The minimum distance between a dental implant and the periodontal ligament (PDL) of adjacent teeth should be 1 mm to preserve the vitality and health of the PDL and surrounding bone. Maintaining this space prevents damage to the periodontal ligament and root surface, which can lead to complications such as root resorption or loss of tooth vitality. Additionally, this clearance allows for adequate blood supply and ensures proper osseointegration of the implant without compromising the structural integrity of neighboring teeth. Less than 1 mm increases the risk of inflammatory reactions and bone loss. Therefore, a minimum of 1 mm is critical for long-term implant success and periodontal health.

Reference: Contemporary Implant Dentistry, Carl E. Misch, 4th Edition.