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Quintessence Publishing: Journals: QI
Quintessence International

Edited by Eli Eliav

ISSN 0033-6572 (print) • ISSN 1936-7163 (online)

September 2007
Volume 38 , Issue 8

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Effect of size of defect on the repair strength of amalgam

Chiayi Shen, PhD / Eduardo Mondragon / Ivar A. Mjor, BDS, MSD, MS, Dr Odont

PMID: 17823669

Objectives: This study tested the hypothesis that the size of repair sites on amalgam restorations with mechanical undercuts on the repair surface would affect interfacial strength using a 3-point bending test. Method and Materials: Six groups of 12 rectangular bars each were fabricated from an admix alloy and a spherical alloy. Each specimen was cut into 2 equal-sized end sections, and 1 smaller midsection, which was discarded. A medium-coarse diamond disk was used to roughen and flatten the surface for repair. The 2 end sections were fit back into the original mold. The empty space in the middle was approximately 1, 1.5, and 2 mm, mimicking the size of repair sites to be filled with amalgam. There were 2 groups for each repair size; 1 group had rounded undercuts prepared on the surface for repair with a 1⁄2 round bur, and the other group received no additional treatment. Condensation was carried out with condensers having a dimension slightly less than the width of the repair defect. After 7-day storage, a 3-point bending test was used to determine the repair strengths of the specimens. Results: The strength values ranged from 33.9 to 75.6 MPa, which is comparable to published data. ANOVA showed that the mean strength values were higher with spherical amalgam (P < .0001), were lower with undercut (P = .0148), and increased as the width of repair site decreased (P < .0001). Conclusion: Reducing the dimension of the repair site improved repair strength, but rounded undercuts reduced the repair strength values slightly. (Quintessence Int 2007;38:706.e464469)

Key words:admix, amalgam, condensation, defect, flexure strength, repair, spherical

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