The highest mercury concentration in amalgam filling is found:
Mercury analysis of a large number of restorations reveals that the mercury content of the marginal areas averages between 2% to 3% higher than the bulk of the restoration. This is true regardless of the condensation method or the “dryness” of the increments used to build the restoration.
Reference: PHILLIPS’ SCIENCE OF DENTAL MATERIALS, 12th ed page no 352
At the margin of the restoration
In the centre of the restoration
In the deepest part of the restoration
None of the above