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.e3680

Braz Dent Sci 2023 July/Sept;26 (3): e3838

Eﬀect of novel pre-sintered zirconia surface treatment on shear

bond strength between zirconia and veneering porcelain compared

to conventional surface treatments: an in-vitro study

Efeito de um novo tratamento de superfície de zircônia pré-sinterizada na resistência ao cisalhamento entre zircônia e

porcelana em comparação com os tratamentos de superfície convencionais: estudo in vitro

Ahmed Atef BAIOMY1 , Norhan Naief Abd El HALIEM1 , Hanan Ahmed NAGUIB2 , Amina ZAKI3 

1 - Egyptian Russian University, Faculty of Dentistry. Badr City, Egypt.

2 - Cairo University, Faculty of Dentistry. Cairo, Egypt.

3 - Cairo University, Faculty of Dentistry, Fixed Prosthodontics Department. Cairo, Egypt.

How to cite: Baiomy AA, Haliem NNAE, Naguib HA, Zaki A. Effect of novel pre-sintered zirconia surface treatment on shear bond

strength between zirconia and veneering porcelain compared to conventional surface treatments: an in-vitro study. Braz Dent Sci.

2023;26(3):e3838. https://doi.org/10.4322/bds.2023.e3680

ABSTRACT

Objective: to evaluate the effect of novel zirconia surface treatment method on shear bond strength between

zirconia and veneering porcelain compared to air abrasion and CoJet surface treatment methods. Material and

Methods: twenty-one zirconia ceramic discs were fabricated with diameter of 7mm and 3mm thickness and

divided according to surface treatment into three subgroups, control group I: Air Abrasion (n=7), group II: CoJet

(n=7) and group III: Z-etch (n=7). Porcelain was built over the zirconia specimens with a customized mold and

red in a ceramic furnace. All specimens were thermocycled (20000 cycles) between 5°C – 55 °C with a dwell

time of 30 seconds in distilled water and shear bond strength of veneering porcelain to each zirconia specimen

was tested using a universal testing machine. Results: numerical data were explored for normality by checking

the distribution of data and using tests of normality (Kolmogorov-Smirnov and Shapiro-Wilk tests). One-way

ANOVA test was used to compare between the groups. There was a statistically signicant difference between

the three groups (P-value = 0.002, Effect size = 0.503). Pair-wise comparisons between groups revealed that

Z-etch showed the statistically signicantly highest mean shear bond strength. Conclusion: zirconia coating

using z-etch is showing promising results in promoting higher bond strength than conventional surface treatment

methods as air abrasion and silica coating.

KEYWORDS

Air-abrasion; Dental materials; Shear bond strength; Surface treatment; Z-etch; Zirconia.

RESUMO

Objetivo: avaliar o efeito do novo método de tratamento de superfície de zircônia na resistência ao cisalhamento

entre a zircônia e a porcelana de cobertura em comparação com os métodos de abrasão a ar e jateamento

com CoJet. Material e Métodos: vinte e um discos de zircônia foram confeccionados com diâmetro de 7mm

e espessura de 3mm e divididos de acordo com o tratamento de superfície em três subgrupos, grupo controle

I: Abrasão a ar (n=7), grupo II: CoJet (n=7) e grupo III: Z-etch (n=7). A porcelana foi aplicada sobre os

espécimes de zircônia com um molde personalizado e sinterizada em forno de cerâmica. Todos os espécimes

foram termociclados (20.000 ciclos) entre 5°C - 55°C com um tempo de permanência de 30 segundos em água

destilada e a resistência ao cisalhamento da porcelana de cobertura foi testada através de uma máquina de ensaio

universal. Resultados: os dados numéricos foram avaliados quanto à normalidade, vericando a distribuição

dos dados e utilizando testes de normalidade (testes de Kolmogorov-Smirnov e Shapiro-Wilk). O teste ANOVA

Braz Dent Sci 2023 July/Sept;26 (3): e3838

Baiomy AA et al.

Effect of novel pre-sintered zirconia surface treatment on shear bond strength between zirconia and veneering porcelain compared to conventional surface treatments: an in-vitro study

Baiomy AA et al. Eﬀect of novel pre-sintered zirconia surface treatment on

shear bond strength between zirconia and veneering porcelain

compared to conventional surface treatments: an in-vitro study

INTRODUCTION

Restoring optimum esthetics and function

in restorative dentistry has always been limited

by lack of advanced materials that can provide

both esthetics and withstand occlusal forces.

