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Effect of Erbium, Chromium-doped Yttrium, Scandium, Gallium, and Garnet 2.7 nm Laser on Debonding
World Journal of Dentistry, September-October 2018;9(5):349-354
349
WJDWJD
Effect of Erbium, Chromium-doped Yttrium, Scandium, Gallium,
and Garnet 2.7 nm Laser on Debonding of Computer-aided
Design and Computer-aided Manufacturing Endocrowns
1Ahmed EL Hawary, 2Ahmed Abbas, 3Tarek Harhash
ABSTRACT
The most common method for the removal of all-ceramic res-
torations is to use a highspeed handpiece with a stone or bur.
Unfortunately, this process can be difcult, time-consuming
and may lead to the loss of healthy tooth structures. Lasers
have been suggested and used to remove ceramic or thodontic
brackets, laminate veneers and full anatomical crowns.
Aim: Aim of the present study was to evaluate the debonding
effect of erbium, chromium-doped yttrium, scandium, gallium
and garnet (ErCr:YSGG) on Computer-aided design and com-
puter-aided manufacturing (CAD/CAM) end crown restorations.
Materials and methods: Overall, 30 molar samples were
prepared for this study and divided into two groups as follows:
Group A– (n = 15): Endocrowns subjected to ErCr:YSGG
laser application.
Group B–(n = 15): Endocrowns not subjected to the laser
(control). Endocrowns were fabricated from lithium disilicate
ceramics and manufactured using a CAD/CAM machine.
Cementation was done using Bisco Duo Link Universal™ resin
cement. ErCr:YSGG laser was used with wavelength 2780 nm,
0.3J energy, 10 Hz frequency and 1000 µm tip size. Pull out
test was done using a universal testing machine.
Results: It was found that Non-laser group recorded statisti-
cally signicant (p < 0.05) higher mean value (258.14 ± 63.43 N)
fo r de bondi n g th an Las e r gr oup me a n value (15 6.66 ± 32. 8 9 N)
as indicated by student t-test. Additionally, no carbonization at
the dentin/cement interface was observed.
Conclusion: According to the results of this study, ErCr: YSGG
application can be considered a conser vative method for the
debonding of all ceramic endocrowns.
Clinical signicance: Some practitioners have been against
the use of endocrown restorations due to the difculty faced in
removal and retrieval, the use of laser is an alternative, effective
and conservative method.
Keywords: All ceramic restoration, CAD/CAM, Debonding,
Endocrown, Effect of erbium, Chromium-doped yttrium, Scan-
dium, Gallium and garnet 2.7 nm Laser on Debonding of CAD/
CAM Endocrowns.
How to cite this article: Hawary AEL, Abbas A, Harhash T.
Effect of Erbium, Chromium-doped Yttrium, Scandium, Gallium,
and Garnet 2.7 nm Laser on Debonding of Computer-aided
ORIGINAL ARTICLE
1Department of Prosthodontics, MSA University, National
Institute of Laser Enhanced Sciences, Cairo, Egypt
2,3Department of Prosthodontics, National Institute of Laser
Enhanced Sciences, Cairo University, Cairo, Egypt.
Corresponding Author: Ahmed EL Hawary, Department of
Prosthodontics, MSA University, National Institute of Laser
Enhanced Sciences, Cairo, Egypt, e-mail: ahawary@hotmail.com
10.5005/jp-journals-10015-1561
Design and Computer-aided Manufacturing Endocrowns. World
J Dent 2018;9(5):349-354.
Source of support: Nil
Conict of interest: None
INTRODUCTION
Treatment of grossly damaged endodontically treated
teeth using all-ceramic crown restorations is a problem
facing many practitioners in their daily practice.1 Caries,
fracture and cavity preparation are the main reasons for
the decrease in fracture resistance of root canal treated
teeth, rather than dehydration or physical changes in
dentin.2 Traditionally, the functional and esthetic resto-
ration of teeth with endodontic treatment and extensive
coronal destruction has been achieved by fabricating
crowns supported on cast metal post and cores.3
With the advancement of adhesives and ceramics, a
macro-retentive design is no longer a requirement when
there are sufficient tooth surfaces available for bonding.4 A
new type of restoration was developed consisting of a cir-
cumferential preparation with a 1.0 to 1.2 mm butt margin
and a central retention cavity inside the pulp chamber, thus
constructing both the crown and core as a single unit, i.e.,
a “monobloc”. This restoration is called the Endocrown.5
Removal and retrievability are needed in cases when
the endodontic treatment under the restoration has failed.
