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127
Taiwan Journal of Pediatric Dentistry／臺灣兒童牙醫學雜誌
Vol. 18 No. 4 December 2018
研究論文 Research Article
DOI: 10.6319/TJPD.201809_18(4).0001
Retentive Strengths for Prefabricated Primary Molar
Zirconia Crowns Using Five Dierent Cements
Luz Adriana Rosato, DDS, MSD1, Jung-Wei Chen, DDS, MS, PhD2, Clyde Roggenkamp,
DDS, MSD, MPH3, Jui-Min Su, DDS, MS4
◆Dr. Rosato is a practitioner in Newark, California, while completing this paper she was a pediatric dental resident of Advanced Education
Program in Pediatric Dentistry, Department of Pediatric Dentistry at Loma Linda University. 1
◆Dr. Chen is professor and program director, Advanced Education Program in Pediatric Dentistry, Department of Pediatric Dentistry at
Loma Linda University. 2
◆Dr. Roggenkamp is an associate professor, Department of Restorative Dentistry at Loma Linda University. 3
◆Dr. Su is an assistant professor, Department of Prosthodontics at Loma Linda University.4
Abstract
Purpose: To assess retentive strengths of 5 commercially available cements with prefabricated primary molar
zirconia crowns.
Methods: Seventy ve prefabricated primary molar zirconia crowns were cemented on extracted human teeth using
5 dierent cements (Ketac Cem Maxicap, FujiCEM 2, BioCem, RelyX Unicem 2 and RelyX Luting Plus
Automix N=15 per group). Following thermocycling, 5000 cycles from 5º to 55º C, crown retentive
strengths data were collected and statistically analyzed using one-way ANOVA with LSD post hoc test (P
<0.05).
Results: Mean retentive strengths are: Ketac Cem 482.4N±87, FujiCEM 2 354.9N±121, BioCem
462.7N±138, RelyX Unicem 2 409.0N±171 and RelyX Luting 233.5N±170. e retentive strengths
were statistically signicant (P=0.014) among the 5 groups, but not the cement failure rankings (P=0.47).
Conclusions: There is a significant difference in the retentive strengths for cementing prefabricated primary molar
zirconia crowns among the 5 different cements. Ketac Cem has the highest retention force, followed
by BioCem, RelyX Unicem, Fuji CEM II, and RelyX Luting. e majority of cement failures occurred
between the cement and the tooth.
Key words: Prefabricated, zirconia crowns, retention, cement
Corresponding author: Jung-Wei Chen, DDS, MS, PhD
Address: Loma Linda University School of Dentistry, Department
of Pediatric Dentistry
11092 Anderson Street, Loma Linda, CA, 92350
Tel: +1-909-558-4690
Fax: +1-909-558-0322
E-mail: jwchen@llu.edu
128 臺灣兒童牙醫學雜誌Taiwan Journal of Pediatric Dentistry Vol. 18 No. 4 December 2018
研究論文 Research Article
DOI: 10.6319/TJPD.201809_18(4).0001
▍Methods
Seventy-five extracted human posterior teeth were
used, with 1-mm deep circumferential grooves placed around
the roots for retention. Teeth were mounted in Ultradent
plastic specimen molds (Ultradent products, Inc. South
Jordan, UT) using office paper binder clips to hold them
centered on each hole and maintaining the long axis of each
tooth perpendicular to the base of the mold. e holes in the
Ultradent molds were lled with self-cure EpoxyCure 2 epoxy
resin (Buehler, Lake Bluff, IL). Each tooth was embedded
with the cemento-enamel junction (CEJ) at least 1 mm above
the level of the epoxy. Specimens were maintained in 100%
humidity during the entire length of the study.
Teeth were prepared to fit primary molar zirconia
crowns in accordance with the manufacturer's recommended
tooth reduction for the crowns (EZ Pedo, Loomis, CA). e
occlusal surfaces of the preparations were cut flat with the
EZ-Prep 001 donut-shaped bur. Axial reduction was with
the bur perpendicular to the occlusal table. The handpiece
was secured in an apparatus to orient the bur parallel to the
long axis of the tooth. An EZ-Prep 002 bur was used to create
a chamfer margin equal to the full thickness of the bur tip.
