Complete dentures consist of two main parts, namely the artificial teeth and the denture base. As described previously, an artificial tooth is used to restore the appearance of the natural tooth, its occlusion, oral function, and to assist in word pronunciation. The dental base is the foundation of the artificial tooth and can be used to restore the defective soft and hard tissues. Biting force is distributed from the artificial tooth through the denture base to the oral mucosa and bone tissues. Since tooth support cannot be obtained, the denture base of complete dentures covers a larger area of oral mucosa than that of RPDs complete dentures can fulfill all of these functions. Unlike RPD’s, with complete dentures connectors are not used as there is no need for space to install a major connector onto the complete denture, and minor connectors cannot be used since no healthy abutment is available.

Retention of a complete denture benefits from both sub-pressure and adherence to the underlying tissue.¹² Sub-pressure will occur between the denture base and oral mucosa if they are attached close to each other and a good peripheral seal is applied. A peripheral seal is the tight contact formed by the marginal surface of the denture with the oral mucosa. The posterior edge of the upper denture (postdam area) is of vital importance during speech. The atmospheric pressure outside the dental base presses it firmly onto the oral mucosa. Good adsorption is mainly ascribed to a thin sticky layer of saliva between the dental base and oral mucosa that contributes greatly to retention. Thus, the large dental base area is important to guarantee retention of the complete dentures. Of course, it should not disturb normal oral function or reduce comfort.

When the prosthetic plan is made, the effects of oral hard and soft tissues on necessary retention should be considered carefully. If there is large tuberosity, sharp bone apexes, or hyperplastic oral mucosa, the denture cannot remain stable. Sometimes a special oral operation is needed to resolve these problems before prosthetic treatment, as retention of complete dentures would otherwise be dramatically decreased. If the jaw bone, especially the residual alveolar ridge, has been seriously absorbed and becomes narrow and flat, or if the oral mucosa has lost its initial elasticity and thickness, retention is dramatically decreased. In these cases, additional affiliations, like implants, may become necessary.