made. As a result, very little extra investment cost was
needed for the dentist. The lower cost probably explains
why Procera rather than Cerec was the CADCAM that took
off among dentists.

At the time the first ceramic Procera crowns were intro-
duced, ceramic restorations were often cemented with
zinc phosphate or glass ionomer cements, despite the fact
that research had started to show the advantages with res-
in bonded ceramic restorations [10]. Resin bonding was
achieved by first etching the ceramic surface with hy-
drofluoric acid and treating the ceramic surface with a si-
lane [10]. However, acid etching did not work on the
hydrofluoric acid resistant A1203 copings. Because of the
acid resistance of A1203, and the knowledge that existed
when the first Procera crowns were introduced at the end
of the 80th and the early 90th, the first Procera crowns were
cemented with zinc phosphate and glass ionomer ce-
ments [11]. These cements were used because it was be-
lieved that the high fracture toughness of Al203 copings,
a property superior to that of traditional dental ceramics,
would result in strong ceramic crowns. Several years earli-
er McLean [ 12] had showed that after seven years of clini-
cal service, only 2.1% of anterior aluminous core crowns
cemented with zinc phosphate cement failed. His expla-
nation was that the higher fracture toughness ofAl203 de-
creased the risk of fracturing the all-ceramic crown. In
addition, by using zinc phosphate and glass ionomer ce-
ments rather then resins, Procera profited from other ad-
vantages too. For example, at the time of the introduction
of Procera crowns, dentists were better-trained and more
used to zinc phosphate and glass ionomer cements than
they were with bonding resins. In addition, removal of set
phosphate cement excess was perceived as being easier to
do with zinc phosphate cement than with resin cements.
As a consequence, dentists felt more comfortable with us-
ing zinc phosphate and glass ionomer cements, some-
thing that facilitated the introduction of Procera crowns.
Today, we know the outcome of cementing Procera


crowns with zinc phosphate and glass ionomer cements
[11,13]. Of the placed 87 crowns, 79 had been cemented
with zinc phosphate cement and the remaining 8 crowns
with glass ionomer. After 5 and 10 years of clinical service,
the cumulative survival rate showed to be 97.7% and
93.5%, respectively [11,13]. The failure rate after 10 years
due to coping/porcelain fractures was 5%, while the re-
maining 1.5% failure rate was due to poor marginal fit
that had resulted in caries [13]. In addition to these fail-
ures, minor fractures occurred in 5% of the remaining
crowns[131. These chipped crowns were polished and
continued to function normally. A total of 14% of the
crowns came loose during the observation period and
were recemented [13]. It is important to realize that these
crowns were not included in the failure frequency [13].
However, the published results [13] suggest that the use of
zinc phosphate and/or glass ionomer cement is not a ma-
jor factor considered contributing to permanent failures
of Procera crowns.

During the past few years, ZrO2 has been introduced to
dentistry [14,15]. The partially stabilized ZrO2 has a frac-
ture toughness twice that of A203 [16] suggesting that
ZrO2 based copings could become a major competitor to
Procera in the future. One such ZrO2 based system is the
Decim system that makes ZrO2 copings (DenzirM) by
milling zirconium dioxide rods. These ZrO2 copings, like
the Procera copings, cannot be etched because of the acid
resistance of ZrO2. Although a resin-based cement such as
Panavia is the recommended luting agent for Denzir at the
present time, there is an interest in determining whether
zinc phosphate and glass ionomer cements are acceptable
alternatives. That interest relates primarily to properties
such as simplicity of use, easiness of removing excess from
marginal regions after cementation, and last, but not least
important, easiness of removing a previously cemented
crown if so needed. As we know from the previously quot-
ed Procera study [13], 6.5 % of the crowns were remade
because of coping/dental porcelain fractures and caries
(6.5%). Another 5% suffered from acceptable chipping
[13]. These findings are important, because they suggest
that fractures and caries may require removal of the ce-
ramic restoration. If the coping is well bonded to the
tooth surface, the old unit must be cut away. Such a re-
moval is not easy to do with strong ceramics, and there is
a potential risk that incomplete cooling during cutting
could cause pulp irritations. Because of the latter aspects,
a clinically important question to address is whether zinc
phosphate cemented Denzir crowns compare as well clin-
ically regarding low ceramic fractures as resin based ce-
mented Denzir crowns do. However, before such clinical
trials can be justified ethically, in vitro tests must prove
that the retention of Denzir crowns is as good as that of
Procera crowns. If the retention of Denzir is as good as
that of Procera, one would expect that Denzir crowns will


