Online published on 25 November, 2013.
The purpose of the present in vitro study was to measure and compare the marginal gap of complete crown castings in Cr-Ni alloys prepared with the ringless system and conventional method using scanning electron microscope (SEM).
The study was conducted on 20 specimens. Ten central incisor tooth analogs were prepared for metal ceramic jacket crowns, duplicated and divided into 2 groups of 10 each. Wax patterns of group 1 were prepared and invested in a rigid metal ring where as the patterns of group 2 were invested in a ringless system. Castings were made in Cr- Ni alloy and seated on the respected stone dies. The margin discrepancies at the stone die- casting interface were viewed under SEM.
The difference in the mean marginal gap between the castings made with rigid metal ring and ringless system on labial, lingual, mesial and distal sides was 34.3, 45.4, 21.1 and 26.8 μm. It was statistically significant on the labial, lingual and distal sides at 5% level of reliability.
The ringless technique reduces the restriction of thermal expansion and the marginal discrepancy that is associated with the presence of metal ring.
Marginal gap, metal ring, ringless system, casting, investment expansion
