Over-refractory casting technique as an alternative to one-piece multi-unit fixed partial denture frameworks.
BACKGROUND
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.


OBJECTIVE
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.


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 microm using a traveling microscope (x50). The data were analyzed with 2-way analysis of variance, followed by the Tukey HSD test (alpha=.05).


RESULTS
Marginal discrepancies for the ORT specimens (82.8 +/- 1.7 microm for CP Ti; 64.4 +/- 1.3 microm for Ti-6Al-4V; and 77.2 +/- 1.5 microm for Ni-Cr) were significantly lower than those obtained for the CT specimens (106.3 +/- 2.6 microm for CP Ti; 75.7 +/- 0.8 microm for Ti-6Al-4V; 101.9 +/- 1.7 microm 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).


CONCLUSIONS
The ORT for multi-unit FPD frameworks demonstrated significantly lower marginal discrepancies than the CT.
de Oliveira Correa
Giovani
G
Department of Restorative Dentistry, Piracicaba School of Dentistry, State University of Campinas, UNICAMP, Sao Paulo, Brazil.
Henriques
Guilherme Elias Pessanha
GE
Mesquita
Marcelo Ferraz
MF
Sobrinho
Lourenco Correr
LC
D000497:Alloys; D002133:Calcium Sulfate / Q000737:chemistry; D002858:Chromium Alloys / Q000737:chemistry; D003722:Dental Alloys / Q000737:chemistry*; D003734:Dental Casting Investment / Q000737:chemistry; D003735:Dental Casting Technique / Q000295:instrumentation; D003760:Dental Impression Materials / Q000737:chemistry; D003779:Denture Design; D003830:Denture, Partial, Fixed; D006244:Hardness; D006358:Hot Temperature; D006801:Humans; D008853:Microscopy; D011145:Polyvinyls / Q000737:chemistry; D012833:Siloxanes / Q000737:chemistry; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry
D000497:Alloys; D002858:Chromium Alloys; D003722:Dental Alloys; D003734:Dental Casting Investment; D003760:Dental Impression Materials; D011145:Polyvinyls; D012833:Siloxanes; C034183:vinyl polysiloxane; C031462:titanium alloy (TiAl6V4); D014025:Titanium; D002133:Calcium Sulfate