Amalgam restoration Class II with poor marginal ridge area. A possible cause for the poor marginal ridge?

Poor marginal ridge in a Class II amalgam restoration is most often caused by FAILURE TO USE A WEDGE (or improper wedging). The WEDGE serves two critical functions: (1) SEPARATES the teeth to compensate for matrix band thickness, and (2) ADAPTS THE MATRIX BAND TO THE GINGIVAL MARGIN to prevent flash/overhang. Without proper wedging, the matrix band doesn't adapt to the proximal surface properly, resulting in poor proximal contacts and marginal ridge defects. C is correct.