Comparison of the Solubility of Conventional Luting Cements with that of the Polyacid Modified Composite Luting Cement and Resin-modified Glass lonomer Cement.

INTRODUCTION: This study was planned to find the solubility of the conventional luting cements in comparison with that of the polyacid-modified composite luting cement and recently introduced resin-modified glass ionomer cement (RMGIC) with exposure to water at early stages of mixing. MATERIALS AND METHODS: An in vitro study of the solubility of the following five commercially available luting cements, viz., glass ionomer cement (GIC) (Fuji I, GC), zinc phosphate (Elite 100, GC), polyacid-modified resin cement (PMCR) (Principle, Dentsply), polycarboxylate cement (PC) (Poly - F, Dentsply), RMGIC (Vitremer, 3M), was conducted. For each of these groups of cements, three resin holders were prepared containing two circular cavities of 5 mm diameter and 2 mm depth. All the cements to be studied were mixed in 30 seconds and then placed in the prepared cavities in the resin cement holder for 30 seconds. RESULTS: From all of the observed luting cements, PMCR cement had shown the lowest mean loss of substance at all immersion times and RMGIC showed the highest mean loss of substanceat all immersion times in water from 2 to 8 minutes. The solubility of cements decreased by 38% for GIC, 33% for ZnPO4, 50% for PMCR, 29% for PC, and 17% for RMGIC. CONCLUSION: The PMCR cement (Principle-Dentsply) had shown lowest solubility to water at the given time intervals of immersion. This was followed by PC, zinc phosphate, and GIC to various time intervals of immersion.

Marginal accuracy of nickel chromium copings fabricated by conventional and accelerated casting procedures, produced with ringless and metal ring investment procedures: A comparative in vitro study.

BACKGROUND: Conventional investing and casting techniques are time-consuming and usually requires 2-4 h for completion. Accelerated nonstandard, casting techniques have been reported to achieve similar quality results in significantly less time, namely, in 30-40 min. During casting, it is essential to achieve compensation for the shrinkage of solidifying alloy by investment expansion. The metal casting ring restricts the thermal expansion of investment because the thermal expansion of the ring is lesser than that of the investment. The use of casting ring was challenged with the introduction of the ringless technique. MATERIALS AND METHODS: A total of 40 test samples of nickel chromium (Ni-Cr) cast copings were obtained from the patterns fabricated using inlay casting wax. The 20 wax patterns were invested using metal ring and 20 wax patterns were invested using the ringless investment system. Of both the groups, 10 samples underwent conventional casting, and the other 10 underwent accelerated casting. The patterns were casted using the induction casting technique. All the test samples of cast copings were evaluated for vertical marginal gaps at four points on the die employing a stereo optical microscope. RESULTS: The vertical marginal discrepancy data obtained were tabulated. Mean and standard deviations were obtained. Vertical discrepancies were analyzed using analysis of variance and Tukey honestly significantly different. The data obtained were found to be very highly significant (P < 0.001). Mean vertical gap was the maximum for Group II (53.64 µm) followed by Group IV (47.62 µm), Group I (44.83 µm) and Group III (35.35 µm). CONCLUSION: The Ni-Cr cast copings fabricated with the conventional casting using ringless investment system showed significantly better marginal fit than that of cast copings fabricated from conventional and accelerated casting with metal ring investment and accelerated casting using ringless investment since those copings had shown the least vertical marginal discrepancies among the four methods evaluated in this study.