Dimensional accuracy of castings produced with ringless and metal ring investment systems.
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.