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Influence of an aerosolized alumino-silica-based surface coating on shear bond strengths of two different types of zirconia

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Influence of an aerosolized alumino-silica-based surface coating on shear bond strengths of two different types of zirconia

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Content Influence of an aerosolized alumino-silica-based surface coating on shear bond strengths of two
different types of zirconia

by
Erin Alyssa Anderson, DDS

A Thesis Presented to the
FACULTY OF THE USC Herman Ostrow School of Dentistry
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
BIOMATERIALS AND DIGITAL DENTISTRY

December 2021

Copyright 2021 Erin Alyssa Anderson, DDS

ii
Acknowledgments

I’d be remiss to not thank the numerous individuals who have made this research project
possible. Firstly, I thank God for enabling me to overcome all obstacles and hardships to allow
me to progress both professionally and personally. Being able to study at one of the top
institutions in the country is no small feat and I’m so grateful that I’ve been equipped to flourish
in such an environment. God is so good! Secondly, my immediate family has played no small
role in all that I’ve accomplished as they’ve continuously supported and encouraged me
throughout the years, reminding me that everything is an endurance test, and I must stay the
course! This advice has seen me through over a decade of school, from Undergraduate studies to
receiving my white coat, to now defending my master’s thesis. My family continues to be the
reason why I thrive, and I will do my best to honor them in everything I do! My past mentors
undoubtedly have prepared me to become the student I am today, and the astute clinician I will
be in the future. Drs. Woods, Searcy, Morton, Jackson, Connell, Salter—I will forever be
grateful for all they have instilled in me and for showing unwavering support along this journey.
My current mentors and advisors, Drs. Phark and Duarte, believed in me from the start of
residency and I’m so grateful they entrusted me with the responsibility of research. I have
learned so much throughout the process--- yes, of course about zirconia, but even more about
research in general, organization, time management, etc. It’s been an invaluable journey and I
don’t take it for granted. Other individuals who played key roles in this research project are Mr.
Tony Seeler and Emil Sahakian of Burbank Dental Lab, (who sintered all my specimens free of
charge in a moment’s notice!) and my coresidents! I’m constantly reminded of the adage “If you
want to go fast, go alone. If you want to go far, go together” when I think of my classmates. I
couldn’t have done any of this alone and especially couldn’t have made it this far.

iii

Thank you Drs. Phark, Duarte and Knezevic for taking the time to review this thesis and for your
invaluable feedback to come!

iv
Table of Contents
Acknowledgments…………………………………………………………………………........................ii
List of Tables………………………………………………………………………………………………v
List of Figures …………………………………………………………………………………………...vi
Abbreviations…………………………………………………………………………………………….vii
Abstract…………………………………………………………………………………….....................viii
Keywords…………………………………………………………………………………..………………x
Introduction……………………………………………………………………………………………......1
Objectives………………………………………………………………………………………………...14
Methods and Materials………………………………………………………………………………...…15
Preparation of specimens…………………………………………………………………...................15
Surface treatment…………………………………………………………………………...................20
Bonding procedure…………………………………………………………………………………….27
Artificial aging……………………………………………………………………………...................28
Shear bond strength (SBS) testing…………………………………………………………………….29
Failure analysis………………………………………………………………………………………..31
Statistical analysis……………………………………………………………………………………..33

Results …………………………………………………………………………………………………...34
Non-aged groups………………………………………………………………………………………36
Aged groups…………………………………………………………………………………………...38

Failure mode analysis...…………………………………………………………..................................40

Macroanalysis…………………………………………………………………………................40

Microanalysis……………………………………………………………………………....…….41

Discussion………………………………………………………………………………………………..43
Accepted surface treatments…………………………………………………………………………..43
Silica-based bonding techniques………………………………………………………………………45
Alumino- silica-based coating’s performance……………………………………………………...…46

Conclusion………………………………………………………………………………………………..55
References………………………………………………………………………………………………..56

v

List of Tables
Table 1: Fracture toughness and biaxial flexural strength values without aging (9, 10) 5
Table 2: IPS e.max ZirCAD LT standard sintering program 18
Table 3: KATANA STML sintering program 18
Table 4: General surface treatment steps and products 21
Table 5: Materials list 22
Table 6: Experimental group setup 23
Table 7: Firing process data for DCMhotbond Zirconnect spray 25
Table 8: SBS for aged and non-aged specimens 35

vi
List of Figures

Figure 1: Cross section of PFZ (a) and monolithic zirconia (b) 2
Figure 2: Zirconia crystal forms; monoclinic (a), tetragonal (b), cubic (c) 3
Figure 3: Zirconia having undergone low-temperature degradation 6
Figure 4: IPS e.max ZirCAD Prime definitive restorations 9
Figure 5: Scored zirconia; mounted zirconia slices in precision sectioning saw 16
Figure 6: Programat S1 Sintering Furnace 17
Figure 7: Cut, polished and sintered zirconia specimens 17
Figure 8: IPS Empress Direct nano-hybrid composite 19
Figure 9: Teflon mold and microscope slides 20
Figure 10: Seating of composite cylinder 28
Figure 11: Mounted specimens for SBS testing 30
Figure 12: Universal Testing machine 30
Figure 13: Failure analysis -Circumscribed cylinder for total bonding area, delineated composite
remnant, and fluorescent mode 32
Figure 14: Failure analysis- light and fluorescent mode (b. Adhesive failure at the zirconia
surface c. Cohesive failure in the composite cylinder d. Mixed failure) 32
Figure 15: SBS of non-aged and aged specimens by surface condition 34
Figure 16: SBS of non-aged specimens by surface condition 37
Figure 17: SBS of aged specimens by surface condition 38
Figure 18: Failure mode analysis by surface treatment, grouped by aging 41
Figure 19: Failure mode analysis of non-aged specimens 42
Figure 20: Failure mode analysis of aged specimens 43

vii
Abbreviations
APA- Airborne- particle abrasion
Alumina- Aluminum trioxide
HF- Hydrofluoric acid
PFZ- Porcelain fused to zirconia
PSZ- Partially-stabilized zirconia
SBS - Shear bond strength
TZP- Tetragonal zirconia polycrystal
Yttria- Yttrium oxide
Zirconia- Zirconium dioxide
10-MDP- 10-methacryloyloxyidecyl-dihyidrogenphosphate

viii
Abstract

Title: Influence of an aerosolized alumino-silica-based surface coating on shear bond strengths
of two different types of zirconia

Objective: To investigate the impact of an aerosolized alumino-silica- based coating technique
on the bond strength of both 3Y-TZP and 4Y-PSZ dental zirconia types, as compared to
standard, accepted zirconia surface treatments.
Methods and Materials: Four surface treatments used to modify the zirconia surface were
compared to evaluate the shear bond strength (SBS) between two zirconia types and two aging
mechanisms. Two currently accepted surface treatments (airborne -particle abrasion and
tribochemical coating) were compared against an experimental aerosolized alumino-silica- based
coating technique, with an additional round of airborne- particle abrasion, per manufacturer
instructions, and without the additional airborne-particle abrasion. Treated zirconia surfaces then
received resin-composite cylinders (IPS Empress Direct, Ivoclar Vivadent, Schaan,
Liechtenstein) cemented using a dual-cure resin cement (RelyX Ultimate Adhesive Resin
Cement, 3M, St. Paul, MN, USA). After dividing the 240 total zirconia specimens into non-aged
(24-hour water storage) or aged (60 days artificial aging/ thermocycling 20,000 cycles) groups,
testing commenced using a notched shear bond strength test.
Results: No significant differences were found between zirconia types at p>0.001, nor between
the four surface treatments with the exception of comparing SBS outcomes of tribochemical
coated (CO)- and the aerosolized alumino-silica- based coating with APA (ZCS)-treated

ix
specimens (p=0.00038). Significant differences (p<0.00001) in SBS between non-aged and aged
specimens were revealed.
Conclusion: The aerosolized alumino-silica-based coating technique, whether with the
additional round of airborne- particle abrasion or not, did not produce significantly greater SBS
outcomes than currently accepted surface treatments.
Clinical significance: Currently accepted surface treatments like airborne-particle abrasion and
tribochemical coating are encouraged as surface treatments before bonding to zirconia. As SBS
outcomes between surface treatments were different between aged and non-aged groups, future
research is indicated to assess the stability and longevity of aerosolized alumino-silica-based
coated-surfaces before clinical recommendations are made.

x
Keywords

Shear bond strength, notched-edge shear bond strength test, surface treatment, zirconia ceramic,
aerosolized alumino-silica-based coating technique

1
Introduction

Zirconia as a dental material
Zirconium- dioxide, more commonly referred to as, simply, “zirconia” was first referenced in the
realm of dentistry in the 1970s; today, zirconia has not only been implemented for dental use, but
has been widely adapted in numerous capacities, including full- and partial-coverage
restorations, fixed partial dentures, endosseous implant fixtures and abutments, all ceramic
frameworks and post and core systems (1, 2). These applications are possible by employing the
two types of dental zirconia layered complexes, including the bilayer, where porcelain is used to
cover or veneer a strong, opaque zirconia core, commonly referred to as “porcelain fused to
zirconia” or “PFZ”, and single layer, in which the entire prosthesis consists of zirconia as a
monolith (Figure 1). From long-span fixed partial dentures to complex all-ceramic restorations,
zirconia’s applicability and diversity are possible due to its unique yet exemplary mechanical
properties (3). For example, attributing to their chemical inertness, frameworks made of zirconia
are resistant to the effects of aggressive chemical agents such as inorganic and organic dissolving
agents, as well as strong acids and alkalis. Such stability in the face of chemical alteration
predicts superior long-term performance in the fluctuating oral environment—a true advantage in
tandem with zirconia’s widely recognized property of unparalleled strength, amongst others (3,
4).

