[34] who found no statistical difference in color rebound between 6 months and 2 years. Further study is required to address the limitations of the present study. CONCLUSION Within the limits of this study, it was determined that the degree of whitening was the same Tofacitinib purchase for both power bleaching in a dental office setting and the at-home bleaching technique. There was no difference in color regression between at-home and power bleaching at the 2 week, 1 month and 3 month follow-up periods. Regression of the whitening effect occurred after 6 months. Regression was more rapid with power bleaching than with home bleaching. As for the matter of post-treatment sensitivity, both bleaching methods are clinically identical at different time intervals.

Footnotes Source of Support: This study was supported by grant from the Research Council of Mashad University of Medical Sciences, Iran. Conflict of Interest: None declared
One of the most important principles of shaping the root canal system is to maintain the original canal anatomy during a continuously tapering preparation. It is difficult to achieve this goal, especially in curved root canals because endodontic instruments are manufactured from straight metal blanks. This results in a tendency of the instrument to straighten itself inside the root canal. Thus, some areas in root canals tend to be over or under prepared.[1] Even if rotary nickel-titanium (Ni-Ti) instruments are able to maintain the canal shape in severely curved canals, the technique each rotary instrument uses can also affect the procedure.

Today, most rotary instrument systems use the crown-down technique. The technique was introduced in 1984 for manual instrumentation, in which larger files precede smaller ones, which then in turn progress further apically.[2] Lately, a new rotary instrument system, Mtwo (VDW; Munich, Germany) was introduced. With the evident design differences, the working method for the Mtwo, called single-length technique, was new for the rotary Ni-Ti systems. Actually, this was the ��standardized technique,�� which used in-hand preparations as all instruments are taken to full working length (WL) from the beginning. This new instrument system and the technique were compared with the other Ni-Ti rotary systems in previous studies.[3,4,5,6,7,8,9,10,11] However, to the best of our knowledge, the shaping ability of an instrument system using the single-length technique has not been compared previously with an instrument system using crown down technique under ��operator-related variables�� controlled Cilengitide conditions. In a previous study, we developed a computer-controlled device to control the operator-related variables and to test four different instrument systems under more standardized conditions.