UNIVERSIDADE ESTADUAL PAULISTA
“JÚLIO DE MESQUITA FILHO”
Instituto de Ciência e Tecnologia
Campus de São José dos Campos
ORIGINAL ARTICLE DOI: https://doi.org/10.4322/bds.2023.e4001
1
Braz Dent Sci 2023 Oct/Dec;26 (4): e4001
Evaluation of short- and long-term bond strength of zirconia after
different surface treatments
Avaliação da resistência de adesão de curto e longo prazo de zircônia após diferentes tratamentos de superfície
Nicolas PINTO-PARDO
1
, Priscilla LEDEZMA ARAYA
1
, Matias DEISCHLER
1
, Leonardo AGUILERA
1
, Pablo READI
2
1 - University Viña del Mar, Odontología, Escuela de Ciencias de la Salud. Viña del Mar, Chile.
2 - Universidad del Desarrollo, Facultad de Odontología. Santiago, Chile.
How to cite: Pinto-Pardo N, Ledezma Araya P, Deischler M, Aguilera L, Readi P. Evaluation of short- and long-term bond strength of
zirconia after different surface treatments. Braz Dent Sci. 2023;26(4):e4001. https://doi.org/10.4322/bds.2023.e4001
ABSTRACT
Objective: The aim of the study was to evaluate the short and long-term effects of different surface treatments
on the bond strengths of zirconia. Material and Methods: 225 blocks of sintered zirconia samples (4 x 4 x
3 mm) were divided into ve groups and subjected to different surface treatments: control group (without
surface treatment), alumina group (sandblasting [25-µm-aluminum-oxide]), alumina+Ambar Universal-APS
(AU) group, CoJet group (silica-coated [30-μm silica-modied aluminum particles]), and CoJet+AU group.
Subsequently, zirconia samples were cemented against resin samples (total dimensions: 8x8x6mm) and assigned
to three storage conditions: dry, humid (articial saliva at 37°C for 30-days) or thermocycling [100.000-cycles]
(n=15 per group). The microtensile bond strength (µTBS) was determined using a universal testing machine.
The failure modes were observed and analyzed using a stereomicroscope. Normality tests, descriptive statistics,
and two-way ANOVA, followed by post-hoc comparisons, were performed to evaluate the effect of surface
treatments and storage conditions on µTBS (α=0.05). Results: μTBS was inuenced by surface treatment in
the short and long-term (P<0.0001). The highest values were found in CoJet+AU in dry (33.51 ±2.48 MPa),
humid (32.87 ±2.68 MPa) and thermocycling (21.37 ±1.68 MPa) storage conditions compared with others.
Interestingly, no signicant differences in μTBS were found among alum +AU and CoJet alone under any of
the three storage conditions. Adhesive failure increased in all groups after thermocycling, but CoJet+AU had
the lowest values of adhesive failure compared with others. Conclusion: The combination of CoJet and Ambar
universal as a surface treatment for zirconia specimens provides signicantly higher short and long-term bond
strengths of adhesive cementation.
KEYWORDS
Adhesives; CoJet; MDP; Sandblasting; Zirconia.
RESUMO
Objetivo: O objetivo do estudo foi avaliar os efeitos de curto e longo prazo de diferentes tratamentos de superfície
na resistência de adesão da zircônia. Material e Métodos: 225 blocos de amostras de zircônia sinterizada
(4 x 4 x 3 mm) foram divididos em cinco grupos e submetidos a diferentes tratamentos de superfície: grupo
controle (sem tratamento de superfície), grupo de alumina (jateamento de 25 μm de óxido de alumínio), grupo
alumina+Ambar Universal-APS (AU), grupo CoJet (partículas de alumínio modicadas por sílica de 30 μm), e
grupo CoJet+AU. Posteriormente, as amostras de zircônia foram cimentadas em amostras de resina (dimensões
totais: 8x8x6mm) e designadas para três condições de armazenamento: seco, úmido (saliva articial a 37°C por
30 dias) ou ciclagem térmica (100.000 ciclos) (n=15 por grupo). A resistência de adesão de microtensão (µTBS)
foi determinada usando uma máquina de teste universal. Os modos de falha foram observados e analisados
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Braz Dent Sci 2023 Oct/Dec;26 (4): e4001
Pinto-Pardo N et al.
Evaluation of short- and long-term bond strength of zir conia after different surface tr eatments
Pinto-Pardo N et al.