2

Figure 1: Cross section of PFZ (a) and monolithic zirconia (b)

Although encompassing appealing mechanical properties, even being dubbed “ceramic steel,”
zirconia’s chalk-white appearance limits its adaptation to less- esthetic areas (5); thus, to
implement zirconia in more esthetic areas, most dental zirconia systems indicate preforming
extrinsic characterization to enhance its appearance. As aforementioned, zirconia can be
implemented in dentistry as either a monolith or as PFZ with a porcelain- layered zirconia core.
Although monolithic zirconia largely lacks satisfactory translucency and other optical properties
to closely mimic natural tooth structure, its PFZ counterpart is not without flaw. Traditional
veneer/core structures are more esthetic in terms of shade and translucency, though are prone to
failure via chipping and delamination of the veneered porcelain, aided by the presence of
residual thermal stresses (6). PFZ’s monolithic counterpart avoids such issues at the expense of
its esthetic appeal, prompting ongoing research to produce a more translucent yet mechanically
sound monolithic zirconia (6, 7).

3
Research upholds zirconia’s raved mechanical properties which are influenced by its unique
biomaterial characteristics. At a rudimentary level, the polymorphous zirconia ceramic can exist
in three different, crystalline forms depending on temperature including monoclinic, tetragonal,
and cubic phases (Figure 2) (8). The monoclinic phase is the only phase in which zirconia is
stable at room temperature; however, the mechanical and optical properties of the monoclinic
crystal phase are insufficient for clinical use (5). Hence, stabilizing the crystalline structure
metamorphosis of the more functionally- and optically- acceptable tetragonal and cubic phases is
required and can be achieved using stabilizing oxides, with yttrium oxide, or yttria, being the
most widely used (5).

Figure 2: Zirconia crystal forms; monoclinic (a), tetragonal (b), cubic (c)

Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP), have been traditionally utilized as 3Y-
TZP (3 mol % yttria) in dentistry as it is the strongest and toughest dental ceramic. The
metastable tetragonal crystal form is advantageous to utilize as it exhibits an ability to suppress
or blunt crack propagation. The mechanism of action for this phenomenon includes the energy of
a free surface of the crystals adjacent to a developing crack overcoming the effect of the dopant,

4
permitting the transformation from tetragonal to monoclinic phase, resulting in local expansion
which effectively closes the crack and retards further crack development. This unique property of
Y-TZP zirconia has been called ‘transformation toughening’ and is auspicious where crack
propagation is a constant consideration as it promotes increased fracture toughness (6, 9).

The content of yttria can vary within the zirconia in which the amount significantly affects both
mechanical and optical properties (9). As zirconia is traditionally dull white in color, akin to the
opacity of a household ceramic tile, its opacity is able to mask the underneath structure, e.g.,
metal or tetracycline-stained tooth structure. The sought-after optical property of increased
translucency can be explained by the isotropic quality of the cubic phase that prohibits
birefringence of the remaining tetragonal phase, reducing the optical scattering coefficient (6).
Translucency is also influenced by the microstructure and shows an inverse relationship between
the number of grain boundaries and grain size (55). The higher the sintering temperature and the
yttria content (and with more cubic phase) is, the bigger the fraction of cubic crystalline phase
inside the zirconia (9); thus, in zirconia with a lower yttria content (and subsequent less cubic
phase), accommodations must be made to account for the opacity since decreased yttria promotes
decreased translucency. Similarly, increasing the yttria content thereby increases the
translucency to produce a more esthetically appealing block, although simultaneously decreases
the flexural strength of the zirconia (Table 1) (56).

5

Table 1: Fracture toughness and biaxial flexural strength values without aging (9, 10)
3Y-TZP 4Y-TZP 5Y-TZP
Biaxial flexural strength (N/mm
2
) 899- 1109 750- 1120 540- 747
Fracture Toughness (MPa m
1/2
) 4.22- 4.31 3.48- 3.86 2.47- 2.79
Wear depth (µm) 10± 3.9 19.8± 3.8 10.9± 6.8
Martens hardness (N/mm
2
) 5655- 7711 7084- 8901 7849- 9129
Translucency (%) 26.5- 27.2 33.4- 33.9 34.8- 35.7

3Y-TZP (3 mol % yttria) is historically the strongest and toughest dental ceramic, but at the
expense of acceptable optical properties (9). First-generation 3Y-TZPs contained 0.25 wt%
alumina-sintering aid and exhibited excellent flexural strengths; However, first generation
zirconia exhibited high opacity because of the inherent birefringence of noncubic zirconia
phases, resulting in light scattering from grain boundaries, pores, and additive inclusions. They
were chiefly indicated for framework materials in porcelain-veneered crowns and fixed dental
prostheses (FDPs) in posterior and anterior regions (1). Years after the 3Y-TZP pioneer was
introduced with its extraordinary flexural strength but poor optical properties, additional
materials were introduced to address these optical shortcomings. The second 3Y-TZP zirconia
generation showed some difference in the degree of light transmittance, by only varying the
alumina content, which was reduced from 0.25 wt.% to 0.05 wt.% (6, 11). The lower content of
alumina made the tetragonal phase of the material less stable and thus more susceptible to low-
temperature degradation, a spontaneous transformation to monoclinic phase from tetragonal (12).
This phenomenon is facilitated in surface grains in a humid atmosphere at low temperatures

6
which later progresses towards the bulk of the material while the water penetrates into the
material (13). At the same time the alumina grain size is decreased and repositioned to the
zirconia grain boundaries (Figure 3).

Figure 3: Zirconia having undergone low-temperature degradation

The desire for a translucent zirconia to mimic the
natural tooth more closely was fulfilled with the
development of the third-generation zirconia (5Y-
TZP) zirconia in 2015 to address typical subpar
esthetics. 5Y-TZP contains, in contrast to the other
generations, approximately 50% of cubic phase
compared to the tetragonal phase (6). The cubic
phase is achieved due to a higher content of yttrium
oxide in zirconia material which makes the zirconia
both more stable and more resistant to hydrothermal
aging. More specifically, the zirconia is subsequently less susceptible to low temperature
degradation (6, 9); however, one disadvantage of this zirconia is the decrease in both flexural
strength and fracture toughness due to the stable cubic lattice and its lower or lack of ability of
stress-induced transformation toughening (6, 9).

7
Because the third generation of zirconia did not fulfill the mechanical requirements for long span
dental restorations, a new, fourth generation (4Y-TZP) with approximately 30% of cubic phase
in proportion to the tetragonal phase was developed as a compromise between the second and the
third zirconia generations (9). 4Y-TZP (4 mol % yttria) reveals a competitive flexural strength
with a less opaque appearance as compared to the 3Y-TZP.

Decreasing the crystal size is another way to achieve stability of the tetragonal phase at room
temperature— an effect which has been attributed to a surface energy difference (5). Small
tetragonal grains transformation, which should prompt a volume increase, is discouraged by the
compressive stresses expressed onto these grains by their nearby counterparts, thus giving rise to
another zirconia form: metastable tetragonal partially stabilized zirconia (PSZ) at room
temperature (5).

Monolithic monochromatic zirconia can be colored internally or externally via shade gradients
per block and external staining, respectively, to account for the evidenced opacity and decreased
translucency (14). The most common staining technique for zirconia and glass ceramics involves
staining the external ceramic surfaces utilizing two separate cycles of firing e.g., staining and
glaze layer; additionally, it’s also possible to stain some ceramics prior to the crystalizing
process, although with unconfirmed durability. This multi-layered shade technology mimics the
shade-gradient of natural teeth using pigmentation only, whereas having the same generation of
zirconia within each blank, and therefore, obtaining color gradient with no difference in the
flexural strength between the enamel and dentin layers (15, 16).

8
Another multi-layered technology has been introduced, integrating different generations of
zirconia together in one blank aiming to merge the advantages of both 2
nd
and 3
rd
generations of
zirconia, being both functional and esthetic in terms of translucency. This combination is mainly
between a high-flexural strength 3Y-TZP in the dentin/body area for higher stability and a high-
translucency 5Y-TZP in the incisal or occlusal area for better esthetics (Figure 4) (17). Cube X
2

(Dental Arts Laboratories, Peoria, IL, USA) cubic zirconia is a commercial dental zirconia that
combines generations and boasts promoting a conservative tooth preparation while showcasing
the translucency of lithium disilicate but with the strength of zirconia (57). IPS e.max ZirCAD
Prime (Ivoclar Vivadent, Schaan, Liechtenstein) is a more well-known example of a multi-
generation- layered zirconia currently on the market. Its fabrication includes “gradient
technology” that involves three processing steps:
1. Optimized conditioning of indigenous powders to adjust the sintering kinetics of 3Y-
TZP and 5Y-TZP for uniform shrinkage
2. Filling technology which omits the look of visible layers of color and offers a change
in material composition to provide both stellar esthetics and strength
3. Cold isostatic pressing is one processing step within the distinct pressing technology
which improves the microstructure of the material via uniformly compacted sides,
optimizing its translucent properties and allowing the material to be sintered at shorter
intervals (59).

9
Figure 4: IPS e.max ZirCAD Prime definitive restorations

Bonding to zirconia
Zirconia has become a paradigm amongst dental materials as it boasts superior qualities such as
strength and toughness; nonetheless, establishing a predictable bond to zirconia is an ongoing
challenge (2, 6). Zirconia restorations can be either luted or bonded, with the former indicated
given the tooth preparation has adequate retention provided by acceptable length of axial walls
and an optimum near parallelism of axial walls, whereas the latter may be better served when
micromechanical retention is questionable (18, 19). With bonding or adhesion, durable zirconia
bonds have been established by implementing both chemical and mechanical surface
pretreatments (16, 20, 21). Previous studies have highlighted sound resin-to-zirconia chemical
bonds via the application of a 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-
containing agent like luting resins or primers while mechanical treatment relies on surface
roughness alteration via airborne oxide ceramic or silica-modified oxide ceramic particle
abrasion (17, 22, 23). Contrary to its glass-ceramic relatives requiring the use of hydrofluoric or
phosphoric acid to establish micromechanical retention, sufficient zirconia surface roughness is
not produced with the use of these acids (2, 21); further, the use of silane is not indicated as

10
zirconia’s matrix is devoid of silica. Due to these complexities, alternative surface treatments
have been proposed and studied.

