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Apexification aims to induce apical closure of the open root apex with a hard-tissue barrier, against which a root filling can be compacted. Mineral trioxide aggregate (MTA) is a potential apical barrier material with good sealability and a high degree of biocompatibility. The main technical problem associated with placement is to prevent overfill and underfill. This paper demonstrates retreatment of an open apex tooth by placement of an apical barrier using MTA and PRF membrane as an internal matrix followed by application of anatomical post and core. This new technique is particularly advantageous in teeth which have open apex, root canals that are not round, wide canals and thin radicular dentin. How to cite this article Chande KP, Manwar NU, Chandak MG, Lokade J. Retreatment of a Mutilated Tooth with Open Apex by using PRF, MTA and Anatomic Post. Int J Prosthodont Restor Dent 2013;3(3):105-110.

Background and objectives This in vitro study evaluated and compared the abrasion resistance of types IV and V gypsums, resin-modified type IV and type V gypsums, synthetic gypsum, and epoxy resin die material at two different time intervals spanning a period of 24 hours. Materials and methods A total of 10 dies of each die material were fabricated and tested for abrasion resistance at each time interval. An average of five readings was taken for the test, measuring the rate of abrasion of the materials. Results All the tested properties of the epoxy resin material were far superior to those of the other materials (being tested). Resin-modified type IV gypsum had significantly better abrasion resistance than its type V counterpart at setting. However, when tested at 24 hours, both materials had comparable resistance to abrasion, which was the highest among the gypsum-based materials. Interpretation and conclusion Epoxy die resin had the most superior physical properties of all. A significant decrease in the rate of abrasion (-38 to -83%) was noted, when the gypsumbased products were tested at 24 hours. From the data obtained in this study, it is recommended that when gypsum-based materials are used, to wait at least 24 hours prior to separating casts from impressions (and subsequent laboratory procedures) to avoid damage to the casts and dies. Abbreviations RR IV: Resin modified type IV gypsum; RR V: Resin modified type V gypsum; S: Synthetic gypsum; V: Type V gypsum; IV: Type IV gypsum. How to cite this article Wankhade SV, Sanghavi KV, Rajguru V, Lokade J. A Comparative Evaluation of Six Commonly used Types of Die Materials for the Property of Abrasion Resistance, at Two Time Intervals: An in vitro Study. Int J Prosthodont Restor Dent 2013;3(1):1-6.