Statement of problem
Soldering has been suggested to achieve acceptable fit of multi-unit fixed partial denture (FPD) frameworks of 3 or more elements. However, distortion of the entire framework may occur.
The purpose of this study was to evaluate marginal fit in 1-piece-casting FPD frameworks comparing 2 casting techniques: the conventional technique (CT) and the over-refractory technique (ORT). The techniques were evaluated on castings made from commercially pure titanium (CP Ti; Tritan), titanium-aluminum-vanadium (Ti-6Al-4V), and nickel-chromium (Ni-Cr; VeraBond II) alloys.
Material and methods
A metal master cast including 3 preparations was created to simulate a 5-unit FPD. The metal cast was duplicated in vinyl polysiloxane for fabrication of 60 working casts. For the CT, 0.7-mm-thick patterns were waxed on the casts using an electrical wax-dipping unit. Patterns were removed from the preparations before investing. For the ORT, the silicone impressions were poured with an investment material (Rematitan for CP Ti and Ti-6Al-4V, and Talladium for Ni-Cr). The patterns were waxed on the refractory casts, and the assembly was invested. Both CT and ORT (n=10), CP Ti, and Ti-6Al-4V frameworks were cast using an arc-melting titanium vacuum-casting machine. The Ni-Cr frameworks were cast using an automated centrifugal-casting machine. The mean marginal discrepancies of the frameworks were measured at the mesial, distal, buccal, and lingual interfaces. Marginal gap measurements were recorded 3 times for each surface to the nearest 0.5 μm using a traveling microscope (×50). The data were analyzed with 2-way analysis of variance, followed by the Tukey HSD test (α=.05).
Marginal discrepancies for the ORT specimens (82.8 ± 1.7 μm for CP Ti; 64.4 ± 1.3 μm for Ti-6Al-4V; and 77.2 ± 1.5 μm for Ni-Cr) were significantly lower than those obtained for the CT specimens (106.3 ± 2.6 μm for CP Ti; 75.7 ± 0.8 μm for Ti-6Al-4V; 101.9 ± 1.7 μm for Ni-Cr) (P<.05). For both techniques, marginal discrepancies were significantly different among the alloys evaluated, presenting the following order from greatest to least marginal discrepancy: CP Ti, Ni-Cr alloy, and Ti-6Al-4V (P<.05).
The ORT for multi-unit FPD frameworks demonstrated significantly lower marginal discrepancies than the CT.
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Piracicaba School of Dentistry, State University of Campinas, UNICAMP, Piracicaba, Sao Paulo, Brazil
Supported by grant No. 01/07945-3 from Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP), Brazil.
© 2006 The Editorial Council of The Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.