title: Effect of two different soft liners and thicknesses mediating stress transfer for immediately loaded 2-implant supported mandibular overdentures: A finite element analysis study.
abstract: BACKGROUND
  The use of soft liners as female receptacles for ball attachments retaining immediately loaded implant overdenture has been recommended to enhance osseointegration and provide a shock absorbing effect. However, which liner and which thickness is still unclear.
  
  
  OBJECTIVE
  The purpose of this finite element analysis (FEA) study was to evaluate the effect of a 2- and 4-mm thickness of thermoplastic resin (TRL) and silicone-based liners (SBL) on the displacement and stresses transmitted to immediately loaded implants retaining a mandibular overdenture.
  
  
  METHODS
  Four 3-dimensional (3D) FEA models of a mandibular implant overdenture retained by 2 ball attachments (2 models for each lining material with 2- or 4-mm liner thicknesses) were developed. Implants were placed in the canine regions and surrounded by a 1-mm cylinder of immature bone simulating immediate loading. A vertical and an oblique load of 150 N were applied in the right premolar molar regions. Stresses and displacement were set as output variables.
  
  
  RESULTS
  Replacing the TRL by the SBL was associated with a decrease in stresses by 73% and in displacement by at least 46%. Increasing the thickness of any liner decreases stresses by 45% during vertical loading and by 25% during oblique loading and decreases displacement by 61.5% during vertical loading and by an average of 32.5% during oblique loading. None of the liners exceeded the experimental risk limits for micromotion at the bone-implant interface (50 μm).
  
  
  CONCLUSIONS
  In immediately loaded mandibular implant overdentures, both SBL and TRL decrease the micromotion of implants and the stresses at the bone-implant interface. However, SBL is more effective. The thickness of both liners seems to play a major role in decreasing the stresses and displacement of periimplant tissues.
authors.affiliation: Associate Professor of Prosthodontics, Faculty of Oral and Dental Medicine, Cairo University, Cairo, Egypt. Electronic address: iman.abdelwahab@dentistry.cu.edu.eg.
authors.forename: Iman Abd-Elwahab
authors.initials: IA
authors.lastname: Radi
authors.affiliation: Associate Professor of Removable Prosthodontics, Faculty of Dental Medicine, Al-Azhar University, Cairo, Egypt.
authors.forename: Nesrin
authors.initials: N
authors.lastname: Elmahrouky
mesh_terms: D003799:Dental Stress Analysis; D003822:Denture Liners; D003828:Denture, Overlay; D020342:Finite Element Analysis; D006801:Humans; D057893:Immediate Dental Implant Loading / Q000295:instrumentation / Q000379:methods*; D008334:Mandible