⦁ Conventional Acrylic Complete Denture
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.
The stability and longevity of complete dentures are crucial. Commonly used complete dentures are made from composite resins (Figure 3.22a). The obvious advantages of these kinds of materials are that they are low-cost, easy to fabricate, and repair. However, low strength and poor aging properties always reduce the longevity of complete dentures made of resins. Alternatives with improved properties can be found among metal materials, especially pure titanium or titanium alloy denture bases (Figure 3.22b). Compared to conventional composites, titanium-based denture bases are not as popular. This is mainly due to high price, the complex process of installation, and difficulties with repair. A dental base made from a composite resin strengthened by prefabricated metal meshes or metal wires embedded inside the resin as reinforcement is a good compromise (Figure 3.22c).
Figure 3.22. Three common denture bases are made from different materials for different purposes: (a) Resin base; (b) Metal base; and (c) Metal mesh embedded resin base.
Abrasions of artificial teeth occur and the alveolar ridge will change over time. Therefore, regular re-examination is very important for edentulous patients. Complete dentures should be adjusted to fit any new oral settings and to keep them in good condition with continued good oral function