The first set of teeth which erupt into the mouth. Each mouth quadrant has 5 teeth—2 incisors anteriorly, 1 canine distal to the 2 incisors and 2 molars distal to the canine—to make a total dentition of 20 teeth. The incisors erupt at 6–9 months of age, followed by the first molars at 12–14 months, the canines at 16–18 months, and finally the second molars at 24–30 months. There can be considerable variation in eruption dates, although eruption of the central incisors after the lateral incisors usually indicates some pathology. The primary teeth differ from the permanent teeth in that they have shorter crowns, narrower occlusal surfaces, broader and flatter contact areas, thinner enamel and dentine, longer pulp horns, curved roots (to accommodate the developing permanent successor) with open apices, and are lighter in colour. Primary teeth are normally replaced by teeth of the succeeding permanent dentition but, where a permanent tooth fails to erupt, the primary tooth may be retained into adult life. See also eruption.
Primary (deciduous) dentition