title: The effects of two attachment types on the stresses introduced to the mandibular residual ridge: a 3D finite element analysis.
abstract: OBJECTIVE
  Two commonly used attachment systems for implant-retained overdentures are bar and ball systems. The aim of this study was to compare these two types of attachments on the basis of the stresses introduced to the mandibular posterior residual ridge by an overdenture retained by two implants.
  
  
  METHODS
  A basic model was generated from the data provided by a CT scan of a patient's mandible, the diagnostic casts, and the existing overdenture. Two root-form implants were placed in the anterior mandible. Models were used to simulate two situations: The first model represented an edentulous mandible supporting an overdenture retained by two implants connected with a bar and plastic clip system, and in the second model two ball attachments with nylon caps were used as the retention mechanism. A 35 N vertical load was introduced to the first molar region of each group to simulate the occlusal forces of the maxillary complete denture. The stresses in the mandibular residual ridges under the first molar region were measured using Ansys software.
  
  
  RESULTS
  The bar-retained overdenture introduced higher stresses to the posterior mandibular residual ridge compared to the ball-retained overdenture (0.4 MPa and 0.1 MPa, respectively).
  
  
  CONCLUSIONS
  Within the limitations of this study, the ball system was shown to introduce a lower amount of stress to the posterior mandibular residual ridge compared to a bar and clip system.
authors.affiliation: Department Prosthodontics, Boston University School of Dental Medicine, Boston, MA 02118, USA. mhdashti@bu.edu
authors.forename: Mohammad Hossein
authors.initials: MH
authors.lastname: Dashti
authors.forename: Parsa
authors.initials: P
authors.lastname: Atashrazm
authors.forename: Mehdi Imani
authors.initials: MI
authors.lastname: Emadi
authors.forename: Shiva
authors.initials: S
authors.lastname: Mishaeel
authors.forename: Sepideh
authors.initials: S
authors.lastname: Banava
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D001696:Biomechanical Phenomena; D001732:Bite Force; D003198:Computer Simulation; D000044:Dental Abutments; D003724:Dental Arch / Q000502:physiology; D015921:Dental Implants; D003764:Dental Materials / Q000737:chemistry; D019094:Dental Prosthesis, Implant-Supported; D003781:Denture Retention / Q000295:instrumentation*; D003826:Denture, Complete, Lower; D003828:Denture, Overlay; D005260:Female; D020342:Finite Element Analysis; D006047:Gold Alloys / Q000737:chemistry; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007575:Jaw, Edentulous / Q000000981:diagnostic imaging / Q000503:physiopathology; D008334:Mandible / Q000000981:diagnostic imaging / Q000502:physiology*; D008875:Middle Aged; D008954:Models, Biological; D013314:Stress, Mechanical; D014025:Titanium / Q000737:chemistry; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D000180:Acrylic Resins; D015921:Dental Implants; D003764:Dental Materials; D006047:Gold Alloys; D014025:Titanium