The angle formed by the occlusal rest and the vertical minor connector should be less than 90° to ensure effective transmission of occlusal forces along the long axis of the abutment tooth. This acute angle allows the minor connector to provide adequate support and stability while minimizing leverage and displacement that could damage the tooth or the prosthesis. A less than 90° angle also facilitates proper adaptation of the rest seat and helps maintain the rigidity of the framework, ensuring controlled and favorable force distribution during function.

Reference: Contemporary Removable Partial Prosthodontics, Jacob S. Segal, 5th Edition.