Evaluation of short- and long-term bond strength of zirconia
after different surface treatments
INTRODUCTION
New ceramics have been developed to meet
the functional and aesthetic requirements of
dentistry [1]. Its main characteristics include
translucency, biocompatibility, high mechanical
resistance, and color mimetics to obtain high
aesthetic results [2]. Zirconium oxide ceramics
(ZrO
2
, 3
rd
generation) have been widely
used in prosthetic dentistry, and the clinical
success of restorations depends not only on
esthetic or functional results but also on bond
durability between dental tissues and prosthetic
substrates [3-6].
Yttrium-stabilized tetragonal zirconia
polycrystals (Y-TZP) are widely used in aesthetic
dentistry because of their excellent mechanical
and esthetic properties owing to the stabilization
of the tetragonal phase [7,8]. Its mechanical
properties are comparable to those of metals, but
the naturality of color increases its election [9].
Y-TZP crowns can be cemented by conventional
or resin cements, and the latter reports the highest
bond strength values to teeth structures [8,10];
however, the authors reported a high level of
debonding of Y-TZP crowns [11-14].
To improve the adhesion rates of non-silicate
ceramics such as Y-TZP, many surface treatments
have been evaluated [15], including solutions
composed of multiple acids, such as phosphoric
acid (H
3
PO
4
) [16] or hydrouoric acid (HF) [17]
with poor results because of the absence of a glass
phase in its structure [7].
Airborne-particle abrasion (APA) as
surface treatment is an appropriate method for
increasing the surface energy and wettability of
substrates to improve their bond strength [18].
The generated surface roughness helps create an
active surface with micromechanical gearing into
the connection interface [19-21]. APA treatment
with aluminum oxide could increase the bond
strength in Y-TZP crowns, although the results
are contradictory [22-25].
Chemical surface treatments can also increase
bond strength during crowns cementation [26].
Few studies have shown that a tribochemical
silica-coated (TSC) [27-30] or a functional
monomer of 10-methacrylixydecyl dihydrogen
phosphate (MDP) [31] can increase the bond
strength between cement and ceramic crowns.
New zirconia cementation protocols use self-
adhesive resin cements and new universal
adhesives that contain MDP, producing
Y-TZP crowns with stable and durable bond
strength [32-34].
During the consumption of food and liquids,
dental materials undergo thermal cycling [35].
To simulate temperature variations in the
oral cavity, thermal cycling-controlled water
baths have been used in in vitro studies [36].
It is currently reported the use of thermal cycles
between 5°C and 55°C to simulate the aging
of dental materials [37] and 100.000 cycles is
equivalent to 10 years of in vivo function, which
is considered a long-term time period for dental
material evaluations [38].
The effect of the combination of sandblasting
and universal adhesives containing MDP on
Y-TZP samples and the long-term bond strength
after adhesive cementation has not been fully
elucidated. The aim of this in vitro study was to
evaluate the effects of different surface treatment
methods in combination with or without MDP
monomers on the microtensile bond strength
(µTBS) between zirconia samples and resin
usando um estereomicroscópio. Testes de normalidade, estatísticas descritivas e ANOVA de duas vias, seguidas
de comparações pos-hoc, foram realizados para avaliar o efeito dos tratamentos de superfície e das condições de
armazenamento na µTBS (α=0.05). Resultados: A μTBS foi inuenciada pelo tratamento de superfície a curto e
longo prazo (P<0.0001). Os valores mais altos foram encontrados em CoJet+AU nas condições de armazenamento
a seco (33.51 ±2.48 MPa), úmido (32.87 ±2.68 MPa) e ciclagem térmica (21.37 ±1.68 MPa) em comparação
com os outros. Curiosamente, não foram encontradas diferenças signicativas na μTBS entre alum +AU e CoJet
sozinho em nenhuma das três condições de armazenamento. A falha adesiva aumentou em todos os grupos após
a ciclagem térmica, mas CoJet+AU teve os valores mais baixos de falha adesiva em comparação com os outros.
Conclusão: A combinação de CoJet e Ambar Universal como tratamento de superfície para espécimes de zircônia
proporciona resistências de adesão signicativamente mais altas a curto e longo prazo para cimentação adesiva.
PALAVRAS-CHAVE
Adesivos; CoJet; MDP; Jateamento-de-areia; Zircônia.
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Pinto-Pardo N et al.
