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.2024.e4275
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Braz Dent Sci 2024 Apr/June;27 (2): e4275
This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
Rebonding strengths of lithium disilicate and feldspathic veneers
debonded by Er,Cr:YSGG laser
Resistência de recolagem de facetas de dissilicato de lítio e feldspáticas descoladas por laser Er,Cr:YSGG
Ahmed Ibrahim YOUSSEF1,2 , Marwa Mohamed WAHSH2 , Ghada Abd EL FATTAH2 , Talaat Mohamed SAMHAN1 ,
Nobert GUTKNECHT3,4†
1 - Misr International University, Faculty of Oral and Dental Medicine, Department of Fixed Prosthodontics. Cairo, Egypt.
2 - Ain Shams University, Faculty of Dentistry, Fixed Prosthodontics Department. Cairo, Egypt.
3 - RWTH Aachen University, Department of Restorative Dentistry, Academic Postgraduate Master Program. Aachen, Germany.
4 - Aachen Dental Laser Center. Aachen, Germany.
† - In memorian
How to cite: Youssef AI, Wahsh MM, El Fatta GA, Samhan TM, Gutknecht N. Rebonding strengths of lithium disilicate and feldspathic
veneers debonded by Er,Cr:YSGG laser. Braz Dent Sci. 2024;27(2):e4275. https://doi.org/10.4322/bds.2024.e4275
ABSTRACT
Objective: The aim of this study is to identify the shear bond strength of rebonded CAD/CAM laminates made
of lithium disilicate or feldspathic ceramics after debonding using Er,Cr:YSGG lasers. Material and Methods:
Eighty bovine teeth (N=80) were used as a bonding substrate, which were divided into four main groups (20
each) according to the ceramic material and cement-curing mode used as follows: Group AL: lithium disilicate
(IPS E.max) with light-cured resin cement, Group AD: lithium disilicate (IPS E.max) with dual-cured resin cement,
Group BL: feldspathic porcelain (VITA MARK II) with light-cured resin cement, and Group BD: feldspathic porcelain
(VITA MARK II) with dual-cured resin cement. Half the number of each subgroup (n=10/subdivisions) were
tested for their shear bond strength without debonding, while the other half of the specimens were tested after
Er,Cr:YSGG laser debonding and rebonding. A three-way ANOVA test was used to study the effect of ceramic
and curing on shear bond strength. Bonferroni’s post-hoc test was used for pairwise comparisons when the
ANOVA test was signicant. Results: After rebonding and using the light-cure mode, there was no statistically
signicant difference between the mean shear bond strength of the two ceramics (P-value = 0.065). However,
after rebonding and using the dual-cured mode, E.max showed signicantly lower shear bond strength than VITA
(P-value < 0.001). Conclusion: Ceramic type, the cement’s curing mode, and rebonding after laser irradiation
all had a signicant effect on the mean shear bond strength.
KEYWORDS
Ceramic veneers; Debonding; Er,Cr: YSGG; Feldspathic; Laser.
RESUMO
Objetivo: Identicar a resistência de cisalhamento de laminados CAD/CAM recolados, feitos de cerâmica de
disilicato de lítio ou feldspática, após descolamento utilizando lasers Er,Cr:YSGG. Material e Métodos: Oitenta
dentes bovinos (N=80) foram utilizados como substrato de colagem, divididos em quatro grupos principais
(20 cada) de acordo com o material cerâmico e o modo de cura do cimento utilizado da seguinte forma: Grupo
AL: disilicato de lítio (IPS E.max) com cimento resinoso fotopolimerizável, Grupo AD: disilicato de lítio (IPS
E.max) com cimento resinoso de dupla cura, Grupo BL: porcelana feldspática (VITA MARK II) com cimento
resinoso fotopolimerizável, e Grupo BD: porcelana feldspática (VITA MARK II) com cimento resinoso de dupla
cura. Metade do número de cada subgrupo (n=10/subdivisões) foi testada quanto à resistência de cisalhamento
sem descolamento, enquanto a outra metade dos espécimes foi testada após descolamento e recolagem a laser
Er,Cr:YSGG. Um teste ANOVA de três vias foi usado para estudar o efeito da cerâmica e da cura na resistência
de cisalhamento. O teste post-hoc de Bonferroni foi usado para comparações pareadas quando o teste ANOVA
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Braz Dent Sci 2024 Apr/June;27 (2): e4275
Youssef AI et al.