A meta-analysis of conventional endodontic treatment pre-
viously conducted has reported a success rate in the range
of 78 to 84%.6 The major causes of endodontic failures were
inadequate obturation (45%) followed by missed canals
(32%) and then fractured or dislodged instruments (14%).7
As is the case in all ceramic veneers, the most common
method for removal of all ceramic endocrown restorations
is to use a highspeed handpiece with diamond stone.8
Unfortunately, due to the high bond strength and color
matching qualities of resin bonded ceramics and tooth
structure, this process can be difficult, time-consuming
and may lead to unnecessary loss of healthy tooth struc-
ture. The search for alternative methods that could safely,
quickly and predictably debond endocrowns without the
risk of iatrogenic damage to underlying tooth structure
was therefore greatly needed, seriously investigated and
would be encouraged and welcomed.
Ahmed EL Hawaryi et al.
350
Since the early 1995, lasers have been used experimen-
tally to remove ceramic orthodontic brackets, which was
afterward used in the debonding and removal of porce-
lain veneers and lam inate veneers. Tocchio et al.9 used Nd:
YAG laser at a wavelength of 1060 nm. Oztoprak et al.10
found that laser application significantly decreased the
required debonding load for porcelain laminate veneers.
Debonding was said to occur by three main effects,
thermal softening, where the bonding agent is softened
by heat. Secondly, thermal ablation where resin tempera-
ture is raised with high enough laser energy and finally
thermally induced photoablation when laser energy
interacts with the resin material.9,11
MATERIALS AND METHODS
A total of 30 freshly extracted human teeth were selected
for this study. They were inspected under proper illumi-
nation and magnification (× 2.5) to ensure the absence of
cracks or fracture. Teeth of average crown length 6 ± 1 mm,
a mesiodistal dimension with average 10 ± 1 mm and
buccolingual dimension with average 12 ± 1 mm were
selected, while smaller teeth were discarded. The teeth
were placed in sodium hypochlorite (NaOCl) 2.5% for
24 hours to remove any attached debris. Teeth were then
stored in normal tap water during the experimentation
period at room temperature.
The samples were then divided into two groups, Group
A n = 15: endocrowns subjected to Er Cr: YSGG laser appli-
cation and group B n = 15: endocrowns not subjected to the
laser (control). The sample teeth were then placed within
epoxy resin blocks. Teeth within their respective epoxy
blocks were placed on a surveyor (BEGO paraflex, Bremen,
Germany) with an attached straight handpiece (Fig. 1) and
were marked at a level 1 mm above the cementoenamel
junction, demarcating the level of decoronation. using a
medium grit disc attached to the straight handpiece the
Fig. 1: Surveyor with attached handpiece
Fig. 2: Endocrown preparation
Fig. 3: Designing of the endocrown copings with
occlusal extension and channel
teeth were cut uniformly at the desired level. Access cavity
and intracoronal endocrown preparation were performed
using an Endo-Z bur (Fig. 2), followed by root canal treat-
ment and obturation for all samples.
Rosetta® SM (HASS, Korea) lithium disilicate glass
ceramic blocks were used for the fabrication of the endo-
crown copings. Scanning of the prepared sample teeth
using Freedom HD extra oral scanner, DOF inc.©, Korea
and designing of the endocrown copings were performed
using Exocad softwareVhf, Germany. Cement gap was
designed to be 0.08 mm, and the occlusal surface was
designed with an occlusal extension of 5 mm height and
3 mm thickness with a 2-mm wide channelwas added
on the occlusal extension to provide a way of pulling the
coping during testing (Fig. 3).
To fabricate the endocrown copings, animes-icore®
(Germany) CORiTEC milling machine was used. After
milling was completed, the endocrown copings were
cemented to their respective samples using Bisco
(Illinois, USA) Duo Link Universal™ resin cement, to
Effect of Erbium, Chromium-doped Yttrium, Scandium, Gallium, and Garnet 2.7 nm Laser on Debonding
World Journal of Dentistry, September-October 2018;9(5):349-354
351
WJD
ensure the standardization of the cementation proce-
dure a custom-made cementation device was used for
these procedures (Fig. 4). All samples then underwent
5000 thermocycling cycles with dwell times set at 25
seconds in each water bath with a lag time of 10 seconds
in between.
