Which of the following factors is considered an unlikely causative factor for root resorption?

Root resorption is a common concern in orthodontics, where the roots of the teeth can diminish in length during treatment due to various factors. Among the factors listed, previous trauma is considered the least likely to cause root resorption in the context of ongoing orthodontic treatment.

Tooth mobility is often associated with periodontal health and can indicate an underlying issue that may contribute to root resorption. Overcrowding can create additional tension on the roots as teeth are moved into proper alignment, increasing the risk of resorption. Tooth morphology directly affects how a tooth interacts with surrounding tissues and how forces are distributed during orthodontic treatment, influencing the likelihood of resorption.

On the other hand, while previous trauma can lead to a number of dental issues, including potential resorption in certain scenarios, it is less consistently recognized as a direct causative factor compared to the other options during orthodontic treatment. The timing and nature of the trauma, combined with the body's healing response, can contribute to lasting effects on the tooth that differ significantly from those observed with the mechanical forces of orthodontics.