Abstract
The aim of this study was to evaluate the shear bond strength (SBS) of metallic orthodontic brackets bonded to bovine teeth using light-activated or chemically activated composite resins. One hundred and twenty bovine mandibular incisors were divided into 6 groups (n=20), according to the bonding materials: Transbond XT (T); Enforce Dual (ED); Enforce chemical (EC); Enforce Light-activated (EL); Concise Orthodontic (C); and RelyX Unicem Capsule (UN). Metallic brackets were positioned and firmly bonded to the teeth. Light-activation for T, ED, EL and UN was carried out with four exposures on each side of the bracket with 20 s total exposure times using XL2500 (3M ESPE). EC and C were chemically cured. Next, all specimens were stored in deionized water at 37 °C for 24 h. The shear bond strength was carried out at a crosshead speed of 1.0 mm/min. Data were subjected to one-way ANOVA and Tukey's test (α=0.05). The adhesive remnant index (ARI) was evaluated at 8× magnification. C (17.72 ± 4.45) presented significantly higher SBS means (in MPa) than the other groups (p<0.05), followed by EC (11.97 ± 5.77) and ED (10.57 ± 1.32). EL (5.39 ± 1.06) and UN (4.32 ± 1.98) showed the lowest SBS means, while T (9.09 ± 2.56) showed intermediate values. For ARI, there was a predominance of score 0 for EC, C and UN, and score 3 for T, ED and EL. In conclusion, the activation mode influenced the SBS.
Highlights
The light-cured composite resins are routinely used for bonding orthodontic brackets to the teeth [1,2]
No statistically significant difference was found between Enforce Light-activated (EL) and Unicem Capsule (UN); Enforce chemical (EC) and Enforce Dual (ED) (10.57±1.32); or between T and ED (p>0.05)
An adequate polymerization of composite resins under brackets is important to reduce the debonding during orthodontic treatment [9,10]
Summary
The light-cured composite resins are routinely used for bonding orthodontic brackets to the teeth [1,2]. Failures with light-cured composite resins have been attributed to moisture contamination or incomplete polymerization when considering the light exposure time or limited depth polymerization [4], which varies with the light penetration into the material [5]. Dual-curing resin cements could be used for bonding orthodontic brackets to enamel especially when effective light-activation is not possible. They are used to ensure the polymerization of the resin cement, even below opaque and thick restorations, where the light is not able to reach [6]
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