the repeated fracture of a complete denture (C.D.) base is a problem among edentulous patients,it demonstrates a critical determination of the mechanical properties of the acrylic resin in service.This study aimed to evaluate the effect of different nanoparticles as reinforced materials used to repair midline fracture with different joint surface contours,on the mechanical properties of the repaired denture base.Methodology:45 complete dentures with different joint contours.was divided into 3 groups,Group A:fifteen C.D. with rounded joint contours fracture line,Group B: fifteen C.D. with rabbet-shaped fracture line contours.Group C:fifteen C.D. with butt fracture line contour. samples of further groups subdivided into 3 sub-groups ,Group A1,A2,and A3 groups repaired with self-cured acrylic resin,titanium dioxide nanoparticles,zirconium oxide nanoparticles,respectively (5% by weight).Group B1,B2,and B3 groups were repaired with self-cured acrylic resin, titanium dioxide nanoparticles material,and zirconium oxide nanoparticles,respectively (5% by weight). Group C1,C2, and C3 were repaired with self-cured acrylic resin,titanium dioxide nanoparticles,and zirconium oxide nanoparticles,respectively (5% by weight).Data were analyzed using independent sample t-tests (p ≤ 0.05).Results:There was a significant difference in micro-hardness and roughness of Group A with round joint contour than Group B and Group C.where it shows a superior surface roughness and hardness to other groups.For sub-groups,there was a non-significant difference in the repaired dentures treated with the addition of TiO2 or ZnO2 nanoparticles reinforced materials compared with the group treated with self-cured acrylic resin,Conclusion:addition of 5% weight TiO2 nanoparticles or ZnO2 to acrylic resin improved its mechanical properties,in repairing midline fracture of C.D., whether they being rounded, rabbet, or butt-joint contours.