A comparison of the rigidity of five mandibular major connectors for partial removable dental prostheses via load deflection.

Statement of Problem: The rigidity of the major connector for partial removable dental prostheses (PRDP) has not been well defined. There is little scientific evidence to support specific standards relative to the dimensions of a casting and their effect on long-term function of the PRDP or the supporting tissues.
Purpose: The purpose of this study was to compare in vitro the effects of load deflection of 5 clinically used mandibular major connector forms.
Material and Methods: A partially edentulous dental cast of a patient with the mandibular anterior teeth remaining was used as the test model. Lingual plate (LP), continuous bar (CB), sublingual bar (SB), lingual bar (LB), and dental lingual bar (DLB) specimens (n=5) were waxed on identical refractory casts, then cast in cobalt base alloy and finished. Each specimen was placed on a custom test table and statically loaded in the contralateral second molar region with 500 g in the horizontal and vertical planes. Deflections were measured at the terminal abutment rest seat, anterior to the load. Comparisons between group means were evaluated using the Dunnett T3 method, assuming unequal variances, for all pairwise tests at a .05 significance level and for 95% confidence intervals for group mean differences. Differences within the groups for vertical versus horizontal deflections were compared using a paired t test and Bonferroni correction (alpha=.05 for all tests).
Results: Horizontal deflection between LP and LB, CB and LB, and SB and LB were significant, with the first in each comparison having the least amount of deflection. A significant difference was also seen in the vertical deflection, with the first in each comparison observed to have deflected the least for LP versus CB, LP versus LB, LP versus DLB, CB versus DLB, LB versus DLB, and SB versus DLB. The amount of vertical deflection was significantly greater than the horizontal deflection for all 5 mandibular major connectors (P< or =.033).
Conclusions: In the horizontal plane, a significant difference in the amount of deflection was seen between the LP and LB, CB and LB, and LB and SB. In the vertical plane, the LP deflected significantly less than the CB, LB, and DLB. In addition, the DLB deflected significantly more in the vertical plane when compared to the CB, LB, and SB. All 5 mandibular major connectors had a significantly greater amount of vertical deflection as compared to horizontal deflection.
(Copyright © 2010 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Mosby, Inc. All rights reserved.)