Rebonding strengths of lithium disilicate and feldspathic v eneers debonded by Er ,Cr:YSGG laser
Youssef AI et al. Rebonding strengths of lithium disilicate and feldspathic
veneers debonded by Er,Cr:YSGG laser
INTRODUCTION
Nowadays, the dental industry has witnessed
the emergence of a wide array of innovative
materials that can be employed for aesthetic
restorative purposes. These materials can be
utilized either directly or indirectly, offering a
versatile range of applications. The ceramics
are among the most sought-after and highly
acclaimed restorative materials for the laminate
veneers [1]. They possess remarkable esthetic
qualities, particularly when manufactured using
the layering technique [2,3]. The materials
frequently employed for laminate veneers include
feldspathic porcelain and lithium disilicate.
These two types of veneers boast a multitude of
advantages and features. Feldspathic porcelain
veneers are suitable prosthetic restorations in the
frontal area due to their long-term survival rates,
conservative nature, longevity, biocompatibility,
and aesthetics. These desirable strength
values include exural strength (62–90 MPa),
compressive strength (172 MPa), shear strength
(110 MPa), and modulus of elasticity (69 GPa)
[4]. As for the lithium disilicate, it is composed
of high concentration of crystals which results
in a exural strength similar to enamel (360–
400 MPa). Apart from having a low refractive
index and a high translucency, lithium disilicate
is also known for a unique characteristic known as
the “Umbrella Effect,” which permits light to pass
through the substance and partially absorb light.
This characteristic makes lithium disilicate highly
aesthetically pleasing and makes the adhesive
processes easier [5].
Notably, the implementation of cutting-
edge Computer-aided design and Computer-
aided manufacturing (CAD/CAM) technology
in the production process renders these veneers
exceptionally durable. Furthermore, their
construction in thin layers obviates the need for
tooth preparation. In essence, this remarkable
characteristic of ceramic veneers ensures the
preservation of the tooth structure [6].
However, certain local failures might arise,
such as discoloration, microleakage, ditching at
the margins, or simple fractures. These failures
would necessitate repair or replacement [7].
Currently, the prevailing technique for eliminating
all-ceramic restorations entails employing a
high-speed handpiece with a diamond. Owing
to the remarkable color-matching capabilities
of both resin-bonding cement and the veneers
themselves with the underlying tooth structure,
the removal of veneers without causing harm to
the natural tooth underneath can prove to be
challenging and time-consuming, even with the
aid of magnication [8,9]. The enamel, serving
as a substrate, plays a crucial role in the long-
term success of porcelain veneers. However,
the bond strength will significantly decline if
veneer preparations are excessively aggressive,
resulting in substantial dentin exposure studies
have shown that when Ceramic Laminate Veneers
were glued to 100% enamel on the finishing
surfaces, their shear bond strength test result was
around 20 MPa, which is double that of veneers
bonded to dentin. Additionally, enamel has a
higher degree of mineralization than dentin, and
the production of resin protrusion in enamel is
facilitated by the honeycomb structure that results
from the demineralization of hydroxyapatite.
Nonetheless, dentin has a higher concentration
of organic components and contains a signicant
amount of water in its tubules. The collagen bre
network can collapse as a result of improper acid
etching and drying, which signicantly affects
dentin bonding [10]. Hence, it can be inferred
that numerous dentists might be interested in
discovering a safe, predictable, and efficient
method for debonding ceramic veneers without
causing any further iatrogenic damage to both
the laminate veneer and the underlying tooth
structure [9].
A novel technique for the removal of
laminate veneers has recently been developed
using the Er:YAG laser (2940 nm), which is
a type of laser that contains erbium-doped:
foi signicativo. Resultados: Após a recolagem e usando o modo de fotopolimerização, não houve diferença
estatisticamente signicativa entre a resistência de cisalhamento média das duas cerâmicas (valor de P = 0,065).