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II


0 12.0


Figure I
The metal dies were machined in carbon steel according to
the specifications shown in the drawing. At the bottom of the
die a hole, 6.0 mm in diameter was drilled and later on used
for attaching the die to the testing machine.




provide as good or even better clinical results than those
reported with zinc phosphate or glass ionomer cemented
Procera crowns [11,13].

Because of the above considerations, the objectives of this
study was to determine in vitro whether Denzir copings ce-
mented with zinc phosphate cement to metal dies could
provide as good retention strength as Procera crowns ce-


mented to similar metal dies. We also wanted to deter-
mine if sandblasting would improve the retention of the
Denzir copings, or if retention over time would behave
differently if the cemented crowns were stored in water or
artificial saliva.

Methods
Metal dies
Thirty-six metal dies were machined out of carbon steel to
dimensions shown in Figure 1. During the machining
procedure all the surfaces to which the zinc phosphate ce-
ment would be attached were finished to roughness val-
ues around 6.3 Jim. The reason we used the 6.3 jim surface
roughness was that a preliminary evaluation of dies with
surface roughness values of 3.2, 6.3, 8.0 and 12.5 jim had
revealed that a surface roughness value of 6.3 jim was ide-
al for our study. With such surface texture, the cement did
not separate from the cement-model surface. Instead it
fractured within the cement or at the crown-cement
interface.

To verify the surface roughness values, the finished die
surfaces were recorded with a profilometer (Federal
Surfanalyzer System 5000, Federal Products Co, Provi-
dence, RI). The surface roughness value, R,, represents the
arithmetic average of the absolute values of the measured
roughness profile height deviations taken within the
scanned length and measured from the mean line. These
scanned recordings were made in a cervical to occlusal di-
rection over a length of 3 mm on each metal die. The sur-
face roughness value for that distance was then used to
determine the average value for all the dies.

Impressions and gypsum dies
Before impressions were made of the metal dies, a 1.6 mm
thick ring was inserted and located to the marginal part of
the simulated crown preparation (Figure 2). Impressions
were then made in a polyvinylsiloxane impression mate-
rial (Light Body, President, Coltene AG, Altstatten, Swit-
zerland) supported by an individual tray. The tray had
been covered with an adhesive to secure a reliable tray-im-
pression attachment, and the space between the tray and
the die was 2 mm. One hour after the impression had
been made it was poured with a Type IV gypsum (Silky-
Rock, Whip-Mix Corporation, Louisville, KY) and allowed
to set during the night. After impression removal and die
inspection, the 36 gypsum dies were sent to laboratories
making Denzir and Procera copings.

Ceramic copings
Twenty-four Denzir and twelve Procera copings were or-
dered from Denzir and Procera certified laboratories. All
ceramic copings were made 0.6 mm thick and with a ce-
ment space corresponding to 60 jim. That spacing started
0.8 mm from the cervical margin and reached its maximal


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Co


m






LC) C
o c'.j


Figure 2
A metal ring, shown to the left (side and top view), was
placed on the metal die (grey field on the die shown to the
right) before the impression was made.




thickness after 1.2 mm from that margin. When the
copings arrived from the laboratories, all 36 copings were
checked regarding their fit.

Sandblasting
Twelve of the Denzir copings were sandblasted on the in-
ner surfaces with A1203 (particle size = 50 itm) using an
air pressure of 2 bars (200 kPa). The sandblasting process
was done with the sandblasting tip located at a distance of
10 mm from the ceramic surface. The centre of the sand-
blasting stream targeted the transition from the occlusal to
the proximal inner surfaces. The entire inner surface was
then sandblasted by rotating the coping four times, each
time 90 degrees. Each of these locations was sandblasted
for 5 s.

