Effect of abutment total occlusal convergence, material type, and cement type to dislodgment of cement-retained, implant-supported restorations
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Purpose of the study . The purpose of this study was to evaluate the effect of abutment total occlusal convergence (TOC), abutment material type, and cement type on the uniaxial tensile resistance to dislodgment of cement-retained, implant-supported metal copings. Materials and methods . Eight implant abutments were fabricated using CAD-CAM technology. Four abutments had a TOC of 10 degrees and the other four had 20 degrees. Half of the abutments were made of titanium and half were made of zirconia for equal distribution within each TOC group. 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) (Fuji Plus) or a resin cement that contained a 10-Methacryloyloxydecyl dihydrogen phosphate (MDP) monomer (Panavia F 2.0). Each of the eight experimental groups had a unique combination of abutment TOC, abutment material, 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 9 times to obtain 10 measurements for each group. Surface area for each abutment was calculated and used for the calculation of the tensile strength. A 3-way ANOVA with a significance level of .05 was used to determine whether there were any differences in strength by TOC, abutment material, or cement. A follow up post hoc Tukey HSD test was performed to determine specific group differences. Results . Three-way ANOVA revealed a significant interaction effect between abutment material and cement type ( p <0.5). No other main effects or interactions were statistically significant. Post hoc Tukey HSD test showed that the retention values were significantly higher for zirconia abutments than titanium abutments when using RMGI cement (5.74 MPa and 4.80 MPa, respectively), and significantly higher for titanium abutments than zirconia abutments when using resin cement (6.97 MPa and 4.79 MPa, respectively), regardless of the TOC. Conclusions . Within the parameters and limitations of this study, it can be concluded that there was no difference between 10 and 20 degree TOC of implant abutment walls in retention of cemented metal copings. Resin-modified glass ionomer cement provides significantly higher retention than MDP containing resin cement when used on zirconia abutments, but significantly lower retention when used on titanium abutments. Clinical significance . Implant abutments used for retaining a cemented crown can be designed to have 10 or 20 degree TOC. Resin cements containing MDP provide higher retention than resin-modified glass ionomer when used on titanium abutments. RMGI cements provide higher retention than resin cements containing MDP when used on zirconia abutments.