Photoelastic study of the support structures of distal-extension removable partial dentures.
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.
Costa
Marcio Magno
MM
Department of Removable Prosthodontics and Dental Materials, Faculty of Dentistry, Federal University of Uberlandia, Uberlândia, Brazil. marciocosta@umuarama.ufu.br
da Silva
Marco Antonio Moreira Rodrigues
MA
Oliveira
Sonia Aparecida Goulart
SA
Gomes
Vanderlei Luiz
VL
Carvalho
Polliane Morais
PM
Lucas
Barbara Lima
BL
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