The Effect of Angle of Convergence of Abutments on Fracture Resistance of Three –Unit Fixed Partial Denture Fabricated with IPS-Empress2
Advisors: Dr. Farideh Geramipanah- Dr. Hamid Jalali
Written by: Dr. Leila Sedighpour HK
Dental School, Tehran University of Medical Sciences
Connecter area shows the weakest zone of all-ceramic fixed partial dentures, where most catastrophic failures of the prostheses tend to occur.
The aim of present study was to test the influence of angle of convergence of abutment on fracture resistance of three-unit fixed partial denture made of IPS-Empress2.
Forty extracted human premolars and molars were use to reproduce twenty 3-unit fixed partial dentures for replacement of second premolar. Teeth were prepared similarly according to guidelines for all-ceramic crowns and bridges, with the exception of angle of convergence of abutment preparation. Two groups with total occlusal convergence of angles of 12 degrees and 22 degrees were prepared and randomly assigned in 10 per group. Fixed partial dentures were fabricated with uniform thickness of 0.8 mm of core material of IPS-Empress2 and bonded to the corresponding models. Connector dimensions were set to 4×4 mm2 in height and width respectively. The gingival embrasures carved to a curvature with radius of 0.9 mm. All specimens underwent preload cycles of 10,000 cycles with 40 N at the frequency of 1.3 HZ loaded to fracture in a universal testing machine at a cross head speed of 1mm/min. Student t-test was applied to the mean failure data to detect any difference in mean fracture resistance of two groups.
Mean failure loads and standard deviations of 12 degrees and 22 degrees group were 1009.12±208.05 N and 1182.72±144.67 N respectively. Student t-test revealed a significant difference (P < 0.05) between mean failure loads according to the degree of convergences of test groups.
Within the limitation of the present study the following conclusion was made: mean failure loads of the investigated FPDS with taper of 22 degrees of abutments were significantly higher than FPDS with 12 degrees.
In the present study increasing the angle of convergence of abutments from 12 degrees to 22 degrees increased the fracture resistance of all-ceramic FPDS fabricated with IPS-Empress2.