Attachment Mechanisms for Removable Implant Restorations
Thomas J. Salinas, DDS
A recent survey confirmed that approximately 10.5% of the American patient population (over 25 million people) is edentulous.1 Due to advances in medical technology and healthcare, the average life expectancy has increased steadily over the past 25 years. Each of these independent factors continues to contribute to an increasing number of people who cannot tolerate conventional removable prosthodontics. The use of osseointegrated technology has been successfully demonstrated in the edentulous patient to significantly improve support, retention, and stability in the experienced denture wearer.2
Either implant-supported or implant-retained prostheses may be stress broken with selected attachment mechanisms or rigid attachments that are used for precise assembly and disassembly. The typical implant-retained overdenture model for the mandible relies on the placement of two fixtures that should be parallel for prosthetic simplicity in the canine region. This parallelism allows independent stud attachments to be utilized effectively without the need for a bar attachment mechanism. More elaborate mechanisms and/or increased numbers of implants - particularly needed for the maxilla - can incorporate the use of a bar attachment with stress-breaking mechanisms. Prosthetic attachments can be either a metal-to-metal plunger/receptacle or a metal-plastic connection that allows a degree of stress breaking. The issue that often presents itself in partially tissue-borne prostheses such as these is wear of the attachment mechanism(s). Recall appointments can often be an appropriate time to replace or repair worn components. Attention should be given to the opposing dentition, however, and the scenario of wear and function that will be undertaken. In order to minimize stress on the attachments, it may be prudent to deliver an implant-retained restoration to oppose an arch that has also been restored with an implant-retained restoration or a conventional complete denture.
An implant-supported restoration should likewise oppose either a fixed or an implant-supported reconstruction. Precision attached mechanisms - in conjunction with electrical discharged machining (spark erosion) - can create a metal-based overdenture that has the benefits of a fixed restoration, while permitting the removal of the prosthesis for hygiene procedures. In comparison to stress-broken designs, virtually no wear is introduced to the attachment mechanism, which makes this restoration an appealing alternative for reconstruction of the edentulous mandible. Spark-eroded overdentures are more advantageous for the edentulous maxilla since replacement of teeth, alveolus, and phonetic physiology is best obtained with a stable overdenture design.3 The solution of an attachment mechanism for a prosthesis of this nature can vary with swivel latches spark-eroded to the underlying bar primarily indicated for the maxilla. Other attachments for metal-based precision overdentures in extensively resorbed mandibles are better suited for a plunger/axle attachment to traverse the extensive volume of restorative material present.
Implant overdenture attachments should be simplistic in design when indicated for partially tissue-borne prostheses, since inherent wear may often result in repairs or replacement of the attachment mechanism(s). Implant-supported overdentures may conversely require more complex and sophisticated designs to make them precision-attached with minimal movement. Contemporary techniques of machining and metallurgical engineering have resulted in sophisticated development of what is considered a true state-of-the-art design for contemporary implant dentistry.
- 1. Marcus SE, Drury TF, Brown LJ, Zion GR. Tooth retention and tooth loss in the permanent dentition of adults: United States, 1988-1991. J Dent Res 1996;75:684-695.
- 2. Zarb G, Albreksston T. Tissue Integrated Prosthesis. Carol Stream, IL: Quintessence;1983.
- 3. Salinas TJ, Finger IM, Clark RS, Thaler JT. Spark erosion implant-supported overdentures: Clinical and laboratory techniques. Impl Dent 1992;1(3):246-251.
*Assistant Professor, Department of Prosthodontics, Louisiana State University School of Dentistry, New Orleans, Louisiana.