The purpose: This in-vitro study aimed to analyze and compare the effect of thermo-mechanical stresses on mandibular denture base deformation for three-dimensional dentures printing (3D printing) compared to those fabricated by conventional processing techniques with different arch forms (square, ovoid and tapering). Materials and methods: A total of 30 mandibular denture bases were fabricated, they divided according to the technique of denture construction into two main groups; GI: Mandibular dentures constructed by additive manufacturing technique, GII: mandibular dentures constructed using water bath curing method, each group was sub-divided according to the arch form into three equal sub groups (square, ovoid and tapered). The bases were subjected to thermo-mechanical cycling. Deformation was verified by superimposing the output of each STL file of the scanned mandibular dentures prior and following thermo-mechanical cycling procedure. Data were statistically analyzed. Results: One Way ANOVA test was used to compare more than 2 independent groups and Two Way ANOVA test was used to compare effect of combined independent factors on single continuous parametric outcome. Higher mean deformation was found in favor to the square arch Form, with statistically significant difference in GI. For the combined effect of deformation, there was statistically significant effect on deformation of complete denture in favor to GI . Conclusion: Supporting on the results of this research, it might be terminated that increased deformation was found for the 3d printed denture bases rather than the conventional heat-cured group. Moreover square arch forms introduced higher deformation values for both groups.