What are sigmoid and stephens curve in dentistry?

In dentistry, the sigmoid curve and the Stephens curve describe patterns related to jaw movement. The sigmoid curve refers to the S-shaped path the condyle (the rounded end of the lower jaw) follows when the mouth opens and closes, showing how the jaw moves from rotation to translation as it widens. The Stephens curve describes the movement of the mandible during lateral (side-to-side) excursions, illustrating how the jaw shifts and the condyle on the opposite side moves forward and inward. Both curves help dentists and specialists understand functional jaw motion, diagnose occlusal issues, and plan treatments such as orthodontics, prosthodontics, and TMJ-related care.