No entanto, após a recolagem e usando o modo de dupla cura, o E.max apresentou resistência de cisalhamento
signicativamente menor que o VITA (valor de P < 0,001). Conclusão: O tipo de cerâmica, o modo de cura do
cimento e a recolagem após irradiação a laser tiveram efeito signicativo na resistência de cisalhamento média.
PALAVRAS-CHAVE
Laminados cerâmicos; Descolagem de cerâmica; Er,Cr; YSGG; Cerâmica feldspática; Laser.
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Youssef AI et al.
Rebonding strengths of lithium disilicate and feldspathic v eneers debonded by Er ,Cr:YSGG laser
Youssef AI et al. Rebonding strengths of lithium disilicate and feldspathic
veneers debonded by Er,Cr:YSGG laser
yttrium aluminum garnet [11]. This technique
was inspired by its successful application on
orthodontic ceramic brackets in the 1990s [12,13].
The Erbium, Chromium: YSGG (2780 nm) laser
is an additional form of erbium laser. It uses a
solid crystal of yttrium scandium gallium garnet
doped with erbium and chromium as its active
medium. When the samples were viewed under
a scanning electron microscope, the effect of
Er:YSGG on debonding revealed that the bulk of
the adhesive failures of the cements occurred in
this manner [14]. So, Er,Cr:YSGG laser has no
effect on tooth structure roughness or topography
as well as on calcium and phosphorus content of
enamel of tooth structure after debonding [15].
The investigation into the application of
erbium lasers as a secure and efcient removal of
ceramic sample veneers has shown encouraging
outcomes. However, there is a lack of research on
the surface properties of removed veneers and the
durability of reattached restorations, necessitating
further investigation [16]. Therefore, it is
important to examine the impact of Er,Cr:YSGG
laser debonding on the shear bond strength of
reattached CAD/CAM blocks made of feldspathic
or lithium disilicate. The null hypothesis of
our study states that there are no substantial
effects on the shear bond strength of rebonded
feldspathic or lithium disilicate porcelain veneers,
after being debonded by laser.
MATERIAL AND METHODS
Sample size calculation
Based on a prior work by Karagoz-Yildirak
and Gozneli [17], who also investigated a related
concept about leucite and lithium disilicate
veneers debonded with Er:Yag laser, the sample
size was determined. By implementing a two
tailed Z test for difference between independent
proportions with an alpha level of 5% and a
power of 80%. The sample size needed was
104 (13 per group) in order to detect a difference
of 20%.
Grouping
A total number of 80 specimens were used
in this study. Specimens were randomly divided
into four main groups (20 each) according to the
ceramic material and cement-curing mode used
as follows:
Group AL:lithium disilicate (IPS E.max) with
Light cured resin cement (RelyX Veneer,
3M™, USA).
Group AD: lithium disilicate (IPS E.max) with
Dual cured resin cement (RelyX ultimate
clicker, 3M™, USA).
Group BL: Feldspathic porcelain (VITA
MARK II) with Light cured resin cement.
Group BD: Feldspathic porcelain (VITA
MARK II) with Dual cured resin cement
Each group were further sub-divided into
two sub-groups (10 each) as follows:
Subgroup S1: specimens tested for their
shear bond strength without debonding.
Subgroup S2: specimens tested for their
shear bond strength after rebonding.
Sample Preparation
Freshly extracted bovine teeth that had been
preserved in a saline solution were utilized as the
bonding substrate and subsequently secured in an
acrylic mold. A specic mold was created for each
individual bovine tooth, which was then lled with
cold cure acrylic resin (Cold cure acrylic resin,
Acrostone Dental & Medical Supplies, Egypt), that
had been color coded for the purpose of facilitating
differentiation between various groups. Prior to
pouring the cold cure acrylic resin into the molds,
Vaseline was applied to serve as a separating
medium. The teeth were then xed in the cold cure
acrylic resin before it fully set. To prepare the labial
surfaces of the teeth, depth orientation grooves
measuring 0.3 mm in depth were initially placed
using a depth cutting stone (MANI, INC., Japan).
