Fractures extending into the dentine always cause some irritation to the vital pulp. If the fracture is not accompanied by a continual microbial stimulus, then pulpal reactions will be mild and temporary, unless the fracture is caused by an excessive force that has also damaged pulpal circulation.
Fractures that go deeper and reach the pulp always cause pulpal damage that easily becomes irreversible, unless protection of pulp is accomplished within 24 hours of the trauma.