Influence of attachment design and material on the retention of resin-bonded attachments.

Objectives: The purpose of this laboratory study was to evaluate the influence of the attachment design and material on the retention of resin-bonded attachments (RBAs) before and after dynamic loading. Materials and methods: Forty-eight caries-free human premolars were prepared for RBAs fabricated either from a CoCr alloy or from zirconia ceramic. Specimens were divided into three groups (n = 16 each). Two groups had a standard attachment design for alloys (group M made from a CoCr alloy and group Z1 made from zirconia ceramic). The third group had an attachment design optimized for zirconia ceramic (group Z2 made from zirconia ceramic). Attachments were bonded to the acid-etched enamel of the premolars using a phosphate monomer containing adhesive resin. Subgroups of eight specimens each were either debonded using a tensile force in a universal testing machine at a cross-head speed of 2 mm/min (S) or were exposed to dynamic loading with 50 N over 1200,000 loading cycles in a chewing simulator prior to debonding (D). Results: There were no significant differences in the initial failure loads of groups. With the exception of subgroup Z1-D, all specimens survived the dynamic loading. Statistical analysis showed that dynamic loading caused a significant decrease of failure loads in group Z1. In contrast, subgroup Z2-D exhibited significantly higher failure loads compared to the subgroup Z1-D. Conclusions: The results suggest that zirconia RBAs fabricated with an optimized attachment design may be a valid clinical alternative to metal RBAs. Clinical relevance: Clinical data on the long-term potential of zirconia RBAs is required before these restorations can be recommended for general use. [ABSTRACT FROM AUTHOR]