(is bur has a taper of 8 degrees giving a total convergence
of 16 degrees). With the EZ-Prep 004 ame bur, the chamfer
margin was then removed. Final axial tooth preparations
ended with margins feathered as the manufacturer
recommended. See Fig. 1. EZ Pedo size 4 for first primary
▍Introduction
Zirconia crowns have recently found favor as adequate
restorations for permanent teeth.1 In the past decade, factors
of esthetics, cost, toxicity and durability of tooth-colored
restorative materials have increasingly influenced treatment
planning in pediatric patients as well.2,3 Yttrium-oxide
stabilized zirconia (Y-TZP) is chemically and dimensionally
stable, has high mechanical strength and fracture-resistance,
making it an attractive material for restorative dentistry.4-6
When placing zirconia crowns for primary teeth, the tooth
must be reduced to t the crown only passively, causing less
retention than custom made crowns. Furthermore, due to
non-adhesive characteristics of the material, cementation of
zirconia crowns can be challenging.3
Zirconia crowns are made of a crystalline dioxide of
zirconium with mechanical properties that are comparable
to those of metals, but with greater esthetic quality.7 Because
zirconia crowns for primary teeth are prefabricated and non-
adjustable, manufacturers recommend a passive seating when
cementing them.8 Zirconia crowns that are custom-made
can be cemented using conventional adhesive methods, with
resin-based luting agents reportedly providing high retention
and improved marginal adaptation.9 Although a PubMed
search shows many studies have evaluated the retentive
strength of zirconia crowns for permanent teeth, there are
none for primary teeth. Currently, some prefabricated zirconia
crown manufacturers recommend either glass ionomer or
resin modied glass ionomer cements, however no literature
publications were found to support the use of any particular
cement.
Retentive strength data are very important to predict
the long-term clinical performance of zirconia crowns for
primary teeth.10 The objective of this study is to investigate
the retentive strength of prefabricated primary molar zirconia
crowns (EZ Pedo, Loomis, CA) cemented with 5 different
commercially available cements (Ketac Cem Maxicap,
FujiCEM 2, RelyX luting plus automix, RelyX Unicem 2 and
BioCem), and identify their cementation failure paern.
Fig. 1. Tooth mounted in epoxy block, handpiece
held by surveyor type positioning guide.
129
Taiwan Journal of Pediatric Dentistry／臺灣兒童牙醫學雜誌
Vol. 18 No. 4 December 2018
occlusal surfaces was recommended by the manufacturer.
After removing excess cement it had to set for 5 min per
manufacturer recommendations.
Twenty-four hours following cementation, all
specimens underwent 5,000 thermal cycles between
water temperatures of 5o C and 55o C, in accordance
with International Organization of Standardization (ISO)
specifications.11,12 Beading wax was placed as a seal around
the margin (crown-tooth interface) and on the top part of
the epoxy block. e crown part of each specimen was then
embedded in self-cure epoxy resin blocks that adapted to the
receiving xture of the Instron E3000 (InstronR, Northwood,
MA). See Fig. 2. Each specimen was placed in the Instron
E3000 for crown pull-off testing at a speed of 0.5 mm/min,
and maximum forces (Newtons) of removal were recorded.
See Fig. 3.
Specimens were then evaluated according to cement
failure ranking as follows: 1- cement failure with >75% of
cement left on the tooth, 2- cement failure with 51-75%
cement le on the tooth, 3- failure with 50% of cement le on
DOI: 10.6319/TJPD.201809_18(4).0001
陳容維 等/Jung-Wei Chen et al
molars were tried on and used for this study. To have a
standard prep, a negative impression of the internal surface of
the crown was made and the dimensions were taken directly
from the impression. e measurements were ≤6 mm mesio-
distally, ≤7 mm bucco-lingually, ≥2 mm axial height on the
mesial and distal side and ≥4 mm axial height on the buccal
and lingual surface. Final tooth dimensions after reduction
had to suit these criteria so that the zirconia crown would t
onto the prepared tooth passively.
