Definition The changes one would expect in the ‘average’ child.
Incisors are usually spaced and upright. No spacing indicates the probable crowding of successors (Fig. 1). ‘Primate’ spacing may exist distal to cs and mesial to cs. Distal surfaces of es are flush in most cases. By 5-6 years, an edge-toedge occlusion with incisor attrition is common.
Primary to mixed dentition
• 1 1 or 6s are usually the first to erupt; mild incisor crowding is common (Fig. 2) but tends to resolve by 9 years with an increase of about 2-3mm in intercanine width.
• Space for 21[12 i s provided by existing incisor spacing, by intercanine width growth, and by their greater proclination than ba ab. 111 are usually distally inclined initially; median diastema reduces with 212 eruption. As 3 3
migrate and press on the roots of 212, their crowns, and to a lesser extent those of 111, are frequently flared distally with a median diastema -‘ugly duckling’ stage (Fig. 3). This usually corrects as 3s erupt.
• Space for 3, 4, 5s is provided by the slightly greater mesiodistal width of c, d, es. Greater leeway space in the mandible (-2-2.5mm) than in the maxilla (-1-1.5mm) with mandibular growth creates a Class I molar relationship.
Dental arch development
With the exception of intercanine width increase, dental arch size alters minimally after the primary dentition erupts. Permanent molars are accommodated by growth at the back of the arch. Alveolar bone growth maintains occlusal contact as the face grows vertically.