Although the modulus of elasticity of the human periodontal ligament (E) values used in dentistry widely ranged from 0.01 to 175 MPa, the exact E value has not been determined. This study aimed to verify whether and how E values affect the stress distribution over the tooth and periodontium structures, and to determine the appropriate E range. A 3D multi-component human first premolar model was created based on a cone-beam computed tomography dataset. Finite element analysis was performed to analyze stress distribution and deformation of the structures under an average Asian occlusal force with different E values (0.0689-68.9 MPa). The low E caused excessive PDL deformation, contributing to a non-uniform stress distribution and localized stress concentration, especially in the cementum, enamel, and dentin. With the low E value, the stress magnitude was overestimated by 1,195%, potentially leading to erroneous conclusions regarding material failure and tooth movement. The E value significantly affects the stress magnitude and distribution over the tooth and periodontium. The appropriate E range of 0.964 ± 0.276 MPa is suggested for human first premolars to ensure accurate and reliable FEA simulations and help avoid misinterpretation of the stress results, which could compromise orthodontic planning and restoration design.