Surface treatment rationale
To enhance the bond strength of both composite resins and resin cements to the zirconia surface,
different surface-altering treatments have been proposed to either micromechanically or
chemically encourage the resin-ceramic bonding (7). Since zirconia-based ceramics cannot be
roughened by hydrofluoric acid due to their inadequate silica content, airborne-particle abrasion
via the use of either 50- or 110-µ alumina particles has been shown throughout literature to
effectively to clean and condition the ceramic surface as well as to increase the surface
roughness while creating micromechanical adaptation between a composite resin and ceramic
surface (16, 20, 24). However, air-abrasion has been documented to potentially diminish the
mechanical properties of the ceramic itself by initiating microcracks and other surface defects
that can act as stress concentration sources, which might reduce the fracture strength of the
ceramic or lead to failure, although much literature also exists upholding its effectiveness (25,
26). Therefore, reducing the pressure during air-abrasion or omitting air-abrasion completely
might be advantageous in reducing the negative surface effects caused by air-abrasion (20).

Silica based ceramics do not rely on micromechanical modification via airborne particle abrasion
but rather via HF acid application. Chemical bonding to the ceramic surface is based on the
reaction between the silica of the ceramic material and the silane coupling agent. Silane coupling
agents increase the surface energy and wetting ability of the ceramic surface and thus enhance
the interaction between ceramic and composite resin. Contrarily, due to zirconia’s lack of silica

11
content, HF acid etching and application of a silane coupling agent will not suffice to provide
any retention; thus, special functional monomers have been used in resin cements, adhesives, or
even alone to improve the adhesion to zirconia (21, 27, 28). These materials present a chemical
affinity for metal oxides and can include phosphate ester monomers, such as 10-
methacryloyloxyidecyl-dihyidrogenphosphate (MDP), phosphoric acid monomers, e.g., 6-
methacryloyloxyhexyl phosphonoacetate (6-MHPA), phosphoric acid acrylate monomers and
others like MEPS (thiophosphoric methacrylate). Since some monomers present few marked
advantages when used by themselves, they are often combined or used alongside air-abrasion
techniques and have reported promising results (56).

Another surface-altering treatment, tribochemical silica coating, relies on the limited silica
content of zirconia to support the use of silica-coating techniques, proposed to increase the
surface silica content and to establish siloxane bonding (22). In this treatment, the ceramic
surface is airborne-particle abraded with aluminum-oxide particles modified with a silica
coating, and the blasting pressure results in the embedding of silica particles onto the ceramic
surface. Therefore, tribochemical silica coating combines both micromechanical and chemical
retention produced by airborne-particle abrasion and silanization of the silicated ceramic surface,
respectively (29).

Experimental procedures and products are continuously explored in search of a reliable zirconia
bonding surface treatment. As such, selective infiltration etching (SIE), a hot etchant technique,
was developed to transform the non-bonding surface of zirconia into a highly retentive surface
through the introduction of inter-grain nano-porosity where the adhesive resin-composite can

12
infiltrate and interlock (4). Authors concluded that this technique in combination with primers
prompted a significant improvement of zirconia–resin bond strength although the longevity of
the bonding was not assessed (4, 15).

Recently, an aerosolized alumino-silica-based coating technique (DCMhotbond Zirconnect
Spray, Dental Creativ Management, Rostock, Germany) has been introduced. This technique
relies on the formation of an evenly thin layer of glass matrix, which is sintered onto the bonding
surface. After sintering, this coating layer is air-abraded with alumina particles, HF etched and
then primed prior delivery using resin cement. As we know, the use of HF acid is ineffective on
zirconia’s silica-free surface, but the deposition of silica into the zirconia surface along with the
use of silane has proven beneficial in some studies (4, 30). With this novel technique, a glassy
matrix is deposited onto of the zirconia surface instead of producing a mechanically embedded
silica particle laden surface, as found with tribochemical coating. Bonding to zirconia remains
somewhat illusive as gaps in knowledge remain regarding establishing a predictable and
consistent bonding surface via micromechanical and/or chemical retention, especially
considering novel zirconia materials featuring combined gradients, variable mechanical
properties based on content, etc. On the basis of proven bonding techniques, the use of this
aerosolized alumino-silica- based coating and protocol simulate the bonding to conventional
glass-ceramics and has been proposed to be superior in terms of strength and durability as
compared to other bonding techniques based on the necessary mechanical and chemical
alteration (16). The present study is indicated as it intends to assess the influence of an
aerosolized alumino-silica- based coating technique on the subsequent bond strengths of two

13
different zirconia types, in hopes to identify a bonding surface that supports consistent and
predictable bonding to zirconia.

14
Objectives
The objective of the present study is to investigate the impact of an aerosolized alumino-silica-
based coating technique on the bond strength of both 3Y-TZP and 4Y-PSZ dental zirconia types,
as compared to standard, accepted zirconia surface treatments.

The null hypotheses tested will be:
(1) Surface treatment: There will be no significant difference in bond strength between the
aerosolized alumino- silica-based coating technique, standard techniques based on
alumina air-abrasion, and tribochemical coating.
(2) Zirconia: There will be no significant difference in bond strength between the 3Y-TZP
and 4Y-PSZ zirconia.
(3) Aging: There will be no significant difference in bond strength between the artificially
aged (aged) and 24-hour water storage (non-aged) specimens.

15
Methods and Materials

Various surface treatments used to modify the zirconia surface were compared to evaluate the
SBS between two zirconia types and two aging mechanisms. Treated zirconia surfaces received
resin-composite cylinders (IPS Empress Direct, Ivoclar Vivadent, Schaan, Liechtenstein)
cemented using a dual-cure resin cement (RelyX Ultimate Adhesive Resin Cement, 3M, St. Paul,
MN, USA) and tested using a notched shear bond strength test. A total of 240 zirconia specimens
were divided by zirconia type [4Y-PSZ (KATANA STML) or 3Y-TZP (ZirCAD LT)], surface
conditioning treatments and aging/nonaging—24-hour water storage or artificial aging via
thermocycling.

Preparation of specimens

Zirconia
A total of 240 square-shaped zirconia specimens were fabricated from zirconia pucks measuring
a 98.5 x 22mm (disc) and 20.2 x 19.2 x 17.8 mm— either a multilayered 4Y-PSZ (KATANA
STML, Kuraray Noritake, Tokyo, Japan) or a monolayered 3Y-TZP (ZirCAD LT, Ivoclar
Vivadent, Schaan, Liechtenstein) zirconia grade. Unsintered zirconia pucks were first measured
and then scored to produce slices (Figure 5), which were cut again to produce square shaped
specimens measuring 12.5 x 12.5 x 1.25 mm using a precision sectioning saw (IsoMet 1000;
Buehler, Lake Buff, IL, USA) with a diamond blade (102 mm dimension, 0.3 mm thickness;
IsoMet Blade 15LC, Buehler, Lake Buff, IL, USA) at a speed of 800 RPM under continuous
water cooling (Figure 5). Samples were cut at the initial desired size of 12.5 x 12.5 x 1.25 mm to

16
account for an anticipated 20% sintering shrinkage. After sintering, 80% of the initial sample
size remained, revealing samples measuring 10 x 10 x 1 mm. They were fully sintered
(Programat S1 Sintering Furnace, Ivoclar Vivadent, Schaan, Liechtenstein) according to
manufacturer’s instructions (Table 2; Table 3) and then ultrasonically cleaned in 99% isopropyl
alcohol (Mountain Falls Products, TN, USA) for 10 min and thoroughly air-dried using an oil-
free compressed air stream for 5 s. Cut, polished and sintered specimens are shown in Figure 7.

Figure 5: Scored zirconia; mounted zirconia slices in precision sectioning saw

17

Figure 6: Programat S1 Sintering Furnace

Figure 7: Cut, polished and sintered zirconia specimens

18

Table 2: IPS e.max ZirCAD LT standard sintering program
Temperature 1
[
o
C]
Temperature 2
[
o
C]
Heating- up rate
[
o
C/min]
Holding time
[min]
Heating phase 20 900 10 -
Holding phase 900 900 - 30
Heating phase 900 1550 3.3 -
Holding phase 1550 1550 - 120
Cooling phase 1550 900 10 -
Cooling phase 900 300 8.3 -
switch off

Table 3: KATANA STML sintering program
Temperature 1
[
o
C]
Temperature 2
[
o
C]
Heating- up rate
[
o
C/min]
Holding time
[min]
Heating phase 20 900 10 -
Holding phase 900 900 - 30
Heating phase 900 1550 10 -
Holding phase 1550 1550 - 120
Cooling phase 1550 900 10 -
Cooling phase 900 300 10 -
switch off

19

Composite cylinders:
A nano-hybrid composite (IPS Empress Direct B1E, Ivoclar Vivadent, Schaan, Liechtenstein;
Figure 8) was layered into preformed Teflon molds (bonding mold insert, Ultradent, South
Jordan, UT, USA) in two increments against glass, microscope slides (Surgipath Microslides
1x3x1 mm, Leica Biosystems, Nussloch, Germany) to fabricate composite cylinders with 2.38
mm diameter and 3 mm height (Figure 9). The mold was filled with composite resin up to half of
the mold’s depth using a composite instrument (UP1; Hu Friedy, Chicago, IL, USA) and
condenser (#PLG1/2; Hu Friedy, Chicago, IL, USA), light cured at standard power mode for 20
s using a 4 LED light curing unit (Valo, Ultradent, South Jordan, UT, USA) at standard power
mode (1000 mW/cm
2
, wavelength 385-515 nm), from 1 mm away with the lens of the light
curing unit placed immediately on top of the bonding mold. A final, second layer was applied,
and light cured for 20 s. A black, ultrafine, permanent marker (Sharpie, Newell Brands, Atlanta,
GA, USA) dot was made directly onto the top surface of the final composite layer, to denote the
non-bonding surface. The opposing bottom surface was flat, smooth and shiny due to
condensation against the microscope slide. This surface was used as the bonding surface.
Composite cylinders were fabricated two days prior to bonding and stored in a clean, air-tight
container to prevent contamination.

