Review of attachments for removable partial denture design: 1. Classification and selection.

An attachment is a mechanical device, other than a clasp assembly, that functions as a direct retainer. Attachments for removable partial denture treatment are reviewed and a method for classifying different types of attachments is provided. Attachments are categorized as precision or semiprecision, depending upon the method of manufacture; internal or external, according to their intracoronal or extracoronal location relative to the abutment tooth; and rigid or resilient, as determined by the amount of movement allowed between the component parts. They are also classified by design. The advantages and disadvantages of attachment use as well as indications and contraindications are considered. Additionally, the conventional clasp-type direct retainer is compared to attachments.