A less-than-90-degree internal angle between major and minor connectors is described as which RPD feature that provides mechanical retention?

A less-than-90-degree internal angle between major and minor connectors is described as which RPD feature that provides mechanical retention?

• A. Finish lines
• B. Major connectors
• C. Minor connectors
• D. Indirect retainers

Answer: (A)

The concept here is how the geometry at the interface between major and minor connectors adds retention. When the internal angle formed where a minor connector meets the major connector is less than 90 degrees, it creates a slight undercut—often described as a dovetail—that helps lock the framework against dislodgement. This geometric interlock provides mechanical retention without additional clasps or attachments. Finish lines are terms from tooth preparation in fixed prosthodontics and don’t describe RPD retention here. Major connectors are the primary cross-arch links and provide rigidity, not this localized interlock. Indirect retainers help resist vertical dislodgement for the denture base but are not about the angle between major and minor connectors. The feature described by the less-than-90-degree angle is the minor connector interface forming a retentive undercut.

The concept here is how the geometry at the interface between major and minor connectors adds retention. When the internal angle formed where a minor connector meets the major connector is less than 90 degrees, it creates a slight undercut—often described as a dovetail—that helps lock the framework against dislodgement. This geometric interlock provides mechanical retention without additional clasps or attachments.

Finish lines are terms from tooth preparation in fixed prosthodontics and don’t describe RPD retention here. Major connectors are the primary cross-arch links and provide rigidity, not this localized interlock. Indirect retainers help resist vertical dislodgement for the denture base but are not about the angle between major and minor connectors. The feature described by the less-than-90-degree angle is the minor connector interface forming a retentive undercut.