Figure 8: IPS Empress Direct nano-hybrid composite

20

Figure 9: Teflon mold and microscope slides

Surface treatment

The surface of zirconia ceramic was modified using various proven and an experimental surface-
altering treatment (Table 4, Table 5) to evaluate the SBS between two zirconia types and two
aging mechanisms. After SBS testing, both statistical and failure analysis commenced to aid in
determining which surface treatment promoted the greatest SBS and the predominating failure
mode, respectively. Group setup, considering surface treatment, zirconia type and aging, is
outlined in Table 6.

21
Table 4: General surface treatment steps and products
Surface Treatment Treatment steps and products
S- Sandblasting or airborne
particle abrasion (APA) using
50 μm Al2O3 particles
(control)
1. 50 μm Al2O3 particles (Deldent Ltd., Petach Tikva, Israel)
2. Clearfil Ceramic Primer Plus (Kuraray Noritake, Tokyo, Japan)
CO- Silica coating using 30
µm SiO particles (control)
1. CoJet, 3M, St. Paul, MN, USA
2. Ultradent silane, South Jordan, UT, USA
ZC- DCMhotbond Zirconnect
Spray (Dental Creativ
Management, Rostock,
Germany) without additional
APA
(experimental)
1. 110 μm Al2O3 particles (Deldent Ltd., Petach Tikva, Israel)
2. Spray
3. Sintering
4. 5% HF IPS Ceramic Etching Gel (Ivoclar Vivadent, Schaan,
Liechtenstein)
5. Ultradent silane, South Jordan, UT, USA
ZCS- DCMhotbond Zirconnect
Spray (Dental Creativ
Management, Rostock,
Germany) with additional
airborne-particle abrasion
(experimental)
1. 110 μm Al2O3 particles (Deldent Ltd., Petach Tikva, Israel)
2. Spray
3. Sintering
4. Additional airborne particle abrasion
5. 5% HF IPS Ceramic Etching Gel (Ivoclar Vivadent, Schaan,
Liechtenstein)
6. Ultradent silane, South Jordan, UT, USA

22

Table 5: Materials list
Type of
material
Product Composition Manufacturer Expiration
Date
Lot
Number
Zirconia KATANA
STML
ZrO 2 + HfO 2: 88-93%
Y 2O 3: 7-10%
Other oxides: 0-2%
Kuraray Noritake,
Tokyo, Japan
11-30-2024
04-30-2024
EBWMG
DZVOV
IPS e.max
ZirCAD LT
ZrO₂ 88.0-95.5; Y₂O₃ 4.5-6.0;
HfO₂ ≤ 5.0; Al₂O₃ ≤ 1.0;
other oxides ≤ 1.0
Ivoclar Vivadent,
Schaan,
Liechtenstein
11-30-2024 Z00YBL
Alumino-silica
coating
DCMhotbond
Zirconnect
spray
SiO 2, Al 2O 3, % withheld
Dental Creativ
Management,
Rostock, Germany
06-08-2021 75
Cement Rely X
Ultimate resin
cement
Monomer: Methacrylates
Other: Additives, Initiators,
Filler, Pigments
3M, St. Paul, MN,
USA
08-18-2022 7649742
Tribochemical
coating
Silica-modified
Al2O3 particles
(CoJet Sand)
Al 2O 3 >97%
Synthetic amorphous silica,
fumed, crystalline free
<5%
Titanium dioxide <0.6%
3M, St. Paul, MN,
USA
11-30-2023 7546680
Airborne-
particle
abrasive
Al2O3 particles
50 μm

Deldent Ltd, Petach
Tikva, Israel

Al2O3 particle,
110 μm

Deldent Ltd, Petach
Tikva, Israel

Composite IPS Empress
Direct
composite
Monomer: Dimetharylates
Fillers: Mixed oxide along
with Copolymers,
trifluoride, Barium glass,
SiO 2 and Ytterbium
Others: Stabilizers,
Additives, Initiators and
Pigments
Ivoclar Vivadent,
Schaan,
Liechtenstein
10-22-2021 V37008
Primer Clearfil
Ceramic
Primer Plus
Ethanol >80%
3-trimethoxysilylpropyl
methacrylate <5%
10-Methacryloyloxydecyl
dihydrogen phosphate
Kuraray Noritake,
Tokyo, Japan
09-30-2023 BH0058
Etchant IPS Ceramic
Etching Gel
Hydrofluoric acid 4.5%
Ivoclar Vivadent,
Schaan,
Liechtenstein
04-25-2024 Z015FK
Silane Ultradent
silane
Methacryloxy propyl
trimethoxy silane; isopropyl
alcohol
Ultradent Products,
South Jordan, UT,
USA
02-29-2024 BKLH2

23
Table 6: Experimental group setup
Surface treatment
Material Aging
Sandblasted
(S)
Zirconnect
(ZC)
Zirconnect +
sandblasting
(ZCS)
CoJet (CO)
ZirCad
(Z)
Non-aged ZSNA ZZCN ZZCSNA ZCONA
Aged ZSA ZZCA

ZZCSA ZCOA
Katana
(K)
Non-aged KSNA KZCNA KZCSNA KCONA
Aged KSA KZCA KZCSA KCOA

S- Groups ZSA, ZSNA, KSA, KSNA
First, zirconia specimens were airborne particle abraded using 50 μm white Al2O3 particles
(Deldent Ltd., Petach Tikva, Israel) dispensed at an air pressure of 1 bar using a fine airborne
particle- abrasion unit (basic quattro IS; Renfert, Hilzingen, Germany) from a fixed distance of
10 mm for 13 s, ensuring the nozzle was perpendicular to the surface. Ultrasonic cleaning
(Quantrex PC3; L&R Manufacturing, Kearny, NJ) in 99% isopropyl alcohol (Mountain Falls
Products, TN, USA) for 10 min followed, afterwards being thoroughly dried using a Kimwipe
(Kimberly-Clark, Irving, TX, USA) (2, 31). Then, one drop of Clearfil Ceramic Primer Plus

24
(Kuraray Noritake, Tokyo, Japan), a phosphate monomer (10-methacryloyloxydecyl dihydrogen-
phosphate, MPD) containing primer was applied directly to the sandblasted or airborne particle
abraded (APA) ceramic’s surface using a microbrush (Microbrush Disposable Micro-Applicator;
Microbrush, Grafton, WI) to achieve a single layer. After leaving undisturbed for 10 s, the
treated surface was sufficiently dried via oil-free compressed air for 5 s.

ZC – Groups ZZCA, ZZCNA, KZCA, KZCNA
First, bonding surfaces of zirconia specimens had airborne particle abrasion applied using 110
μm white Al2O3 particles at an air pressure of 2 bar via a fine airborne particle- abrasion unit
(basic quattro IS; Renfert) from a fixed distance of 10 mm for 13 s, ensuring the nozzle was
perpendicular to the surface. Ultrasonic (Quantrex PC3; L&R Manufacturing) cleaning in 99%
isopropyl alcohol (Mountain Falls Products, TN, USA) for 10 min followed, afterwards being
thoroughly dried using a Kimwipe (2, 31). DCMhotbond Zirconnect spray (Dental Creativ
Management) was shaken for a minimum of 3 min and until rotation of the mixing ball in the
container was audible. The APA zirconia surface was sprayed evenly for 1 s from a distance of
20 cm. This distance was ensured by maintaining the spray nozzle’s tip at the height of an
affixed string at 20 cm. The coated surface was dried at 450 ◦C for 2 min (Programat CS3
Furnace, Ivoclar Vivadent, Schaan, Liechtenstein), heated at 1000 ◦C for 1 min and cooled to
room temperature (Table 7). After cooling, 1 drop of 5% HF IPS Ceramic Etching Gel (Ivoclar
Vivadent, Schaan, Liechtenstein) was applied to the treated surface for 60 s, rinsed with distilled
water for 20 s and air-dried using an oil-free compressed air stream for 5 s. One drop of
Ultradent silane (Ultradent Products, South Jordan, UT, USA) was applied in a single layer, left
undisturbed for 1 min then air-dried utilizing an oil-free compressed air stream for 5 s.

25
Composite cylinder bonding commenced immediately after surface treatment and followed the
steps outlined below.
It’s noteworthy to indicate that this protocol deviated from manufacturer’s recommendations as
an additional round of airborne particle abrasion is indicated after sintering is completed. To
compare the effect of that additional round of airborne particle abrasion, this group was directly
etched after sintering, omitting that second abrasive step, whereas the following group is carried
out as per manufacturers intended.

