The minimum occlusal clearance for an all-metal crown is 1-1.5 mm to provide sufficient space for the metal alloy thickness while maintaining crown strength and proper occlusion. Less than 1 mm clearance risks inadequate crown thickness, leading to fracture or distortion during function. More clearance than necessary may cause excessive tooth structure removal, compromising tooth integrity. This dimension ensures a durable restoration with optimal fit and occlusal harmony, critical for longevity and patient comfort.

Reference: Sturdevant's Art and Science of Operative Dentistry, Roberson, 6th Edition.