After all teeth were prepared, rinsed with water, and
dried with gauze to avoid excessive drying, they were
randomly divided into 5 groups (N=15) for cementation. All
cements were mixed and applied according to manufacturer's
instructions and seated with finger pressure by the same
investigator. Group 1 was cemented with glass Ionomer
cement, Ketac Cem Maxi Cap (3M ESPE St. Paul, MN).
This cement comes in a capsule that requires being held in
an activator for 4 sec, then placed in an amalgamator for 10
sec. e manufacturer recommends removing excess cement
after 7 minutes from the beginning of the mix. Group 2
was cemented with Resin Modified Glass Ionomer cement
FujiCEM 2 (GC America Inc. Alsip, IL). is cement and the
following 3 cements come in an automix syringe. Working
time for FujiCEM 2 is 2 min 15 sec, and finishing can be
done 4 min 30 sec after seating. Group 3 was cemented
with Resin Modified Glass Ionomer with added calcium
and phosphates, BioCem (NuSmile, Ltd. Houston, TX).
A flash light-cure for 5 sec is required on facial and lingual
surfaces before removing excess cement, then light-curing
an additional 10 sec on the facial and lingual a er removing
excess cement. Group 4 was cemented with Self-adhesive
Resin Cement, RelyX Unicem 2 (3M ESPE St. Paul, MN)
for which the manufacturer recommended a ash light-cure
of 2 sec, then removing the excess cement, followed by light-
curing for an additional 20 sec on facial, lingual and occlusal
aspects. Finally, group 5 was cemented with Resin Modi ed
Glass Ionomer, RelyX Luting plus Automix (3M ESPE St.
Paul, MN). Tack light-curing for 5 sec on buccal, lingual and
Fig. 2. Illustration of cross section of the specimen
preparation for retention strength test using Instron
E3000.
130 臺灣兒童牙醫學雜誌／ Taiwan Journal of Pediatric Dentistry Vol. 18 No. 4 December 2018
研究論文 Research Article
DOI: 10.6319/TJPD.201809_18(4).0001
ANOVA with LSD post hoc tests and Kruskal-Wallis test (P
<0.05) were performed using IBM SPSS 22.0 (Chicago, IL).
▍Results
Descriptive statistics for the retentive strength for the
5 di erent cement groups are summarized in Table 1. Ketac
Cem has the highest retention force, followed by BioCem,
RelyX Unicem, Fuji CEM II, and RelyX Luting. (Fig. 4) One-
way ANOVA showed a signi cant di erence in retention load
among the 5 groups (P =0.014). LSD Post Hoc test showed
there was a significant difference in the retention between
Ketac Cem and FujiCEM 2 (P=.016), Ketac Cem and RelyX
Luting (P=.004), FujiCEM and BioCem (P=.040), BioCem
and RelyX Luting (P=.011). RelyX Unicem had no signi cant
di erence with any of the other cements (Table 2).
Cement failure rankings were recorded in Table 3. Most
of the failures are in categories 4 and 5 which indicated more
than 50% of cement le on the crown. FujiCEM 2 had 100%
of the specimens in category 5, BioCem had 78% in category
the crown and 50% le on the tooth, 4- failure with 51-75%
of the cement le on the crown, and 5- failure with >75% of
cement le on the crown.
In some cases there were substrate failures in which
either the root fractured or the grip of the epoxy holding
the root or zirconia crown failed. For tooth fracture cases a
completely new specimen was made and the test repeated.
For specimen grip failures, the crown or the root, whichever
was involved, was remounted in the epoxy resin and the
Instron tests repeated. When these second tests were done,
the higher retention value of the two tests was used. If there
was a dislodgement of the specimen from the epoxy in the
second test, then the higher force from the 2 tests was used,
assuming that the cement strength was the greater of those 2
forces.
