Spur gears are essential components widely used for transmitting motion and power across various industries. In addition to traditional metal materials, polymers are increasingly utilised in gear manufacturing due to their numerous advantages. These include excellent specific mechanical and tribological properties, self-lubrication, high shock resistance, and resistance to oils and chemicals. As a result, polymer gears are commonly found in applications such as toys, mechatronic devices, computers, and laboratory instruments, where lightweight and cost-effective solutions are required. To ensure optimal performance and durability, assessing the mechanical behaviour of polymer spur gears is crucial. Several analytical and numerical techniques, including the finite element method (FEM), are widely employed to evaluate their structural response. In FEM simulations, gear teeth are often modelled as cantilever beams subjected to a moving load along the involute profile, allowing for an accurate estimation of their mechanical behaviour under different operating conditions. This study focuses on evaluating the dynamic performance of a polyamide (PA12) spur gear through a static analysis approach. Specifically, it investigates the gear mesh stiffness (GMS) by comparing different load amplitude modelling methods. The findings provide valuable insights into stiffness variations, contributing to the advancement of polymer gear design and optimization.