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18 rev port estomatol med dent cir maxilofac. 2021;62(1):16-22

ments, testing the following hypotheses: the type of failure static solution (0.5% chloramine) at 4°C, according to the ISO/
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is not significantly influenced by the adhesive system or the TS 11405:2003. Their roots were sectioned, and their crowns
surface treatment. were polished with a prophylactic brush using pumice and
water. Their enamel was conditioned for 30 seconds with a 35%
phosphoric acid solution (Transbond XT Etching Gel, 3M
Material and methods Unitek St Paul MN, USA), washed with running water for 15
seconds, and dried with an air spray for 5 seconds. The Trans-
The study sample consisted of 90 self -curing PMMA discs (SR bond XT Primer adhesive was applied to the enamel surface,
Ivocron, Ivoclar Vivadent Inc, Amherst NY, USA) of standard- and the Transbond XT Light Cure Adhesive Paste composite to
ized dimensions (7.5 x 3 mm), fabricated according to the the bracket base. Excess removal and polymerization of the
manufacturer’s instructions. The PMMA discs were subjected composite were performed as previously described for the ex-
to 500 cycles of thermocycling between 5ºC and 55ºC (20 sec- perimental groups.
onds each bath) and stored in distilled water at 37ºC for 55 After bonding the brackets, all specimens were embedded
days. The sample was randomly divided into three groups of in self -curing PMMA (Orthocryl, Dentaurum GmbH & Co., Ip-
30 specimens each, depending on the surface treatment per- springen, Germany), using steel cylinders (12 -mm high/13 -mm
formed: no treatment, 50 -μm aluminum sandblasting (ASB diameter) as casts for the acrylic. The sample was stored in
o
group), or tungsten bur (TB group). Each group was then divid- distilled water at 37 C for 7 days, during which it was subject-
ed into two subgroups, according to the combination of adhe- ed to a new thermocycling process of 500 cycles in two distilled
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sive materials to be tested: MMA monomer for 25 seconds fol- water baths at 5 C and 55 C.
lowed by Transbond XT Primer (3M Unitek, St Paul MN, USA); Bond strength tests were performed using an Instron uni-
or Scotchbond Universal Adhesive (3M ESPE, St Paul MN, USA). versal testing machine (model 4502, Instron Ltd., Bucks, UK)
The adhesive system was applied following a standardized with a 1 kN load cell. Shear forces were applied to the brackets
protocol (Figure 1). A lower incisor metal bracket with a at a crosshead speed of 1 mm/min through a stainless -steel
0.018 -inch slot, 0° torque and angulation (Mini -Twin, Ormco, loop placed under the gingival wings. The maximum forces at
2
Orange CA, USA), and a 9.9 mm base was bonded to each spec- the moment of debonding were recorded in Newton (N) and
imen. Transbond XT Light Cure Adhesive composite (3M Unitek, divided by the bracket base’s nominal area, converting the val-
St Paul MN, USA) was placed at the bracket base, and manual ues to MegaPascal (MPa).
pressure was exerted to express excess adhesive, which was The bases of the 105 brackets and their adhesion surfaces
removed with a periodontal probe. The composite resin was were examined with a stereomicroscope (Nikon SMZ -2, Nikon
polymerized with a 1200 mW/cm LED light (Bluephase 20i, Europe BV, P.O.B. 7609, The Netherlands) using a 20x magnifi-
2
Ivoclar Vivadent Inc, Amherst NY, USA) for 20 seconds: 10 on cation factor. The type of failure was scored between 0 and 3,
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the mesial side and 10 on the distal side of each bracket. according to the adhesive remnant index (ARI): Index 0 –
The control group consisted of 15 freshly extracted intact 100% of adhesive remaining in the bracket base; Index 1 –
human mandibular incisors, which were stored in a bacterio- mixed failure, with 50–100% of remaining adhesive on the

Figure 1. Diagram of the experimental design.