title: Covering of fiber-reinforced composite bars by adhesive materials, is it necessary to improve the bond strength of lingual retainers?
abstract: OBJECTIVE
  The objectives were to evaluate the shear bond strength (SBS) of fiber-reinforced composite (FRC) retainers when bonding them to teeth with and without covering the FRC bars using two different adhesive systems.
  
  
  METHODS
  Hundred and twenty extracted human maxillary premolars were randomly divided into eight groups (n = 15). FRC bars (4 mm length, Everstick Ortho(®), Stick Tech, Oy, Turku, Finland) were bonded to the proximal (distal) surfaces of the teeth using two different adhesives (Tetric Flow [TF, Ivoclar Vivadent, Switzerland] and resin-modified glass ionomer cement [RMGIC, ODP, Vista, CA, USA]) with and without covering with the same adhesive. Specimens were exposed to thermocycling (625 cycles per day [5-55°C, intervals: 30 s] for 8 days). The SBS test was then performed using the universal testing machine (Zwick, GMBH, Ulm, Germany). After debonding, the remaining adhesive on the teeth was recorded by the adhesive remnant index (0-3).
  
  
  RESULTS
  The lowest mean SBS (standard deviation) was found in the TF group without covering with adhesive (12.6 [2.11] MPa), and the highest bond strength was in the TF group with covering with adhesive (16.01 [1.09] MPa). Overall, the uncovered RMGIC (15.65 [3.57] MPa) provided a higher SBS compared to the uncovered TF. Covering of FRC with TF led to a significant increase in SBS (P = 0.001), but this was not true for RMGIC (P = 0.807). Thermal cycling did not significantly change the SBS values (P = 0.537). Overall, eight groups were statistically different (ANOVA test, F = 3.32, P = 0.034), but no significant differences in bond failure locations were found between the groups (Fisher's exact tests, P = 0.92).
  
  
  CONCLUSIONS
  The present findings showed no significant differences between SBS of FRC bars with and without covering by RMGIC. However, when using TF, there was a significant difference in SBS measurements between covering and noncovering groups. Therefore, the use of RMGIC without covering FRC bars can be suggested, which can be validated with in vivo studies.
authors.affiliation: Dental Research Center, Department of Orthodontics, Dental Research Center of Mashhad University of Medical Sciences, School of Dentistry, Mashhad, Iran.
authors.forename: Farzin
authors.initials: F
authors.lastname: Heravi
authors.affiliation: Department of Orthodontics, Hormozgan University of Medical Sciences, Bandarabbas, Iran.
authors.forename: Navid
authors.initials: N
authors.lastname: Kerayechian
authors.affiliation: Dental Research Center, Department of Operative Dentistry, Dental Research Center of Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Saied Mostafa
authors.initials: SM
authors.lastname: Moazzami
authors.affiliation: Department of Orthodontics, Dental Research Center of Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Hooman
authors.initials: H
authors.lastname: Shafaee
authors.affiliation: Department of School of Dentistry, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Parya
authors.initials: P
authors.lastname: Heravi
keywords: Adhesive; bond strength; fiber-reinforced composite; resin-modified glass ionomer cement