High performance plastic gears are increasingly being used as substitutes for metal gears across various applications, thanks to their numerous advantages. These include lighter weight, no requirement for lubrication, cost-effective mass production, significantly improved NVH characteristics, and resistance to chemicals and corrosion. However, they also present certain disadvantages compared to metal gears, such as reduced load-bearing capacity, sensitivity to temperature, and lower manufacturing precision. Common failure modes for plastic spur gears include thermal overload, fatigue, and wear. To ensure the gearbox operates reliably, it is essential to design each gear carefully to prevent failure during its intended lifespan while operating under specified conditions. This study offers an in-depth review of the current models used to assess thermal, fatigue, and wear failure modes, highlighting their limitations and suggesting ways to improve them. Additionally, experimental techniques are discussed, which can be used to determine gear-specific material properties necessary for evaluating individual failure modes.