title: In vitro debonding of orthodontic retainers analyzed with finite element analysis.
abstract: OBJECTIVE
  The aim of this in vitro study was to determine the load and deflection at failure of different lingual retainers bonded with composite to enamel in a standardized three-point bending test. The results were rationalized with finite element analysis (FEA) models.
  
  
  METHODS
  Four types of multistranded wires, Dead Soft Respond, Twisted ligature, Penta-One, Gold-plated Penta-One, and two glass fibre-reinforced composite retainers, Fibre 07 and Fibre 09, were bonded to enamel with composite and submitted to a three-point bending test. The load and deflection at failure and the mode of debonding were recorded. The stiffness of the wires was determined and all experimental data were used in FEA models to rationalize the observed values and mode of debonding.
  
  
  RESULTS
  Significant higher load and deflection were found for the most flexible retainers Twisted ligature and Dead Soft Respond. All retainers failed between the wire and composite, which was confirmed by FEA showing the highest stress in the composite around the retainer. The FEA models showed that the amount of composite used for bonding the retainers should be 2-4mm.
  
  
  CONCLUSIONS
  Based on the in vitro results, optimal bonding of lingual retainers can be achieved by flexible retainers, bonded with intrinsically strong composites. According to the FEA models the retainer should be bonded with 2-4mm composite, leaving the critical 'free-wire' length for the success of the retainer system.
authors.affiliation: Department of Dental Materials Sciences, ACTA, University of Amsterdam and VU University, The Netherlands A.Milheiro@acta.nl.
authors.forename: Ana
authors.initials: A
authors.lastname: Milheiro
authors.affiliation: Department of Dental Materials Sciences, ACTA, University of Amsterdam and VU University, The Netherlands.
authors.forename: Niek
authors.initials: N
authors.lastname: de Jager
authors.affiliation: Department of Dental Materials Sciences, ACTA, University of Amsterdam and VU University, The Netherlands.
authors.forename: Albert J
authors.initials: AJ
authors.lastname: Feilzer
authors.affiliation: Department of Dental Materials Sciences, ACTA, University of Amsterdam and VU University, The Netherlands.
authors.forename: Cornelis J
authors.initials: CJ
authors.lastname: Kleverlaan
mesh_terms: D000818:Animals; D002417:Cattle; D003188:Composite Resins / Q000737:chemistry; D003722:Dental Alloys / Q000737:chemistry; D001840:Dental Bonding / Q000379:methods; D003743:Dental Enamel / Q000648:ultrastructure; D003764:Dental Materials / Q000737:chemistry; D055119:Elastic Modulus; D004548:Elasticity; D004868:Equipment Failure; D020342:Finite Element Analysis; D005898:Glass / Q000737:chemistry; D006047:Gold Alloys / Q000737:chemistry; D008422:Materials Testing; D016382:Orthodontic Appliance Design; D018704:Orthodontic Retainers; D009969:Orthodontic Wires; D018583:Pliability; D013314:Stress, Mechanical
chemical_list: D003188:Composite Resins; D003722:Dental Alloys; D003764:Dental Materials; D006047:Gold Alloys; C009753:fiberglass