This idea has greatly changed in the past few

decades due to advancements in material

science and introduction of recent generations

of dental zirconia [1]. Zirconia has been through

a long journey of material science research and

subsequent advancements to tweak its properties

to meet the goal of esthetics and function. Among

these methods was the addition of stabilizing

oxides as yttria to help make the material in

its strongest form possible at room and mouth

temperature [2]. This resulted in a phenomenon

of transformation toughening, which can only

resist primary cracks but cannot resist any

secondary forces in the same area where the crack

was arrested before [3-5].

On the other hand, bonding to zirconia

was a challenge as well due to lack of silica

content within the material that can provide

chemical bonding to either silica in the veneering

porcelain or to resin cement. To overcome such

problem, many materials and methods have been

introduced to modify the surface of zirconia by

increasing surface area available for bonding [6].

The use of air abrasion in treating the surface

of zirconia has been advocated in literature and

widely used to enhance the bonding to zirconia.

The use of several particles has been studied

and 50 µm aluminum oxide particles are the

most used particles in blasting zirconia surface

to create micro irregularities or roughness to

enhance micro mechanical interlocking with

either resin cement or veneering porcelain [5,7].

CoJet method has also been introduced to

modify the surface of zirconia by addition of silica

particles to the aluminum oxide particles to embed

them in the surface of zirconia and provide a

chemical bond between embedded silica and resin

cement [8-11]. However, due to the nature of the

application of both methods, the blasting action

of aluminum oxide particles adversely affects the

mechanical properties of zirconia. The energy

caused by the collision between aluminum oxide

and zirconia results in phase transformation

from the higher strength tetragonal phase into

less resistant to crack and weaker phase called

monoclinic phase. Many studies have conrmed

the high concentration of monoclinic phase on

the surface of zirconia after air abrasion and

subsequent phase transformation [12-14]. That

created a need for a new surface treatment method

that can be applied safely without any adverse

effects to the zirconia or the operator and can

prevent the creation of monoclinic phase after its

application to avoid weakening the material and

shortening its service time in the oral environment.

In addition, can create good bond strength

between zirconia and veneering porcelain or resin

cement [2].

A novel approach composed of a suspension

(Z-etch, IDS CAD, USA) was introduced to

enhance the surface of zirconia for better bonding.

This suspension is constituted of zirconia nano

particles and carbon particles suspended in

distilled water with specific concentration.

The method of application is by brushing it over

the surface of zirconia before sintering to create

surface roughness. While some authors compared

the effect of z-etch using different concentrations,

others compared it to other less common methods

as hydrofluoric acid or nontreated zirconia

de um fator foi utilizado para comparar os grupos. Houve uma diferença estatisticamente signicativa entre os

três grupos (P-valor = 0,002, tamanho do efeito = 0,503). As comparações pareadas entre os grupos revelaram

que o Z-etch apresentou a resistência de união ao cisalhamento estatisticamente signicativamente mais alta.

Conclusão: o revestimento de zircônia utilizando Z-etch mostrou resultados promissores para o aumento da

resistência de união em comparação aos métodos convencionais de tratamento de superfície, como abrasão a

ar e revestimento de sílica.

PALAVRAS-CHAVE

Abrasão dental por ar; Materiais dentários; Resistência ao cisalhamento; Tratamento de superfície; Z-etch; Zircônia.

Braz Dent Sci 2023 July/Sept;26 (3): e3838

Baiomy AA et al.

Effect of novel pre-sintered zirconia surface treatment on shear bond strength between zirconia and veneering porcelain compared to conventional surface treatments: an in-vitro study

Baiomy AA et al. Eﬀect of novel pre-sintered zirconia surface treatment on

shear bond strength between zirconia and veneering porcelain

compared to conventional surface treatments: an in-vitro study

as control group. No scientific research has

compared this material to other well-established

methods such as CoJet and air abrasion to nd out

its performance in comparison to them [15-18].

The aim of this study was to evaluate the effect

of novel zirconia surface treatment method on shear

bond strength between zirconia and veneering

porcelain compared to air abrasion and CoJet

surface treatment methods. Fractured specimens

were analyzed using stereomicroscope to determine

the mode of bond failure. The null hypothesis tested

was that z-etch surface treatment does not have a

signicant difference from other surface treatment

methods regarding shear bond strength values

between zirconia and veneering porcelain.

