Retention force of cements onto implant supported crowns

Methods:  A total of 100 Direct standart titanium implant abutments and analogs were used with each group of 20 being subdivided into two groups (n=10).  After abutments had been scanned, metal copings were designed by a Computer Aided Design/Computer Aided Manufacturing (CAD/CAM) system with two cement gap values (20 and 40 µm). Metal copings with a loop on the occlusal surface were obtained by means of direct metal laser sintering of a Co-Cr powdered alloy. The copings were luted using following  five cements: RelyX U200, Mis Crown Set, Poly F, GC FujiCEM and Multilink N under static load of 5 kg. After cementation, all specimens were thermal cycled 1000 times with 30 seconds dwell-time between 5°C and 55°C then subjected to pull-out test using a universal testing machine at a crosshead speed of 0.5 mm/min. The mean force required to dislodge copings from abutment was determined. Data were analyzed with two-way ANOVA, followed by multiple comparisons using Tamhane tests test (α=0.05).

Results: Statistical analysis revealed that significant differences were observed among cement groups (p<0.05). Poly F and Multilink N had the highest and the least mean retentive strength, respectively. No significant difference was found between RelyX U200 and Mis Crown Set. GC FujiCEM was superior to all cement groups except for Poly F. Increasing the cement gap from 20 to 40 µm improved retention significantly  for each cement group (p<0.05).

Conclusion: Within the limitations of this study, cements presented is meant to be a guide for the clinician in deciding with convenient way in enchancing retention between CAD/CAM fabricated metal copings and implant abutments.