Evaluation of short- and long-term bond strength of zir conia after different surface tr eatments
Pinto-Pardo N et al.
Evaluation of short- and long-term bond strength of zirconia
after different surface treatments
blocks in different storage environments during
short or long-term in vitro aging. The rst null
hypothesis of the present study posited that the
µTBS between zirconia-resin blocks would not
be significantly affected by the combination
of surface treatment and the use of an MDP-
containing adhesive, regardless of the storage
conditions or time. The second null hypothesis
posited that the in vitro aging duration (short- vs.
long-term) would not signicantly inuence the
µTBS between zirconia-resin blocks, regardless
of the combination of surface treatment and the
use of an MDP-containing adhesive.
MATERIAL AND METHODS
Samples
A total of 225 zirconia samples (4 × 4 ×
3 mm) were cut from pre-sintered green zirconia
blocks [3
rd
generation]; (Cercon Zirconia,
Degodent, Harnau, Germany) using a diamond
cutting saw (Isomet 1000; Buehler, Lake Bluff, IL,
USA). Specimen surfaces were then sequentially
polished with 600-1200-2000-2400 grit silicon
carbide abrasives (3M ESPE, St. Paul, MN,
USA). After polishing, all samples were sintered
at 1,350°C for 2 h (Heat DOU; Degodent,
Harnau, Germany). The samples were cleaned
ultrasonically in an acetone solution for 5 min
and then air-dried. A total of 225 composite
resin samples (Opallis [FGB, Brazil])
(4 mm × 4 mm × 3 mm) were fabricated using a
custom silicone mold. Two composite resin layers
(1.5 mm) were applied to the custom mold and
each layer was light-polymerized (Demi Ultra;
Kerr) separately for 20 s.
Surface treatments
Zirconia samples were randomly divided and
assigned to 5 different surface treatments: (1)
Control group: no surface treatment; (2) Alumina
group (Alum): aluminum oxide airborne-particle
abrasion (25 µm particle size, WA25, Heraeus
Kulzer, Hanau, Germany) was sandblasted with
a pressure of 0.45 MPa (15 s/cm2) at a distance
of 10 mm; and (3) Alumina + AU group (Alum +
AU): alumina airborne-particle abrasion and
universal adhesive “Ambar APS” (FGM, Brazil)
application; (4) CoJet group: silica-coated
airborne-particle abrasion (30 µm particle size,
CoJet, 3M ESPE) blasted onto the bonding surface
of zirconia samples with a pressure of 0.45 MPa
(15 s/cm
2
) and a distance of 10 mm; (5) CoJet +
AU group: silica-coated airborne-particle abrasion
and universal adhesive “Ambar APS” (FGM,
Brazil) application.
Bonding procedure
The zirconia and resin samples were bonded
with resin cement “Allcem dual” (FGM, Brazil)
after surface treatments under a constant load
of 1 kg/F to standardize the exerted pressure.
Excess resin cement was removed using foam
pellets, and glycerin was applied around the
bonding margin to prevent the formation of an
oxygen inhibition layer. All cemented samples
were light-polymerized (Demi Ultra; Kerr) from
four sides for 20 s each.
Environment storage
The experimental groups were then divided
into three subgroups: (1) dry environment, (2)
storage in articial saliva (ISO/TR10271) at 37°C
for 30 days, and (3) subjected to 100.000 thermal
cycles in articial saliva (5°C and 55°C).
Microtensile bond test
All the samples were then mounted in acrylic
tubes, and µTBS (MPa) [39] was evaluated using
a universal testing machine (T-6102K; Bisco) at
a crosshead speed of 1.0 mm/min until failure.
Cross-sections of the ceramic samples were
analyzed using a microscope (Leica DM500; Leica
Microsystems) at ×40 magnication to assess
the fractured interfaces. Failure conditions were
classied into three types: adhesive (failure at the
bonding interface), cohesive (failure in zirconia,
resin, or resin cement), and mixed (adhesive and
cohesive failures).
Statistical analysis was performed using
the GraphPad Prism software (version 9.0)
for Windows 10. µTBS values were analyzed
using 2-way ANOVA followed by post-hoc
pairwise comparisons to evaluate the effects of
surface treatments, storage conditions, and their
interactions. Tukey’s test was used for multiple
comparisons.
