Abstract
The aim of this study was to assess the influence of etching and light-curing time on the shear bond strength (SBS) and adhesive remnant index (ARI) of a resin-modified glass ionomer cement (RMGIC) upon debonding of orthodontic brackets. Sixty-eight bovine permanent incisors were obtained and embedded in acrylic resin. Edgewise metallic brackets were bonded to the teeth with Fuji Ortho LC RMGIC. The specimens were randomly assigned to 4 groups, using the following etching and light-curing times: G1: 10% polyacrylic acid and 40 s (control); G2: 37% phosphoric acid and 40 s; G3: 10% polyacrylic acid and 50 s; and G4: 37% phosphoric acid and 50 s. Shear test was performed at 0.5 mm/min and the ARI was assessed. G2 (3.6 ± 0.98 MPa) presented significantly higher (p<0.05) SBS than G1 (2.76 ± 0.86 MPa) and G4 (2.86 ± 0.68 MPa), and there was no statistically significant difference (p>0.05) between G2 and G3 (2.94 ± 0.67 MPa). ARI presented prevalence of scores 2 and 3 in all groups. RMGIC SBS enhanced with 37% phosphoric acid etching and 40 s light-curing time, but this did not occur when the light-curing time was increased, regardless of the acid used. RMGIC presented prevalence of failures at the adhesive/bracket interface.
Highlights
Since etching was introduced by Buonocore (1) and Newman (2) began direct bonding of orthodontic attachments, composite resin has been the most commonly used bonding system in Orthodontics due to its higher bond strength compared to other materials (3)
Methods of increasing resin-modified glass ionomer cement (RMGIC) shear bond strength (SBS) are sought due to its higher biocompatibility when compared to composite resins
A lack of standardization in the methods used for bond strength testing in Orthodontics makes comparison of different studies difficult and often impossible (12)
Summary
Since etching was introduced by Buonocore (1) and Newman (2) began direct bonding of orthodontic attachments, composite resin has been the most commonly used bonding system in Orthodontics due to its higher bond strength compared to other materials (3). Composite resin presents some disadvantages such as the lack of fluoride protection, which increases the risk of white spot formation close to bonded orthodontic brackets (4), the need of a completely dry operative field throughout the bonding procedure (5), and the possibility of enamel damage during debonding (3). All these shortcomings led to the introduction of fluoride-releasing composite resins for clinical purposes. The use of these materials were later discontinued either due to an increased incidence of bond failure or because composite resin released fluoride in very small amounts (6,7). The favorable characteristics of GICs include continuous fluoride release, acting as a reservoir of fluoride absorbed from toothpastes and oral rinses (6), both inhibiting bacterial acid metabolism and activity (9) and minimizing enamel decalcification (6); biocompatibility; chemical bonding both to enamel and dentin that makes etching treatment of enamel unnecessary (3); effective bonding in a moist environment without the need for an additional bonding agent layer; and higher frequency of bond failure either at the adhesive-bracket interface or cohesive fracture in
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