Inner surface roughness
The inside of each coping was scanned with the profilom-
eter. The scans were collected within the 0.5 to 1.5 mm in-
terval from the cervical margin. From these scans the Ra
values were calculated.

Cementation
The 1.6 mm ring, located in the cervical region of the
preparation when the silicone impression was made was
removed and replaced with a 1.55 mm thick washer with
an outer diameter of 18 mm (Figure 3). A zinc phosphate


Figure 3
Before the copings were cemented, the metal ring shown in
Figure 2 was removed and replaced with a machined washer,
shown to the left (side and top view). The placement of that
washer is shown as the grey field on the die to the right.





cement (Phosphate Cement, Heraeus Kulzer, Dormagen,
Germany) was mixed on a room tempered glass plate. For
each portion, 1.2 g powder was mixed with 0.5 mL liquid.
The powder was divided into six portions (two 1/16th,
one 1/8t, and three 1/4th portions). First, one 1/16th por-
tion was mixed for 10 s, then the second 1/16th portion
for 10 s, followed by the 1/8th portion for another 10 s. A
1/4th portion was then added and mixed for 15 s followed
by another 1/4th portion, also mixed for 15 s. The final 1/
4th was then added and mixed for 30 s. Thus, a total mix-
ing time of 1 min and 30 s was used. The mixed cement
was then placed inside the ceramic coping, which was ro-
tated 90 degrees as the coping was seated on the metal die.
Thirty seconds after completed mixing, a load of 2 N was
placed on the crown, and the load acted on the crown for
5 min. Excess material was removed after 7.5 min counted
from the time the coping was loaded with the 2 N load.

Retention force
Fourteen days after cementation, half of the specimens (3
Denzir as received, 3 Denzir being sandblasted, and 3
Procera, all stored in distilled water; and 3 Denzir as re-
ceived, 3 Denzir being sandblasted, and 3 Procera, all
stored in artificial saliva) were tested in tension (Figure 4)
until failure using a specially designed testing device in an
Instron Universal Testing machine at a load rate of 0.5
mm/min. After one year (3 Denzir as received, 3 Denzir
being sandblasted, and 3 Procera, all stored in distilled



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Table I: Ra mean values (Mean) and standard deviations (SD) for the different coping materials expressed in microns.

Material Treatment Mean SD

Denzir Sandblasted 2.01 0.65
Denzir Untreated 2.13 0.52
Procera Untreated 2.47 0.76





Table 2: Results of ANOVA evaluation

Source F Anova SS Mean Square F Value Pr>F


MATER
STORAGE
TIME
MATE R*STO RAGE
MATER*TIME
STORAGE*TIME


261306.722
1827002.778
2628721.778
2620642.389
299347.722
1814409.000


130653.361
1827002.778
2628721.778
1310321.194
149673.861
1814409.000


0.7522
0.0553
0.0235
0.0737
0.7220
0.0561


water; and 3 Denzir as received, 3 Denzir being sandblast-
ed, and 3 Procera, all stored in artificial saliva), the re-
maining 18 specimens were also tested as described
earlier.

Fifteen minutes after the initiation of the cementation
process the cemented copings with the steel dies and
washers were transferred to distilled water or artificial sa-
liva and then stored in an oven at 37C. The artificial sa-
liva [17] was of the following composition: 0.1 L each of
25 mM K2HPO4, 24 mM Na2HPO4, 150 mM KHCO3,
100 mM NaCl, and 1.5 mM MgCl2. To this were added
0.006 L of 25 mM citric acid and 0.1 L of 15 mM CaCl2.
The pH was then adjusted to 6.7 with NaOH or HC1 and
the volume made up to 1 L. To avoid bacterial growth, we
added 0.05% by weight thymol to the artificial saliva. All
chemicals were ACS-grade (American Chemical Society).

