Related Experiment Video
Updated: Jul 11, 2026
Quasistatic Mechanical Testing for Computer-Aided Design and Manufacturing Occlusal Veneers Cemented to Milled Dentin Analog Material
Published on: December 20, 2024
Effect of size of defect on the repair strength of amalgam
Chiayi Shen1, Eduardo Mondragon, Ivar A Mjör
1Department of Dental Biomaterials, College of Dentistry, University of Florida, Gainesville, FL 32610-0446, USA.
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.
