A bitewing shows a mesial amalgam on tooth 18 with a gingival overhang and a very light proximal contact. What caused this?

Correct answer: A. Inadequate wedging with poor adaptation of the matrix band

• A. CORRECT. Both faults trace to a single cause. Without a properly placed WEDGE the band does not seal at the gingival margin, so amalgam extrudes beyond it and forms an OVERHANG. The same wedge is responsible for pressing the band against the adjacent tooth and providing the slight separation that compensates for band thickness — so without it the contact is also LIGHT. One error, two visible consequences.
• B. Over-trituration affects working time and setting expansion, not band adaptation.
• C. Moisture contamination affects strength and, in zinc alloys, causes delayed expansion — it does not produce overhangs.
• D. Pulpal floor depth relates to the occlusal portion and has no bearing on the proximal contour.

Note: Overhangs are not merely cosmetic. They are plaque-retentive, unreachable by floss, and a well-documented cause of localised periodontal bone loss — they must be removed or the restoration replaced.