During dental treatment, if a tooth were fractured suddenly by unnoticed tooth crack or vertical root fracture, it would be very embarrassing and frustrating experiences to dentists. But if it were once diagnosed as one of these teeth fracture, dentist should know about the etiology, course of fracture development, treatment modality to avoid argument with patient. In here cases and diagnostic skills, etiology and treatement methods of tooth fracture originated by internal stress and masticatory force were discussed to help dentists.