Surface treatment effects on amalgam repair strength

Purpose: To determine whether the use of microetching and bonding agents could improve the shear bond strength between aged and freshly added dental amalgam, simulating an amalgam repair. Materials and Methods: Aged amalgam surfaces were treated with either a carbide bur or carbide bur + microetcher (Al₂20₃3 abrasive). Five commercially-available adhesive systems were tested. Fresh amalgam was condensed through a split mold onto each prepared amalgam surface. Two control groups were included: a positive control consisting of non-repaired amalgam, and a negative control consisting of aged specimens which received neither carbide bur nor microetching preparation prior to the addition of fresh amalgam. In addition, one group received only carbide bur and another received only carbide bur and microetching treatments, without any adhesive. Following storage and thermocycling, each specimen was tested for shear bond strength. Results: The mean shear bond strength of the repaired samples treated with carbide bur alone (25.8 MPa) was not exceeded by any of the other treatments. Neither microetching nor use of an adhesive agent significantly improved amalgam-to-amaleam shear bond strength. In some cases, use of an adhesive agent significantly decreased the shear bond strength of repaired amalgam samples.