Support is the principle that describes how well the underlying mucosa (oral tissues, including gums) keeps the denture from moving vertically towards the arch in question during chewing, and thus being excessively depressed and moving deeper into the arch. For the mandibular arch, this function is provided primarily by the buccal shelf, a region extending laterally from the back or posterior ridges, and by the pear-shaped pad (the most posterior area of keratinized gingival formed by the scaling down of the retro-molar papilla after the extraction of the last molar tooth). Secondary support for the complete mandibular denture is provided by the alveolar ridge crest. The maxillary arch receives primary support from the horizontal hard palate and the posterior alveolar ridge crest. The larger the denture flanges (that part of the denture that extends into the vestibule), the better the stability (another parameter to assess fit of a complete denture). Long flanges beyond the functional depth of the sulcus are a common error in denture construction, often (but not always) leading to movement in function, and ulcerations (denture sore spots).
If cared for properly, dentures should last a minimum of 5 years. Over time, the bone shrinks and causes the denture to become loose. The rate that this happens varies with each individual, but can be controlled by visiting a dentist regularly to ensure that the denture is fitting properly. An ill-fitting denture causes the bone to shrink more rapidly. To prolong the life of a denture, a dentist will often use a denture liner to refit the internal surface of the denture to the oral tissues.
