Emergence of adult teeth. Coloured X-ray of the teeth of a six-year-old child. A mix of adult and child (milk) teeth are seen. Adult teeth are beginning to erupt and displace the corresponding milk teeth, the roots of which are reabsorbed. The adult teeth are permanent teeth that 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 up to 32 adult teeth.