Dentures are removable tooth replacements that are chosen usually because of their relatively low cost compared to fixed alternatives.
Partial Dentures are used in situations where there are still remaining teeth that are strong enough to support or retain the partial denture. Without sufficient tooth or bone support, the abutment (support) teeth would likely fail.
Full Dentures are made when ALL of the remaining teeth are missing, and the patient wants a relatively inexpensive way to replace the teeth. The denture can be made prior to extracting the teeth, and placed in the mouth at the time of tooth removal. The advantage of this is that the patient has teeth right away after extraction, avoiding the social embarrassment of being seen by peers without their teeth while waiting for the extraction sites to heal. The disadvantage is that with teeth in the way at the time of denture fabrication, there is a less precise fit of the denture to the remaining ridge of the teeth, and it may be necessary to make a second denture after the healing time has completed. As the gum tissues shrink during healing, a series of soft liners are typically placed in the denture during the healing phase to help the patient become comfortable with their denture. After the healing phase has completed, a hard reline is necessary to tighten the fit, provided the treatment denture fit and appearance can serve as the final denture.
Implant replacements can be used as a root for single tooth replacement (Crown), for supporting a fixed bridge, OR for holding an attachment to help hold a denture in place, OR to hold an abutment that can help SUPPORT a denture. Most commonly, dentures are used for the first purpose mentioned, single tooth because they offer some important advantages.