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Quintessence International



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Quintessence Int 38 (2007), No. 8     26. July 2007
Quintessence Int 38 (2007), No. 8  (26.07.2007)

Online Article, Page 706, PubMed:17823669

Online Article: Effect of size of defect on the repair strength of amalgam
Shen, Chiayi / Mondragon, Eduardo / Mjor, Ivar A.
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.

Keywords: admix, amalgam, condensation, defect, flexure strength, repair, spherical