Following this, a customized parallel device was
employed to achieve standardized preparation
and smooth the labial surface. For 30 seconds, the
teeth were etched using a 37% phosphoric acid gel
(Scotch Bond phosphoric acid etching gel, 3MESPE,
Germany). After that, a further 30 seconds of
air-water rinsing was performed. Following
application and activation for 15 seconds, the
bonding agent (Adper Single bond 2, 3MESPE,
USA) was light cured (MINILEDTM, Acteon,
France) in accordance with the manufacturer’s
instructions.
Fabrication of laminates
Using a low-speed, high-precision diamond
saw (Isomet diamond saw 4000, Buehler, USA.),
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Braz Dent Sci 2024 Apr/June;27 (2): e4275
Youssef AI et al.
Rebonding strengths of lithium disilicate and feldspathic v eneers debonded by Er ,Cr:YSGG laser
Youssef AI et al. Rebonding strengths of lithium disilicate and feldspathic
veneers debonded by Er,Cr:YSGG laser
the specied lithium disilicate (IPS E.max CAD,
Ivoclar Vivadent, Liechtenstein) and Feldspathic
glass-matrix ceramic (Vita Mark II, VITA Zahnfabrik,
Germany) LT A1 CAD/CAM blocks were sliced to
dimensions of 10×10 mm in accordance with the
size of the blocks (C14 & I14). A standardized
thickness of 0.7 mm was applied to all groups
based on recommendations for all-ceramic
samples [10,11]. The slices were cut using an
integrated coolant delivery system that tracked
the position of the blade at a constant feed rate
and inundated the samples from both sides of the
blade, cutting off 14.7 mm per minute at 2500 rpm
in increments of 50 rpm. Figure 1. To crystallize all
the ceramic samples, a furnace (EP3010 programat,
Ivoclar Vivadent, Schaan, Liechtenstein) was used
(Table I). Glazing were done to the out surface
after crystallization process .Afterwards both
ceramic samples, were etched using 9.5% HF acid
(ITENA Porcelain Etch, France) for a period of
20 seconds [18]. The samples were subsequently
rinsed with an air and water spray. Finally, the
ceramic sample was silanized (97% ethyl alcohol,
ITENA Porcelain Etch, France) in accordance with
the instructions provided by the manufacturer.
Laminates cementation
After teeth specimens and ceramic
samples preparation and surface treatment,
the cement was then applied according to their
corresponding group. Cement was applied using
either light cured resin cement or dual cured resin
cement. After applying cement for 30 seconds,
a 50 N force was applied perpendicularly to
the external surfaceusing a dental surveyor
and light-activated for 40 seconds LED curing
light (MINILEDTM, Acteon, France) using an
11-mm-diameter tip that is positioned 1.0 mm
from the sample’s surface to direct the light bean
on the top surface. Following the cementation
process, the samples were kept for 24 hours at
37 °C in distilled water.
Laser debonding
WaterLase IPLUS Er;Cr:YSGG (Biolase, USA)
was used to apply a laser beam of wavelength
2780 nm using the following specic settings
(Table II) for each group except the specimens of
the rst subdivision, which were tested for their
shear bond strength without debonding and were
considered a control group. In order to standardize
energy density, the turbo handpiece was placed
perpendicular to the ceramic samples’ surfaces
at a distance that was conrmed by a specially
designed positioner with a circular clockwise
motion from the outer circle of the cemented
veneer sample towards the center. The procedure
was repeated until the strokes under the samples
veneer exhibited distinct auditory and tactile
sensations indicating debonding [17].
The debonded samples were subsequently
examined for any damage using a
stereomicroscope.
Rebonding debonded samples
A finishing bur (MANI, INC, Japan) was
used to remove the adhesive resin remains
from the tooth surfaces, creating a uniformly
smooth surface in preparation for the rebonding
processes that followed. Then the same ceramic
specimens were used after evaluation and were
cemented by light or dual-cured resin cement
corresponding to their group.
Table I - Firing protocol steps
Standby
temp (B)
(C°)
Closing
time (s)
(mm:ss)
Heating
Rate (t)
(°C/min)
Holding
Time (H)
(Min.)
Holding temp (T)
(°C)
Max
Temp. (°C)
Vacuum
On (V1)
(°C)
Vacuum
Off (V2)
(°C)
Long time
cooling
(L) (°C)
403 06:00 90 00:10-07:00 830-850830-850 917 550 830-850 710
Information presented here was obtained from manufacturer technical and informative publication.
