Background: Screw loosening is one of the most common problems associated with implant-supported prostheses. The type and material of the abutment play an important role in the esthetic appearance of implant-supported restorations. Metal abutments create an unaesthetic grayish halo in the gingival margin of the implant due to the reflection of light from the surface of Titanium abutment. Zirconia is highly popular for the fabrication of abutments due to its optimal color, along with the quality of light transmission and its resistance. The present study aimed to evaluate the torque loss in Titanium and one-and two-piece zirconia abutments under cyclic loading. Methods: In general, 24 abutments in three groups (n=8) of one-and two-piece zirconia abutments, and Titanium abutments were evaluated in this experimental study. The abutments were attached to the analog of fixtures with 30 N/cm torque and the samples were subjected to loads applied to the center of abutments at 30° angle. After cyclic loading, the removal torque value was measured for each abutment and its numerical mean was calculated as well. Finally, the groups were compared using SPSS16 via ANOVA and Games-Howell tests at a 0. 05 level of significance. Results: The mean removal torque value was 23. 925, 23. 913, and 22. 538 N/cm in Titanium and two-and one-piece zirconia abutments, respectively, with no statistically significant difference in between (P>0. 05). Conclusions: The highest mean removal torque value belonged to prefabricated Titanium abutments while the lowest value was related to one-piece zirconia abutments.

Titanium (Ti) is the ninth most abundant element on earth. The Titanium mineral ores are widely distributed in different parts of the world. The two main ores of Titanium include rutile (TiO2) and ilmenite (FeO. TiO2). It is aimed to provide the readers with an insight to the main processes currently employed to extract and recover Titanium tetrachloride (TiCl4) from different Titanium ores. Due to the crucial importance of TiCl4 catalyst in the synthesis and polymerization of polyolefins, the present work examines the literature and developments made in the processing of ilmenite and rutile ores for the extraction of TiCl4. The attention has been paid to the chlorination processes and the main parameters affecting the recovery of TiCl4. Different approaches developed to date are reviewed. Different processes, reaction mechanisms and conditions as well as the kinetic models developed for extraction and purification of TiCl4 in fluidized bed reactors are also reviewed. A literature survey on the combined fluidized bed reactor systems developed for achieving a high-grade synthetic rutile via selective chlorination of low-grade Titanium ores having high metal oxides content such as magnesium oxide (MgO) and calcium oxide (CaO) is also reported. Different strategies adopted to avoid agglomeration process during the extraction process are discussed too.