MATERIAL AND METHODS

Yttria stabilized zirconium oxide discs

(3Y-TZP) used for core manufacturing of the

discs used as core materials (Bio ZX2, Dental

Direkt GMBH, Germany). Feldspathic porcelain

used as a veneering material over the zirconia

discs to test the shear bond strength between the

two materials after different surface treatment

(Ceramco PFZ, Dentsply Sirona, USA) (Table I).

Air abrasion

Fifty µm aluminum oxide particles were used

to performing the air-abrasion method.

CoJet

CoJet (3M, ESPE) was used to perform

silica coating. CoJet is composed of silica and

aluminum oxide powders. The aim of CoJet sand

blasting was to embed silica particles into the

surface of zirconia and thus modify the surface

to be more chemically bondable.

Z-etch

Z-etch (Z-etch, IDS CAD, USA) was the novel

material used to modify the zirconia surface

before sintering procedure. It is composed of

zirconia and carbon nanoparticles suspension.

The aim of the application of the material was

to increase the zirconia surface area, roughness,

and porosity.

Sample size

Sample size was determined based upon

the results of a pilot study conducted on three

specimens in each group, the effect size (f) for

one-way ANOVA was 0.895. Using alpha (α)

level of (5%), β level of 0.8 (Power = 80%); the

minimum estimated sample size was a total of

18 specimens (6 specimens per group). Sample

size calculation was performed using G*Power

version 3.1.9.2

Twenty-one zirconia discs were designed in

CAD software with dimensions of 7mm diameter

and 3mm thickness and then subdivided into

3 subgroups according to surface treatment,

control group I: Air Abrasion (n=7), group II:

CoJet (n=7) and group III: Z-etch (n=7).

Twenty-one porcelain discs were molded

and fired over the zirconia discs to reach

nal dimensions of 5mm diameter and 3mm

thickness.

Table I - Showing materials used in this study

Material Manufacturer Chemical Composition %

Bio ZX2

Zirconium

Dental Direkt

GmbH, Germany

Zirconium oxide 70-100%

Aluminum oxide 0-1%

Yttrium oxide 3-15%

Hafnium oxide 1-5%

Ceramco

PFZ

Dentsply Sirona,

USA

Sodium Potassium Aluminosilicate SiO2, Al2O3, Na2O, K2O, SnO2, CeO2,

Pigments, 1.3-Butanediol Xi Not mentioned

Z-etch Dmax

Zirconium Dioxide ≤15%

Water ≥85%

Carbon not mentioned

CoJet 3M ESPE

Aluminum Oxide > 95%

Synthetic Amorphous Silica, Fumed, < 5%

Crystalline free

Braz Dent Sci 2023 July/Sept;26 (3): e3838

Baiomy AA et al.

Effect of novel pre-sintered zirconia surface treatment on shear bond strength between zirconia and veneering porcelain compared to conventional surface treatments: an in-vitro study

Baiomy AA et al. Eﬀect of novel pre-sintered zirconia surface treatment on

shear bond strength between zirconia and veneering porcelain

compared to conventional surface treatments: an in-vitro study

Sample preparation

Dental direct zirconia-based disc

(DDBioZX2) was selected with a diameter of

98.5mm and thickness of 16mm and scaling

factor of 1.237 which was predetermined by the

manufacturer to compensate for the shrinkage of

the zirconia after the sintering process.

Zirconia discs were designed using CAD

software (Fusion 360 2.0.15293 x86_64) with

the desired dimensions (7mm diameter and

3mm thickness). After completion of the design,

the digital .stl files were loaded in the CAM

software of the milling machine (Dental CAM 7,

Vhf GMBH, Germany). The milling process and

machine milling strategy were fully automated

processes without any interference in a dry

mode as required by the manufacturer and

the machine milling strategy with the required

zirconia milling burs (Vhf S1, VHF GMBH,

Germany).

After completion of the milling procedure,

zirconia discs were separated from the discs

using a diamond coated bur. In addition,

600,800,1000,1200,2000 grit sandpaper were

used to standardize the surface of the samples.

Each sample was moved in 4 directions (right,

left, up, down) by the same operator 10 times

in each direction per sandpaper so that all

specimens were subjected to the same pressure

at the same time from the operator.

After sanding the discs, they were submerged

in a closed bottle containing distilled water and

placed in an ultrasonic cleaner to clean the surface

of the samples from all residues from the sanding

and surface nishing process. The samples were

left for 10 minutes in the ultrasonic cleaner. After

ultrasonic cleaning, steam cleaner was used to

clean the surface then air dried in an electric oven

for 20 minutes at 200 °C.

