Investigating failure behavior and origins under supposed "shear bond" loading. Issue 7 (July 2015)

• Record Type: Journal Article
• Authors: Sultan, Hassam; Kelly, J. Robert; Kazemi, Reza B.
• Is Part Of: Dental materials. Volume 31:Issue 7(2015)
• Page Start: 807
• Page End: 813
• Publication Date: 2015-07
• Subjects: Dentistry -- Periodicals; Dental materials -- Periodicals; 617.695
• DOI: 10.1016/j.dental.2015.04.007
• Languages: English
• ISSNs: 0109-5641

Abstract

<abstract abstract-type="author" id="abs0005"> <title id="sect0005">Abstract</title> <sec> <title id="sect0010">Purpose</title> <p id="spar0005">This study evaluated failure behavior when resin-composite cylinders bonded to dentin fractured under traditional "shear" testing. Failure was assessed by scaling of failure loads to changes in cylinder radii and fracture surface analysis. Three stress models were examined including failure by: bonded area; flat-on-cylinder contact; and, uniformly-loaded, cantilevered-beam.</p> </sec> <sec> <title id="sect0015">Methods</title> <p id="spar0010">Nine 2-mm dentin occlusal dentin discs for each radii tested were embedded in resin and bonded to resin-composite cylinders; radii (mm) = 0.79375; 1.5875; 2.38125; 3.175. Samples were "shear" tested at 1.0 mm/min. Following testing, disks were finished with silicone carbide paper (240–600 grit) to remove residual composite debris and tested again using different radii. Failure stresses were calculated for: "shear"; flat-on-cylinder contact; and, bending of a uniformly-loaded cantilevered beam. Stress equations and constants were evaluated for each model. Fracture-surface analysis was performed.</p> </sec> <sec> <title id="sect0020">Results</title> <p id="spar0015">Failure stresses calculated as flat-on-cylinder contact scaled best with its radii relationship. Stress equation constants were constant for failure from the outside surface of the loaded cylinders and not with the bonded surface area or cantilevered beam. Contact failure stresses were constant over all specimen sizes. Fractography reinforced that failures originated from loaded cylinder surface and were unrelated to the bonded surface area.</p> </sec> <sec> <title id="sect0025">Conclusions</title> <p id="spar0020">"Shear bond" testing does not appear to test the bonded interface. Load/area "stress" calculations have no physical meaning. While failure is related to contact stresses, the mechanism(s) likely involve non-linear damage accumulation, which may only indirectly be influenced by the interface.</p> </sec> </abstract>