Statistical evaluation
The force values, needed to dislodge the copings, were
used for the statistical evaluation. One-way and two-way
ANOVA:s were used to determine significant differences
between materials, storage medium and storage time as
well as interactions of these (ANOVA, SAS Institute, Cary,
NC, USA). Comparisons between the individual groups
were also conducted using Duncan's multiple range tests.
All test were conducted on the 95% significance level.

Results
Metal dies
The profilometer readings of the metal die surfaces gave
an average surface roughness value (Ra) of 5.49 + 0.98


gm. These roughness values were primarily based on wave
shaped surface where the distance between the peaks was
around 200 gm and where the main peak-to-main valley
distance was around 20 gm (Figure 5).

Ceramic copings and effect of sandblasting
The surface roughness values of the insides of the different
coping groups are shown in Table 1. No significant differ-
ence existed between the three combinations (p =
0.2239).

Retention force
The statistical analysis revealed that the most important
factor affecting the retention force was storage time (Ta-
bles 2 and 5). There was no difference between the two
main materials or whether the Denzir copings had been
sandblasted or not (Table 3).

Comparing the storage media could not prove whether
such a difference existed (p = 0.082) (Table 4). In this
comparison, no consideration was taken for the different
material groups and storage times. When storage time
only was compared there was a significant increase in re-
tention force with time (Table 5).

As seen in the Tables 6, 7 and 8, there are large differences
among the different test groups (standard deviation ~30%
of the mean value). From Table 2, we can also see that
there are no significant interactions, although the materi-
al/storage and storage/time interactions are pretty close.





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66.5 mm




Metal band






SP 300.0 mm




Coping Pi



























Figure 4
The die with the cemented coping was inserted into a specially designed testing device (left drawing). The washer was located
under the horizontal top bar shown above and the die protruded through that bar. A metal pin (P) was inserted through a
metal band and a hole drilled through the die. That attachment is shown in the central drawing. The 300.0 mm long metal band
was attached to the universal testing machine that generated a recordable force (in the direction of the arrow shown in the fig-
ure). The metal band and the attachments are shown in the reduced drawing to the right.









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100.0


Figure 5
Surface profile of the metal die in contact with the zinc phosphate cement.


Of the Procera copings, two copings fractured during test-
ing after 14 days of storage and one coping fractured after
one year. Of all tested Denzir copings, not a single coping
fractured. However, careful inspection with transillumi-
nating light revealed that one of the Denzir copings tested
after 1 year had a crack that extended from the cervical re-
gion to the occlusal region.

Discussion
Effect of coping composition and sandblasting
Table 1 shows that there was no significant difference in
surface roughness between the three evaluated ceramic
coping groups. The low value of the sandblasted Denzir
copings suggest that the machining process generated a
surface roughness that was at least as rough as a machined
and sandblasted Denzir surface. Because of these findings,
sandblasting conducted under the conditions evaluated in
this study is not recommended for Denzir copings.

Effect of storage
The statistical evaluation of variables such as material,
storage and time as well as interactions of these variables
revealed that storage time was significant regarding reten-
tion force (Table 2). Storage medium and interaction be-
tween time and storage medium were almost significant
on the 95% significance level.


There was no difference between the three material groups
regarding retentive force (Table 3). That finding most like-
ly relates to the similarities in surface roughness values
among the three groups (Table 1). The similarities in re-
tentiveness among the three material groups are
important. Because of the published success rate of
Procera after 10 years in clinical service [13], our in vitro
results suggest that Denzir copings, sandblasted or not,
and cemented with zinc phosphate cement are likely to
perform equally well as Procera crowns, at least regarding
retention.

Based on the lower fracture frequency identified among
the Denzir copings, our findings suggest that Denzir cop-
ings might perform even better than Procera crowns. Of
the twelve tested Procera copings, three complete fractures
occurred in the Procera copings, while of the twenty-four
tested Denzir copings only one had a detectable crack that
did not even result in a clear fracture during testing. At the
present time, though, one cannot exclude that these differ-
ences are coincidental. However, the higher fracture
toughness of Denzir, almost twice as high as that of
Procera, probably explains the lower fracture tendency of
Denzir identified in this study.