Figure 1 - Cutting lithium disilicate blocks.
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Youssef AI et al.
Rebonding strengths of lithium disilicate and feldspathic v eneers debonded by Er ,Cr:YSGG laser
Youssef AI et al. Rebonding strengths of lithium disilicate and feldspathic
veneers debonded by Er,Cr:YSGG laser
Shear bond strength testing
A universal testing machine (Instron, North
America) was used to investigate the difference
between the shear bond strength of the control-
irradiated group (without being debonded by
laser) and the lasered groups after rebonding.
The samples were mounted onto the machine
and were adjusted to guarantee that the shearing
blade’s 1-mm-thick edge was positioned as
near to the tooth-ceramic interface as possible.
At a crosshead speed of 1 mm/min, the shear
force was applied. The values of the shear bond
strength were noted in MPa [19].
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). For Non parametric data;
Mann–Whitney U test was used to compare the
two ceramics. Surface roughness (Ra) and EDX
data showed a non-normal distribution so we
used a non-parametric test, while debonding
time and shear bond strength data showed a
normal distribution so we used a parametric
test. Non-parametric data were presented as
median and range values while parametric data
were presented as mean, standard deviation and
95% Condence Interval for the mean values.
For non-parametric data; Mann–Whitney U test
was used to compare between two ceramics.
The Kruskal-Wallis test was used to study the
effect of curing on (Ra). Dunn’s test was used for
pair-wise comparisons.
For parametric data, Student’s t-test was
used to compare between debonding times of
two ceramics.Three-way ANOVA test was used to
study the effect of ceramic and curing on shear
bond strength. Bonferroni’s post-hoc test was
used for pair-wise comparisons when the ANOVA
test was signicant. The signicance 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
The findings of the three-way ANOVA
(Table III) indicated that the mean shear bond
strength was statistically signicantly inuenced
by the ceramic type, curing mode, and rebonding
on their own, irrespective of the effects of other
factors. The mean shear bond strength was also
statistically signicantly affected by the interaction
between the three factors. The variables are
dependent on one another because of their
statistically signicant interaction.
IPS E.max CAD had a statistically signicant
lesser mean shear bond strength than VITA
(at P-value <0.001, Effect size = 0.788)
and at P-value <0.001, Effect size = 0.935)
correspondingly in the control group, regardless
of whether light or dual cure resin cement
was used. While E.max showed statistically
signicantly lower mean shear bond strength
than VITA (at P-value <0.001, Effect size =
0.939) after rebonding and using dual-cure mode,
there was not a statistically signicant distinction
between the mean shear bond strength of the two
ceramics after rebonding and using light cure
mode (P-value = 0.065, Effect size = 0.102).
Table II - WaterLase parameters for debonding procedures
Operation Mode Free Running Pulse
Hand piece Turbo handpiece (MX7)
Repetition rate 20 Hz
Power 4.5 W
Pulse duration (60µs) H mode
Air 60%
Water 80%
Non-Contact mode 5mm away
Table III - Three-way ANOVA results for the effect of different variables on mean shear bond strength in Mpa
Source of variation Type III sum of
Squares df Mean
Square F-value P-value Effect size
(Partial eta squared)
Ceramic Type 130770.660 1 130770.660 690.468 <0.001* 0.956
Curing Mode 48839.132 1 48839.132 257.870 <0.001* 0.890
Rebonding 7636.932 1 7636.932 40.323 <0.001* 0.558
Ceramic x Curing x Rebonding interaction 8564.402 1 8564.402 45.220 <0.001* 0.586
df: degrees of freedom = (n-1). *Significant at P ≤ 0.05.
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Youssef AI et al.
Rebonding strengths of lithium disilicate and feldspathic v eneers debonded by Er ,Cr:YSGG laser
Youssef AI et al. Rebonding strengths of lithium disilicate and feldspathic
veneers debonded by Er,Cr:YSGG laser
Regarding the control group, whether with
E.max or VITA, light curing modes revealed a
mean shear bond strength that was statistically
substantially lower than that of dual curing
(P-value = 0.003, Effect size = 0.242; and
P-value <0.001, Effect size = 0.629). After
rebonding whether with E.max or VITA, Mean
shear bond strength was statistically considerably
lower in light curing modes (P-value <0.001,
Effect size = 0.541) and in dual curing (P-value =
0.003, Effect size = 0.966), respectively.
