Which of the following is an infrabulge component?

Which of the following is an infrabulge component?

• A. I-bar
• B. Ring clasp
• C. T-bar
• D. L-bar

Answer: (D)

The concept being tested is where retentive components sit relative to the survey line (height of contour). Infrabulge components lie below that line, meaning their retentive parts engage undercuts from beneath the tooth and are designed to approach the tooth from an apical direction. The L-bar fits this idea because its retentive segment is positioned below the height of contour and extends to engage an undercut from beneath the tooth, typically crossing the facial/lingual surface in the infrabulge region. The other options are designed to gain retention from above the survey line—above or around the tooth surface—rather than from below, which is why they are not infrabulge components.

The concept being tested is where retentive components sit relative to the survey line (height of contour). Infrabulge components lie below that line, meaning their retentive parts engage undercuts from beneath the tooth and are designed to approach the tooth from an apical direction. The L-bar fits this idea because its retentive segment is positioned below the height of contour and extends to engage an undercut from beneath the tooth, typically crossing the facial/lingual surface in the infrabulge region. The other options are designed to gain retention from above the survey line—above or around the tooth surface—rather than from below, which is why they are not infrabulge components.