The finish line in fixed prosthodontics refers to the precise boundary where tooth preparation ends. It is critical because it determines the exact margin where the crown or restoration will fit. A well-defined finish line ensures optimal adaptation of the prosthesis, proper marginal seal, and preservation of periodontal health. Incorrect finish line placement can lead to poor fit, plaque accumulation, and secondary caries. Therefore, recognizing the finish line as the termination point of the preparation is fundamental for successful prosthodontic treatment.

Reference: Principles and Practice of Prosthodontics, Shillinburg HT, 5th Edition.