Something that effectively closes or secures. An anterior oral seal is formed by lip contact or contact between the lower lip and the tongue or palatal mucosa. Border seal see peripheral seal. A posterior palatal seal is the seal at the posterior border of an upper denture obtained by producing extra pressure on the palatal mucosa, by creating a ridge or post-dam in the denture. A posterior oral seal is created by the contact of the soft palate against the dorsum of the tongue during speech or swallowing.