RESULTS
The mean µTBS values are presented in
Table I. Surface treatment of zirconia samples
(F [4, 210] = 436.1, P<0.0001) and storage
conditions (F [2, 210] = 475.5, P<0.0001)
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Pinto-Pardo N et al.
Evaluation of short- and long-term bond strength of zir conia after different surface tr eatments
Pinto-Pardo N et al.
Evaluation of short- and long-term bond strength of zirconia
after different surface treatments
significantly affected µTBS. Regarding the
interaction between variables, the two variables
showed a signicant difference (F [8, 210] =
4.102, P = 0.0001).
The bond strength values in the dry
condition among the experimental groups
were significantly different from those in the
control group (P<0.0001). The combination of
CoJet + AU demonstrated the greatest mean
values of μTBS (33.51 ±2.47 MPa) compared
with CoJet (26.61 ±2.50 MPa), Alum + AU
(25.48 ±1.84 MPa), Alum (22.63 ±1.86 MPa)
and control (12.97 ±2.61 MPa).
When the zirconia samples were stored
in humid conditions for 30 days (37°C),
all experimental groups showed significant
differences compared to the control group
(P<0.0001). CoJet + AU obtained the higher
mean values of μTBS (32.87 ±2.67 MPa)
compared with CoJet (26.19 ±1.99 MPa), Alum +
AU (24.83 ±2.40 MPa), Alum (22.10 ±3.05 MPa)
and control (12.36 ±2.93 MPa) (Figure 1).
For the zirconia samples exposed to
thermocycling (100.000), even though all groups
had reduced µTBS values, all experimental groups
showed signicant differences compared to the
control group (P<0.0001). CoJet + AU obtained
the higher mean values (21.37 ±1.68 MPa)
compared with CoJet (16.13 ±1.50 MPa),
Alum + AU (16.11 ±1.60 MPa), Alumina
(12.11 ±1.68 MPa) and control (6.19 ±1.13).
These results show that the combination of
CoJet + AU yielded the highest µTBS values under
all storage conditions. These results showed that
the most effective surface treatment for zirconia
under all conditions was the combination of
CoJet + AU (Figure 1).
Tukey’s multiple comparison test showed
significant differences between CoJet + AU
and all experimental groups in all storage
environments (P<0.0001). Interestingly,
signicant differences were observed between
CoJet and Alum + AU under dry conditions
(P=0.0001), but no differences were reported
between the two groups under humid conditions
(P=0.9315) or after thermocycling (P>0.9999).
Signicant differences were observed between
Alum + AU and Alum under dry conditions
(P=0.0043), humid conditions (P=0.0073),
and after thermocycling (P<0.0001) (Figure 1).
These results showed that Ambar Universal
increased µTBS after sandblasting treatments
under all storage conditions.
Table I - Mean ± standard deviation of µTBS (MPa) after surface treatments in different storage conditions
Storage conditions Control Alum Alum + AU CoJet CoJet + AU
Dry 12.97 ±2.61 22.63 ±1.86
a
25.48 ±1.84
b
26.61 ±2.50
b
33.51 ±2.47
c
Humid 12.36 ±2.93 22.10 ±3.05
a
24.83 ±2.40
b
26.19 ±1.99
b
32.87 ±2.67
c
Thermocycling 6.19 ±1.13 12.11 ±1.68
a
16.11 ±1.60
b
16.13 ±1.50
b
21.37 ±1.68
c
a
<0.0001 compared with control.
b
<0.0001 compared with control / Alum.
c
<0.0001 compared with control / Alum / CoJet.
Figure 1 - Microtensile bond strength of samples after different surface treatments in three storage conditions. D: dry condition, H: humid
condition and T: thermocycling. Groups: Control, Alum (alumina), Alum + AU (alumina + Ambar universal), CoJet and CoJet + AU (Ambar
universal). ns: not significant, ** P<0.01 and ***P<0.0001.
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Pinto-Pardo N et al.
Evaluation of short- and long-term bond strength of zir conia after different surface tr eatments
Pinto-Pardo N et al.
Evaluation of short- and long-term bond strength of zirconia
after different surface treatments
The correlation matrix showed a signicant
relationship among all surface treatments tested
(r=0.9993, P=0.0233 for alum, r=0.9998,
P=0.0119 for Alum + AU, r=0.9990, P=0.0290 for
CoJet, and r=0.9994, P=0.0218 for CoJet + AU)
in the increase of µTBS in all storage conditions
compared with the control group. Interestingly,
Ambar Universal showed a signicant relationship
with the increase in µTBS in all storage conditions
in sandblasting groups (CoJet AU vs. CoJet:
r=0.9999, P=0.0073 and Alum + AU vs. Alum:
r=0.9998, P=0.0114) (Figure 2).