Table 7: Firing process data for DCMhotbond Zirconnect spray
Starting temperature 450◦C
Drying process 2 min
Firing temperature 1000 ◦C
Climb rate 60 ◦C/min
Hold time 1 min
Vacuum on 450 ◦C
Vacuum until 1000 ◦C

ZCS– Groups ZZCSA, ZZCSNA, KZCSA, KZCSNA
First, bonding surfaces of zirconia specimens had airborne particle abrasion applied using 110
μm white Al2O3 particles at an air pressure of 2 bar via a fine airborne particle- abrasion unit
(basic quattro IS; Renfert) from a fixed distance of 10 mm for 13 s, ensuring the nozzle was

26
perpendicular to the surface. Ultrasonic (Quantrex PC3; L&R Manufacturing) cleaning in 99%
isopropyl alcohol (Mountain Falls Products, TN, USA) for 10 min followed, afterwards being
thoroughly dried using a Kimwipe (2, 31). DCMhotbond Zirconnect spray (Dental Creativ
Management) was shaken for a minimum of 3 min and until rotation of the mixing ball in the
container was audible. The APA zirconia surface was sprayed evenly for 1 s from a distance of
20 cm. This distance was ensured by maintaining the spray nozzle’s tip at the height of an
affixed string at 20 cm. The coated surface was dried at 450 ◦C for 2 min (Programat CS3
Furnace, Ivoclar Vivadent, Schaan, Liechtenstein), heated at 1000 ◦C for 1 min and cooled to
room temperature (Table 7). After cooling, 110 μm white Al2O3 particles were again dispensed,
but this time at a reduced air pressure of 1 bar, per manufacturer instructions, using a fine
airborne particle- abrasion unit (basic quattro IS; Renfert) from a fixed distance of 10 mm for 13
s, ensuring the nozzle was perpendicular to the surface. Ultrasonic (Quantrex PC3; L&R
Manufacturing) cleaning in 99% isopropyl alcohol (Mountain Falls Products, TN, USA) for 10
min followed, afterwards being thoroughly dried using a Kimwipe (Kimberly-Clark, Irving, TX,
USA) (2, 31). After cooling, 1 drop of 5% HF IPS Ceramic Etching Gel (Ivoclar Vivadent,
Schaan, Liechtenstein) was applied to the treated surface for 60 s, rinsed with distilled water for
20 s and air-dried using an oil-free compressed air stream for 5 s. One drop of Ultradent silane
(Ultradent Products, South Jordan, UT, USA) was applied in a single layer, left undisturbed for 1
min then air-dried utilizing an oil-free compressed air stream for 5 s. Composite cylinder
bonding commenced immediately after surface treatment and followed the steps outlined below.

27
CO- Groups ZCOA, ZCONA, KCOA, KCONA
The ceramic surface was tribochemically silica coated via the use of 30 μm silica modified
Al2O3 particles (CoJet Sand, 3M, St. Paul, MN, USA). Utilizing an autoclavable clinical APA
(Ultra-Blaster, Ultradent, South Jordan, UT, USA), the abrasive was be applied perpendicular to
the surface at 2 bar pressure from a distance of 10 mm for 20 s. The ceramic surface was then
coated with one drop of silane coupling agent (Ultradent silane, Ultradent Products, South
Jordan, UT, USA) administered in a single layer using a microbrush (Microbrush Disposable
Micro-Applicator; Microbrush, Grafton, WI, USA), left undisturbed for 1 min and dried for 5 s
utilizing a mild oil-free air stream.

Bonding procedure

For all specimens, a dual-cure, universal resin cement (Rely X Ultimate, 3M, St. Paul, MN,
USA) was used for bonding the composite cylinders to the zirconia substrate, which was
performed immediately after surface treatment was performed. A small amount of the cement
(Rely X Ultimate, 3M ESPE, St. Paul, MN, USA) was applied to the unmarked, bonding surface
of the composite cylinder and was seated onto the middle of the bonding surface of each
specimen using a seating device (chewing simulator, CS-3-8; SD Mechatronik, Feldkirchen-
Westerham, Germany) at uniform pressure. Excess cement was removed using a microbrush
(Microbrush Disposable Micro-Applicator; Microbrush, Grafton, WI, USA) (Figure 10). Finally,
the adhesive cement was light polymerized from all four directions on the specimens for 60
seconds each using a 4-LED light curing unit (Valo, Ultradent, South Jordan, UT, USA) at

28
standard power mode (1000 mW/cm
2
, wavelength 385-515 nm), from 1 mm away or
immediately against seating device platform. After bonding, each zirconia subgroup was further
divided into two water storage subgroups to be tested for shear bond strength before artificial
aging, and the other to be tested after artificial aging.

Figure 10: Seating of composite cylinder

Artificial aging

To analyze the effects of aging, specimens were either stored in distilled water for 24 h before
testing (non-aged) or subjected to thermal cycling (aged; Thermocycler THE-1100, SD
Mechatronik, Westerham, Germany) before testing. In accordance with the ISO 29022:2013
thermal cycling commenced in a 5/55
o
C distilled water bath for 20,000 cycles. The number of
20,000 cycles has been reported to represent 2 years of service (32). The transfer time was set at

29
15 s, and the dwell time was set at 15 s. Distilled water (Arrowhead Distilled Water, Nestle,
Arlington, VA, USA) was replaced regularly throughout the aging process. After artificial aging,
specimens were kept in distilled water (Arrowhead Distilled Water, Nestle, Arlington, VA, an
incubator at 37
o
C for 24 h until further testing.

Shear bond strength (SBS) testing

The completed specimens affixed with the cylinders were mounted in a shear device (Notch-
edge crosshead blade, Ultradent, South Jordan, UT, USA) after being gently dried using a paper
towel (Multi-Fold Towels, Scott brand, Neenah, WI, USA) without contacting the cylinder. The
specimen was placed in the holder, equidistant from each side, and the crosshead was aligned as
near as possible from the composite cylinder without touching it (Figure 11). Shear bond
strength (SBS) testing was performed using a universal testing machine (Model 6596; Instron,
Norwood, MA, USA) at a crosshead speed of 1 mm/min (Figure 12). Maximum shear load (N) at
the time of failure was recorded in the software (Bluehill 3, V3.04, Instron, Norwood, MA,
USA). SBS was calculated using the formula: SBS=Fmax/A surface [MPa]. Specimens that de-
bonded before testing or during thermal cycling were counted as 0 MPa (pretesting failures;
PTF). SBS was calculated using the formula: SBS=Fmax/A surface [MPa].

30

Figure 11: Mounted specimens for SBS testing

Figure 12: Universal Testing machine

31
Failure analysis

Upon specimen failure, bonding surfaces of both the zirconia and composite cylinder were
inspected for primary failure mode, occurring as an adhesive failure at the zirconia, adhesive
failure at the composite cylinder, cohesive failure in zirconia, cohesive failure in the composite
cylinder, cohesive failure in cement or a combination, denoted as “mixed”). Although these
failure mode options exist, only three predominated in the present study: adhesive failure at the
zirconia, adhesive failure at the composite cylinder, and a mixed variation. Some failure modes
were not expected, such as a cohesive failure in zirconia, due to the well-founded expectation
that the internal forces of zirconia will supersede the strength of the bond between the cylinder
and zirconia, which was upheld in the present study. This primary analysis served as an initial,
macroscopic analysis with the naked eye. A more detailed, microscopic fracture analysis
commenced by analyzing the fractured specimen surfaces using a stereo microscope in both light
and fluorescent modes (Carl Zeiss Meditec, Jena, Germany) at x60 to x200 magnification. This
allowed for visualization of cement remnants, to aid in the determination of what fracture mode
predominated and which others were present, if any. Image analysis software (Fiji ImageJ, V1.0,
National Institutes of Health (NIH), Bethesda, MD, USA)) was employed for further analysis to
offer general quantitative data regarding multiple fracture modes. After downloading all 480
images (one light- and one fluorescent-mode photo per specimen) into our image analysis
software, each bonding surface was analyzed. After circumscribing the outline of the composite
cylinder to determine the total bonding area, a freehand tool in the software was used to delineate
areas of different predominating failures, when applicable. With those areas identified and
outlined, different failures were able to be determined and quantified by using the identified area

32
and dividing it into the total area, multiplied by 100 to provide the associated percentage (Figure
13, Figure 14).

Figure 13: Failure analysis -Circumscribed cylinder for total bonding area, delineated composite remnant, and fluorescent mode
to aid in identification of remaining composite

Figure 14: Failure analysis- light and fluorescent mode (b. Adhesive failure at the zirconia surface (debonding at the zirconia-
cement interface) can be confirmed by fluorescent mode analysis which is completely devoid of composite c. Cohesive failure in
the composite cylinder (failure within the composite cylinder) can be confirmed by retained composite on the zirconia surface d.
Mixed failure (a combination of specific failure modes) can be evidenced here by composite remnants (yellow delineation within
red total bonding surface demarcation, and yellow arrows in fluorescent mode photo) and failure at the zirconia-cement
interface (yellow arrow in light mode photo.

33

Statistical analysis

Statistical analysis was conducted using a nonparametric test for the zirconia types, surface
treatments and aging factors from the SBS data due to a lack of homogeneity of variances
(Levene test, p=0.002) as well as normally distributed data (Kolmogorov-Smirnov Test,
p=0.00136). Further, the Kruskal-Wallis test was employed to detect overall differences for the
factor’s material and aging parameter. Group-wise comparisons were conducted separately for
each material with Mann-Whitney test using Bonferroni correction due to multiple comparisons
(⍺=0.001) using a statistical analysis software (SPSS version 19, IBM, Armonk NY, USA).

34
Results

The values of shear bond strength (SBS) for both non-aged and aged specimens are depicted in
Figure 15 and listed in Table 8.

