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rev port estomatol med dent cir maxilofac . 2017;58(2):65-70 69

discussing the limitations of the ARI to characterise the frac- Considering similar surfaces subjected to the same surface
ture. Those two studies did not associate the ARI to bond treatment (sandblasting) and adhesive (light-cured bis-GMA-
2
strength or surface. However, the third one found a qualita- based composite resin), bis-acrylic surfaces showed bond

tive association between the ARI score and the effectiveness strength mean values ranging from 3.75 ± 0.08 MPa5 to
2
5,7
of bracket/acrylic surface bond, and not a direct association 13.1MPa. Some studies obtained mean values that were not
with the amount of bond strength or the bond failure clinically acceptable. On the other hand, one study2 found
5
10
mode. One study determined the adhesion failure mode higher values, which seems to be related to the type of surface
and showed different failure modes in PMMA (adhesive fail- since it may provide a chemical cross-link with the bifunction-
ures independently of storage time) and bis-acryl (adhesive al acrylates present on it. The better performance after ther-
and cohesive failures at one-week storage and mostly cohe- mocycling could also be explained by the same reason. In ad-
sive failure at one-month storage). Moreover, only one study dition, the authors reported the influence of the surface
associated a reduction in bond strength with an interface treatment on the obtained results.
9
temporary crown/adhesive failure. The failure mode was Sandblasting was evaluated as a surface treatment by oth-
reported by one article without index categorisation and er studies on this and other surfaces. 5,7,9,11,12 This type of sur-
was found to be adhesive failure type in all specimens. 4 face treatment showed to enhance more the adhesive strength
Surface roughness / Scanning Electron Microscopy (SEM). than other surface treatments like sandpaper SiC, mono-
2,9
12
9
Two studies evaluated the surface roughness using scan- mer, etching 7,12 and diamond bur. Laser Er:YAG irradiation
ning electron microscopy (SEM) after different acrylic caused an even greater increase in bond strength in a study 7
surface treatments. One performed a quantitative anal- where authors used SEM to determine the surface roughness
12
ysis and the other a qualitative analysis. One study after different surface treatments but did not conduct any
7
stated that the diamond bur created the highest rough- comparative description of the type of surface material used.
ness on the acrylic followed by sandblasting, and that Other authors measured the surface roughness after different
5

etching and monomer or plastic conditioner applications acrylic surface treatments. Results showed that the diamond
resulted in scarce acrylic alterations. The other publi- bur created the highest roughness on the acrylic, followed by
12
cation only described the appearance of the surfaces sandblasting, and that etching and monomer or plastic condi-

after three different surface treatments. 7 tioner applications resulted in scarce acrylic alterations. 5
Storage time and solution. Storage methods were men- Bond strength was also influenced by the type of adhe-
tioned in all publications, except for one. Eight stud- sive. 9,10,11,13 Acrylic resins performed better than composite
13
ies 2,4,5,7,8,9,10,12 presented the storage time and solution resins and the presence of cyanoacrylate enhanced both ma-
and one only the storage time. 11 terials performance. This finding reinforces the idea that there
Crosshead speed. The included data showed the use of is a chemical bond important to increase the bond strength of
diverse crosshead speeds in shear tests, namely, 0.5 mm/ brackets to acrylic surfaces.
min, 5,9,10,12,13 1 mm/min 2,7,8,11 and 5 mm/min. 4 According to the obtained results, it seems plausible to
suggest that the chemical strength between the type of surface
and adhesive, as well as the mechanical strength provided by
Discussion the surface treatment, should be considered as intervening
factors in the deficit adhesion to provisional acrylic surfaces.
Great diversity was noticed in the experimental conditions The results regarding the influence of thermocycling pre-
for bond strength testing. This situation had already been sented contradictory data. 2,7,11 However, it is still considered
stated in the literature for orthodontic brackets adhesion to as the reference technique for simulating ageing in the mouth
14
1
enamel and ceramics. In the literature search performed by environment. 16
the authors, no systematic review about the present issue Since this review was on in vitro studies, other factors were
was found. Therefore, it was assumed that this would be the considered important for bond strength, such as samples stor-
frst systematic review on the bond strength of orthodontic age and crosshead speed. This is in agreement with a similar
brackets to provisional acrylic materials. However, a great di- study conducted on the bond strength of brackets to enamel. 1
versity of experimental conditions on this issue was noticed, All the included publications provided storage methods, ex-
and, because of that lack of standardisation, the studies could cept for one study that performed the shear test immediately
only be evaluated individually. 1 after the brackets bonding to the surfaces. In most studies, the
Even though the comparison between different methods samples were kept in distilled water during at least one day at
cannot be performed, the results can predict the mechanical 37ºC. 2,4,5,7-10,12 Only in one study was the storage time longer
strength of the bracket to acrylic interfaces if factors are con- since it was one of the variables in the study and considered
sidered separately. to be an important factor. 5
Clinically acceptable shear bond strength values were stat- Crosshead speed has been controversially reported in the
15
ed to be higher than 5.9 MPa. However, bond strength to literature. Its influence on the adhesion between brackets and
18
acrylic provisional materials revealed values ranging from 0 enamel 1,17 or ceramics was reported in some papers. On the
11
MPa to 19.82 ± 2.93 MPa, depending on some factors. For other hand, other studies showed no influence. 19,20 Little or no
2
instance, the type of surface, 2,4,5 the treatment, 2,5,7,9,11 the type data was found regarding the influence of crosshead speed on
of adhesive 9,10,11,13 and the thermal cycling were found to acrylic surfaces. Even though the included studies used differ-
2,7
cause differences in shear bond strength values. ent crosshead speeds, 2,4,5,7-13 none discussed this factor.