title: Photoelastic study of the support structures of distal-extension removable partial dentures.
abstract: OBJECTIVE
  The double system of support, in which the distal-extension removable partial denture adapts, causes inadequate stress around abutment teeth, increasing the possibility of unequal bone resorption. Several ways to reduce or more adequately distribute the stress between abutment teeth and residual ridges have been reported; however, there are no definitive answers to the problem. The purpose of this study was to analyze, by means of photoelasticity, the most favorable stress distribution using three retainers: T bar, rest, proximal plate, I bar (RPI), and circumferential with mesialized rest.
  
  
  METHODS
  Three photoelastic models were made simulating a Kennedy Class II inferior arch. Fifteen dentures with long saddles, five of each design, were adjusted to the photoelastic patterns and submitted first to uniformly distributed load, and then to a load localized on the last artificial tooth. The saddles were then shortened and the tests repeated. The quantitative and qualitative analyses of stress intensity were done manually and by photography, respectively. For intragroup analyses the Wilcoxon test for paired samples was used, while for intergroup analyses Friedman and Wilcoxon tests were used to better identify the differences (p < 0.05).
  
  
  RESULTS
  The RPI retainer, followed by the T bar, demonstrated the best distribution of load between teeth and residual ridge. The circumferential retainer caused greater concentration of stress between dental apexes. Stress distribution was influenced by the type of retainer, the length of the saddle, and the manner of load application.
  
  
  CONCLUSIONS
  The long saddles and the uniformly distributed loads demonstrated better distribution of stress on support structures.
authors.affiliation: Department of Removable Prosthodontics and Dental Materials, Faculty of Dentistry, Federal University of Uberlandia, Uberlândia, Brazil. marciocosta@umuarama.ufu.br
authors.forename: Marcio Magno
authors.initials: MM
authors.lastname: Costa
authors.forename: Marco Antonio Moreira Rodrigues
authors.initials: MA
authors.lastname: da Silva
authors.forename: Sonia Aparecida Goulart
authors.initials: SA
authors.lastname: Oliveira
authors.forename: Vanderlei Luiz
authors.initials: VL
authors.lastname: Gomes
authors.forename: Polliane Morais
authors.initials: PM
authors.lastname: Carvalho
authors.forename: Barbara Lima
authors.initials: BL
authors.lastname: Lucas
mesh_terms: D001696:Biomechanical Phenomena; D000044:Dental Abutments; D016734:Dental Clasps; D003799:Dental Stress Analysis; D003819:Denture Bases; D003779:Denture Design; D003781:Denture Retention / Q000295:instrumentation / Q000379:methods*; D003832:Denture, Partial, Removable; D004548:Elasticity; D007839:Functional Laterality; D006801:Humans; D008334:Mandible; D003765:Models, Dental; D018709:Statistics, Nonparametric; D013314:Stress, Mechanical