Dimensional accuracy of castings produced with ringless and metal ring investment systems.
BACKGROUND
The ringless casting procedure is in use in clinical dentistry, although there is no adequate scientific data to support its use.


OBJECTIVE
This study compared the vertical margin accuracy of lost wax castings produced with the conventional casting technique using a metal ring and a technique that uses a ringless system.


METHODS
From copings fabricated on a metal die, 30 castings were produced from a high palladium alloy for metal ceramic restorations (Argedent). Ten castings were cast with Bellavest T (Bego) phosphate-bonded investment with the ringless technique, 10 were cast with the same investment with a metal ring, and the final 10 were cast using Hi-temp (Whip Mix) phosphate-bonded investment with a metal ring. The internal surface of the castings were not modified before seating with finger pressure. For vertical margin discrepancy measurements, an optical microscope at a magnification of 100x was used. Data were analyzed with 1-way multivariate ANOVA (repeated measures) and the Student-Newman-Keuls test.


RESULTS
When following the manufacturers' recommendations, the castings of the ringless technique provided less vertical margin discrepancy (mean value 181 +/- 71 microm) than the castings produced with the conventional metal ring technique (290 +/- 87 microm and 291 +/- 88 microm). The difference was significant (P <. 001).


CONCLUSIONS
The ringless technique may produce accurate castings for use in fixed prosthodontics, therefore further investigation is needed to develop a protocol for its use.
Lombardas
P
P
Columbia University, School of Dental and Oral Surgery, New York, N. Y., USA. lombarda@otenet.gr
Carbunaru
A
A
McAlarney
M E
ME
Toothaker
R W
RW
D000704:Analysis of Variance; D003442:Crowns; D003734:Dental Casting Investment; D003735:Dental Casting Technique / Q000295:instrumentation*; D006801:Humans; D016876:Metal Ceramic Alloys; D003765:Models, Dental; D010865:Pilot Projects; D017755:Prosthesis Fitting; D015203:Reproducibility of Results
D003734:Dental Casting Investment; D016876:Metal Ceramic Alloys