Regarding E.max with light-curing mode, the
mean strength of shear bond did not vary in a way
that was statistically signicant (P-value = 0.598,
Effect size = 0.009). While with dual curing
mode, rebonding revealed a mean shear bond
strength that was statistically notably greater than
the control (P-value <0.001, Effect size = 0.840).
While rebonding demonstrated a statistically
significant lower mean shear bond strength
than control for VITA with light curing mode
(P-value <0.001, Effect size = 0.848). Rebonding
demonstrated a statistically signicant increase
in mean shear bond strength compared to the
control group (P-value <0.001, Effect size =
0.853) for VITA with dual curing mode Table IV.
Scan Electron Microscope Evaluation:
▪ The IPS Emax CAD displayed the characteristic
rod-shaped, randomly arranged, and interlocked
lithium disilicate crystals encased in a glass matrix.
The microstructure of the VITA MARK II
was characterized by a porous substance with
roughly 4 µm grains of aluminum, potassium,
and sodium-based silicate. This material was
described as having a honeycombed surface
Figure 2. Failure Mode Analysis from SEM
pictures with magnication (500 X) (Figure 3).
After SBS testing following rebonding
of laser debonded ceramic specimens, failure
mode analysis showed no statistically signicant
difference in the distribution of different modes
of failures within both ceramic materials.
The highest percentage of samples had an
adhesive failure, (P-value = 0.998, Effect size
= 0.118) (Figure 4). The SEM images with
magnication (500 X).
DISCUSSION
The removal of ultrathin laminate veneers
is a challenging and unavoidable procedure due
to their possible fractures, incorrect placement,
or recurrent caries.The enhanced bonding of
the veneers to the enamel surface using resin
cements causes difculties upon their removal.
The conventional method of laminates removal
using drills, impose a great risk to the tooth
structure underneath because of the lack of
color contrast between the teeth, adhesive resin
contact, and the restoration [20]. Recently, the
introduction to laser technology has provided
a more comfortable and conservative approach
Table IV - The mean, standard deviation (SD) values and results of three-way ANOVA test for comparison between shear bond strength values
with different interactions of variables
Bonding/
Rebonding Curing E.max VITA The P-value
(effect of ceramic)
Effect size
(Partial eta squared)
Mean SD Mean SD
Control
LC cement 91.3 11.3 186.2 15.1 <0.001* 0.788
DC cement 27.2 6.1 214 16.7 <0.001* 0.935
P-value (curing mode) <0.001* 0.003*
Effect size (Partial eta squared) 0.629 0.242
Rebonding
LC cement 86.7 11 70.1 12.7 0.065 0.102
DC cement 140.1 16 332.5 17.5 <0.001* 0.939
The P-value (Effect of curing) <0.001* <0.001*
Effect size (Partial eta squared) 0.541 0.966
The P-value
(Effect of
rebonding)
LC cement 0.598 <0.001*
DC cement <0.001* <0.001*
Effect size
(Partial eta
squared)
LC cement 0.009 0.848
DC cement 0.840 0.853
*Significant at P ≤ 0.05.
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Rebonding strengths of lithium disilicate and feldspathic v eneers debonded by Er ,Cr:YSGG laser
Youssef AI et al. Rebonding strengths of lithium disilicate and feldspathic
veneers debonded by Er,Cr:YSGG laser
for the removal of ceramic veneers [21]. This
approach has proved great success in previous
studies, however, it is worth noting that
only a limited number of studies have been
conducted in this particular area of research.
Consequently, it became a matter of interest to
examine the alterations in shear bond strength of
reattached veneers samples subsequent to laser
debonding [9,22].
Two specic types of materials were chosen:
lithium disilicate (IPS E.max) and feldspathic
porcelain (Vita Mark II). These materials were
chosen due to their ability to offer a satisfactory
level of esthetics and mechanical properties.
Both materials were utilized in the form of CAD/
CAM blocks in order to ensure standardized
manufacturing techniques [6].
