The present study was conducted to evaluate the effect of different crown wall thicknesses (0.5mm, 1mm and 1.5mm) on the fracture load, marginal accuracy, and translucency of monolithic CAD-CAM manufactured lithium disilicate and Zirconia crowns. Materials and Methods: 60 monolithic single were constructed using CAD/CAM machine divided into two groups according to the material of construction Group (E): Monolithic IPS e.max CAD lithium disilicate crowns and Group (B): Monolithic BruxZir Solid zirconia based crowns. Each group was divided into three subgroups according to the axial wall thickness of the crown into Subgroup (0.5): 0.5 mm margin thickness, Subgroup (1): 1mm margin thickness and Subgroup (1.5): 1.5mm margin thickness. The Vertical Marginal gap was determined using Digital microscope, while translucency parameter was determined using a Spectrophotometer, then the fracture load was determined using universal testing machine and finally fracture pattern was detected by scanning electron microscope. The collected data were statistically analyzed. Results: Vertical marginal gap values for both groups (E and B) were within the acceptable clinical range. The translucency parameters (TP) values in group E revealed a higher mean value than in group B for all subgroups. The fracture load in group B revealed a higher mean value than in group E for all subgroups.
Conclusion: Increasing the wall thickness can effectively increase the fracture strength while decrease the marginal gap and translucency of the monolithic lithium disilicate ceramic crowns and zirconia crowns.