title: Photoelastic analysis of the distribution of stress in different systems of overdentures on osseous-integrated implants.
abstract: OBJECTIVE
  The aim of this study was to evaluate the distribution of generated stress around implants and adjacent bone tissue using different implant-retained overdenture designs through photoelastic analysis.
  
  
  METHODS
  Over an edentulous human mandible, achieved from a human model, 2 or 4 microunit analog abutments were embedded (Master; Conexao Systems Prosthodontics, São Paulo, Brazil), settled in the interforaminal region. Three models of photoelastic resin (Araltec Chemicals Ltda, Hunstman, Guarulhos, São Paulo, Brazil), with 2 or 4 incorporated implants and microunit abutments, were obtained from molds using silicone for duplication. Inclusion, finishing, and polishing procedures were applied on the frameworks. This study was based on 3 different mechanisms of implant-retained mandibular overdentures: O'ring (GI), bar-clip (GII) (both with 2 implants), and their association (GIII) (with 4 implants). After the adaptation of each overdenture system on the photoelastic models, 100-N alternate occlusal loads were applied on back-side and front-side regions. The photoelastic analysis was made with the aid of a plain polariscope linked to a digital camera, Sony Cybershot α100, which allowed visualization of the fringes and registration of images on digital photographs.
  
  
  RESULTS
  The results demonstrated higher tension concentrated over the GIII, with a flat distribution of stress to the posterior ridge and overload on the posterior implants. GI showed the smaller stress level, and GII, intermediate level; there was distribution of stress to the posterior ridge in these 2 groups.
  
  
  CONCLUSIONS
  The use of bar attachment proved to be a better alternative, because it showed a moderate level of tension with a more uniform stress distribution and possessed higher retention than did the ball system.
authors: Department of Prosthodontics and Periodontics, Piracicaba Dental School, State University of Campinas, Piracicaba, Brazil.
authors: Ana Carolina Masarolo
authors: AC
authors: Machado
authors: Leandro
authors: L
authors: Cardoso
authors: William Cunha
authors: WC
authors: Brandt
authors: Guilherme Elias Pessanha
authors: GE
authors: Henriques
authors: Mauro Antonio
authors: MA
authors: de Arruda Nóbilo
mesh_terms: D001732:Bite Force; D000044:Dental Abutments; D003758:Dental Implantation, Endosseous / Q000379:methods*; D019094:Dental Prosthesis, Implant-Supported; D003799:Dental Stress Analysis / Q000379:methods*; D003779:Denture Design; D003781:Denture Retention / Q000295:instrumentation / Q000379:methods*; D003828:Denture, Overlay; D004853:Epoxy Resins; D006801:Humans; D057893:Immediate Dental Implant Loading; D007575:Jaw, Edentulous / Q000601:surgery; D008334:Mandible / Q000601:surgery; D003765:Models, Dental; D010796:Phthalic Anhydrides
chemical_list: D004853:Epoxy Resins; D010796:Phthalic Anhydrides; C005752:araldite