Influence of different materials on retention behavior of CAD-CAM fabricated bar attachments

Loss of retention with implant overdentures is a problem that might be addressed with materials such as a recently introduced biocompatible high-performance polymer (BioHPP). However, in vitro studies investigating this product are lacking.

The purpose of this in vitro study was to assess the retentive behavior of implant overdentures and the loss of retention from clip wear when used with computer-aided design and computer-aided manufacturing (CAD-CAM) fabricated bar attachments from cobalt-chromium (Co-Cr), zirconia (ZrO₂), and BioHPP to identify the optimal material in terms of minimal loss of retention and minimal wear.

Three CAD-CAM bar attachments were fabricated from the different materials and cemented to a completely edentulous mandibular model for testing. Twelve plastic clips were allocated to each material and subjected to 1095 dislodgement cycles to simulate a year of clinical use. A universal testing machine was used to measure the retentive force of dislodgement of each clip for each material before and after cycling. An inverted optical measuring microscope was used to quantify the amount of wear on each clip. One-way repeated-measures ANOVA was used to analyze the results among the materials and the decrease in retention force. The paired t test was used to compare clip measurements before and after testing (α=.05).

BioHPP bars retained retention significantly better than Co-Cr or ZrO₂, with a lower percentage decrease in mean retentive force. Clips used with BioHPP bars also exhibited the least wear. However, Co-Cr and ZrO₂ displayed similarly higher initial retentive values in comparison with BioHPP, with Co-Cr displaying the highest final retention.

BioHPP appears to be a strong candidate to replace Co-Cr or ZrO₂ for fabricating bar attachments as it displayed minimal loss of retention and led to the least wear of the clip, thereby reducing replacement frequency.