Original article Evaluation of shear bond strength of veneering ceramics and zirconia fabricated by the digital veneering method Ji-Young Sim MS a , Wan-Sun Lee MPH a , Ji-Hwan Kim MPH, PhD a, * , Hae-Young Kim DDS, PhD b , Woong-Chul Kim MPH, PhD a a Department of Dental Laboratory Science and Engineering, Graduate School, Korea University, Anam-dong 5-ga, Seongbuk-gu, Seoul 136-713, Republic of Korea b Department of Public Health Science, Graduate School & BK21+ Program in Public Health Science, Korea University, Anam-dong 5-ga, Seongbuk-gu, Seoul 136-713, Republic of Korea j o u r n a l o f p r o s t h o d o n t i c r e s e a r c h 6 0 ( 2 0 1 6 ) 1 0 6 – 1 1 3 a r t i c l e i n f o Article history: Received 6 June 2015 Received in revised form 14 October 2015 Accepted 4 November 2015 Available online 8 December 2015 Keywords: Zirconia core Shear bond strength Layering method Heat pressing method Digital veneering method a b s t r a c t Purpose: The purpose of this study was to evaluate the shear bond strength (SBS) of veneering ceramic and zirconia fabricated by the digital veneering method. Methods: A total of 50 specimens were fabricated, i.e., 10 specimens each for the metal- ceramic (control) group and the four zirconia groups. The zirconia groups comprised speci- mens fabricated by the digital veneering method, the heat pressing method, and hand layering method for two groups, respectively. Furthermore, the shear bond strength was measured with a universal testing machine (Model 3345, Instron, Canton, MA, USA) and statistically analyzed using one-way ANOVA set at a significance level of P < 0.05. The corresponding mode of failure was determined from Scanning Electron Microscope (FESEM JSM 6701F, Jeol Ltd., Japan) observations. Results: One-way analysis of variance (ANOVA) revealed that the metal-ceramic group had the highest SBS (43.62 MPa), followed by the digital veneering method (28.29 MPa), the heat pressing method (18.89 MPa), and the layering method (18.65, 17.21 MPa). The samples fabricated by digital veneering had a significantly higher SBS than the other zirconia samples (P < 0.05). All of the samples exhibited mixed failure. Conclusions: Veneering ceramic with a zirconia core that was fabricated via the digital veneering method is believed to be effective in clinical use since, its shear bond strength is significantly higher than that resulting from the conventional method. # 2015 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved. * Corresponding author at: Department of Dental Laboratory Science and Engineering, College of Health Science, Korea University, Anam- dong 5-ga, Seongbuk-gu, Seoul 136-713, Republic of Korea. Tel.: +82 2 3290 5666; fax: +82 2 940 2879. E-mail address: [email protected](J.-H. Kim). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/jpor http://dx.doi.org/10.1016/j.jpor.2015.11.001 1883-1958/# 2015 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved.
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Original article
Evaluation of shear bond strength of veneeringceramics and zirconia fabricated by the digitalveneering method
Ji-Young Sim MSa, Wan-Sun Lee MPHa, Ji-Hwan Kim MPH, PhDa,*,Hae-Young Kim DDS, PhDb, Woong-Chul Kim MPH, PhDa
aDepartment of Dental Laboratory Science and Engineering, Graduate School, Korea University, Anam-dong 5-ga,
Seongbuk-gu, Seoul 136-713, Republic of KoreabDepartment of Public Health Science, Graduate School & BK21+ Program in Public Health Science, Korea University,
Anam-dong 5-ga, Seongbuk-gu, Seoul 136-713, Republic of Korea
j o u r n a l o f p r o s t h o d o n t i c r e s e a r c h 6 0 ( 2 0 1 6 ) 1 0 6 – 1 1 3
a r t i c l e i n f o
Article history:
Received 6 June 2015
Received in revised form
14 October 2015
Accepted 4 November 2015
Available online 8 December 2015
Keywords:
Zirconia core
Shear bond strength
Layering method
Heat pressing method
Digital veneering method
a b s t r a c t
Purpose: The purpose of this study was to evaluate the shear bond strength (SBS) of
veneering ceramic and zirconia fabricated by the digital veneering method.
Methods: A total of 50 specimens were fabricated, i.e., 10 specimens each for the metal-
ceramic (control) group and the four zirconia groups. The zirconia groups comprised speci-
mens fabricated by the digital veneering method, the heat pressing method, and hand
layering method for two groups, respectively. Furthermore, the shear bond strength was
measured with a universal testing machine (Model 3345, Instron, Canton, MA, USA) and
statistically analyzed using one-way ANOVA set at a significance level of P < 0.05. The
corresponding mode of failure was determined from Scanning Electron Microscope (FESEM
JSM 6701F, Jeol Ltd., Japan) observations.
Results: One-way analysis of variance (ANOVA) revealed that the metal-ceramic
group had the highest SBS (43.62 MPa), followed by the digital veneering method
(28.29 MPa), the heat pressing method (18.89 MPa), and the layering method
(18.65, 17.21 MPa). The samples fabricated by digital veneering had a significantly
higher SBS than the other zirconia samples (P < 0.05). All of the samples exhibited mixed
failure.
Conclusions: Veneering ceramic with a zirconia core that was fabricated via the digital
veneering method is believed to be effective in clinical use since, its shear bond strength
is significantly higher than that resulting from the conventional method.