After cleaning, an online research

randomization software (randomizer.org) was

used to allocate each sample to its designated

testing group randomly.

Z-etch application

According to recommendations of the

manufacturer and due to the nature of application,

z-etch was applied before sintering process to its

subgroup. The z-etch bottle was shaken well and

dispensed in a small porcelain palette. A brush

was used to paint it over the surface of the

specimen in one coat according to manufacturer’s

instructions. It is important to note that number

of layers or coats of application can affect the

resultant shear bond strength [16].

Sintering process

The discs were placed over zirconia beads in

a plate inside the sintering furnace (Roko Tytan Zr

II, Poland) and sintering parameters were inserted

according to the manufacturer’s sintering schedule.

The time for the sintering cycle was 9.2h (Table II).

Surface treatment and porcelain buildup

Before application of Air abrasion and CoJet

surface treatments 2 devices were designed in

CAD software (Fusion 360 2.0.15293 x86_64)

and 3d printed to ensure the standardization

of tip of the surface treatment device in terms

of distance and angle between the tip and the

specimen. Device A was used with Air abrasion

method and device B was used with CoJet

method to accommodate the different designs of

handpiece used for each method.

Air abrasion

Device A was used to align the tip of the

sandblasting device in a perpendicular direction

Table II - Showing sintering schedule of the zirconia discs as recommended by the manufacturer

Temp.

1 [°C]

Temp.

2 [°C]

Heating rate

[°C/h]

Heating rate

[°C/min]

Dwell time

[min]

Time

[min]

Heating 20 900 480 8 110

Dwell 900 900 30 30

Heating 900 1450 3 3 165

Dwell 1450 1450 120 120

Cooling 1450 200 600 10 125

Total Time: 550

9.2h

Braz Dent Sci 2023 July/Sept;26 (3): e3838

Baiomy AA et al.

Effect of novel pre-sintered zirconia surface treatment on shear bond strength between zirconia and veneering porcelain compared to conventional surface treatments: an in-vitro study

Baiomy AA et al. Eﬀect of novel pre-sintered zirconia surface treatment on

shear bond strength between zirconia and veneering porcelain

compared to conventional surface treatments: an in-vitro study

to the surface of the sample and at 10mm distance

from the surface. The device was used inside the

air abrasion chamber and at an air pressure of

2.8bar and the particles used for air abrasion were

50µm aluminum oxide particles for 10 second

duration per sample (Figure 1a).

CoJet

Device B was used with CoJet powder to

align the tip of the contra angle handpiece at

perpendicular direction to the sample and at

10 mm distance. CoJet sand was added and air

ow of 2.8bar were allowed for 15 seconds per

sample to allow the CoJet particles to blast the

surface of the discs (Figure 1b).

After surface treatment, discs were

ultrasonically cleaned in distilled water to clean

the surface from residues. Steam cleaner was

additionally used to clean the surface of the

specimens followed by air drying using oil free air.

Porcelain mold

A mold was used as a housing to accommodate

the porcelain dough and adapt it to the surface

of the overlying zirconia disc with the required

dimensions of 5mm diameter and 3mm thickness.

The mold was designed using 3d CAD software

(Fusion 360 2.0.15293 x86_64) and 3d Printed

using a desktop LCD 3d Printer (Phrozen Mighty

4K, Phrozen Inc., Taiwan) with the recommended

3d printing parameters for the selected resin

(Phrozen Aqua Grey 4K).

Porcelain discs were made by direct

application over the treated zirconia discs.

A specially designed porcelain mold was made

in fusion 360 CAD design software with internal

dimensions to make a 5mm diameter x 3mm

thickness porcelain discs. However, due to the

shrinkage of the porcelain discs after ring, the

dimensions of the resulting disc was used to

modify the mold dimensions to be able to deliver

the exact dimensions of the porcelain discs after

ring to be 5mm x 3mm (Figure 2).

By measuring the feldspathic disc

dimensions after ring and comparing it to the

planned dimensions, a simple mathematical

equation was used to determine the needed

dimensions of the mold to compensate for the

shrinkage of the porcelain after ring and get

the exact nal dimensions needed after ring

for the discs which were 5mm diameter x 3mm

thickness.