▍Statistical analysis
Data were tabulated in Excel with means, medians, and
standard deviations displayed in graphs and charts. One-way
Fig. 3. Specimen positioned in
the Instron E300 ready for tensile
strength test.
Fig. 4. Line graph of retentive strength and signifi cant difference among
groups.
131
Taiwan Journal of Pediatric Dentistry／臺灣兒童牙醫學雜誌
Vol. 18 No. 4 December 2018
DOI: 10.6319/TJPD.201809_18(4).0001
Table 1. Summary of Descriptive statistics of retentive strength by different cement groups
Mean
(N)
Std Deviation
(N)
95% Confidence Interval for
Mean Minimum
(N)
Maximum
(N)
Lower Bound
(N)
Upper Bound
(N)
Ketac Cem Maxicap 482.45 87.34 434.08 530.82 340.03 604.66
FujiCEM 2 354.99 121.18 287.88 422.11 142.46 565.12
BioCem 462.73 137.82 386.41 539.06 181.64 686.23
RelyX Unicem 2 409.06 171.01 314.36 503.06 38.2 603.6
Relyx Luting Plus Automix 327.77 170.18 233.52 422.01 42.16 540.04
Table 2. LSD Post hoc test summary between the groups
(I) Cement Group (J)Cement Group Mean Difference (I-J)
P
value
Ketac Cem Maxicap FujiCEM 2
BioCem
RelyX Unicem
RelyX Luting
127.46
19.71
73.38
154.68
.016*
.703
.159
.004*
Fuji CEM 2 Ketac Cem
BioCem
RelyX Unicem
RelyX Luting
-127.46
-107.74
-54.07
27.22
.016*
.040*
.298
.599
BioCem Ketac Cem
Fuji CEM 2
RelyX Unicem
RelyX Luting
-19.71
107.74
53.07
134.96
.703
.040*
.301
.011*
RelyX Unicem 2 Ketac Cem
Fuji CEM 2
BioCem
RelyX Luting
-73.38
54.07
-53.67
81.29
159
.298
.301
.119
RelyX Luting Plus
Automix
Ketac Cem
Fuji CEM 2
BioCem
RelyX Unicem
-154.68
-27.22
-134.96
-81.29
.004*
.599
.011
.119
* Indicate the P-value is less than 0.05.
Table 3. Frequency table of cement failure Ranking
Cement failure ranking Ketac Cem
Maxicap FujiCEM 2 BioCem RelyX
Unicem2
Relyx Luting
Plus Automix Total
1. >75% cement le in the tooth
2. 51-75% cement le in the tooth
3. 50% in tooth 50% in crown
4. 51-75% cement le in the crown
5. >75% cement le in the crown
Total
0
0
2
6
0
8
0
0
0
0
11
11
0
0
0
3
11
14
0
0
0
7
5
12
0
0
0
8
4
12
0
0
2
24
31
57
Tooth f ractured
Dislodge from the epoxy block
2
5
2
2
0
1
0
3
0
3
4
14
陳容維 等/Jung-Wei Chen et al
132 臺灣兒童牙醫學雜誌Taiwan Journal of Pediatric Dentistry Vol. 18 No. 4 December 2018
研究論文 Research Article
When the materials were evaluated without pretreatment
of the ceramic, RelyX Unicem (4.9 MPa), Superbond (4.8
MPa), RelyX Luting (4.7MPa), Panavia (4.0 MPa) and
Dyract Cem (3.3 MPa) showed the highest median retentive
strength values and were not signicantly dierent from each
other. The values in the present study were converted into
megapascals (MPa) using a surface area of 0.000118 m2 for
comparison with other studies. Ketac Cem had a relatively
low retentive strength of 1.9 MPa.15 However, in the present
study Ketac Cem had the highest retentive strength with a
mean of 4.6 MPa, which was in the same range as the resin
cements in the study conducted by Ernst et al. In the present
study RelyX Unicem with 3.4 MPa and RelyX Luting with 2.7
MPa had retention strengths lower than the compared study.
e main dierence between the 2 studies is the thickness of
the cement since the present study used prefabricated crowns.
