The longer and more parallel opposing walls of a cast restoration

The gingival-to-occlusal divergence of these preparation walls may range from 2 to 5 degrees per wall from the line of draw. If the vertical walls are unusually short, a maximum of 2 degrees occlusal divergence is desirable to increase retention potential. As the occlusogingival height increases, the occlusal divergence should increase because lengthy preparations with minimal divergence (more parallel) may present diiculties during the seating and withdrawal of the restoration. Sturdevant Operative Dentistry 7th edition page. e97