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.

High speed handpieces.

High speed instruments are versatile instruments used by clinicians of all specialties of dentistry. It is important for clinicians to understand the types of high speed handpieces available and the mechanism of working. The centers for disease control and prevention have issued guidelines time and again for disinfection and sterilization of high speed handpieces. This article presents the recent developments in the design of the high speed handpieces. With a view to prevent hospital associated infections significant importance has been given to disinfection, sterilization & maintenance of high speed handpieces. How to cite the article: Bhandary N, Desai A, Shetty YB. High speed handpieces. J Int Oral Health 2014;6(1):130-2.

Comparative analysis of postcementation hypersensitivity with glass ionomer cement and a resin cement: an in vivo study.

AIM: The aim of this clinical study was to compare the postoperative sensitivity of abutment teeth restored with full coverage restorations retained with either conventional glassionomer cement (GIC) or resin cement. MATERIALS AND METHODS: Fifty patients received full-coverage restorations on vital abutment teeth. Of these, 25 were cemented with GIC (GC Luting and Lining cement) and the other 25 using an adhesive resin cement (Smartcem 2). A randomized single blind study was undertaken for acquiring and evaluating the data. The teeth were examined before cementation, after cementation, 24 hours postcementation and 7 days postcementation. A visual analog scale was used to help the patient rate hypersensitivity. RESULTS: The statistical analysis of the result was done using students paired t-test. No statistically significant difference between Smartcem 2 and GIC was observed, when tested immediately and 24 hours after cementation. Statistically significant difference was seen between Smartcem 2 and GIC when tested 7 days postcementation with a significance level of 0.05. Higher postoperative sensitivity was seen with GIC when compared to resin cement. CONCLUSION: In this study, the incidence of postoperative hypersensitivity after cementation of full-crown restorations with GIC and resin cement was similar when tested immediately. However, 7 days postcementation, abutments with GIC showed higher response compared to resin cement. CLINICAL SIGNIFICANCE: A self-adhesive resin cement can be the material of choice for luting if presence of postoperative sensitivity is of prime consideration. In case GIC is being used, patient should be informed about the presence of sensitivity for a more prolonged period than with resin cement.