When a dentist takes x-rays, they must be careful to correctly interpret the results. In one study, it was found that dental students and new dentists were much more likely than experienced dentists to think the x-ray below showed a fracture in the tooth (pointed by the black arrow). But there is not really a fracture present. The illusion makes the 'fracture line' look darker and more serious to the less experienced dentists than it really is, which can be explained by the mechanism of in the visual system.