Dental X-ray. Coloured X-ray of the head and neck of a 12-year-old girl, seen from the side. In her mouth (lower right) adult teeth are seen emerging as they replace the milk teeth of childhood. The permanent teeth start emerging at around 6 years old, and the last milk tooth is lost at around 12 years old. 20 milk teeth are replaced by 32 adult teeth. The objects at upper left and centre right are used to position the patient's head relative to the X-ray machine. The back of patient's head is placed in the rest at upper left, while the tip of the nose is aligned with the pointer at centre right. This ensures the patient's mouth is centred in the close-up image taken by the panoramic X-ray machine.