title: Effect of the number of supporting implants on mandibular photoelastic models with different implant-retained overdenture designs.
abstract: OBJECTIVE
  The purpose of the study was to evaluate the effect of the number of supporting implants and different retentive mechanisms on load transfer characteristics of mandibular overdentures.
  
  
  METHODS
  Two photoelastic models of edentulous mandibles were fabricated having two and four cylindrical implants (Calcitek, 4 × 13 mm) embedded in the parasymphyseal area. Four attachment systems were evaluated: single anchor attachment (ERA), bar-clip, bar with distally placed ball attachments, and bar with distally placed extracoronal rigid attachments (Easy Slot). A 133 N vertical force was applied unilaterally to the central fossa of the right first molar. The resulting stresses of the models were observed and recorded photographically in the field of a circular polariscope.
  
  
  RESULTS
  The highest stresses were observed with the bar with distally placed extracoronal rigid attachment (Easy Slot) design, followed by bar-ball, bar, and the single anchor attachment (ERA) for both models. The lowest stress was observed with the single anchor attachment (ERA) design for both models. There were slight differences in stress values around implants in both models.
  
  
  CONCLUSIONS
  For all tested attachments on both models, the stress was concentrated on the ipsilateral implant. The bar-clip system allowed the distribution of load to all supporting implants in both models. Although the highest stress level observed with all attachment systems was moderate, the bar-Easy Slot attachment showed the highest stresses. The lowest stress was observed with the single anchor attachment (ERA) design for both models. Varying the number of implants had no significant effect on stress values around supporting implants.
authors.affiliation: Department of Prosthodontics, Bezmialem University School of Dentistry, Istanbul, Turkey.
authors.forename: Gozde
authors.initials: G
authors.lastname: Celik
authors.forename: Bulent
authors.initials: B
authors.lastname: Uludag
mesh_terms: D001696:Biomechanical Phenomena; D001732:Bite Force; D003722:Dental Alloys / Q000737:chemistry; D015921:Dental Implants; D019094:Dental Prosthesis, Implant-Supported; D003779:Denture Design; D003781:Denture Retention / Q000295:instrumentation*; D003826:Denture, Complete, Lower; D003828:Denture, Overlay; D006801:Humans; D007575:Jaw, Edentulous / Q000503:physiopathology; D008334:Mandible / Q000502:physiology*; D008422:Materials Testing; D008953:Models, Anatomic; D013314:Stress, Mechanical
chemical_list: D003722:Dental Alloys; D015921:Dental Implants
keywords: Load transfer; implant-retained overdenture; number of implants; photoelastic stress analysis; prosthesis design