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 cast ings produced with the conventional casting technique using a metal ring an d a technique that uses a ringless system. Material and methods, From copings fabricated on a metal die, 30 castings w ere produced from a high palladium alloy for metal ceramic restorations (Ar gedent). Ten castings were cast with Bellavest T (Bego) phosphate-bonded in vestment 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) pho sphate-bonded investment with a metal ring. The internal surface of the cas tings were not modified before seating with finger pressure. For vertical m argin 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 val ue 181 +/- 71 mu m) than the castings produced with the conventional metal ring technique (290 +/- 87 mu m and 291 +/- 58 mu m). The difference was si gnificant (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.