Equation used was as followed:

1- Measured dimension of the porcelain disc

after ring = A

2- Measured dimension of the porcelain disc

before firing = X which is needed to be

planned in the 3d design

3- Measured dimension of the porcelain disc

before ring in the pilot study= B

4- Measured dimension of the porcelain disc

after ring in the pilot study = C

Then

X AC

= ×

(1)

After application of the porcelain over the

zirconia discs inside the mold the ring program

was adjusted in the ring furnace according to

manufacturer’s ring schedule.

Figure 1 - 3D printed devices to standardize distance and angle for air abrasion and CoJet application (1a) Showing device A used for air

abrasion procedure. (A) Cylinder to hold the air abrasion pen perpendicular to the zirconia specimen. (B) Zirconia disc cavity to hold the zirconia

disc. (C) Base of the device (1b) Showing device B used to standardize the CoJet application. (A) Cylinder to hold the CoJet handpiece. (B)

Cavity to hold the zirconia disc. (C) Base of the device.

Braz Dent Sci 2023 July/Sept;26 (3): e3838

Baiomy AA et al.

Effect of novel pre-sintered zirconia surface treatment on shear bond strength between zirconia and veneering porcelain compared to conventional surface treatments: an in-vitro study

Baiomy AA et al. Eﬀect of novel pre-sintered zirconia surface treatment on

shear bond strength between zirconia and veneering porcelain

compared to conventional surface treatments: an in-vitro study

AGING AND SHEAR BOND STRENGTH

To simulate clinical aging conditions,

all specimens were thermocycled between

5°C – 55 °C for 20000 cycles with a dwell time of

30 seconds in distilled water bath and a transfer

time of 10 seconds after surface treatment in

a thermo-cycling unit (Julabo FT200, Julabo,

Seelbach, Germany).

Shear bond strength was performed using

universal testing machine (Instron universal

testing machine model 3345, England).

Specimens were mounted in lower compartment

and mono beveled chisel with a thickness of

0.5mm was used to perform the shear test in a

direction parallel to the surface of the disc and

at a crosshead speed of 1mm/min.

Measurement of shear bond strength values

were calculated by converting the loads into

MPa by dividing the maximum failure load (N)

by the bonding area (mm2) saved in excel sheet

(Figure 3).

Mode of failure

Mode of failure was analyzed using

stereomicroscope (50X magnification) (MA

100 Nikon, Japan) after performing shear bond

strength.

Surface roughness analysis

After surface treatment, zirconia surface was

inspected at 4,000X magnication using scanning

electron microscopy (SEM). Surface roughness

Figure 2 - Showing the 3D printed device for porcelain application over zirconia discs. (A) Piston used for condensing the porcelain. (B)

Porcelain molding cavity to hold the porcelain slurry. (C) Zirconia disc cavity that contains the zirconia discs. (D) Base for the device to hold

the porcelain mold tightly over the zirconia.

Figure 3 - Graphical representation of shear bond strength test. (A) Porcelain disc. (B) Zirconia Disc. (C) Chisel used to break the sample. (D)

Base of the device made from2 components that close on each other to ﬁx the sample between them.

Braz Dent Sci 2023 July/Sept;26 (3): e3838

Baiomy AA et al.

Effect of novel pre-sintered zirconia surface treatment on shear bond strength between zirconia and veneering porcelain compared to conventional surface treatments: an in-vitro study

Baiomy AA et al. Eﬀect of novel pre-sintered zirconia surface treatment on

shear bond strength between zirconia and veneering porcelain

compared to conventional surface treatments: an in-vitro study

was measured at an area of 100µm width by

60µm height to inspect the surface and evaluate

the microscopic effect of the surface treatment

on the surface of the sample.

Statistical analysis

Numerical data were explored for normality by

checking the distribution of data and using tests of

normality (Kolmogorov-Smirnov and Shapiro-Wilk

tests). Shear bond strength data showed normal

(parametric) distribution. Data were presented as

mean and standard deviation (SD) values. One-way

ANOVA test was used to compare between the three

groups. Bonferroni’s post-hoc test was used for pair-

wise comparisons when ANOVA test is signicant.

The signicance level was set at P ≤ 0.05. Statistical

analysis was performed with IBM SPSS Statistics for

Windows, Version 23.0. Armonk, NY: IBM Corp.

RESULTS

Primary outcome shear bond strength

There was a statistically signicant difference

between the three groups (

-value = 0.002,

Effect size = 0.503). Pair-wise comparisons

between groups revealed that Z-etch showed

the statistically signicantly highest mean shear

bond strength.