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Table 3: Mean retentive forces (Mean) and standard deviations (SD) of the different material groups (DECBL = Denzir sandblasted;
DECUNBL= un-sandblasted; PROCERA) expressed in Newtons. The values are based on pooling the values generated at the two
storage times and the two storage media.


Duncan Grouping


N = number of samples


Table 4: Mean retentive forces (Mean) and standard deviations (SD) of the different storage groups (AS = artificial saliva; Water)
expressed in Newtons. The values generated by pooling the material group values and the two storage times.


Duncan Grouping


N = number of samples


Table 5: Mean retentive forces (Mean) and standard deviations (SD) of the two different time groups (Months) expressed in Newtons.
The values are based on pooling the material groups and storage media results for the two time groups.


Duncan Grouping


N = number of samples


Table 6: Mean retention forces (Mean) and standard deviations (SD) for the different material groups (DECBL = Denzir sandblasted;
DECUNBL= un-sandblasted; PROCERA) and storage groups (AS = artificial saliva; Water) expressed in Newtons. The results are based
on pooling the values for the two storage times.


Mean SD

2184.2 1313.8
1283.3 433.7
1716.3 728.1
2024.5 663.3
2045.0 526.0
1286.0 383.6


N = number of samples


Future studies regarding CADCAM technologies need to
focus on flaw formation that might be induced during
manufacturing. One may suspect that a milling process
like the one used to make the Denzir copings, induce
more flaws than a pressing and sintering technique as the
one used to make Procera copings. However, there is no


proof available supporting that assumption at the present
time. In the case of Procera, one cannot exclude the possi-
bility that flaws are induced when copings are pressed and
that these flaws may not heal completely during sintering.
Besides, during sintering and cooling, thermal stresses
may be induced that trigger crack formation in the future.


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Material

DECUNBL
DECBL
PROCERA


Mean SD

1870.4 683.2
1733.8 1044.7
1665.5 591.4


Storage

AS
WATER


Mean SD

1981.8 886.4
1531.3 597.3


Months


Mean SD

1486.3 547.7
2026.8 891.8


Material

DECBL
DECBL
DECUNBL
DECUNBL
PROCERA
PROCERA


Storage

AS
WATER
AS
WATER
AS
WATER


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Table 7: Mean retention force (Mean) and standard deviation (SD) expressed in Newtons for the different material groups (DECBL =
Denzir sandblasted; DECUNBL= un-sandblasted; PROCERA) and storage times (Months). The results are based on pooling the values
for the two storage media.


Material


Months


DECBL
DECBL
DECUNBL
DECUNBL
PROCERA
PROCERA


Mean SD

1358.8 486.5
2108.7 1351.6
1587.3 558.8
2153.5 722.8
1512.8 662.2
1818.2 524.5


N = number of samples



Table 8: Mean values (Mean) and standard deviations (SD) of the two storage media (AS = artificial saliva; Water) and storage times
(months) expressed in Newtons. The values of the different material groups have been pooled.


Storage

AS
AS
WATER
WATER


Mean SD

1487.1 521.6
2476.6 920.2
1485.6 604.5
1577.0 622.9


N = number of samples


From the above argumentation, flaws may very well be in-
duced during manufacturing of both Denzir and Procera
copings. Thus, differences in either fracture toughness or
flaw sizes/densities, or a combination of the two, would
explain why the Procera copings had higher fracture ten-
dency. The higher fracture toughness of zirconia favours
Denzir and would explain the lower fracture frequency
seen in these copings. However, whether the flaws intro-
duced in Denzir copings are smaller or bigger than those
present in Procera copings is not known and needs to be
investigated further. Flaw formation during manufactur-
ing becomes very important when we compare different
zirconia crowns that now are available on the market.
Some of them are made by milling industrially sintered
and processed zirconia, while other are made by milling
presintered zirconia that is then sintered.

During our evaluation, we used the force levels generated
by the copings that fractured during testing. One could ar-
gue that such values should be excluded because the sam-
ples fractured. However, we did not exclude those samples
of the following reasons: First. the force levels on the cop-
ings that fractured were not lower than those of those that
did not fracture. Second, we were not able to determine
whether the fracture occurred before or after debonding
had occurred because of the speed of the dislodgement/
fracturing process.


