title: Tensile bond strength of light-cured resin-reinforced glass ionomer cement with delayed light exposure.
abstract: In the clinical situations, the time intervals between material mixing and light exposure during bracket bonding, using light-cured resin-reinforced glass ionomer cement (LCGIC), may vary for each individual bracket. This study determined the tensile bond strengths of LCGIC subjected to various time intervals, and evaluated the durability with thermocycling. Comparisons were made between LCGIC and light-cured composite resin (LCR). Two hundred and forty bovine teeth were chosen as specimens. Light exposure was performed 5, 10, 20, and 40 min after the commencement of powder/liquid mixing. The durability was evaluated by thermocycling for 2000 times at temperatures between 5 degrees C and 55 degrees C, with a 30-s dwell time. Tensile bond strengths of LCGIC and LCR after 5 min, representing the general condition in clinical use, equaled 5.7 +/- 1.5 MPa and 5.1 +/- 2.6 MPa, respectively. For the LCGIC groups, no significant differences were seen between bond strengths with and without thermocycling. Also, no significant differences were noted among any time intervals. For the LCR groups, there were also no significant differences with and without thermocycling. The tensile bond strength of LCR showed highly significant differences within groups across time. Compared with LCR, the failure sites for brackets bonded with LCGIC appeared to be predominantly at the bracket/adhesive interface. The standard deviations of LCR were high when compared with those of LCGIC. The bond strength of LCGIC with or without thermocycling surpassed the clinically required minimum. LCGIC may be an advantageous alternative to LCR for orthodontic bracket bonding.
authors.affiliation: Department of Orthodontics, The Nippon Dental University School of Dentistry at Tokyo, 2-3-16 Fujimi, Chiyoda-ku, Tokyo 102-8158, Japan.
authors.forename: F
authors.initials: F
authors.lastname: Ando
authors.forename: A
authors.initials: A
authors.lastname: Komori
authors.forename: I
authors.initials: I
authors.lastname: Kojima