CoJet showed statistically signicantly lower

mean value. Air abrasion showed the statistically

signicantly lowest mean shear bond strength

(Table III) (Figure 4).

Secondary outcome mode of failure

After analysis of the mode of failure. It was

divided into 3 categories:

a- Adhesive failure: failure occurs at the interface

between the two materials with no remnants

of porcelain over the zirconia surface.

b- Cohesive failure: failure occurs predominantly

within the structure of the same material

whether porcelain or zirconia.

c- Mixed: adhesive failure between 2 materials

at the interface with porcelain remnants over

zirconia

After inspection of the specimens using

the same observer with the above criteria for

categorizing the observed failure, it could be

found that z-etch showed the highest percentage

of mixed failure while air abrasion showed

the highest percentage of adhesive failure

(Figures 5-6).

Scanning electron microscopy

Scanning electron microscope was

used to evaluate the surface of zirconia and

the modification occurred at two different

magnification levels 4000x and 15000x.Air

abrasion and CoJet electron microscope share a

common crater like depressions which conrms

Figure 4 - Bar chart representing mean and standard deviation

values for shear bond strength of the three groups.

Figure 5 - Mode of failure according to each group.

Table III - Descriptive statistics and results of one-way ANOVA test for comparison between shear bond strength (MPa) of the three groups

Air abrasion CoJet Z-etch

-value

Eﬀect size

(Eta squared)

Mean SD Mean SD Mean SD

14.63 C1.7 19.91 B5.82 23.61 A3.19 0.002* 0.503

*Signiﬁcant at P ≤ 0.05.

Diﬀerent superscripts indicate statistically signiﬁcant diﬀerence between groups.

Braz Dent Sci 2023 July/Sept;26 (3): e3838

Baiomy AA et al.

Effect of novel pre-sintered zirconia surface treatment on shear bond strength between zirconia and veneering porcelain compared to conventional surface treatments: an in-vitro study

Baiomy AA et al. Eﬀect of novel pre-sintered zirconia surface treatment on

shear bond strength between zirconia and veneering porcelain

compared to conventional surface treatments: an in-vitro study

the damage that occurs to the surface of zirconia

due to blasting power of the aluminum oxide

and silica particles which are needed to increase

surface area and roughness of the surface and

increase bond strength mechanically (Figure 7).

On the other hand, Z-etch showed a pattern

of bead like appearance over the surface of

zirconia and with 15000x magnication a cloud

or scaffold appearance of zirconia appears with

no other sign of damage of the surface of the

specimens as it air abrasion and CoJet subgroups

(Figure 7).

Surface roughness analysis

Surface roughness analysis showed that the

highest mean surface roughness Ra was in case

of Z-etch surface treatment (Ra [µm] = 15.97)

followed by CoJet (Ra [µm]=15.12) and air

abrasion (Ra [µm]= 14.7) (Table IV) (Figure 8).

DISCUSSION

The bonding to zirconia has always been a

point of interest in the literature due to its wide

applications in the dental eld whether for xed

restorations or for implant supported prosthesis.

Many methods have been introduced to enhance

the bond to zirconia whether from the intaglio

side or the external porcelain veneering side.

In the present study, yttria stabilized zirconia

(3Y-TZP) was selected as it is the most common

used type for veneering technique by porcelain

to enhance its esthetic properties and outcome.

The compatible porcelain veneering system was

selected based on manufacturer instructions

for the suitable veneering porcelain systems.

Air abrasion as a surface treatment method is

the most popular method used for treating the

surface of zirconia. In addition, it has been widely

used in literature while CoJet silica coating can

provide effective bond strength values because

of surface modication and silica embedding in

the surface of zirconia [6,7,19,20].

The null hypothesis was rejected due to

the results that showed significant difference

between different surface treatment methods.

The Macro shear bond strength test is the

most widely used test in evaluating bond strength

Figure 6 - Mode of failure under stereomicroscope (A) adhesive failure in air abrasion group (B) mixed failure in air abrasion group (C) mixed

failure in CoJet group (D) adhesive failure in CoJet group (E) adhesive failure in z-etch group (F) mixed failure in z etch group.

Braz Dent Sci 2023 July/Sept;26 (3): e3838

Baiomy AA et al.

