Effect of Abutment Total Occlusal Convergence and Cement Type on Retention of Cement Retained Implant-Supported Restorations

The purpose of this study was to evaluate the effect of abutment total occlusal convergence (TOC), and cement type on the uniaxial tensile resistance to dislodgment of cement-retained, implant-supported metal copings. Six titanium implantabutmnets were constructed using CAD-CAM technology. Two abutments have TOC 6˚, Two abutments have TOC 8˚, and Two abutments have TOC 12˚. Identical copings were cast to fit each abutment with a loop incorporated that was engaged by the testing unit. The copings were cemented using either a resin-modified glass ionomer (RMGI) (Rely™ X U 200 Automix) or self adhesive resin cement that contained a 10 Methacryloyloxydecyl dihydrogen phosphate (MDP) monomer (Multilink® N). Each of the experimental groups had a unique combination of abutment TOC, and cement.Specimens were aged using a thermocycling unit with water between 5 and 55 degrees Celsius with 15 seconds in each bath and a 5 seconds dwell time, for 540 cycles. A universal testing machine was used to test uniaxial tensile strength. Cement was cleaned using thermal, mechanical, and physical methods, and surface finish was reestablished.This procedure was repeated to obtain different measurements for each group. Surface area for each abutment was calculated and used for the calculation of the tensile strength. One way ANOVA followed by pair-wise Newman-Keuls post-hoc tests were performed to detect significance between subgroups. Pair-wise student t-test was performed to detect interaction between variables of significant effect.P values ≤ 0.05 are considered to be statistically significant in all tests. Regardless of the cement type, totally it was found that Group A recorded the highest retentive force meanvalues followed by Group B while Group C recorded the lowest retentive force mean values. The difference between all groups was statistically significant (p 0.05). Irrespective of convergence groups, totally it was found that Multilink N group recorded statistically significant (p<0.05) higher retentive force mean values than Rely X U200 one.