How is primary retention of Class II gold inlay achieved?

Primary retention of Class II gold inlays is typically achieved by utilizing a combination of techniques such as adding an occlusal dovetail, increasing parallelism of walls, and lengthening axial walls. This is because these methods allow for a better fit of the inlay, which results in improved retention and stability. Options A, C, and D may also play a role in the retention of the inlay, but they are not the primary methods used. Bonding agents, chemical adhesion, and silane coupling agents may aid in retention, but they are not the main techniques used in achieving primary retention for class II gold inlays.