What is the characteristic of the retentive clasp in relation to the height of contour (HOC)?

The retentive clasp is designed to engage an undercut area of the tooth, which is located cervical to the height of contour (HOC). This engagement provides the necessary retention for the removable partial denture. The HOC marks the broadest part of a tooth's contour, and to achieve effective retention, the clasp arm must be positioned below this contour in a region that allows it to flex and provide a gripping force on the tooth. When the clasp is cervical to the HOC, it can fit into the undercut area effectively, securing the prosthesis in place as the clasp exerts a retentive force during function.

Understanding the position of the clasp relative to the HOC is crucial in prosthetic design to ensure that it functions well and remains unnoticed during normal oral activities.