Which portion engages the undercut in the cervical 1/3?

Which portion engages the undercut in the cervical 1/3?

• A. Only the tip of the retentive arm
• B. The entire retentive arm
• C. The middle portion
• D. The terminus

Answer: (A)

Retention from a clasp comes from engaging a shallow undercut on the tooth. In the cervical third, the undercut is small, so the design uses just a tiny area to capture it. That’s why only the tip of the retentive arm enters the cervical undercut. The rest of the arm stays in contact with the tooth surface (the middle portion and the end) without binding. This setup provides secure retention while allowing easy seating and removal and minimizes stress on the tooth. If more of the arm engaged the undercut, seating would be harder, removal could require more force, and there would be greater lever forces on the tooth.

Retention from a clasp comes from engaging a shallow undercut on the tooth. In the cervical third, the undercut is small, so the design uses just a tiny area to capture it. That’s why only the tip of the retentive arm enters the cervical undercut. The rest of the arm stays in contact with the tooth surface (the middle portion and the end) without binding. This setup provides secure retention while allowing easy seating and removal and minimizes stress on the tooth. If more of the arm engaged the undercut, seating would be harder, removal could require more force, and there would be greater lever forces on the tooth.