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  • Title: The effect of design modifications on the torsional and compressive rigidity of U-shaped palatal major connectors.
    Author: Green LK, Hondrum SO.
    Journal: J Prosthet Dent; 2003 Apr; 89(4):400-7. PubMed ID: 12690354.
    Abstract:
    STATEMENT OF PROBLEM: Rigidity is a requirement of removable partial denture frameworks. Although commonly used by dentists, the U-shaped (horseshoe) maxillary major connector lacks the rigidity of other maxillary major connector designs. PURPOSE: The purpose of this study was to determine the effects of changing width, thickness, and shape on the rigidity of U-shaped maxillary major connectors. MATERIAL AND METHODS: Five nickel-chrome alloy frameworks were fabricated from the same master cast for each of 4 different U-shape removable partial denture designs. The designs were an 8-mm wide U-shaped strap with a 6-mm posterior strap (A-P strap), a 13-mm-wide U-shape strap (Wide), an 8-mm-wide U-shape strap that widened to 13 mm at the midline (Notch), and an 8-mm-wide U-shaped strap that was twice the thickness of the other straps (Thick). A fifth group of 5 frameworks was made by removing the posterior strap from the A-P strap frameworks (A strap). Two testing points were marked on each framework corresponding to the first premolar and second molar positions. The frameworks were mounted in a universal testing machine, and vertical (torsional) and horizontal (compressive) loads were applied using a 10-kN load cell at a cross-head speed of 2 mm/min until a deflection of 1 mm occurred. A force-deflection curve was generated for each test, and slope of the curves (N/mm) was compared with analysis of variance and Scheffe's F test (alpha=0.05). RESULTS: The Thick group was found to be significantly more rigid (P<.05) than the other frameworks when torsional loads were applied to both the premolar (22.42 N/mm) and molar (10.88 N/mm) areas, and when a compressive load was applied to the premolar (232.85 N/mm) area. The A-P strap group was significantly more rigid (P< or =.05) than the other designs when a compressive load was applied to the molar (69.56 N/mm) area. Both the Thick and A-P strap groups were significantly more rigid (P<.05) than the Notch and A strap groups in all tests. CONCLUSION: Doubling the thickness of the anterior strap of a U-shaped maxillary major connector improved the rigidity of the framework to torsional loads. A posterior strap became more effective in maintaining framework rigidity to compressive forces as the length of the arch increased.
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