Lasing was performed using a Waterlase iPlus,
BIOLASE© Inc. (Irvine, USA) ErCr: YSGG (erbium, chro-
mium-doped yttrium, scandium, gallium, and garnet)
unit, under the laser parameters shown in Table 1.
Laser irradiation was started on the occlusal surface of
the samples, the irradiation tip was moved in a back and
forth movement, like painting the surface with imagi-
nary 2 mm stripes, starting from one contact point to
the other for 30 seconds. This was repeated three more
times covering the whole of the occlusal surface, after
which, the same irradiation pattern was performed along
the buccal and lingual walls. Finally, the proximal walls
were irradiated in the same fashion but in a direction
parallel to the long axis of the tooth (Fig. 5). This pattern
resulted in a total irradiation time of approximately 4
minutes, and the irradiation distance was 5 mm away
from the ceramic surface, no changing in the transpar-
ency of the ceramics or discoloration was observed
during irradiation.
Pull out testing of the samples using a univer-
sal testing machine (Model 3345; Instron Industrial
Products, Norwood, USA) was performed with a load
cell of 5000 N and data were recorded using Bluehill
Litecomputer software. The endocrown coping was
suspended from the upper movable compartment of
the testing machine by orthodontic wire loop (1.5 mm)
through the hole made during milling. The device was-
subjected to a slowly increasing upward vertical load
(5 mm/min) until total dislodgment of the crown. The
load required to dislodgment was recorded in Newton.
RESULTS
The results were analyzed using Graph Pad Instat
(Graph Pad, Inc.) software for windows. A value of
p < 0.05 was considered statistically significant. Continu-
ous variables were expressed as the mean and standard
deviation. After homogeneity of variance and normal
distribution of errors had been confirmed, a student t-test
was done for compared pairs. Sample size (n = 15) was
large enough to detect large effect sizes for main effects
and pair-wise comparisons, with the satisfactory level
of power set at 80% and a 95% confidence level. Descrip-
tive statistics of retention (N) showing mean, standard
deviation (SD), minimum, maximum and 95% confidence
intervals (CI) (low and high) values for both lased and
non-lased are summarized in Table 2 and graphically
drawn in Graph 1.
It was found that the retention mean ± SD values
recorded for the laser group were (156.66 ± 32.89 N) with
the minimum value (106.25 N) and the maximum value
(232.02 N). Meanwhile, the retention mean ± SD values
recorded for the non-laser group were (258.14 ± 63.43 N)
with the minimum value (155.96 N) and the maximum
value (253.09 N).The non-laser group recorded statisti-
cally significant (p < 0.05) higher mean value (258.14 ±
63.43 N) than Laser group mean value (156.66 ± 32.89 N)
as indicated by student t-test.
Table 1: Laser parameters
Wavelength 2780 nm
Energy 0.3 J
Pulse Duration 60 µs (H-mode)
Frequency 10 Hz
Average Power 3 W
Peak Power 5000 W
Tip Size MZ10 (1000 µm)
Fig. 4: Custom made cementation device
Fig. 5: Laser irradiation of the samples
Ahmed EL Hawaryi et al.
352
DISCUSSION
Recently, CAD/CAM endocrowns has served as a new
method for restoring endodontically treated teeth instead
of using a post and core.12 Endocrowns are onlays that
build up and restores damaged coronal potion of a tooth,
having an extension into the pulp chamber of said tooth.13
This extension serves to provide better stabilization and
improve adhesion of the restoration.14 Usually, removal
of endocrown restorations was done using a diamond
stone or bur, this process was difficult, time consuming
and unconservative.
In this study, natural human caries free molars were
selected for clinical simulation, as recommended by
Aktas et al.15 Decoronation of the tooth was performed
using a surveyor to insure uniformity across all samples,
it was done at a level of 1 mm above the cemento-enamel
junction in accordance with Rocca et al.16 Milling of
the endocrown samples was done using a CAD/CAM
machine to provide predictable quality to the final resto-
ration as well as save time. The use of CAD/CAM offers
a more accurate fit, higher durability and more ease of
construction, by eliminating human error.17 Prepared
teeth were scanned, and an 80-µm relief18 cement space
was chosen when designing the endocrown copings,
this amount of space was considerate optimal by Wilson
et al.19 finding out that there was a significant correlation
between increased cement space and decreased seating
time and seating discrepancy. The occlusal surface of the
endocrown coping was designed with a 5 mm occlusal
extension having a 2 mm channel to allow the pulling the
copings during retention testing, as was recommended
by Saryazdi et al.20
Adhesive cementation of all-Ceramic restorations
is achieved through resin based luting cements, which
require conditioning of both the tooth and the restoration
surface before application of the luting resin cement. In
this study conditioning of the tooth surface was done
through a combination of selective etching and bonding.
