these new materials, these situations may lead to early
debonding of orthodontic brackets [4]. Furthermore, in
orthodontics the goal is not a maximum bond strength,
but one that is adequate to withstand orthodontic
forces. Finally, the bond should be reversible i.e. it
should be easy to remove brackets without damaging
the enamel or the restored teeth.
Currently, there are several studies about the different
surface conditioning protocols for orthodontic bonding
to porcelain materials. They enhance the adhesion
either by mechanical conditioning such as “roughness by
airborne particle abrasion” or by chemical conditioning
such as the use of hydrofluoric acid etch of glass-based
ceramics to increase the bond strength and/or silane
coupling agents or oxidic primers which change the
wettability of the surface, or by combination of both
mechanical and chemical surface treatments [10-12].
Although there is increased use for MZ crowns in dental
practice, there is not enough information available about
how to bond orthodontic brackets on MZ [13]. The most
commonly method used to evaluate the performance
of orthodontic bonding systems and the bonding
technique is by measuring shear bond strength [14].
Doing this, one should consider the effect of orthodontic
forces applied and the stress induced by water storage
and thermocycling on the bond strength. This should
be simulated in vitro as an accelerated ageing process
[13]. In shear bond strength testing, the ideal direction
of pull is parallel to the loading interface. It has been
recognized that the direction of the debonding force
will affect the results [15]. In clinical orthodontic practice,
bonding the brackets and placement of arch wire might
be done in the same visit. Hence, force could be applied
to the bracket within the first hour after bonding and
regardless of the relatively low magnitude of the force,
it could have an adverse effect on the bond strength.
It was reported that the polymerization of adhesives
should quickly reach a minimum value to enable the
adhesive to resist bonding failure when tying in initial
arch wires [16].
The objective of this study was to evaluate the thermo
cycling effect accompanied by orthodontic force on
the micro shear bonding strength of orthodontic resin
cement on glazed monolithic zirconium oxide surface
conditioned by air abrasion with silica coated alumina
particles.
The following null hypotheses were tested: 1) The
thermo cycling (TC) does not influence the shear bond
strength, 2) The orthodontic load does not influence
the shear bond strength, and 3) The orthodontic load
with TC does not influence the shear bond strength.
2. Material and methods
The types, brands, manufacturers and chemical
composition of the material used in this study are listed
in Table 1.
2.1. Specimen Preparation
One monolithic zirconium oxide (MZ) material was
tested in this study (Zenostar, Ivoclar Vivadent,
Schaan, Liechtenstein). The specimens were received
in nonsintered blocks. They were cut into squares
approximately (9 mm × 9 mm × 4 mm). They were
Stomatology Edu Journal
Table 1. Types, brands, manufacturers and chemical compositions of the
material used in this study.
Type and
Brand
Manufacturer Chemical composition
Wieland, Ivoclar
Vivadent Zirconium dioxide (ZrO 2 + HfO 2
+ Y 2 O 3 ) > 99.0%, yttrium oxide
(Y 2 O 3 ) 4.5 ≤ 6.0%
Hafnium oxide (HfO 2 ) ≤ 5.0 %,
aluminum oxide (Al 2 O 3 ) + other
oxides ≤ 1.0 %
Glaze spray IPS e.max
Ceram Isobutane 30-60%, propan-2-ol
25-40%
Acratray
Acrylic Powder
(blue) Henry Schein;
Melville NY,
USA Poly Methyl methacrylate
(PMMA), calcium carbonate,
titanium dioxide, benzoyl
Peroxide
Acrylic Liquid
(Self cure) Henry Schein Methyl methacrylate (MMA),
benzophenone, hydroquinone
CoJet Sand 3M ESPE; St
Paul, MN, USA 30-μm Al 2 O 3 SiO 2
Monobond
Plus Ivoclar
Vivadent;
Schaan,
Liechtenstein Ethanol, 3-trimethoxysilylpropyl
methacrylate, methacrylate
phosphoric acid ester, disulfide
methacrylate
Ivoclar Vivadent Bis-GMA 50-100%
urethane dimethacrylate 10
< 20%
1,10-decandiol dimethacrylate
10 < 20%
ORTHO
TECHNOLOGY SS Straight Lengths 0.14.
Dentsply GAC
international,
INC Bohemia,
NY, USA Stainless Steel.
Zenostar
Heliosit
Orthodontic
Adhesive
Orthodontic
wire
Orthodontic
brackets
BONDING ORTHODONTIC RESIN CEMENT TO ZIRCONIUM OXIDE UNDER
ORTHODONTICS LOAD AND THERMOCYCLING EFFECT
then sintered in a furnace at 1530°C (Sintramat S1 High
Temperature Furnace, Ivoclar Vivadent) with a heating
rate of 8°C/min and a holding time of two hours.
All the specimens were glazed with (IPS e.max
Ceram glaze spray, Ivoclar Vivadent) according to the
manufacturer’s directions (770°C). The glazing material
was applied in an even layer on the specimen in the
usual manner and then all the specimens were fired
according to the manufacturer’s direction in a furnace
(Programat EP 5000, Ivoclar Vivadent). After completion
of the firing process the samples were removed from
the furnace and allowed to cool to room temperature
in a place protected from draft.
All specimens were then embedded in autopolymer-
izing acrylic resin (powder and liquid, Acratray Blue,
Henry Schein, Melville, NY, USA). First, the specimens
were held in place on a smooth surface with a piece of
two-sided adhesive tape. Then, powder and liquid of
acrylic resin was mixed (1:3) and poured into the molds
to produce cylinders measuring 2.5 cm in diameter and
2.3 cm in length (Ultradent Products, South Jordan, UT,
USA). After autopolymerization started, the mold was
placed in a container with cold water to decrease the
polymerization temperature.
After polymerization, the cylinders were removed from
the mold and the two-sided adhesive tape was removed.
The specimen surfaces were then cleaned with ethanol
(Ta