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Background: Gypsum products are being used for construction of dental prosthesis. Most of the researches done so far on gypsum materials are on its use as fixed and removable prosthodontics. And although many studies have looked at a multitude of means for altering its properties, relatively less has been explored on examining the abrasion resistance of the gypsum product itself. Objectives: The current study was done to determine the abrasion resistance of three commercially available type IV gypsum products on application of three die-hardeners when abraded with 20gm and 50gm load stylus. Methods: An experimental in vitro study was done in the Dept. of Prosthodontics, UP Dental College & Research Center and the Dept. of Pharmacy, BBD National Institute of Technology & Management, Lucknow. A standardized machined die was fabricated so that the die consisted of 27 vertical ridges of 1mm depth. Three type IV gypsum products viz., Kalrock, Elite Rock and Denstone Plus and three die-hardeners viz., Hartebad die-hardener, Handae die-hardener and Maarc die-hardener were included in the study. 40 samples were prepared from each of the die-stones by pouring into impressions made by using the putty-wash technique. Resultantly, 120 samples were prepared which were let to mature. These 120 samples were divided into 24 groups, each group consisting of 5 samples. They were grouped as uncoated, coated with Hartebad die-hardener, coated with Handae die-hardener and coated with Maarc die-hardener. They were sub-grouped further for abrading under 20gm and 50gm loads by using an abrasion-testing machine. After 10 oscillations, the loss of mass was measured using analytical electronic machine. The different findings were compared by using appropriate statistical analytic tests. Results: The abrasion resistance of type IV gypsum products increased with the application of surface-hardeners irrespective of the load and Elite Rock showed better abrasive resistance while Denstone Plus showed lesser abrasion resistance among all the type IV gypsum products tested. Conclusion: Elite Rock when coated with Hartebad die-hardener showed maximum abrasion resistance irrespective of the load applied.

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BACKGROUNDEndodontic success lies in proper instrumentation and removal of all pulp tissue, necrotic material and microorganisms from the root canal. Traditionally, the point of termination for endodontic instrumentation and obturation has been determined by taking radiographs. But just how accurate is this radiographic measurement? The purpose of this study was to compare the accuracy of third generation electronic apex locator and radiographic technique.