Figure 15: SBS of non-aged and aged specimens by surface condition

0
5
10
15
20
25
30
Sandblasted (S) Zirconnect (ZC) Zirconnect + Sandblasting
(ZCS)
CoJet (CO)
KNA ZNA KA ZA

35

Table 8: SBS for aged and non-aged specimens
Surface treatment
Material Aging
Sandblasted
(S)
Zirconnect
(ZC)
Zirconnect +
sandblasting
(ZCS)
CoJet (CO)
ZirCad
(Z)
Non-aged
ZSNA
25.48 ± 4.72
aA

ZZCNA
26.81 ± 4.89
aA

ZZCSNA
21.36 ± 5.86
aA

ZCONA
24.26 ± 5.11
aA

Aged
ZSA
7.60 ± 4.68
aB

ZZCA
2.21 ± 3.70
abB
ZZCSA
1.93 ± 1.11
bB

ZCOA
9.97 ± 7.14
aB

Katana
(K)
Non-aged
KSNA
21.35 ± 6.8
aA

KZCNA
25.95 ± 4.78
aA

KZCSNA
21.75 ± 6.54
aA

KCONA
24.63 ± 3.98
aA

Aged
KSA
6.46 ± 3.17
aB

KZCA
20.43 ± 4.75
bA

KZCSA
1.37 ± 2.19
cB

KCOA
12.51 ± 6.18
abB

Within rows: Values with same lower-case letters are not significantly different from each other
Within columns: Values with same UPPER-CASE letters are not significantly different from each
other
Level of significance 0.001

Mean SBS of specimens after 24 hours of water storage as compared to 20,000 thermal cycled-
specimens were compared across 4 different surface treatments as well as 2 zirconia types using
Kruskal-Wallis and Mann-Whitney tests.
Kruskal-Wallis analysis revealed significant differences between all 16 groups with p<0.000001.

36

According to Kruskal-Wallis testing, non-aged specimens presented significantly greater SBS
averages (p<0.00001) than their aged counterparts.
No significant differences were found between the two zirconia types (p=0.2900; Kruskal-
Wallis).

As significant differences between all groups were denoted by Kruskal-Wallis analysis
(p<0.000001), Mann-Whitney testing revealed a significant difference (p=0.00038) in SBS
outcomes between the tribochemically-coated (CO) surface treatment group and Zirconnect
group with additional APA (ZCS) only. Similar SBS values were found amongst all other
treatment groups (Table 8).

Non-aged groups

For non-aged groups, SBS outcomes ranged from 21.35 MPa (KSNA) to 26.81 MPa (ZZCNA)
(Figure 16).

37

Figure 16: SBS of non-aged specimens by surface condition

Zirconia
No significant differences were found between zirconia types at p>0.001. The 3Y-TZP grade IPS
e.max ZirCAD LT (Ivoclar Vivadent, Schaan, Liechtenstein) displayed similar SBS values
ranging from 21.36 MPa (ZZCSNA)- 26.81 MPa (ZZCNA) as compared to 4Y-TZP grade
KATANA STML’s (Kuraray Noritake, Tokyo, Japan) with SBS values ranging from 21.35 MPa
(KSNA) to 25.95 MPa (KZCNA).

Surface treatment
No statistically significant differences between surface treatments were revealed (p>0.001; Table
8). The smallest SBS outcome amongst non-aged specimens was found with the airborne particle
0
5
10
15
20
25
30
Sandblasted (S) Zirconnect (ZC) Zirconnect + Sandblasting
(ZCS)
CoJet (CO)
KNA ZNA

38
abrasion (S) surface treatment group KSNA (21.35 MPa) while the surface treatment group ZC
with no additional airborne particle abrasion ZZCNA (26.81 MPa) revealed the greatest average
SBS, although Mann-Whitney analysis revealed all outcomes were similar and thus not deemed
significant.

Aged groups

For aged groups, average SBS ranged from 1.37 (KZCSA) to 20.43 MPa (KZCA); Figure 17.

Figure 17: SBS of aged specimens by surface condition

0
5
10
15
20
25
Sandblasted (S) Zirconnect (ZC) Zirconnect + Sandblasting
(ZCS)
CoJet (CO)
KA ZA

39
Zirconia
No significant differences were found between zirconia types at p>0.001. The 3Y-TZP grade IPS
e.max ZirCAD LT (Ivoclar Vivadent, Schaan, Liechtenstein) displayed similar SBS values
ranging from 1.93 MPa (ZZCSA)- 9.97 MPa (ZCOA) as compared to 4Y-TZP grade KATANA
STML’s (Kuraray Noritake, Tokyo, Japan) with SBS values ranging from 1.37 MPa (KZCSA) to
20.43 MPa (KZCA).

Surface treatment
The smallest SBS outcome amongst aged specimens was found with the Zirconnect with
additional airborne particle abrasion surface treatment group KZCSA (1.37 MPa) while the
surface treatment group ZC with no additional airborne particle abrasion (KZCA, 20.43 MPa)
revealed the greatest average SBS.

Within the material ZirCad LT (Z), groupwise comparison reveals that group ZZCSA (1.93
MPa) showcasing the Zirconnect with additional airborne-particle abrasion is statistically
significant from group ZCOA (9.97 MPa) with tribochemical coating and group ZSA (7.60 MPa)
with only airborne particle abrasion; However, groups ZSA (7.60 MPa), ZZCA (2.21 MPa) and
ZCOA (9.97 MPa) are not significantly different from each other.
Further, for the material Katana STML (K), group KZCSA (1.37 MPa) is statistically different
from all other groups: KSA (6.46 MPa), KZCA (20.43 MPa) and KCOA (12.51 MPa). Although
groups KSA (6.46 MPa) and KZCA (20.43 MPa) are significantly different from each other,
group KCOA (12.51 MPa) is not significantly different from groups KSA (6.46 MPa) or KZCA
(20.43 MPa) (Table 8).

40
Failure mode analysis

Macroanalysis

Six possible failure modes include an adhesive failure at the zirconia surface, an adhesive failure
at the composite cylinder, a cohesive failure in zirconia, a cohesive failure in composite, a
cohesive failure in cement, or a combination of failures (mixed). Of all possible modes of failure,
only three were relevant and expected due to the nature of the present study: adhesive failures at
the zirconia surface (Ad- zirconia), and cohesive failures in the composite cylinder (Co-
composite) and in cement (Co- cement) (Figure 14). The current study did not report any
cohesive failures of zirconia, for example, or failures within the zirconia, as the material’s
internal forces disallowed fracture or deformation, as compared to the strength the adhesive bond
at the interface of the two materials. Failure mode analysis revealed adhesive failure at the
zirconia surface as the primary failure mode, confirmed initially via macroscopic analysis with
the naked eye. Groups ZZCA and KZCSA, both utilizing Zirconnect but KZCSA with an
additional airborne-particle abrasion application, experienced 8 pre-test failures, each, while no
other treatment group reported more than two pre-test failures: (ZSA=2; ZZCSA=1; remaining
groups= 0 pre-test failures). General failure modes include a total of 210 adhesive failures at the
zirconia surface (87.5%), 13 cohesive failures in the composite cylinder (5.41%), and 17 mixed
failures (7.08%). For further analysis of mixed failures, as well as to confirm all results of
macroanalysis, microanalysis was employed for specific failure mode evaluation for each
specimen.

41

Figure 18: Failure mode analysis by surface treatment, grouped by aging

Microanalysis

Microscopic fracture analysis was conducted by analyzing the fractured specimen surfaces using
a stereo microscope in both light and fluorescent modes (Carl Zeiss Meditec, Jena, Germany) at
x60 to x200 magnification. After downloading all 480 images (one light- and one fluorescent-
mode photo per specimen), into our image analysis software (Fiji ImageJ, V1.0, National
Institutes of Health (NIH), Bethesda, MD, USA) each bonding surface was analyzed. After
circumscribing the outline of the composite cylinder to determine the total bonding area, a
freehand tool in the software was used to delineate areas of different predominating failures,
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
ZSA
ZZCA
ZZCSA
ZCOA
KSA
KZCA
KZCSA
KCOA
ZSNA
ZZCNA
ZZCSNA
ZCONA
KSNA
KZCNA
KZCSNA
KCONA
Adhesive (AD)- zirconia Cohesive (Co)- composite Cohesive (Co)- cement

42
when applicable. With those areas identified and outlined, different failures were able to be
determined and quantified by using the identified area and dividing it into the total area,
multiplied by 100 to provide the associated percentage (Figure 13, Figure 18).

For all non-aged groups, adhesive failures at the zirconia surface predominated as the primary
failure type, showcasing a range of 64.53- 84.11% of the failure mode. Cohesive failures in the
composite cylinder ranged from 1.71- 11.22% of the failure mode while cohesive failures in
cement ranged from 8.56- 32.32% (Figure 19).

Figure 19: Failure mode analysis of non-aged specimens

Of all non-aged specimens, 12 (10%) failed cohesively in composite while 9 (7.5%) failed
cohesively in cement, whereas 82.5% of specimens (99 total) experienced adhesive failure at the
zirconia surface.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
ZSNA ZZCNA ZZCSNA ZCONA KSNA KZCNA KZCSNA KCONA
Adhesive (AD)- zirconia Cohesive (Co)- composite Cohesive (Co)- cement

43

Of all aged specimens, 2 (1.66%) failed cohesively in composite while 9 (7.50%) failed
cohesively in cement, whereas 90.83% of specimens (109 total) experienced adhesive failure at
the zirconia surface (Figure 18).
For all aged groups, an adhesive failure at the zirconia surface predominated as the primary
failure type, averaging from 64.81- 93.23% of the failure mode. Cohesive failures in the
composite cylinder ranged from 0- 5.20% of the failure mode while cohesive failures in cement
ranged from 2.85- 31.19% (Figure 20).

Figure 20: Failure mode analysis of aged specimens

Discussion
Accepted surface treatments

0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
ZSA ZZCA ZZCSA ZCOA KSA KZCA KZCSA KCOA
Adhesive (AD)- zirconia Cohesive (Co)- composite Cohesive (Co)- cement

44
The 1
st
null hypothesis predicting no differences would result amongst surface treatments was
rejected due to statistically significant differences between groups ZCS and CO; however, no
other differences in SBS were deemed significant amongst other surface treatment groups as
shown in Table 8.

