title: Effect of size of defect on the repair strength of amalgam.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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).
  
  
  CONCLUSIONS
  Reducing the dimension of the repair site improved repair strength, but rounded undercuts reduced the repair strength values slightly.
authors.affiliation: Department of Dental Biomaterials, College of Dentistry, University of Florida, Gainesville, FL 32610-0446, USA.
authors.forename: Chiayi
authors.initials: C
authors.lastname: Shen
authors.forename: Eduardo
authors.initials: E
authors.lastname: Mondragon
authors.forename: Ivar A
authors.initials: IA
authors.lastname: Mjör
mesh_terms: D003723:Dental Amalgam / Q000737:chemistry*; D017269:Dental Prosthesis Repair / Q000379:methods*; D019232:Dental Restoration Failure; D003793:Dental Restoration, Permanent / Q000295:instrumentation / Q000379:methods*; D018583:Pliability; D013718:Tensile Strength