In vitro evaluation of resin-retained extracoronal precision attachments.

The bond strength of resin-bonded restorations supporting extracoronal precision attachments retaining distal extension removable partial dentures was evaluated. Rigid bars of different lengths were attached to retainers with and without precision attachments. Retainers covering large areas of the teeth and having a generous "wraparound" design were used, but the teeth were not prepared to enhance resistance form. The retainers without attachments resisted forces as large as 200 N. When less circumferential tooth coverage was used, lower bond strength values were recorded. Four attachments of different loading designs were used. The precision attachments frequently became disengaged before the retainers debonded. Some low bond strengths indicated that there is a measure of unpredictability in the technique.