Although, Peumans et al.,21 claimed that additional selec-
tive etching of enamel does not significantly affect the
bonding of ceramic restorations, selective etching was
done using 37% phosphoric acid on enamel to ensure
maximum bonding and higher retention rate between
the restoration and prepared teeth as concluded by
Szesz et al.22
In this present study it was decided against using
abrasion in the conditioning of the endocrown samples
because of the difficulty in production of uniform rough-
ness on the fitting surface of the restoration and fear of
the potential damage it may cause to the margin which
might lead to poor marginal adaptation as noted by
Fleming and Addison.23 Acid etching was performed
on the ceramic surface using 9.5% hydrofluoric acid
creating a surface that is more accepting for bonding,24
after which, the application of a silane coupling agent
is of utmost importance to increase the chemical bond
strength between the resin cement and the endocrown
as recommended by Matinlinna et al.25
Debonding of all ceramic restorations is based on
the thermal softening of the adhesive resin cement.10
This is achieved through thermal-mechanical inter-
action on the water content in those cements under
laser application,26 despite resin cements being gener-
ally less soluble that other luting cements, they still
absorb water which in turn allows laser penetration
and ablation.27
ErCr: YSGG laser was used in this present study as per
the recommendation of Gurney et al.,28 who stated that
although it has a less coefficient and has less wavelength
than Er: YAG lasers traditionally used in debonding pro-
cedure studies, ErCr: YSGG has the same strong absorp-
tion in water and lower absorption in hard dental tissues.
Laser parameters used were set according to Gurney’s
study and the laser application procedure was based on
the protocol first suggested in 2014 by Rechmann et al.29
This protocol recommended that the tip be placed 5 mm
away from the ceramic surface and then a cross hatch
Table 2: Descriptive statistics of retention results (Mean ± SD) between lased and non-lased groups
Variable Mean ± SD
Range 95%CI
Minim. Maxim. Lower Upper
Group A-Laser 156.66 32.89 106.25 232.02 138.44 174.87
B-Non-laser 258.14 63.43 155.96 253.09 223.01 293.26
Graph 1: Column chart showing retention results mean values
for both lased and non-lased groups
Effect of Erbium, Chromium-doped Yttrium, Scandium, Gallium, and Garnet 2.7 nm Laser on Debonding
World Journal of Dentistry, September-October 2018;9(5):349-354
353
WJD
pattern was drawn as if “painting with a paint brush” on
the ceramic surface. This procedure resulted in between
3 to 4 minutes of laser irradiation.
Pull out test was chosen in this study, as it has
several advantages over other testing methods,30 such
as having better stress distribution, the ability to test
irregular surfaces and its efficiency in testing small
areas. Results of the pull-out test showed statistical
significance between both groups, those with laser
application before debonding (group A) and those
without (group B), this was in accordance with all previ-
ous studies regarding the effect of laser on debonding
of either ceramic brackets, laminate veneers or full
coverage crowns. But as of writing, this study is the
first to prove it on endocrowns that have a much larger
thickness than those previously mentioned especially
in the intra-radicular portion of the endocrown present
within the pulp chamber. Scanning electron microscope
images of both the tooth and the restoration surface
of group A showed both surfaces covered with the
bonding cement indicating an adhesive failure of the
cement upon laser application, which is in accordance
with Morford et al.31 findings.
CONCLUSION
According to the results of this present study, laser
application, specifically that of ErCr: YSGG could be
considered an effective and conservative method for
the debonding and subsequent removal of all ceramic
endocrown restorations.
CLINICAL SIGNIFICANCE
Some practitioners have been against the use of endo-
crown restorations because of the difficulty of its
removal when needed, according to this present study it
is advisable to use ErCr: YSGG laser in the conservative
removal of such restorations.
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