Which of the following is NOT an advantage of a flexible (thermoplastic nylon) denture compared with a conventional acrylic one?

Correct answer: C. Reduced rigidity

• A. Incorrect (this IS an advantage). The material engages soft-tissue undercuts that a rigid base could not, so insertion is easy and many patients report better initial comfort.
• B. Incorrect (this IS an advantage). Nylon-based materials are essentially unbreakable in normal handling, unlike brittle heat-cured acrylic.
• C. Correct — reduced rigidity is a DISADVANTAGE, not an advantage. A denture base must be RIGID to distribute occlusal load broadly across the supporting tissues. A flexible base transmits load unevenly and concentrates it, accelerating residual ridge resorption. Flexible dentures are also difficult to reline or repair and cannot carry conventional rests, so support and stability are poor.
• D. Incorrect (this IS an advantage). Tooth- or tissue-coloured flexible clasps eliminate visible metal, which is the main reason patients request them.

Note: Flexible dentures are best regarded as an interim or esthetic compromise — the loss of rigidity is a genuine biomechanical liability for long-term use.