title: Comparison of clasp retention on enamel and composite resin-recontoured abutments following repeated removal in vitro.
abstract: BACKGROUND
  Loss of prosthetic retention over time is a concern with removable prostheses. Use of composite resin to modify an abutment contour receiving a removable partial denture clasp may offer a reasonable, less invasive method of improving removable prosthesis retention.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the removal force of clasps over composite resin-recontoured abutments during a simulated 4 years of service.
  
  
  METHODS
  Twenty first mandibular premolars were selected to form 2 groups of specimens (n=5) resembling a tooth-supported edentulous space. A packable composite resin (Filtek P60) was used to create a 0.25-mm undercut on the buccal abutment surfaces of the composite resin group. Teeth in the natural abutment group were mounted in angulation to produce 0.25-mm undercuts on the buccal surfaces. The chrome-cobalt framework consisted of 2 individually fabricated T-clasps. Both groups were subjected to 4500 cycles of repeated removal using a small shaker. Removal forces were recorded before the repeated removal test (T(0)), after 500 and 1000 cycles, and at 1000-cycle intervals thereafter. The mean values of forces between the 2 groups were compared at each stage using the Mann-Whitney test (alpha=.05).
  
  
  RESULTS
  No debonding occurred during the test. At T(0), the highest and lowest force values were observed in the composite resin group (3.75 N and 17.5 N, respectively). There was a significant difference between the removal forces of the 2 groups after 500 cycles and at test completion (P=.008). Retention loss was 3 times greater in the composite resin group than in the natural abutments group (53.65% vs. 15.80%).
  
  
  CONCLUSIONS
  Within the limitations of the study, removal forces of the composite resin-recontoured abutments were threefold less than those of natural abutments after 4 years of simulated service.
authors.affiliation: Dental School, Tehran University of Medical Sciences, Tehran 14176-14411, Iran.
authors.forename: Simindokht
authors.initials: S
authors.lastname: Zarrati
authors.forename: Leyla
authors.initials: L
authors.lastname: Sadighpour
authors.forename: Ghasem
authors.initials: G
authors.lastname: Jahanian
mesh_terms: D003188:Composite Resins; D000044:Dental Abutments; D016734:Dental Clasps; D003743:Dental Enamel; D019554:Dental Restoration Wear; D003799:Dental Stress Analysis; D003781:Denture Retention / Q000295:instrumentation*; D006801:Humans; D019231:Tooth Preparation, Prosthodontic
chemical_list: D003188:Composite Resins