The effect of connector design on flexural and fracturestrength in implant-supported bridge restorationsmanufactured with CAd-CAM system

The aim of this in-vitro study is to investigate the fracture and flexural strength of three- unit implant supported fixed dental prostheses (monolithic zirconia (VITA YZ ST) and lithium disilicate-based (e.max Press)) restorations at different connector cross-sectional area, produced on ti-base abutments using the CAD-CAM system. 12 implant analogues were placed in acrylic models in pairs. After the ti-base abutments were torqued on the analogs, their digital impressions were taken. Bridge design was planned; maxillary canine and 2nd premolar as abutment and 1st premolar as pontic. In the total group, 42 samples were manufactured and divided into 2 groups (n=21) according to the material type, then each group was divided into 3 subgroups (n=7) according to the connector cross-sectional area (9 mm 2 , 12 mm 2 , 15 mm 2 for monolithic zirconia; for lithium disilicate 12 mm 2 , 16 mm 2 , 20 mm 2 ). A thermal cycle of 5000 cycles was applied to the samples at a temperature of 5-55 °C. Prepared specimens were subjected to fracture strength test at a universal test machine. The results were formulated and flexural strength data were obtained. Differences between two independent groups were analyzed using Mann Whitney U, and whether there was a difference between more than two independent groups using the Kruskal Wallis Test (p=0.05). Average fracture and flexural strength values in monolithic zirconia samples are respectively; 1207.21 N (9 mm 2 ), 1594.59 N (12 mm 2 ), 2074.67 N (15 mm 2 ) and 99.77 MPa (9 mm 2 ), 107.16 MPa (12 mm 2 ), 113.32 MPa (15 mm 2 ) in lithium disilicate based samples; 500.84 N (12 mm 2 ), 685.75 N (16 mm 2 ), 859.94 N (20 mm 2 ) and 33.66 MPa (12 mm 2 ), 37.46 MPa (16 mm 2 ), 37.61 MPa (20 mm 2 ). The fracture and flexural strength of monolithic zirconia material was statistically significantly higher than that of lithium disilicate material (p<0.05). As a result, increasing the connector cross-sectional area increases the strength significantly (p<0.05). In the posterior region, monolithic zirconia bridges are strongly recommended, while lithium disilicate bridges can be recommended if they have sufficient connector cross-sectional area. Keywords: monolithic zirconia, lithium disilicate, ti-base abutment, connector, strength