Storage of the copings in artificial saliva resulted in force
values almost significantly higher than those stored in wa-
ter (Table 4). A possible explanation is that some of the
ions, for example phosphate ions, diffused into the ce-
ment and pushed the setting reaction toward an increased
precipitation reaction. Such an explanation can be related
to the setting reaction of zinc phosphate cements. As the
storage time increased, the required force needed to dis-
lodge the copings also increased (Table 5). A likely expla-
nation is that as time passed the setting reaction became
more complete. There is also a possibility that corrosion
of the steel dies and release of iron ions from the dies af-
fected the setting reaction of the zinc phosphate cement.
Such a corrosion process might also have increased the
surface roughness at the cement-dye interface and thereby
also increased the mechanical retention.

Even though time improved the retention of the cemented
copings, one should not extrapolate that value to the clin-
ical situation. Clinically, the coping would be exposed to
different loads during the entire observation time. In our
study, no such forces acted on the cemented coping from
time of cementation to time of testing. However, the im-
proved results with time shows that storage media such as
water and artificial saliva by themselves do not decrease
the retention force. This finding is important, because it
implies that other factors are more important when we try
to explain why the retention of zinc phosphate cemented


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crowns sometimes fail over time. Loading conditions and
fracture toughness of the luting agent are such factors.

Our results suggest that a clinical evaluation of Denzir
crowns cemented with zinc phosphate cement are likely
to perform as well as Procera crowns cemented with zinc
phosphate cement. However, based on Burke et al.'s [5]
review, which supported the use of resin cements, one can
question the rational of even considering using zinc phos-
phate cement as a luting agent in a clinical study. There are
at least two reasons justifying such a clinical study. First,
by assuming that the high success rate of zinc phosphate
cemented Procera crowns is likely to be equally high with
Denzir copings, justifies such a study ethically. Second,
the simplicity of using zinc phosphate cements, their ease
of removal from marginal regions after setting, and the
ease with which a zinc phosphate cemented crown can be
removed if remake is needed, are beneficial clinical advan-
tages that cannot be neglected.

Having justified the use of zinc phosphate cement in a
clinical study, it is also important to emphasize that such
an evaluation should consider retention and solubility of
the luting agent too. In the Procera study conducted by
Odman and Andersson [13], retention failures requiring
recementation were not included in their impressive suc-
cess rate. Present evidences suggest that resin bonding im-
proves the results with ceramic restorations [5], even
though these claims are not conclusive [18,19]. There is
no doubt that retention is an important factor to consider,
but one must also accept that strong bonding can also be
a drawback if the crown needs to be removed. In the latter
case, a well-bonded ceramic restoration can be a bigger
clinical challenge than the need for recementing a less
well-bonded restoration.

One often hears the claim that resin cements decrease the
fracture frequency of ceramics. Such a claim is justified for
some ceramic systems, but is may not be valid when we
are dealing with high strength ceramic copings like the
ones used in both Procera and Decim. Instead, some clin-
ical studies dealing zinc phosphate cemented alumina
copings are so good that one can question whether resin
bonded copings will outperform these results. It is first
when comparative studies take all these pros and cons
into consideration, as we know whether resin bonded alu-
mina or zirconia copings outperform zinc phosphate ce-
mented alumina or zirconia copings.

Conclusions
Denzir copings, cemented with zinc phosphate cement to
steel dies, perform at least as well as Procera copings ce-
mented with the same zinc phosphate after storage in wa-
ter and artificial saliva for one year when tested in vitro.
The use of sandblasting under the conditions given in this


study does not enhance the internal surface roughness or
the retentiveness of the Denzir copings. During a one-year
storage time in water or artificial saliva, the retentiveness
did not decrease. Instead, the retentiveness of the samples
increased.

Competing interests
Decim AB, SkellefteA, Sweden, funded this study. The con-
tract was supervised by the University of Florida through
University Project Number 00032218 and covered all ex-
penses associated with this project.