The failure mode results are presented
in Table II. Surface treatment of the zirconia
samples (F [4, 210] = 592.8, P<0.0001)
and storage conditions (F [2, 210] = 766.4,
P<0.0001) signicantly affected the failure mode.
Regarding the interaction between variables, the
two variables showed a significant difference
(F [8, 210] = 11.01, P< 0.0001). No cohesive
failures were observed after the µTBS testing.
The percentage of failure mode values in
the control group was significantly different
from those in the experimental groups under all
storage conditions (P<0.0001). Experimental
groups reported significant differences in
adhesive failures between them under all storage
conditions (P<0.0001), except between Alum +
AU and CoJet (dry P=0.6369, humid P=0.289,
and thermocycling P=0.9845).
Under dry conditions, the combination
of CoJet + AU demonstrated the lowest mean
values of adhesive failures (9.27% of adhesive vs.
90.73% of mixed) compared with CoJet (20.80%
of adhesive vs. 79.20% of mixed), Alum + AU
(24.13% of adhesive vs. 75.87% of mixed), Alum
(49.47% of adhesive vs. 50.53% of mixed), and
control (75.93% of adhesive vs. 24.07% of mixed)
(Figure 3a).
Under humid conditions, the combination
of CoJet + AU showed the lowest mean values
of adhesive failures (11.27% of adhesive vs.
88.73% of mixed) compared with CoJet (26.33%
of adhesive vs. 73.67% of mixed), Alum + AU
(31.00% of adhesive vs. 69.00% of mixed), Alum
(55.00% of adhesive vs. 45.00% of mixed), and
control (76.73% of adhesive vs. 23.27% of mixed)
(Figure 3b).
Finally, after thermocycling, CoJet + AU
surface treatment showed the lowest mean
values of adhesive failures (45.80% of adhesive
vs. 54.20% of mixed) compared with CoJet
(70.47% of adhesive vs. 29.53% of mixed),
Alum + AU (71.73% of adhesive vs. 28.27% of
mixed), Alum (83.33% of adhesive vs. 16.67%
Figure 2 - Correlation matrix of microtensile bond strength (MPa) and Storage conditions of samples after different surface treatments. D: dry
condition, H: humid condition and T: thermocycling. Groups: Control, Alum (alumina), Alum + AU (alumina + Ambar universal), CoJet and CoJet
+ AU (Ambar universal).
Table II - Percentage (%) of failure mode after surface treatments in different storage conditions
Storage conditions
Control Alum Alum + AU CoJet CoJet + AU
Adhe / Mix Adhe / Mix Adhe / Mix Adhe / Mix Adhe / Mix
Dry 75.93 / 24.07 49.47 / 50.53 24.13 / 75.87 20.80 / 79.20 9.27 / 90.73
Humid 76.73 / 23.27 55.00 / 45.00 31.00 / 69.00 26.33 / 73.67 11.27 / 88.73
Thermocycling 100 / 0 83.33 / 16.67 71.73 / 28.27 70.47 / 29.53 45.80 / 54.20
No cohesive failures were showed after µTBS testing. Failure mode: Adhe: Adhesive. Mix: Mixed (adhesive and cohesive).
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Pinto-Pardo N et al.
Evaluation of short- and long-term bond strength of zir conia after different surface tr eatments
Pinto-Pardo N et al.
Evaluation of short- and long-term bond strength of zirconia
after different surface treatments
of mixed), and control (100% adhesive vs.
0% mixed) (Figure 3c). These results showed
that Ambar universal decrease the percentage
of adhesive (Figure 4a) and mixed (Figure 4b)
failures compared with sandblasting alone after
in vitro “intra-oral aging,” suggesting that the
combination of sandblasting of CoJet or Alum +
AU increase the “adhesive” properties during
zirconia cementation.
DISCUSSION
Zirconia, a commonly utilized aesthetic
material in prosthetic dentistry, has a notable
limitation owing to its lack of a glass phase.
