When preparing a gold crown on a tooth with minimal remaining structure, which feature is MOST important to improve retention?

Retention grooves (placed in the axial walls) are the primary method to improve retention and resistance form in compromised preparations with minimal tooth structure. For gold crowns, grooves in the lingual surface or vertical grooves in the axial walls significantly increase resistance to displacement. Increasing taper would REDUCE retention. Auxiliary features like grooves, boxes, and pins compensate for inadequate height of contour.