A young boy grins to reveal his milk (or deciduous) teeth. The deciduous teeth are progressively lost in preparation for the appearance of adult teeth. There are 20 such teeth, consisting of incisors (central pair), canines (small) & molars only. Between the ages of 6 & 12 years both adult & milk teeth are present (ie a mixed dentition). The set of 32 adult teeth (the permanent dentition) is usually present by the age of 21 years.