This absence prevents hydrouoric acid etching,
thereby reducing the surface energy and
wettability of the material, which are crucial
factors for enhancing the bonding strength
during cementation [8]. Consequently, achieving
zirconia restorations with high bond strength can
be particularly challenging owing to their weaker
bond interface with tooth substrates. However,
studies have shown improvements in bond
strength through surface modications of zirconia
when adhesive cements are employed [10,32].
Nanotechnology has also emerged as a
promising field for enhancing the properties
of dental materials [40]. The use of nanoscale
fillers in dental adhesives could enhance
mechanical properties, increase the surface area
for bonding, and improve resistance to wear
and degradation [41]. Nanoscale modications
of zirconia, such as nanoparticle coated or the
Figure 4 - Comparison of failure modes percentage in dry condition
(baseline) vs thermocycling (bars). a) Adhesive failure. b) Mixed
failure. Red forms: baseline during adhesive or mixed failures.
Groups: Control [white], Alum (alumina) [light green], Alum + AU
(alumina + Ambar universal) [dark green], CoJet [light blue] and
CoJet + AU (Ambar universal) [dark blue].
Figure 3 - Failure modes percentage after different surface
treatments in three storage conditions. a) Dry condition. b) Humid
condition. c) Thermocycling. Groups: Control, Alum (alumina),
Alum + AU (alumina + Ambar universal), CoJet and CoJet + AU
(Ambar universal). ns: not significant and ***P<0.0001.
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Pinto-Pardo N et al.
Evaluation of short- and long-term bond strength of zir conia after different surface tr eatments
Pinto-Pardo N et al.
Evaluation of short- and long-term bond strength of zirconia
after different surface treatments
creation of nanotextured surfaces, could also
potentially improve the adhesion of zirconia with
resin cements [42].
In our study, we observed that all tested
surface treatments elevated µTBS in comparison
to the control group, and a decrease in µTBS
was observed after subjecting the samples to
humid conditions and thermocycling [43,44].
This decrease is generally attributed to the
different thermal expansion coefcients of the
various materials involved, such as adhesives,
resin cement, and zirconia. The thermal stresses
induced by thermocycling can lead to the
formation of micro-cracks and degradation at the
interfaces, hence reducing bond strength [45].
However, the combination of CoJet + Ambar
Universal showed the highest bond strength in the
short and long-term of in vitro aging compared
to the other groups.
It has been reported that materials with
silica-rich surfaces exhibit enhanced adhesion
properties between the hydroxyl group on the
silica surface and a silane coupling agent [46].
TSC or ‘silicatization’ treatment has been shown
to increase µTBS due to the creation of both
micromechanical and chemical modifications
on the zirconia surface [47,48]. Further studies
have reported that chemical conditioning
(siloxane network) is more important than
micromechanical modifications during resin-
ceramic cementation [49,50]. Despite these
ndings, it has been reported that the combination
of surface treatment with aluminum oxide
and silane, while increasing the wettability of
resin cements and bond strength relative to
controls, is not expected to result in any chemical
reactions [51].
The process of TSC sandblasting is particularly
intriguing, as it transfers mechanical energy in the
form of kinetic energy to the treated surface. This
process results in a local temperature increase
owing to the kinetic energy generated when the
TSC particles strike the zirconia. The resultant
thermal energy aids in the melting of silica
particles, leading to chemical conditioning
of the zirconia surface [52]. Moreover, the
sandblasting pressure of 0.28 MPa (indicated by
the manufacturer) was not sufcient to obtain
a homogeneous TSC layer [52]. Furthermore,
García-de-Albeniz et al. (2023) [53] reported
a direct relationship between the pressure of
airborne particle abrasion, the amount of silica
layer over zirconia, smaller particle size during
sandblasting procedures, and an increase in bond
strength after cementation [54,55], suggesting
that pressure and particle size are critical for
achieving higher bond strength results, as well
as the type of surface treatment.
Our results showed that Ambar Universal
increased the µTBS of the zirconia samples after
sandblasting. Moreover, the combination of CoJet
and Ambar Universal obtained the highest µTBS
results in the long-term (10 years of intraoral
aging), suggesting a predictable protocol for
zirconia adhesive cementation. Remarkably,
the Alumina and Ambar Universal combination
yielded results similar to those of CoJet alone in
humid conditions and post-thermocycling aging.
This implies another viable alternative for surface
treatment in the absence of silicatisation.