In 2010, Heintze conducted a systematic review
evaluating laboratory studies of the adhesive properties of
luting agents in crown retention tests.16 He chose 18 studies
that reflected clinical situations. These studies involved
human teeth in which the occlusal surfaces were trimmed at,
a dental surveyor was used for mounting the teeth and a pre-
set taper used to standardize the preparations.17-19 In general,
these studies reported that the resin luting agents had higher
stress failure limits than glass ionomer cements. However, in
some cases there was no statistically signicant dierence.16
This differs from the present study because there was a
statistically signicant dierence among the cements studied,
with glass ionomer (Ketac Cem) having the highest tensile
strength, followed by the RMGI with calcium phosphate
(BioCem). There was no statistically significant difference
between Ketac Cem and BioCem.
Zirconia crowns for primary teeth cannot be adjusted,
and require only a passive seating for their cementation,
which can compromise their retention.9 The cement
thickness when cementing these prefabricated crowns is not
uniform and may be greater than the thickness of a custom
made crown. us, the excess space needs to be compensated
5, Ketac Cem Maxicap had 75% in category 4, RelyX Luting
plus automix had 66% in category 4 and RelyX Unicem
presented 58% in category 4. However, the Kruskal-Wallis test
determined that there was no signicant dierence in cement
ranking failure among the 5 cements (P =0.47).
▍Discussion
Results of this study indicate a significant difference
in the retentive strengths among the 5 cements tested in
cementing prefabricate primary zirconia crowns. Rippe et al.13
evaluated the tensile retention of custom made crowns made
of Y-TZP with different types of cements. They used self-
cured resin cement, dual-cure Bis-GMA-based resin cement,
resin modified glass ionomer cement, self-adhesive cement,
and zinc phosphate. ey found that resin cements (Multilink
and RelyX ARC) demonstrated signicantly higher retention
values relative to those obtained for the self-adhesive resin
cement, glass ionomer, and zinc phosphate cements; with
mean tensile strengths of 200.9 N for Multilink and 223.44 N
for RelyX ARC respectively.13 e results in the present study
were higher for all the cements used, with the mean tensile
strength ranging between 327.22 N and 482.45 N.
Palacios et. al. evaluated resin cement with adhesive
agent, resin modified glass ionomer, and self-adhesive resin
cement. They measured removal strength of custom-made
zirconium oxide ceramic copings designed with CAD/CAM
technology for permanent teeth and found the 3 cements had
no statistical difference, with 647.78 N for RelyX Unicem,
652.68 N for Panavia and 782.04 N for RelyX Luting.14 e
values on that study were higher than those in the present
study. However, it is important to remember that the crowns
used in the present study are prefabricated crowns retroed
to primary teeth.
Another study by Ernst et al. evaluated the retentive
strength of zirconium oxide ceramic crowns on extracted
teeth. They studied 8 different cements including resin
cements, compomer, resin modified glass ionomer cement,
glass ionomer cement, and a self-adhesive resin luting cement.
DOI: 10.6319/TJPD.201809_18(4).0001
133
Taiwan Journal of Pediatric Dentistry／臺灣兒童牙醫學雜誌
Vol. 18 No. 4 December 2018
study did not perform any surface treatment to the tooth
or to the crown. A study by Rippe et al.,13 tested 3 different
types of surface treatments: cleaning with isopropyl alcohol,
tribochemical silica coating, or application of a layer of glass
porcelain plus silanization.13 However, the tensile strength
values of the cements in that study were lower than the values
in the present study, which did not employ any crown surface
treatment.