Authors' contributions
Decim supplied us with the steel dies. Mr. E Mondragon
made the impressions and the stone dies. A Procera labo-
ratory and a Decim laboratory made the copings. Mrs. I
Garcea did the surface measurements and prepared the ar-
tificial saliva. Dr. K-JM S6derholm contributed with all
other research components related to this project (experi-
mental design, sandblasting, cementation, testing, statisti-
cal evaluation and final report).

Acknowledgements
Decim AB, Skelleftea, Sweden through University of Florida Project
Number 00032218, funded this project.

References
I. Mormann WH, Brandestini M and Lutz F The Cerec system: com-
puter-assisted preparation of direct ceramic inlays in I
setting. Quintessenz 1987, 38:457-470
2. Mormann WH and Brandestini M Cerec-System: computerized
inlays, onlays and shell veneers. Zahnarztl Mitt 1987, 77:2400-
2405
3. Horn HR Porcelain laminate veneers bonded to etched
enamel. Dent Clin North Am 1983, 27:671-684
4. Mormann WH, Brandestini M, Ferru A, Lutz F and Krejci I Marginale
Adaptation von adhAsive Porzelaninlays in vitro. Schweiz
Monatsschr 1985, 95:1119-1129
5. Burke FJT, Fleming GJP, Nathanson D and Marquis PM Are adhesive
technologies needed to support ceramics- An assessment of
the current evidence. J Adhes Dent 2002, 4:7-22
6. Andersson M, Bergman B, Bessing C, Ericson G, Lundquist P and Nil-
son H Clinical results with titanium crowns fabricated with
machine duplication and spark erosion. Acta Odontol Scand
1989, 47:279-86
7. Nilson H, Bergman B, Bessing C, Lundquist P and Andersson M Tita-
nium copings veneered with Procera ceramics: a longitudi-
nal clinical study. IntJ Prosthodont 1994, 7:115-119
8. Andersson M, Razzoog ME, Od6n A, Hegenbarth EA and Lang BR
Procera: a new way to achieve an all-ceramic crown. Quintes-
sence Int 1998, 29:285-296
9. Persson M, Andersson M and Bergman B The accuracy of a high-
precision digitizer for CAD/CAM of crowns. J Prosthet Dent
1995, 74:223-229
10. Roulet J-F, Soderholm K-JM and Longmate J Effects of treatment
and storage conditions on ceramic/composite bond
strength. Dent Res 1995, 74:381-387
I I. Od6n A, Andersson M, Krystek-Ondracek I and Magnusson D Five-
year clinical evaluation of Procera AIICeram crowns.J Prosthet
Dent 1998, 80:450-456
12. McLean JW Dental Ceramics: Proceedings of the First Inter-
national Symposium on Ceramics. Chicago: Quintessence 1983,
13. Odman P and Andersson B Procera allceram crowns followed
for 5 to 10 years: a prospective clinical study. Interj Prosthodont
2001, 14:504-509



Page 10 of 11
(page number not for citation purposes)


BMC Oral Health 2003, 3








BMC Oral Health 2003, 3


http://www.biomedcentral.com/1472-6831/3/1


14. Meyenberg KH, Luthy H and Scharer P Zirconia posts: a new all-
ceramic concept for nonvital abutment teeth. j Esthet Dent
1995, 7:73-80
15. Sadoun M and Perelmuter S Alumina-zirconia machinable abut-
ments for implant-supported single-tooth anterior crowns.
Pract Periodontics Aesthet Dent 1997, 9:969-970
16. Richerson DW Modern ceramic engineering. Marcel Dekker Inc.,
New York 1992, 360
17. Arvidson K and Johansson EG Galvanic current between dental
alloys in vitro. Scandj Dent Res 1985, 93:467-473
18. McCommic JT, Rowland W, Shillingburg HT and Duncanson MG Ef-
fect of luting media on the compressive strengths of two
types of all-ceramic crown. Quintessence Int 1993, 24:405-408
19. Sjogren G, Lanitto R and Tillberg A Clinical evaluation of all-ce-
ramic crowns (Dicor) in general practice. J Prosthet Dent 1999,
81:277-284

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