The present study’s setup is in line with others’ as both chemical and micromechanical retention
is indicated for a successful bond to zirconia. The more traditional means of zirconia bonding
involves establishing both micromechanical and chemical retention via the use of airborne-
particle abrasion and functional monomers, respectively. Airborne-particle abrasion acts to
produce surface irregularities that will function to create an interlocking with resin. Since
zirconia ceramic contains metal oxides, chemical retention is promoted via surface treatment
with primers containing adhesive functional monomers such as 10-methacryloyloxy decyl
dihydrogen phosphate (10-MDP) and is often recommended to improve the bonding of resins to
the ceramic (21, 27, 28). Adhesive monomers such as the aforementioned are believed to have
the ability to form chemical bonds with metal oxides, van der Waals forces or other secondary
forces, or hydrogen bonds at the resin-ceramic interface. Previous literature has proven the
chemical nature of the bond between the zirconia ceramic surface and MDP (17, 21, 31, 33-35).
These interfacial forces improve the surface wettability of the zirconia ceramic surface and,
therefore, resin bonding (20). The present study’s results of no significant differences existing
between surface treatments (or slight increases in SBS with APA (S) or tribochemically-coated
(CO) surfaces as compared to ZC or ZCS treatments) are in accordance with previous
experimental studies supporting the use of MDP to increase the bonding effectiveness to zirconia
(20).

45
Contrastingly, bonding to zirconia but utilizing glass ceramic bonding concepts offers a protocol
that has been met with satisfactory but variable results as glass deposition techniques differ (i.e.,
tribochemical coating providing confined spots of silica compared to the more uniform silica
covering provided by a glaze.
Bonding to glass ceramics requires a deposit of silica that is roughened via hydrofluoric acid
etching which leads to the creation of rougher surface as the bonding surface, providing micro-
mechanical interlocking to resin composite cements (25). Additionally, the silica layer atop the
zirconia surface can chemically bond to silane-containing primers in which the silane acts to
create cross linkages with methacrylate groups in composite cements which predictably increases
the bond strength and bond reliability (4, 25). Whereas APA or (S) groups rely on the concept of
APA and application of an adhesive functional monomer, Zirconnect groups (Z, ZCS) and
tribochemical coated- (CO) specimens depend on the aforementioned glass ceramic concepts.

Silica-based bonding techniques

Just as the effectiveness of tribochemical coating hinges on the retention and availability of silica
particles, the effectiveness of the alumino- silica-based coating relies on the same for effective
bonding using silane (22). Attempts to identify a consistent adhesive method to zirconia-based
ceramics have been made in previous literature, although research is ongoing with the present
study investigating the effectiveness of an alumino- silica-based coating, DCMhotbond
Zirconnect spray. The main concerns with these novel techniques are thickness of the coating
layer, bond strength and durability. Hydrofluoric acid (HF) etching and silanization of the
ceramic layer was expected to contribute to greater bond strength which did promote comparable

46
SBS outcomes in the present study, although not statistically significant (36, 37). Few studies
exist on the analysis of an alumino- silica-based coating like DCMhotbond, and those that do
report contradictory analysis and theory. Indrani DJ et al. (10) concluded that infiltration of the
filler particles of resin cement into the irregularities formed on the alumino- silica surface was
impossible due to the prevalence of microcracks, leading to a weakened coating layer and
subsequent poor micro-mechanical interlocking. The effect of this potential phenomenon did not
appear to reflect in the present study as SBS of ZC groups were not statistically different from
other surface treatment groups. Literature reveals that the application of a ceramic coating
provides notable and predictable mean bond strength values, which is consistent with the
findings from several previous studies (19, 38, 39). This finding may be attributed to the silica
composition of the coated layer on zirconia surface via different techniques e.g., selective
infiltration etching, (38) glazing techniques, (40) ceramic liner (39). To produce
micromechanical retention when bonding to glass ceramics or when utilizing available
embedded or layered silica, ceramic pores are created by selectively dissolving the amorphous
silica glass phase. As the crystalline structure is exposed after HF acid exposure and dissolution
of the glass phase, an irregular microstructure with a higher surface area is left behind,
improving bonding due to increased bonding area.

Alumino- silica-based coating’s performance

47
According to Mann-Whitney analysis, ZCS prompted the lowest SBS outcome amongst aged
specimens (KZCSA=1.37 MPa) and almost tied with KSNA (21.35 MPa) for lowest SBS
amongst non-aged specimens (ZZCSNA= 21.36 MPa). SBS outcomes generally improved with
accepted treatments of airborne-particle abrasion and tribochemical coating, in comparison to the
aerosolized alumino-silica-based surface coating, with and without the additional airborne-
particle abrasion. Amongst aged IPS e.max ZirCad LT (Z) specimens, tribochemical coating
(CO) influenced a SBS outcome of 9.97 MPa, followed by the airborne particle abrasion (7.60
MPa), then ZC application alone (2.21 MPa) and lastly ZCS with additional airborne-particle
abrasion (1.93 MPa). ZCS surface treatment also prompted the least SBS outcome amongst non-
aged ZirCad LT specimens as well (ZZCSNA=21.36 MPa). Based on ZirCad LT’s (Z) SBS
outcomes for both ZC and ZCS, a reduced SBS was revealed compared to S and CO treatments,
suggesting the ineffectiveness of the experimental silica-based coating. Considering ZC and ZCS
experimental treatments, Katana STML (K) specimens revealed a trend consistent with ZirCad
LT (Z) in that ZCS revealed reduced SBS values for aged specimens (1.37 MPa; KZCSA)
compared to 20.43 MPa (KZCA) as well as non-aged (21.75 MPa; KZCSNA) compared to 25.95
MPa (KZCNA). Albeit at a reduced pressure of 1 bar, airborne-particle abrasion in the ZCS
groups could essentially disrupt the “glassy matrix” the Zirconnect provides, leaving spaces
devoid of the silica particles required for a stable bond to silica. The alumino- silica-based
coating being subject to alteration or removal by additional airborne particle abrasion may
explain the trend of ZCS surface treatment exhibiting a significantly lower SBS than the ZC
group. Although controversial views of airborne-particle abrasion promoting substrate flaws and
introducing microcracks exist, numerous in vitro reports have upheld airborne-particle abrasion’s
role in achieving a durable bond to high-strength ceramics (26-28, 31).

48

Group KZCA (20.43 MPa) with the Zirconnect application without additional APA revealed a
surprisingly increased SBS outcome compared to its aged, Katana STML counterparts
(KCOA=12.51 MPa; KSA=6.46 MPa; KZCSA= 1.37 MPa). This result can potentially be
influenced by the physical nature of the ceramic surfaces, namely, the surface roughness.

As airborne-particle abrasion can alter the bonding surface topography and subsequent surface
roughness, studies were compared to reveal any trends but with contradictory results. In Zhao et
al.’s study, a larger (110 μm) particle promoted the surface roughness of conventional as well as
highly translucent zirconia, resulting in an increase in the shear bond strength (41). Their study
was conducted with two different particle sizes (50 and 110 μm), just as in the present study.
Contrastingly, the result of Kim HK’s 2021 study revealed that the values for APA zirconia
using 125 μm particles fell below those using 90 μm particles for all three utilized zirconia
grades (42). This may be attributed to the surface flattening, broadening, and material loss
induced by the larger particles (42). The result of the surface topography reported by Inokoshi et
al. (16) found that alumina APA did not significantly change the differing zirconia grade’s
surface topographies, considering the 50 µm alumina particles utilized. Kim HK et al. revealed
that highly translucent zirconia groups (4Y- and 5Y-PSZ) were abraded faster than conventional
3Y-TZP, which was in line with the result of Zhao et al.’s study (41, 42). The highly translucent
zirconia had weaker mechanical properties compared to conventional 3Y-TZP and was not quite
as hard (43, 44); thus, less energy was required for the striking particles to alter the surface
topography, revealing a rougher surface that could encourage a more pronounced interaction
with the ZC and reveal an increased SBS outcome. Considering this rationale, it would be

49
reasonable to expect the 4Y- to develop a more heavily abraded surface, prompting a potential
alteration in SBS; although, studies revealed that up to a certain pressure threshold did the
subsequent surface alteration promote an increased SBS, after which a decreased SBS
predominated (41). Although the results of the present study generally seem to follow the
rationale that airborne particle abrasion does not change surface topography enough to prompt
any considerable changes in SBS, it’s a consideration to explain the increased SBS outcome in
group KZCA; 20.43 MPa.
Operator handling is an additional explanation to potentially explain KZCA’s outcome.
Specimens from this group were subject to a “trial” coating of the Zirconnect spray in an effort
to establish a standardized approach to evenly coating ZC and ZCS specimens. Typically, pilot
specimens are used for “calibration” but due to having a limited number of specimens, pilot
testing was unable to be completed on additional specimens. Although ZC-coated surfaces are
easily wiped away prior to sintering, silica-based coating, undetectable by the naked eye, may
remain. If true, this group may be showcasing the results of a more pronounced silica-based
coating as compared to specimens with a single, thin, and uniform ZC application. This potential
scenario highlights the importance of the standardization of the powder application. Lack of such
will present a challenge when both utilizing the product as a clinician or technician and
comparing as a researcher.

Although the 3Y-TZP and 4Y-PSZ zirconia types encompass different mechanical properties,
SBS outcomes in the present study are comparable Kim HK et al. (42) revealed mechanical
properties of 3Y-TZP as compared to 4Y-PSZ, with the results of this previous research

50
depicting 3Y-TZP as less dense, possessing a lower modulus of elasticity, and having a
decreased hardness as compared to the 4Y-PSZ; however, 3Y-TZP boasted more superior
mechanical properties, by comparison. SEM analysis from the same study (Kim HK, et al, 2020)
(42) revealed grain sizes of the 3Y-TZP ranging from about 280 to 350 nm, whereas larger
grains were observed in 4Y- (416–890 nm). Zirconia with a higher yttria content, or more
translucent zirconia, tends to have larger grains that increase in size with decreased temperature
(6); further, those larger grains have a detrimental effect on the subsequent mechanical
properties, although the minimized grain-boundary light scattering yields more light
transmission, and thus provides a more esthetic ceramic material (9). Despite these differences as
no significant differences in SBS between the zirconia types presented, the 2
nd
null hypothesis
was accepted. Understanding that, within the limitations of this study, different grades or types
of zirconia can be used interchangeably for predictable bonding; thus, further highlighting the
importance of different surface treatment’s influence on SBS.