# 2015 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved.
* Corresponding author at: Department of Dental Laboratory Science and Engineering, College of Health Science, Korea University, Anam-dong 5-ga, Seongbuk-gu, Seoul 136-713, Republic of Korea. Tel.: +82 2 3290 5666; fax: +82 2 940 2879.
plus, BEGO, Bremen, Germany) were used as the metals in this
study. Wu et al. [35] obtained lower bonding strengths in
beryllium-free Ni-Cr alloys compared to their Be-containing
counterparts. In addition, De Melo et al. [36] reported that the
metal-ceramic bonding strength depends on the composition
of the alloy, coefficient of thermal expansion, and thickness of
the oxidation film.
Table 4 – Means of adhesive and cohesive fractured areasin percentages and failure mode. A: adhesive fracturedarea at interface, C: cohesive fractured area withinveneer.
Group Mean of A and C inpercentage
Failure mode (%)
A (%) C (%)
MC 76.2 23.8 Mixed 100
LZL 63.6 36.4 Mixed 100
LZD 37.5 62.5 Mixed 100
IZL 62.2 37.8 Mixed 100
IZP 64.7 35.3 Mixed 100
j o u r n a l o f p r o s t h o d o n t i c r e s e a r c h 6 0 ( 2 0 1 6 ) 1 0 6 – 1 1 3112
Ishibe et al. [18] reported that the sample with upper
porcelain fabricated by hot pressing had a higher SBS
(40.41 MPa) than that of the hand-layered sample (30.03 MPa).
Furthermore, Henriques et al. [37] showed that, compared to the
hand layer method, heat pressing increased the bonding
strength between the zirconia and the ceramic by reducing
the porosity of the ceramic. Although the heat-pressed (IZP)
sample in the present study had a slightly higher mean SBS than
that of the hand-layered (IZL, LZL) samples, the statistical
difference in the strengths was insignificant. The similarity
in the IZP and IZL interfacial bond strength is believed to
result from the ZirLiner coating on the zirconia surface of these
two samples.
Kanat et al. [12] measured a SBS of 49 MPa for a zirconia
sample whose upper porcelain was fabricated via CAD-on
veneering; this samples was stronger than its counterpart,
which was fabricated by the conventional veneering method.
In addition, Guess et al. [38] reported that a CAD/CAM-
veneered zirconia crown, which had fewer inherent flaws, had
a higher resistance to failure than a crown fabricated by the
hand-layering method.
Ceramic tends to fail as a result of the propagation of flaws
and cracks [39]. In a ceramic restoration, the number and size
of the flaws are associated with the materials and fabrication
method [17]. Hence, a digital veneering system, in which the
veneering process is simple and the number of firings is
minimized, was predicted to have the least number of flaws.
The LZD group presented a significantly higher bond strength
compared to the other zirconia groups. This was thought to be
due to the use of a ceramic block and the fabrication of a
specimen by conducting only one firing process for bonding
between the upper ceramic block and the zirconia.
Previous studies reported that the firing process causes
shrinkage of the porcelain and a reduction in the bond
strength of the interface as a result of the rapid change in
temperature [40].
In addition, Al-Dohan et al. [20] reported SBS’s of 22–
31 MPa for all-ceramic restorations with zirconia cores.
Although the bonding strength (28.29 MPa) of the LZD
samples examined in this study fell within the suggested
range, the strengths of the hand-layered and heat-pressed
samples were not within this range. However, direct
comparison may be inappropriate since the factors influenc-
ing the bonding strength (i.e., the shape of the specimens and
area of the contacting surface) in the previous studies differ
from those of the present study.
Cohesive failure, which occurs in the intra-ceramic layer,
was the dominant mode of failure in previous studies of failed
metal-ceramic specimens [18,41]. However, adhesive failure,
in which the oxidation film becomes delaminated from the
metal while remaining attached to the ceramic, occurred
predominantly in this study. This failure results from the
separation of the metal from the ceramic owing to deforma-
tion that stems from the generation of dislocations or cracks
owing to temperature changes that occur at the boundary
surface with increasing thickness of the oxidation film.
All the zirconia samples exhibited mixed failure, which is
consistent with the failure mode of a previous study [41].
Observations of the failed veneer surfaces revealed the
least number of defects, including pores, in the LZD group. As a
result, a higher cohesive strength for the veneering ceramic
compared to the other zirconia groups was predicted.
However, the percentage of the surface that remained with
the veneering ceramic was the highest. This indicated that the
LZD group had the best interface bond strength. Therefore, the
ceramic in the LZD sample should provide better long-term
stability in the intra-oral environment than those fabricated
by either the hand-layering or heat-pressing methods.
In this study, samples fabricated by digital veneering
exhibited the highest SBS of all the zirconia samples. However,
the fact that even this group of samples was still significantly
weaker than those of the MC group, reveals the need for
continuous research in order to improve the bonding strength
of zirconia prostheses. This study is also limited in some
respects. For example, the specimens used did not reflect the
shapes of clinical dental restoration materials and the
experimental conditions did not replicate the intra-oral
environment. Therefore, research that replicates the intra-
oral environment and uses specimens with similar shapes to
those of the dental restoration materials, is required in order
to avoid these limitations.
5. Conclusions
The results of the present study revealed that the method used
to produce veneering ceramics influences the SBS of the
zirconia prosthesis. The digital veneering method is consid-
ered to be effective in clinical use since the consequent SBS is
significantly higher than that resulting from the heat pressing
or layering method.
Conflict of interest
The authors report no conflict of interest directly relevant to
the content of this work.
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