An earlier study by Palacios et al.14 evaluating the
retention of zirconium oxide ceramic crowns, treated the
internal surface of the copings with aluminum oxide abrasion
followed by ultrasonic bath cleaning with isopropyl alcohol.
eir results indicated greater retention dislodgement forces
than the present study, which is likely attributable to the
surface treatment. A study by Ernst et al.15 found that the
pretreatment with Rocatec tribochemical coating did not
significantly improve the retentive strength of the cements
studied.
To avoid any signicant changes in the zirconia crowns'
properties, the present study was challenged to nd a way to
retain the crown portion of the specimen for a pull-off test.
Retention of the crown to the epoxy was mainly due to the
undercut area near the gingival margin of the crown. There
were specimens in which the crown dislodged from the
epoxy before dislodging from the tooth. When this occurred
and the retentive strength was higher than those of the
other specimens in the same group, that value was recorded
as the retention load for that specimen. In cases where the
load before crown dislodgment from the epoxy was low, the
crown was mounted again in an epoxy block and the higher
value was recorded. e cement that had the greatest crown
dislodgement from epoxy was Ketac Cem, which was also
the cement with the greatest mean retention load. It can be
reasonably assumed that crown dislodgment from the epoxy
was because the retentive strength of the cement to the crown
was in excess of the retentive strength of epoxy to the crown.
The present in vitro study tried to simulate mouth
conditions by using human teeth, maintaining all specimens
by the cement. Mehl et al.20 evaluated the influence of glass
ionomer, polycarboxylate or resin cement film thicknesses
on the crown retention after tensile testing. Their results
showed a signicant dierence in retention between cement
thickness of 14.4 ± 3 m and cement thickness of 50 m.20
Other studies associated a decreased test load failure with
increased resin cement thickness.21,22 ese data suggest that
the cement film thickness could have affected the retentive
strength of the crowns in the present study.
Several manufacturers currently fabricate zirconia
crowns for pediatric dentistry: EZ Pedo, Cheng, Kinder
Krown and NuSmile. Their retentive strengths may be
affected by the various internal surface designs of each
manufacturer. For this study EZ Pedo crowns were chosen.
EZ Pedo crowns have a feature called Zir-Lock Ultra, which
are mechanical undercuts designed to double the internal
surface area and provide mechanical undercuts to help lock
the crowns in place. In addition to the grooves, the company
explains that aluminum oxide blasted on inner surfaces creates
surface roughness to further enhance adhesive properties.
EZ Pedo zirconia crowns also have a margin lock feature to
prevent cement washout,23 and may help cement to remain
bonded to the crown.
In the present study, cement failures were evaluated
to assess their nature. The majority of crown dislodgements
occurred as an adhesive failure with 23.3% having >75% of
cement left on the crown. There were no cases with >50%
of cement left on the tooth. The "Zir-Lock Ultra" feature
in the EZ-Pedo prefabricated crowns was possibly a factor
improving the cement retention.
Further studies are recommended to evaluate relative
retention strengths among the several different brands of
prefabricated zirconia crowns.
Surface treatment and exposure to wetness can affect
the physical properties of zirconia.24 A recent systematic
review found that loss of retention caused 19% of the clinical
failures of custom made zirconia crowns.25 Since it followed
the cement manufacturer's recommendations, the present
DOI: 10.6319/TJPD.201809_18(4).0001
陳容維 等/Jung-Wei Chen et al
134 臺灣兒童牙醫學雜誌Taiwan Journal of Pediatric Dentistry Vol. 18 No. 4 December 2018
研究論文 Research Article
3. Dual-cure RMGI (RelyX Luting Plus Automix)
showed the lowest retentive strength of the cements
studied, next to reinforced RMGI (FujiCEM 2).
4. The type of cement did not affect the cement-failure
ranking in these prefabricated zirconia crowns. In
the majority of specimens (70.6%) cement material
remained 100% to 75% on the crown.
▍References
1. Ortorp A, Kihl ML, Carlsson GE. A 5-year retrospective study
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seing. J Dent 2012;40(6):527-30.
