Dental The most common cause of failure of the seal in the posterior palatal area is: A Under extended distal denture border. B Overextended distal denture border. C Distolateral border extended beyond the hamular notch. D All of the above. 💡 Explanation The most common cause of failure of the seal in the posterior palatal area is: ✓ Correct Answer: A. Under extended distal denture border.