Which factor is NOT mentioned as affecting the shape and size of the pulp canal?

The correct response highlights that genetic predisposition is not typically cited as a factor influencing the shape and size of the pulp canal. The pulp canal's morphology is primarily shaped by factors that are more directly related to the dental structures' functional and environmental interactions.

Chemical irritation, resulting from caries and various dental treatments, can lead to changes in the pulp's health and structure, directly affecting the canal's dimensions. Trauma is also a significant factor, as injuries can lead to alterations in the pulp’s morphology due to inflammation or necrosis. Furthermore, the natural function of teeth, including how they bear loads during activities such as chewing, can lead to adaptations in the pulp canal's shape over time.

While genetic factors do play a role in the overall anatomy and development of teeth, they typically do not directly determine the shape and size of the pulp canal itself, which is influenced more by external and functional factors throughout an individual’s life. Thus, choosing genetic predisposition as the option that does not affect the pulp canal is accurate within the context of the question.