2. Zimmerman JA , Feigal RJ, Till MJ, Hodges JS. Parental aitudes
on restorative materials as factors influencing current use in
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3. Ashima G, Sarabjot KB, Gauba K, Mial HC. Zirconia crowns
for rehabilitation of decayed primary incisors: an esthetic
alternative. J Clin Pediatr Dent 2014;39(1):18-22.
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systems with clinical recommendations: a systematic review. J
Prosthet Dent 2007;98(5):389-404.4
5. Piconi C, Maccauro G. Zirconia as a ceramic biomaterial.
Biomaterials 1999;20(1):1-25.
6. Zarone F, Russo S, Sorrentino R. From porcelain-fused-to-
metal to zirconia: clinical and experimental considerations.
Dent Mater 2011;27(1):83-96.
7. Planells del Pozo P, Fuks AB. Zirconia crowns--an esthetic and
resistant restorative alternative for ECC aected primary teeth. J
Clin Pediatr Dent 2014;38(3):193-5.
8. Townsend JA, Knoell P, Yu Q, et al. In vitro fracture resistance
of three commercially available zirconia crowns for primary
molars. Pediatr Dent 2014;36(5):125-9.
9. Koutayas SO, Vagkopoulou T, Pelekanos S, Koidis P, Strub
JR. Zirconia in dentistry: part 2. Evidence-based clinical
breakthrough. Eur J Esthet Dent 2009;4(4):348-80.
10. Edelhoff D, Ozcan M. To what extent does the longevity of
xed dental prostheses depend on the function of the cement?
Working Group 4 materials: cementation. Clin Oral Implants
Res 2007;18 Suppl 3:193-204.
11. Yuasa T, Iijima M, Ito S, et al. Eects of long-term storage and
thermocycling on bond strength of two self-etching primer
adhesive systems. Eur J Orthod 2010;32(3):285-90.
12. Saghiri MA, Asatourian A, Garcia-Godoy F, Gutmann JL,
Sheibani N. The impact of thermocycling process on the
dislodgement force of different endodontic cements. Biomed
Res Int 2013;2013:317185.
13. Rippe M, Amaral R, Amaral R, et al. Evaluation of Tensile
Retention of Y-TZP Crowns Cemented on Resin Composite
Cores: Eect of the Cement and Y-TZP Surface Conditioning.
at 100% humidity and using thermocycling for aging. With
the design of the prefabricated crowns it was expected that
some cement washout would inherently occur. However, in
this study, cement remained bonded to the crown even aer
articial aging.
Palacios et al.14 had added retention bars to the zirconia
crowns to help with the mounting of the crown to the epoxy
block. But since the pediatric zirconia crowns available in the
market are prefabricated, adding the bars was not considered a
feasible option for the present study. Embedding the crown in
epoxy resin in this study was considered an eective method
that might be used for follow-on prefabricated zirconia crown
studies.
It is recognized that the present in vitro study was free
of oral conditions like gum bleeding and saliva contamination
at the time of cementation. These factors potentially affect
retention strengths of the zirconia crowns clinically. Future
investigations might test with known contamination agents,
or assess the relative retentiveness with the same cement but
dierent commercially available crowns.
Instead of using the rst molar zirconia crown as done
in this study, the authors would recommend choosing the
second molar crown because of its more pronounced exterior
buccal undercut contour that can allow beer retention of the
crown to the epoxy block. Long-term clinical studies are also
recommended.
▍Conclusions
1. There is a significant difference in the retentive
strengths among the 5 cements used to cement
prefabricated primary zirconia crowns (ANOVA
P=0.014). Ketac Cem has the highest retention force,
followed by BioCem, RelyX Unicem, Fuji CEM II, and
RelyX Luting.
2. Among the cement types studied, glass ionomer
(Ketac Cem Maxicap) has the greatest retentive
strength followed by RMGI (BioCem) and resin
cement (RelyX Unicem 2).
DOI: 10.6319/TJPD.201809_18(4).0001
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Taiwan Journal of Pediatric Dentistry／臺灣兒童牙醫學雜誌
Vol. 18 No. 4 December 2018
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