Effect of novel pre-sintered zirconia surface treatment on shear bond strength between zirconia and veneering porcelain compared to conventional surface treatments: an in-vitro study

Baiomy AA et al. Eﬀect of novel pre-sintered zirconia surface treatment on

shear bond strength between zirconia and veneering porcelain

compared to conventional surface treatments: an in-vitro study

between ceramics and other substructures.

The lower incidence of pretest failure is one of

the most important features of the shear bond test

among other tests. The micro shear bond strength

was introduced to analyze the bonding stresses

over a smaller area with a more homogenous stress

pattern compared to macro shear. However, the

use of micro shear and its application was a very

technique sensitive procedure that can lead to

inconsistent results if not performed accurately.

The selection of macro shear bond test was due

to its simplicity and the evaluation of secondary

outcomes as failures modes can be interpreted

easily using this test [21-24].

The dimensions of the samples were estimated

to be 7mm diameter and 3mm thickness for

zirconia and 5mm diameter and 3mm thickness

for porcelain and these dimensions were based

upon the ISO standards (ISO 29022:2013) for

notched edge shear bond strength test.

When surface treatment is performed on

ceramics, variables including air pressure, size of

the blasting particles, type of the particles and the

distance between the nozzle tip and the ceramic

surface are vital factors to consider [1,25-27].

All the specied variables for air abrasion, CoJet

and z-etch were based upon manufacturer.

In addition, throughout literature it was

found that optimal pressure for air abrasion and

CoJet to be around 2-2.8bar and the particle

size of air abrasion to be 50µ .These parameters

are an important aspect for surface treatment of

zirconia as any increase in air pressure or particle

size can lead to higher percentage of tetragonal to

Figure 7 - (A) SEM image of zirconia surface after air abrasion at 15000X magniﬁcation (B) SEM image of zirconia surface after air abrasion

at 4000X magniﬁcation (C) SEM image of zirconia surface CoJet at 15000X magniﬁcation (D) SEM image of zirconia surface CoJet at 4000X

magniﬁcation (E) SEM image of zirconia surface after Z-etch at 15000X magniﬁcation (F) SEM image of zirconia surface after Z-etch at 4000X

magniﬁcation.

Table IV - Showing mean roughness values (Ra) for each surface treatment method

Surface Treatment Air Abrasion CoJet Z-etch

Roughness at 4000x (Ra) 14.7 15.12 15.97

Braz Dent Sci 2023 July/Sept;26 (3): e3838

Baiomy AA et al.

Effect of novel pre-sintered zirconia surface treatment on shear bond strength between zirconia and veneering porcelain compared to conventional surface treatments: an in-vitro study

Baiomy AA et al. Eﬀect of novel pre-sintered zirconia surface treatment on

shear bond strength between zirconia and veneering porcelain

compared to conventional surface treatments: an in-vitro study

monoclinic phase transformation which weakens

the zirconia material and makes it less resistant

to stresses under function [5,6, 28-31].

Cleaning the surface of zirconia using

distilled water is an important step to make sure of

absence of surface contamination. In 2020, Attia

and Ebeid [32] evaluated several decontamination

methods for zirconia and it was concluded that

decontamination method has an impact on shear

bond strength to zirconia [32].

Many experimental coatings other than z-etch

have been tested in the literature to enhance

zirconia bond strength as the use of silica coating

technique and the use of Sol-jel dip technique

for silica coating [33-35]. On the other hand,

graphite using graphite leads was used as well

over the zirconia surface followed by Er: YAG laser

application as an experimental coating to enhance

bond strength which showed higher shear bond

strength in comparison to air abrasion [36].

Z-etch was used in this study to prove

its effectiveness in comparison to previous

methods and to address the drawbacks of

conventional methods as phase transformation

from stabilized tetragonal phase to monoclinic

less resistant to fracture phase due to blasting

action to the surface of zirconia and content of

aluminum oxide. The basic principle of using

z-etch was to implement carbon particles as

a carrier for zirconia nanoparticles to provide

hydrogen bond between zirconia surface and

nano zirconia coating. After sintering procedure,

carbon particles evaporate due to high sintering

temperature leaving a rough network of zirconia

nano particles over the zirconia surface [37].

