2). Therefore, no main effects could be shown. The sub-
sequent one-way ANOVA and the Tukey test (α = 0.05)
showed that thermal cycling with load (G1) had the great-
est shear bond strength (8.4 ± 2.8 MPa) while the thermal
cycling alone (G3) had the least shear bond strength (4.7
± 1.1 MPa) among the groups. Comparing the results of
µSBS values for the adhesive system with and without
the application of TC eliminates the effect of the load (G3,
G4) and showed that there was significant difference be-
tween them and there was a significant difference with
load (G1, G2). The result shows a nonsignificant reduction
in µSBS values between the load without TC effect (G2)
and TC without load (G3) (Fig. 5).
Figure 4. Sample loaded in universal Instron machine.
Figure 5. Means and standard deviations of μSBS values between the TC
and non-TC group with or without the orthodontic load. Bars connected
with a line are in the same statistical group (Tukey test, α=0.05).
Figure 6. The principle of CoJet treatment: the silica coated alumina par-
ticles create micro roughness of the surface due to the kinetic energy and
leave silica embedded inside the surface, so it can react chemically with a
primer (Silane) [21].
Table 2. Two-way ANOVA for µSBS values (MPa). Note that the 2-way
ANOVA showed highly significant differences (Model p<0.0001). However
there were higly significant interactions (Load x Thermal).
Source
DF
Anova SS
Mean
Square
F
Value Pr > F
13.25 <.0001
Model 3 110.1178850 36.7059617 Error 56 155.1204133 2.7700074 Corrected
Total 59 265.2382983 Load 1 38.86540167 38.86540167 14.03 0.0004
Thermal 1 3.81528167 3.81528167 1.38 0.2455
Load
+Thermal 1 67.43720167 67.43720 167 24.35 <.0001
Table 3. Means and Standard deviations of the 4 tested groups. Same
letters in the Tukey Grouping column mean no statistically significant dif-
ference.
TRET N Mean STD Tukey Grouping
TC _Load (G1) 15 8.4320 2.76480 A
Control (G4) 15 6.3180 1.09754 B
Load (G2) 15 5.8073 1.06452 B
TC (G3) 15 4.7020 1.04792
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4. Discussion
The first and third null hypotheses had been rejected,
the second one had been accepted.
The conditioning technique used in this study (17),
gritblasting with CoJet (Al 2 O 3 silica coated sand) was
selected for the following reasons: glass based ceramics
can be etched with Hydrofluoric acid (HF) to achieve
an excellent micromechanical surface topography for
bonding. On the other hand, ZrO cannot be etched
with HF at room temperature at all. Sandblasting with
CoJet works well on glass-based ceramics as well. Since
the orthodontists do not know which ceramic has
been used, with the method used they are on the safe
side. It would be the protocol of choice in the clinical
routine [17].
Due to increased esthetics most MZ FDPs are glazed or
stained, according to the study of Canigur et al. [4] “the
CoJet yields higher bond strength values. The CoJet cre-
ates micro retentive sites by increasing surface area and
roughness” [18-20] “silica coated particles not only rough-
en the surface, they also have a chemical effect: because of
blasting pressure, the embedded silica and alumina par-
ticles can then chemically react with the silane coupling
agent“ (Fig. 6) [21]. “The improved chemical bonding with
silane coupling agents in this approach is advocated to be
the key factor for a higher resin bond strength.”
Since the orthodontist does not know the details of
the fabrication process of the crown where a bracket
should be bonded to, it is better to consider the ZrO
surfaces were all glazed. With the gritblasting the glaze
may be partially or totally removed but using CoJet. A
silica layer is deposited regardless of the composition
of the underlying surface, thus allowing the use of
Silane as a primer.
Spontaneous debonding of brackets is one of the most
common clinical problems in fixed orthodontic therapy.
There are two major interfaces that can be subjected to
deboning: the enamel or restorative material/adhesive
interface and the adhesive/bracket interface [22] . In this
study, we tested the restorative material (ZrO)/adhesive
interface and it was decided not to use brackets for the
following reasons: The shear bond strength between
orthodontic cement and the ceramic surface was the
only topic of interest. If we had used brackets we would
have had to deal with the bracket-cement interface as
well, which was investigated in the past abundantly
[23-25]. Furthermore, it was necessary to eliminate
possible confounding factors such as geometry, mesh
design of the bracket base, or bracket material, all of
BONDING ORTHODONTIC RESIN CEMENT TO ZIRCONIUM OXIDE UNDER
ORTHODONTICS LOAD AND THERMOCYCLING EFFECT
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