Page 20 - SPEMD_58-2

76 rev port estomatol med dent cir maxilofac. 2017;58(2):71-78

Figure 3. Comparison between two interfaces. A) bracket Figure 5. Fracture zone on ED sample. Most of fractures
mesh; B) enamel; C) adhesive blister occurred on this zone. The print of enamel crystals were
noticed.

Considering shear bond tests on adhesive groups free of
thermal cycling, G group was the resin composite adhesive
that exhibited the highest bond strength at 11.16 ± 2.95 MPa.
TP group reached values of 8.41 ± 2.06 MPa that was similar to
shear bond values found in previous studies. 13,14,18 However,
shear bond strength values exceeding 15 MPa were also report-
ed in several previous studies. 4,15,16 In this study, TP compomer
achieved clinical acceptable values (above 6 MPa), in agree-
ment with some other recent studies. 5,13-16,18,19 However, sig-
nificant differences were recorded for the test adhesives,
mainly for G and ED, suggesting an influence of the chemical
composition and properties of the adhesive on their bond
strength to the teeth surface. 5,13-16,18
Despite the decrease in bond strength for TP compomer
subjected to thermal fatigue in this study, that is still consid-
ered clinically acceptable considering values recorded above 6
MPa in previous studies. Additionally, the benefits of such or-
thodontic adhesives considering fluoride release and preven-
tion of enamel demineralization supported by several stud-
Figure 4. Fracture surface showing the absence of adhesive ies 3,20 should also be considered on the treatment of caries
remnants bonded to the bracket mesh (arrows) evidencing susceptible patients. Previous studies have reported different
the lack of adhesion between these two material.
results considering the effect of thermal cycling on shear bond
strength for such compomer -based adhesive. 14,21 For instance,
a previous study revealed stable shear bond strength of ortho-
dontic adhesives to enamel after thermal cycling between 5
Discussion and 60 C although samples were tested only for 500 cycles.
o
14
This paper revealed novel information on the behavior of or- Another previous study reported a decrease in shear bond
o
thodontic adhesives subjected or not to thermal cycling. Re- strength after 1000 thermal cycles between 4 and 60 C. Con-
sults showed a detrimental effect of the thermal cycling on cerning the performance of the materials in oral cavity, addi-
the bond strength of the test adhesives to enamel, with a sta- tional tests must be performed for longer period of thermal
tistically signifcant decrease being only recorded for the cycling to simulate the orthodontic treatment time.
compomer group. Such results supported the rejection of the ARI showed most adhesive remnants on enamel surface
null hypothesis of the present study and therefore they are in on the two adhesives that displayed higher and clinically ac-
agreement with the results found in literature. 10,17 ceptable shear bonding values on thermal cycling. However