title: Timing considerations on the shear bond strength of orthodontic brackets after topical fluoride varnish applications.
abstract: OBJECTIVE
  To assess the best temporal association between the application of a fluoride varnish on enamel and bonding procedures.
  
  
  METHODS
  Eighty mandibular bovine incisors were used. Teeth were divided into 4 groups (20 per group); Groups 1-3 were treated with fluoride varnish (Fluor Protector, Ivoclar Vivadent, Schaan, Liechtenstein), and Group 4 served as control with no pretreatment. Tooth were stored in deionized water (37°C) and subjected to thermal cycling for 400 (Group 1), 800 (Group 2), and 2500 (Group 3) cycles corresponding, respectively, to 15, 30, and 90 days in order to simulate the three different timing of bracket bonding. Shear bond strength (SBS) was measured using an Instron Universal Testing machine. Tooth surfaces were examined under a stereomicroscope at 10× magnification to assess the amount of adhesive remnant index (ARI). One-way analysis of variance (ANOVA) and Tukey's honestly significant difference post-hoc test were used for the comparison of SBS values between groups (P< 0.05). The Chi-square test was used to examine differences among ARI scores. (P< 0.05).
  
  
  RESULTS
  One-way ANOVA and Tukey post-hoc test showed that the SBS of different groups were significantly different and was impacted by different timing of bonding (P< 0.05). The main differences were between the control group (17.02 ± 6.38 MPa) and Group 1 (6.93 ± 4.3 MPa). The ARI scores showed that there were no significant differences between the four tested groups.
  
  
  CONCLUSIONS
  The SBS of the brackets bonded 15 days after the application of the fluoride was set back to an optimal value.
authors.affiliation: Department of Biomedical, Surgical and Dental Sciences, School of Dentistry, University of Milan, Milan, Italy.
authors.forename: Gianguido
authors.initials: G
authors.lastname: Cossellu
authors.affiliation: Department of Biomedical, Surgical and Dental Sciences, School of Dentistry, University of Milan, Milan, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Lanteri
authors.affiliation: Department of Clinical, Surgical, Diagnostic and Pediatric Sciences, University of Pavia, Pavia, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Butera
authors.affiliation: Department of Dentistry, Galliera Hospital, Genoa, Italy.
authors.forename: Nicola
authors.initials: N
authors.lastname: Laffi
authors.affiliation: Department of Dentistry, Galliera Hospital, Genoa, Italy.
authors.forename: Alberto
authors.initials: A
authors.lastname: Merlini
authors.affiliation: Department of Biomedical, Surgical and Dental Sciences, School of Dentistry, University of Milan, Milan, Italy.
authors.forename: Giampietro
authors.initials: G
authors.lastname: Farronato
keywords: Fluoride varnish; orthodontic brackets; shear bond strength; topical fluoride