Figure 2 - (A) SEM IPS Emax CAD evaluation at baseline; (B) SEM VITA MARK II evaluation at baseline; (C) After laser debonding processes,
IPS Emax CAD cemented by light cure resin cement evaluation; (D) After laser debonding processes, IPS Emax CAD cemented using Dual cure
resin cement evaluation; (E) Following laser debonding techniques, VITA MARK II was bonded using an assessment of light cure resin cement;
(F) Dual cure resin cement assessment of VITA MARK II cemented following laser debonding processes.
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Youssef AI et al.
Rebonding strengths of lithium disilicate and feldspathic v eneers debonded by Er ,Cr:YSGG laser
Youssef AI et al. Rebonding strengths of lithium disilicate and feldspathic
veneers debonded by Er,Cr:YSGG laser
One group of ceramic samples was adhered
using light cure resin cement due to its desirable
aesthetic properties, low solubility, strong bond
strength, and outstanding mechanical properties
that enhance ceramic restorations and/or serve
to illustrate various curing methods. Dual cure
resin cement was used to cement the other
group [17,23].
Considered as a control group, half the
specimens were put through a shear bond strength
test while the other half were debonded using
Er,Cr:YSGG laser. After debonding, rebonding
Figure 3 - Adhesive failure mode evaluation (500 X) after laser debonding (A) IPS E max CAD cemented by light Cured Resin Cement; (B)
IPS Emax CAD cemented by Dual Cured Resin Cement; (C) VITA MARK II Cemented Light Cure Resin Cementd) VITA MARK II Cemented by
Dual Cure Resin Cement; (D) IPS Emax CAD cemented using Dual cure resin cement evaluation using scan electron microscope after laser
debonding.
Figure 4 - Bar chart representing failure modes of the different groups.
9
Braz Dent Sci 2024 Apr/June;27 (2): e4275
Youssef AI et al.
Rebonding strengths of lithium disilicate and feldspathic v eneers debonded by Er ,Cr:YSGG laser
Youssef AI et al. Rebonding strengths of lithium disilicate and feldspathic
veneers debonded by Er,Cr:YSGG laser
was performed followed by testing the shear bond
strength of the rebonded specimens.
When examining ceramic samples it was
observed that rebonding of both ceramics showed
no statistically signicantly between mean shear
bond strength than control group that was not
previously lasered. The reason for this could be
that there are no signicant changes observed
between the inner surface examined under a
scanning electron microscope before and after
laser debonding techniques. The results of this
study are consistent with Karagoz-Yildirak and
Gozneli [17] whose results showed there was no
signicant difference between the control and
rebonded groups. All-ceramic restorations may
be successfully removed using laser irradiation
without compromising the strength of rebonding .
Regarding curing mode, mode it was
observed that whether with E.max or VITA, light
curing modes exhibited statistically signicantly
lower mean shear bond strength, compared to
dual curing. The strength of bond was additionally
inuenced by the mode of adhesive curing, with
the light curing mode yielding a lower shear
bond strength when compared to the dual curing
mode endorsed by El-Mowafy and Rubo [24],
who emphasized that the development of dual-
cure resin cements was necessary to ensure
polymerization, particularly in areas that could
not be reached by the curing light. Furthermore,
alterations in the shade of the resin cement and
the thickness of the ceramic material may produce
notable discrepancies in the microhardness of the
materials and the nal polymerization outcome.
Hofmann et al. [23] also mentioned that the
energy provided during light polymerization,
which is dened as the product of light intensity
and exposure duration, determines the degree of
conversion in the polymerization reaction.
Up to our knowledge, there is a scarcity
of data regarding the impact on bond strength
subsequent to the rebonding procedure, as well
as there is a complete absence of data on how the
bond strength of rebonded ceramic restorations
is inuenced by laser debonding.
Furthermore, the failure mode serves as
a crucial parameter in assessing the potential
risks associated with tooth and ceramic damage.
A fracture can happen at the surface of the tooth
or inside the ceramic if the force required to detach
the restoration from the tooth is greater than the
cohesive strength of the tooth structures or the
ceramic material. In our study, the examination
of the scanning electron microscope data revealed
that there was no statistically signicant difference
in the baseline and roughness (Ra value) following
the peeling procedure. There was no indication
of any damage, ablation, or ablation pits on the
ceramic laminate’s surface.