MDP-containing silane agents enhance
the bond strength of zirconia samples when
resin cements are used through the phosphate
ester group of the MDP [56]. However, these
agents form weak covalent bridges directly
over zirconia [57]. Nagaoka et al. (2019) [52]
reported that the combination of TSC treatment
and a universal primer containing MDP creates a
polymer network among silica, aluminum oxide,
and methacrylate groups of adhesive agents,
enabling adhesive polymerization between
the resin cement and methacrylate end over
pretreated zirconia. Several studies have reported
that MDP-containing adhesives achieve higher
bond strengths to zirconia frameworks through
chemical reactions of interfacial interactions,
such as van der Waals forces or hydrogen
bonds [58]. Thus, the application of MDP-
containing adhesives to TSC-pretreated zirconia
can generate a stable and durable bond strength
between zirconia and resin cements.
Humid storage conditions and thermocycling
are frequently used to simulate the aging of
adhesive-bond interfaces. The intervals of
temperatures from 5 °C to 55 °C for thermal
cycles are described in accordance with the
ISO TS 11405 technical specication for testing
the adhesion to tooth structure [59]. Further
studies have reported a decrease in bond
strength after artificial aging (water storage
or thermocycling) [35,37,38] and a strong
degradation of the zirconia-cement interface after
water storage at 37°C for 7 days [60].
8
Braz Dent Sci 2023 Oct/Dec;26 (4): e4001
Pinto-Pardo N et al.
Evaluation of short- and long-term bond strength of zir conia after different surface tr eatments
Pinto-Pardo N et al.
Evaluation of short- and long-term bond strength of zirconia
after different surface treatments
Different media have been used for in vitro
intraoral aging simulations (including water,
ethanol, or sodium hypochlorite dilutions) to
degrade bonded interfaces. However, these
media lack the enzymatic activity present in
saliva. Articial solutions replicate the enzymatic
features of human saliva, mimicking the in
vivo biochemical degradation of an adhesive
interfaces. Moreover, recent studies have
suggested the use of mechanical loading in
addition to thermocycling, to replicate the oral
environment more accurately [61,62]. This
could involve simulating biting forces, which
might affect the bond strength of restorations.
Additionally, long-term clinical trials are crucial
for conrming the ndings of in vitro studies.
Interestingly, our study showed that the
combination of CoJet and Ambar Universal
resulted in the lowest values of adhesive failure
after short- and long-term intraoral aging using
artificial saliva as a liquid medium. These
findings confirm a predictable protocol for
zirconia adhesive cementation against enzymatic
degradation during intraoral performance.
CONCLUSIONS
Based on the ndings and limitations of this
in vitro study, the following conclusions were
drawn:
1. The combination of TSC (CoJet) and MDP-
containing adhesives (Ambar) as a surface
treatment for zirconia specimens provides
significantly higher short- and long-term
bond strengths when adhesive cementation
is used, compared with silicatization alone,
aluminum oxide with or without universal
adhesive, or without surface treatment.
2. The combination of aluminum oxide
sandblasting and universal and MDP-
containing adhesives (Ambar) as a surface
treatment for zirconia specimens provides
similar results to TSC alone on the bond
strength after adhesive cementation,
resulting in an adequate alternative when
silicatization is not possible.
Acknowledgements
The authors acknowledge Provitec Laboratory
(Santiago, Chile) for providing zirconia samples
used in this study.
Author’s Contributions
NPP: Conceptualization, Methodology,
Supervision, Formal Analysis, Writing – Original
Draft Preparation, Writing – Review & Editing.
PLA: Conceptualization, Writing – Original Draft
Preparation, Visualization. MD: Investigation,
Resources, Writing – Review & Editing. LA:
Investigation, Resources, Writing – Review &
Editing. PR: Conceptualization, Supervision,
Visualization, Writing – Review & Editing.
Conict of Interest
No conicts of interest declared concerning
the publication of this article.
Funding
The authors declare that no nancial support
was received.
Regulatory Statement
This study was conducted in accordance with
all the provisions of the local human subjects
oversight committee guidelines and policies of
University Viña del Mar. The approval code for
this study is #56-23.
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Nicolas Pinto-Pardo
(Corresponding address)
Universidad Viña de Mar, Escuela de Ciencias de la Salud, Departamento de
Implantología, Odontología, Viña del Mar, Chile.
Email: nicolas.pinto@uvm.cl
Date submitted: 2023 Aug 17
Accept submission: 2023 Oct 16