Marginal leakage at the proximal gingival cavosurface of a recently restored Class II cavity can be caused by which of the following?

The presence of marginal leakage at the proximal gingival cavosurface in a Class II cavity restoration can indeed be attributed to insufficient condensation and neglecting to wedge the matrix.

When performing a Class II restoration, achieving a tight seal and maintaining the integrity of the marginal interface is critical to prevent microleakage. Insufficient condensation means that the restorative material may not be adequately compacted, leading to voids and gaps that can allow for the ingress of bacteria, saliva, or other fluids at the margins of the filling. Additionally, not wedging the matrix properly can lead to a poor adaptation of the material to the tooth structure, again increasing the chances of leakage.

Proper bonding and adequate isolation would typically work to minimize these issues, making those options less likely to contribute to leakage. A smaller matrix, while sometimes beneficial for achieving a better contour, could also create challenges if not used effectively. Lastly, using excessive material and poor technique may lead to other complications, but the direct cause of marginal leakage is more specifically tied to the inadequacies in condensation and matrix wedging.