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Dimensional accuracy of castings produced with ringless and metal ring investment systems
P Lombardas1, A Carbunaru, M E McAlarney
1Columbia University, School of Dental and Oral Surgery, New York, N. Y., USA. lombarda@otenet.gr
Statement Of Problem:
The ringless casting procedure is in use in clinical dentistry, although there is no adequate scientific data to support its use.
Purpose:
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.
Material And 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).
Conclusion:
The ringless technique may produce accurate castings for use in fixed prosthodontics, therefore further investigation is needed to develop a protocol for its use.