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Abstract A suitable compromise between retention and retrievability should be considered in implant supported restorations. Therfore, cement choosing should be based on the need for the retrievability and amount of required retention. The purpose of this in vitro study was to evaluate the effect of two temporary cements (Resin based cement and Eugenol free Zinc oxide cement) on the retention of two titanium implant supported crowns made of (Polymer infiltrated hybrid glass ceramic and Yttrium stabilized tetragonal zirconia). In this in-vitro study, 20 samples including 10 zirconia crowns and 10 VITA ENAMIC crowns were fabricated by CAD/CAM system cemented on titanium implant abutments. Two temporary cement types were used, resin based temporary cement and zinc oxide non eugenol temporary cement. In this study twenty all ceramic crowns were used, they were divided according to crown materials into: group I (n=10): Polymer infiltrated hybrid glass ceramic (VITA ENAMIC™) crowns group II (n=10): Yttrium stabilized tetragonal zirconia (BruxZir™ Shaded Zirconia) crowns. Each group was subdivided according to the cement type used into: Subgroup A (n=5): crowns were cemented on abutments using resin based temporary cement (Dentotemp™) and Subgroup B (n=5): crowns were cemented on abutments using non eugenol zinc oxide temporary cement (Tempbond NE™). Retention of the restoration in these groups was then measured. Dummy implants were inserted in acrylic resin using paralleling device, titanium abutments were screwed on the dummy implants using 1.25mm diameter Hex and tightened with a precise adjustable torque wrench to a 35Ncm. Titanium abutments were sprayed with a reflective spray and digitally scanned using desktop scanner, Crowns were designed as premolars and adjusted on the designing software to fit on the abutments, then mesial and distal wings were added to aid in the test. The design was saved as STL file and sent to the milling machine software were the material was selected and the milling started. VITA ENAMIC™ crowns were separated from the blocks after milling was finished, fitting was checked on the abutments to give its final shape. BruxZir™ Shaded zirconia crowns were separated from the blanks then placed under drying lamp for 45 minutes, then sintered for 6 hours in the sintering furnace at 1550°C. The crowns were left in the furnace for cooling to a temperature below 200◦C, giving its final shape, then fitness on the titanium abutments was checked. Cements were mixed using the manufacturer instructions and applied on the fitting surfaces of the crowns in each group, Crowns were pressed on the abutments by a loading device under 5 kg weight, after setting time the samples were ready for testing. Retention was measured by Nexygen™ Materials Testing Machine (Model LRX-Plus, Lloyd Instruments, Fareham, UK), Data were recorded using computer software (Nexygen-MT-4.6; Lloyd Instruments). Numerical data were explored for normality by checking the data distribution, calculating the mean and median values and using Kolmogorov-Smirnov and Shapiro-Wilk tests. Data showed parametric distribution so; it was represented by mean and standard deviation (SD) values. Two-way ANOVA was used to study the effect of different tested variables and their interaction on retention. Independent t-test was used for different intergroup comparisons. The significance level was set at P < 0.05. Statistical analysis was performed with IBM™ SPSS™ Statistics Version 24 for Windows. |