In an alignment with Morford et al.’s [25]
research, it was noted that the bond between the
veneer and enamel was primarily disrupted at the
veneer cement interface, resulting in the majority of
the veneer surface being left clean, This observation
highlights that during veneer debonding, the
main outcome is laser ablation rather than
cement thermal softening. The main outcome
is laser ablation rather than cement thermal
softening. Considering the mentioned wavelength’s
mechanism, it primarily operates by absorbing
laser energy in water. It is possible conclude that
the energy of Er, Cr: YSGG laser passes through
the veneer and into the resin cement, which then
absorbs the remaining energy and vaporizes the
cement as a result. Once a sufcient amount of
cement is removed from the veneer, it detaches
from the tooth’s surface. It can also be stated that
the cement curing method does not inuence the
debonding process, as it is solely dependent on
the the resin cement’s water content not the other
ingredients. It is now clear that a clean and effective
laser debonding may be accomplished. For pulp
safety, it is also highly recommended to utilize a
potent air-water cooling spray.
Conicting results are present in the existing
literature regarding the impact of repeated
bonding on the shear bond strength of ceramic
brackets. While some studies have shown a
signicant decrease in strength after the second
bonding [23], others have indicated consistent
values comparable to the initial bond strength.
Bulut and Atsü [26] noted that there was no
notable distinction between the initial bonding
strength and the strength after the first and
second rebonding on enamel, or between the
initial bonding strength and the strength after
the rst rebonding on dentin.
In the current study, the bond strength of IPS
E.max cemented using light-curing resin showed
no change from the control group, while the group
re-cemented using dual-cured resin showed a
higher mean shear bond strength than the control
group. Feldspathic VITA MARK II ceramic samples
rebonded using light-cured resin showed a lower
10
Braz Dent Sci 2024 Apr/June;27 (2): e4275
Youssef AI et al.
Rebonding strengths of lithium disilicate and feldspathic v eneers debonded by Er ,Cr:YSGG laser
Youssef AI et al. Rebonding strengths of lithium disilicate and feldspathic
veneers debonded by Er,Cr:YSGG laser
mean shear bond strength than the control, while
when re-cemented using dual-cured resin, a higher
mean shear bond strength was obtained compared
to the control. As a conclusion, the interaction
between the three variables (ceramic type, curing
mode, rebonding after laser irradiation) had a
signicant effect on the mean shear bond strength.
Within the conditions of this study and
according to the study results, the null hypothesis
was approved.
CONCLUSION
In summary, the three factors, namely the
type of ceramic utilized, the mode of curing for the
cement, and the process of rebonding subsequent
to laser irradiation, exerted a noteworthy inuence
on the average shear bond strength. The shear
bond strength of E. Max was unaffected by the
rebonding process following light cure cementation,
whereas the bond strength diminished with vita
restorations. On the other hand, the application of
dual cure cementation for rebonding exhibited an
augmented shear bond strength for both materials.
Author’s Contributions
AIY: Conceptualization, Data Curation,
Formal Analysis, Funding Acquisition,
Investigation, Methodology, Writing – Original
Draft Preparation, Writing – Review & Editing.
MMW: Supervision, Validation, Visualization,
Writing – Review & Editing. GAEF: Project
Administration, Visualization, Writing – Review
and Editing. TMS: Supervision, Data Curation,
Writing – Review & Editing. NG: Supervision,
Formal Analysis Validation, Visualization, Writing
– Review & Editing.
Conict of Interest
There is no conict of interest.
Funding
The authors declare that no nancial support
was received.
Regulatory Statement
This study protocol was reviewed and
approved by the ethical committee of the Faculty
of Dentistry, Ain Shams University, Cairo, Egypt,
protocol number Fpr 19-(119)-M.
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Ahmed Ibrahim Youssef
(Corresponding address)
Misr International University, Faculty of Oral and Dental Medicine, Department of
Fixed Prosthodontics, Cairo, Egypt.
Email: ahmedibrahim2607@gmail.com
Date submitted: 2024 Feb 20
Accept submission: 2024 July 11