The application of z-etch suspension could be

considered fast, effective, and economic method

to modify the surface of zirconia without exposing

the zirconia surface to unnecessary stresses and

energy that cause phase transformation and

subsequent weakening of the material. Acquiring

a strong interface between zirconia and veneering

ceramic is a critical issue that has been addressed

by many researchers. As failure of zirconia is

mainly due to lack of proper bond between

veneering ceramic and zirconia. In addition, the

presence of zirconia surface contaminants and

decontamination techniques before porcelain

application is a crucial aspect that should be

taken into consideration as well. Further research

is needed to address this issue as well [32,38].

Z-etch showed the highest mean shear bond

strength compared to air abrasion and CoJet and

this can be attributed to the mechanism of action

Figure 8 - (A) 3D representation of roughness of the surface (B) 3D representation of roughness of the surface (C) 3D representation of

roughness of the surface.

Braz Dent Sci 2023 July/Sept;26 (3): e3838

Baiomy AA et al.

Effect of novel pre-sintered zirconia surface treatment on shear bond strength between zirconia and veneering porcelain compared to conventional surface treatments: an in-vitro study

Baiomy AA et al. Eﬀect of novel pre-sintered zirconia surface treatment on

shear bond strength between zirconia and veneering porcelain

compared to conventional surface treatments: an in-vitro study

of the material as it forms a cloud like layer of

zirconia over the surface that can provide a

substrate for undercuts and irregularities to engage

the porcelain. This could be better than depending

solely on roughness made by blasting of aluminum

oxide in case of air abrasion and CoJet.

Bae et al. [18] compared the effect of

zirconia slurry application over zirconia and used

air abrasion with 50 µ and 125 µ particle size as

comparator groups. Although Z-etch improved

the shear bond strength in that study by it was

not higher that air abrasion groups and this can

be attributed to different surface conditioning

method after surface treatment and substrate as

this study used Panavia, superbond and Variolink

to test their bond strength to zirconia not as the

present study which addresses the outer surface

of zirconia that received porcelain layering [18].

Jo et al. [16], studied the effect of zirconia

slurry coating as well in 2020 with different

concentrations and it was found that zirconia

coating enhanced the shear bond strength

significantly with the highest value in 50%

concentration of zirconia slurry, The substrate

bonded to that study was resin cement as well as

no previous study studied the effect of z-etch or

coating zirconia on the bond strength between

zirconia and veneering porcelain [16].

This can be confirmed by inspection of

the scanning electron microscope images

showing a cloud like appearance of z-etch and

by the highest roughness values calculated

for z-etch in comparison to air abrasion and

CoJet. The increase in roughness values were in

accordance with Jo et al. [16], as zirconia coating

increases the roughness parameters of the surface

by deposition of nano zirconia particles result in

a cloud like appearance [16].

On the other hand, CoJet showed sig-

nicantly higher shear bond strength compared

to air abrasion which is in accordance with

Baiomy et al. [39] and can be attributed to the

embedded silica on zirconia surface and their

ability to bond chemically with silica content from

porcelain. The measured mean surface roughness

of the specimens conrmed this nding as z-etch

showed the highest values in mean surface rough-

ness compared to other methods [16]. However,

in study by Bae et al. [18] different concentra-

tions of zirconia slurry were evaluated to test

their effect on shear bond strength and surface

roughness was not measured.

Even though surface roughness increased

with increasing the concentration of zirconia

slurry, it was found that it does not increase the

shear bond strength until a certain concentration is

reached. This could mean that there is a bottleneck

for concentration of the zirconia slurry and after it

shear bond strength can decrease signicantly as

conrmed by Jo et al. [16]. In addition, mode of

failure showed that mixed failure is more prone to

occur in z-etch subgroup which can be related to

increased shear bond strength and mean surface

roughness value in z-etch group.

CONCLUSION

Within the limitations of this study, the

application of z-etch to pre sintered zirconia

surface could be an effective method to obtain

increased bond strength between zirconia

and veneering porcelain in comparison to

conventional zirconia surface treatment methods.

Acknowledgements

All co-authors have seen and agree with the

contents of the article and there is no nancial

interest to report.

Author’s Contributions

AAB: Conceptualization. AAB: Methodology.

AAB: Writing – Original Draft Preparation.

NNAEH, HAN, AZ: Writing – Review & Editing.

HAN, AZ: Visualization. HAN, AZ: Supervision.

AZ: Project Administration.

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

Not applicable.

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Ahmed Atef Baiomy

(Corresponding address)

Egyptian Russian University, Faculty of Dentistry

Email: ahmed.baiomy@dentistry.cu.edu.eg Date submitted: 2023 Mar 21

Accept submission: 2023 May 22