title: Retention and wear behaviors of two implant overdenture stud-type attachments at different implant angulations.
abstract: BACKGROUND
  Implant angulation should be considered when selecting an attachment. Some in vitro studies have investigated the relationship between implant angulation and changes in the retention force of the stud attachment, but few studies have evaluated the effect of cyclic loading and repeated cycles of insertion and removal on the stud attachment.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to evaluate the effects of implant angulation on the retentive characteristics of overdentures with 2 different stud attachments, an experimental system and O-rings in red and orange, after cyclic loading and repeated insertion and removal cycles.
  
  
  METHODS
  The canine region of a mandibular experimental model was fitted with 2 implant fixtures with 2 different stud attachment systems at implant angulations of 0, 15, or 30 degrees. A mastication simulator was used to simulate cyclic loading, and a universal testing machine was used to evaluate retentive force changes after repeated insertion and removal cycles. To simulate the numbers of mastication and insertion and removal cycles per annum, 400000 cyclic loadings and 1080 insertion and removal cycles were performed. Wear patterns and attachment surface deformations were evaluated by scanning electron microscopy. Data were analyzed using the Kruskal-Wallis test, Mann-Whitney U test with Bonferroni correction (α=.05/3=.017), and the paired-sample Student t test (α=.05).
  
  
  RESULTS
  When retentive forces before and after testing were compared, O-ring showed significant retention loss at all implant angulations (P<.001). In contrast, the experimental system showed little retention loss in the 0- and 15-degree models (P>.05), whereas the 30-degree model showed a significant increase in retentive force (P=.001). At all implant angulations, retention loss increased significantly for the orange O-ring, followed by the red O-ring, and the experimental system (P<.001). Scanning electron microscopy analysis showed more intense wear in the matrix than the patrix (abutment that matches to matrix) and more severe wear and deformation of the O-ring rubber matrix than of the experimental zirconia ball.
  
  
  CONCLUSIONS
  Upon completion of the experiment, wear and deformation were found for all attachment systems. Even when implants are not installed in parallel, the experimental system can be used without involving great loss of retention.
authors.affiliation: Doctoral student, Department of Prosthodontics, School of Dentistry, Pusan National University, Yangsan, Republic of Korea.
authors.forename: Jae-Won
authors.initials: JW
authors.lastname: Choi
authors.affiliation: Graduate student, Department of Prosthodontics, School of Dentistry, Pusan National University, Yangsan, Republic of Korea.
authors.forename: Ji-Hyeon
authors.initials: JH
authors.lastname: Bae
authors.affiliation: Professor, Department of Prosthodontics, School of Dentistry, Pusan National University, Yangsan, Republic of Korea.
authors.forename: Chang-Mo
authors.initials: CM
authors.lastname: Jeong
authors.affiliation: Associate Professor, Department of Prosthodontics, School of Dentistry, Pusan National University, Yangsan, Republic of Korea. Electronic address: huhjb@pusan.ac.kr.
authors.forename: Jung-Bo
authors.initials: JB
authors.lastname: Huh
mesh_terms: D000044:Dental Abutments; D003757:Dental Implantation / Q000379:methods*; D015921:Dental Implants; D019094:Dental Prosthesis, Implant-Supported; D003799:Dental Stress Analysis; D003834:Denture Precision Attachment; D003781:Denture Retention; D003828:Denture, Overlay; D006801:Humans; D066298:In Vitro Techniques; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D013499:Surface Properties
chemical_list: D015921:Dental Implants