Overdenture prosthesis
Overdentures are full-arch dentures that are supported and/or retained by implants. They are often the first implant restoration for edentulous patients because they require a fewer number of implants, their positioning is flexible, and they are also easy to fabricate, resulting in lower cost. Implants can improve the support, retention and stability of full dentures, which already have their own benefits, such as improved facial esthetics due to soft tissue coverage. Daily maintenance can be performed by the patient, which is easier than with other types of implant-supported dentures. It is a forward-thinking treatment for patients that has been offered for several years and is considered the standard treatment for edentulous patients.
However, overdentures also have disadvantages. Because implants are often placed in the anterior region due to bone availability, bone loss continues into the posterior region and is stimulated by soft tissue support in this area. They require a certain amount of interocclusal space to provide adequate acrylic width, space for the teeth and the required attachments. These attachments wear out and need to be replaced during maintenance sessions.
Overdentures can be divided into two types. Type A are conventional overdentures that are directly connected to the implants by attachments such as a Locator, ERA or an O-ring. This type of overdenture is suitable for cases where little interocclusal space is available and no other treatment is possible. The abutments have different heights to accommodate the different implant positions. In type B overdentures, the prosthesis is connected to the implants by another structure: a bar that is attached to the implants. This structure may be traditionally cast or milled and may include precision attachments to which the prosthesis will be attached. A bar structure can be used to compensate for deviating implant positions. Due to the additional space required to fabricate this structure, a larger interocclusal space is required for this type of overdenture.
The number of implants and the denture design must be determined according to the patient's wishes and possibilities. A minimum of 2 implants between the mental foramina with an overdenture type A is a commonly used option but has a poor prognosis. The ideal treatment plan for patients must include at least 4 implants and an implant-supported type B overdenture that helps maintain bone volume and withstands occlusal loading without involving soft tissue for this purpose. Patients can start their treatment with a type A prosthesis and plan to extend their rehabilitation with more implants and another overdenture to achieve long-term stability.
Bars can have different designs and attachment types. Common types are the Dolder bar, which is egg-shaped, and the Hader bar, which is round. The type of bar and precision attachment determines the type of movement and the direction in which the prosthesis moves, with possible negative consequences such as implant overload, bone loss, and screw loosening. These factors must be considered in treatment planning for any patient requiring a full-arch restoration to ensure predictability.