Aging

The 3
rd
null hypothesis predicting no significant difference in bond strength between the
artificially- aged (aged) and 24-hour water storage (non-aged) specimens was also rejected as
statistical analysis revealed significantly greater SBS outcomes for the non-aged specimens as
compared to their artificially aged counterparts. Several studies used artificial aging via water
storage and thermal cycling to simulate clinical happenings and to identify superior bonding
methods and products (26, 34, 45). More specifically, water adsorption, hydrolyzation and
thermal changes have been proven as intraoral conditions that influence the long-term stability of

51
silane and resin bonds (46). To best replicate the influence of conditions such as the
aforementioned, artificial-aging methods like water storage and thermocycling are upheld as the
nature of the oral environment significantly influences the resin bond to ceramics, especially
regarding high-strength ceramics (1, 26, 46-48).

In studies including artificial aging, shear bond strength was tested and highlighted a significant
decrease after thermal cycling (2, 34, 45). Decreased shear bond strength due to thermal cycling
also was observed in the present study as well, in which water storage commenced in a 37˚C
incubator for 60 days when not alternating between 5/55 ˚C pools during 20,000 thermal cycles.
Other similar studies boast an artificial aging span of 150 days, in which specimens alternate
between 5/55 ˚C pools when not being thermal cycled 20,000 cycles. The significant decrease of
the average SBS outcomes in aged specimens could be attributed to extended water penetration
into the interface of bonded materials, which resulted in hydrolytic degradation of polymer
matrix of the interface components (49). Additionally, temperature changes in the thermocycling
process may exacerbate the coefficient of thermal expansion mismatch of the bonded materials,
which generates mechanical stresses at the bonded interface resulting in strength degradation
(50). Furthermore, the combination of long-term water storage and thermocycling can
considerably decrease the bond strength between composite cement and zirconia as reported by
both Thammajaruk P, Heikkinen TT, and colleagues (48, 51). An additional explanation for the
decrease in bond strength might be the plasticization effect of water on the resin matrix which
had been shown to change the mechanical properties of composite resins (10, 17, 35).

Limitations/Future direction

52

Although in-vitro studies provide useful information, care should be taken when interpreting
them. Even while providing beneficial information and being often considered easier to conduct
than in-vivo simulations, they are not a direct alternative to clinical tests and should be
interpreted as such (2). Nonetheless, in vitro tests have their advantages and provide many
options when considering testing methods. Nominal bond strength tests such as macro-shear,
micro-shear, macro-tensile and micro-tensile bond strength test are widely used to calculate the
bond strength by dividing the maximum force by the bonding area. The lack of an international
standard for testing the bond between composite cements and zirconia explains the variety of
tests used by researchers and the difficulties in comparing data achieved under different
experimental parameters; however, ISO Standard 29022 was adopted after Ultradent’s creation
and effective implementation of the notched-edge shear bond strength testing method, and these
standards can reasonably be considered as the current laboratory standards (52, 58). The
notched-edge shear bond strength test utilizes a crosshead with a notched edge to generate an
even distribution of force and produce more accurate results as compared to those garnered from
use of a straight-edged crosshead. Despite the lack of consensus on which test is the most
appropriate, the macro-shear bond test remains as most frequent methodology used for
measuring the bond strength between composite cements and zirconia (16). This is likely due to
the fact that specimen preparation and the test itself are relatively simple (18, 48). Additionally,
numerous studies exist upholding the reliability of SBS testing (10, 26, 27, 53). Although a noted
limitation of the shear bond test is that it may fail to eliminate nonuniform interfacial stresses
causing cohesive failures in the bonding substrate, the current study found primarily adhesive
failures, which may further highlight the validity of the applied testing method (5, 17).

53
Alternatively, other research upholds the notched-edge shear bond strength testing as
advantageous as using the molded shear blade can be observed in the reduced variability of the
results because the shear blade directly stresses the adhesive interface and may reduce cohesive
fractures (54). As expected, failure mode analysis revealed adhesive failure at the zirconia
surface as the primary failure mode, confirmed via both macroscopic and microscopic failure
analysis. Of all possible modes of failure, only three were relevant and expected due to the nature
of the present study: adhesive failures at the zirconia surface and composite cylinder, and
cohesive failures in cement. The current study did not report many cohesive failures, or failures
within the zirconia, as its inner strength disallowed facture or deformation, as compared to the
strength the adhesive bond at the interface of the two materials. Groups ZZCA and KZCSA, both
utilizing Zirconnect but group KZCSA with an additional airborne-particle abrasion application,
experienced 8 pre-test failures, each, while no other treatment group reported more than two pre-
test failures. These results raise concern regarding the stability of the deposited glassy matrix
layer atop the zirconia surface and cement interfaces. The uptick in pre-test failures in these aged
groups could be attributed to hydrolytic degradation and the plasticization effect of water on the
resin matrix but these effects would expectedly affect all groups in the same manner (10, 17). In
comparison to their aged counterparts, groups ZZCA and KZCSA revealed the greatest
percentage of failure being adhesive at the zirconia and cohesive in cement. Additional research
aimed at confirming which Zirconnect application technique is better indicated to promote stable
bonds to zirconia as well as assessing the necessity of the additional round of airborne particle
abrasion is indicated.

54
Future studies assessing zirconia surface treatment effects on SBS should include artificial aging
of at least 6 months, especially since our aging parameter of 2 months prompted significantly
lower SBS values, as well as for more widespread comparison amongst other studies (7, 55).
More research comparing the surface topography and subsequent roughness of different zirconia
grades after standardized airborne-particle abrasion, tribochemical coating, or any surface
altering treatment may also be indicated to better assess factors influencing the zirconia bond,
especially as new zirconia types are constantly introduced.

55
Conclusion

Within the expressed limitations, the present study reveals:
1) The first null hypothesis that there will be no significant difference in bond strength
between the aerosolized alumino-silica-based coating technique, standard
techniques based on alumina air-abrasion and tribochemical coating was accepted
as the aerosolized alumino-silica-based surface coating did not prompt significantly
significant SBS outcomes as compared to presently accepted surface treatments.
2) The second null hypothesis that there will be no significant difference in bond
strength between the 3Y-TZP and 4Y-PSZ zirconia was accepted as no significant
difference in bond strength between the 4Y-PSZ Katana STML and 3Y-TZP IPS
e.max ZirCAD LT was presented. This suggests that zirconia, despite the grade,
can be used interchangeably for predictable bonding.
3) Although average SBS values for non-aged specimens revealed data in line with
previous studies, aged specimens showcased significantly decreased average SBS
outcomes, prompting the third null hypothesis-- that there will be no significant
difference in bond strength between the artificially aged (aged) and 24-hour water
storage (non-aged) specimens-- to be rejected. This necessitates further long-term
research before actual clinical recommendations are made.

56
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Abstract (if available)

Abstract Objective: To investigate the impact of an aerosolized alumino-silica- based coating technique on the bond strength of both 3Y-TZP and 4Y-PSZ dental zirconia types, as compared to standard, accepted zirconia surface treatments.
Methods and Materials: Four surface treatments used to modify the zirconia surface were compared to evaluate the shear bond strength (SBS) between two zirconia types and two aging mechanisms. Two currently accepted surface treatments (airborne-particle abrasion and tribochemical coating) were compared against an experimental aerosolized alumino-silica- based coating technique, with an additional round of airborne-particle abrasion, per manufacturer instructions, and without the additional airborne-particle abrasion. Treated zirconia surfaces then received resin-composite cylinders (IPS Empress Direct, Ivoclar Vivadent, Schaan, Liechtenstein) cemented using a dual-cure resin cement (RelyX Ultimate Adhesive Resin Cement, 3M, St. Paul, MN, USA). After dividing the 240 total zirconia specimens into non-aged (24-hour water storage) or aged (60 days artificial aging/ thermocycling 20,000 cycles) groups, testing commenced using a notched shear bond strength test.
Results: No significant differences were found between zirconia types at p>0.001, nor between the four surface treatments with the exception of comparing SBS outcomes of tribochemical coated (CO)- and the aerosolized alumino-silica- based coating with airborne-particle abrasion (ZCS)-treated specimens (p=0.00038). Significant differences (p<0.00001) in SBS between non-aged and aged specimens were revealed.
Conclusion: The aerosolized alumino-silica-based coating technique, whether with the additional round of airborne-particle abrasion or not, did not produce significantly greater SBS outcomes than currently accepted surface treatments.

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Asset Metadata

Creator Anderson, Erin (author)

Core Title Influence of an aerosolized alumino-silica-based surface coating on shear bond strengths of two different types of zirconia

School School of Dentistry

Degree Master of Science

Degree Program Biomaterials and Digital Dentistry

Degree Conferral Date 2021-12

Publication Date 03/22/2023

Defense Date 09/16/2021

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag aerosolized alumino-silica-based coating technique,notched-edge shear bond strength test,OAI-PMH Harvest,shear bond strength,surface treatment,zirconia ceramic

Format theses (aat)

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Phark, Jin-Ho (committee chair), Duarte, Sillas (committee member), Knezevic, Alena (committee member)

Creator Email dentdawg2@gmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-oUC112847874

Unique identifier UC112847874

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Legacy Identifier etd-AndersonEr-11513

Document Type Thesis

Format theses (aat)

Rights Anderson, Erin

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Source 20230324-usctheses-batch-1011 (batch), University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

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