title: Comparative study of circumferential clasp retention force for titanium and cobalt-chromium removable partial dentures.
abstract: BACKGROUND
  The interest in using titanium to fabricate removable partial denture (RPD) frameworks has increased, but there are few studies to support its use.
  
  
  OBJECTIVE
  The objective of this study was to compare circumferential RPD clasps made of commercially pure titanium and identical clasps made of 2 different cobalt (Co)-chromium (Cr) alloys by testing insertion/removal and radiographically inspecting the casts for defects.
  
  
  METHODS
  On refractory casts that represent a partially edentulous mandibular right hemi-arch segment, 36 frameworks were cast from commercially pure titanium (n = 12) and 2 Co-Cr alloys (n = 12 each) with identical prefabricated patterns and the manufacturer-designated investment and casting technique. Each group was divided into 2 subgroups, corresponding to .25-mm and .50-mm undercuts, respectively. No polishing procedures were performed to ensure uniformity. Only nodules and burs were carefully removed with tungsten burs under magnification when necessary. The specimens were radiographed and subjected to an insertion/removal test simulating 5 years of framework use. The data were subjected to analysis of variance and the Tukey complementary test (P<.01) to compare the retentive forces of RPDs made with the different materials. The Student t test (P<.01) was used to compare the retentive forces of RPDs fabricated with the same alloy with different undercuts.
  
  
  RESULTS
  A total of 20% of the titanium specimens demonstrated porosity, showing casting difficulties, and any defect detected on the clasps determined the sample replacement. For Co-Cr alloys, casting difficulties were not found. The data were subjected to analysis of variance and the Tukey complementary test to compare materials for the same undercut. For the .25-mm undercut, no significant difference was found between Magnum and Rematitan alloys; they were both different from the Remanium alloy (P<.01). For the.50-mm undercut, no significant difference was found between Co-Cr alloys; they were both different from Rematitan alloy (P<.01). The Student t test used to compare the same alloys with different undercuts showed no significant difference between Remanium with .25-mm and .50-mm undercuts. For Magnum and Rematitan alloys, there was a significant difference between different undercuts (P=.01).
  
  
  CONCLUSIONS
  Within the limitations of this simulation study, the results suggest that commercially pure titanium clasps maintained retention over a simulated 5-year period, with lower retention force than identical Co-Cr clasps.
authors.affiliation: Dental Materials and Prosthesis Department, Ribeirão Preto School of Dentistry, São Paulo University, São Paulo, Brazil.
authors.forename: Renata Cristina Silveira
authors.initials: RC
authors.lastname: Rodrigues
authors.forename: Ricardo Faria
authors.initials: RF
authors.lastname: Ribeiro
authors.forename: Maria da Gloria Chiarello
authors.initials: Mda G
authors.lastname: de Mattos
authors.forename: Osvaldo Luiz
authors.initials: OL
authors.lastname: Bezzon
mesh_terms: D000704:Analysis of Variance; D002858:Chromium Alloys; D003035:Cobalt; D003735:Dental Casting Technique; D016734:Dental Clasps; D003799:Dental Stress Analysis; D003779:Denture Design; D003781:Denture Retention / Q000295:instrumentation; D003832:Denture, Partial, Removable; D008422:Materials Testing; D016062:Porosity; D018709:Statistics, Nonparametric; D014025:Titanium
chemical_list: D002858:Chromium Alloys; D003035:Cobalt; D014025:Titanium