Evaluation of retention in amalgam after bending pins and the associated stresses produced during the bending procedures
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The present study was undertaken to determine if self-threading pins bent to a certain angle have deleterious effects on the tensile strength of a pin-restoration system. The effects of two methods of bending pins, the use of TMS bending tool and the use of an amalgam condensing instrument exerting a direct pushing action on the pin, were compared using a tensil strength test and a photoelastic evaluation. Forty six extracted teeth were prepared to receive one self-threading pin. Each pin, 2 mm long, was bent, using either method, at 15 degrees, 30 degrees, 45 degrees and 60 degrees. A group of unbent pins was left as control. Amalgam was condensed around the pin, completely embedding it. Each specimen was tested in a Intron machine for tensile strength. In the second part of the study, a photoelastic plastic model was used to represent a tooth with lost coronal structures, in which a self threading pin was inserted. The two bending methods were compared for stress production. The results of this study indicated a significant loss of tensile strength of a pin-restoration system when pins were bent at an angle greater than 30 degrees for the bending tool method and greater than 15 degrees with the amalgam condenser method. Furthermore, stresses generated in the tooth by the bending methods were greater with the use of an amalgam condenser than a bending tool. These findings lead to the following conclusions: - Pins should not be bent more than 30 degrees when a bending tool is used. - Pins should not be bent more than 15 degrees when an amalgam condenser is used. - The use of a bending tool is strongly recommended because it does not produce as much stress in dentin as an amalgam condenser.
PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact firstname.lastname@example.org.Some colored photographs also included.Thesis (M.Sc.D.)--Boston University, Henry M. Goldman School of Graduate Dentistry (Operative Dentistry/Biomaterials), 1982.Bibliography: leaves 78-83.93,981 c.1 94,455 c.2.
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