7
Development of the dentition
Table 7.1 Calcification and eruption dates of the primary dentition. The mandibular tooth in any series usually erupts before the maxillary counterpart. Root formation is usually complete 12–18 months after eruption.
| Eruptive sequence | Calcification begins (in utero) | Eruption |
| Central incisors | 12–16 weeks | 6–7 months |
| Lateral incisors | 13–16 weeks | 7–8 months |
| First molars | 14–17 weeks | 12–15 months |
| Canines | 15–18 weeks | 18–20 months |
| Second molars | 16–23 weeks | 24–36 months |
Table 7.2 The second deciduous molars can have various occlusal relationships: distal step; flush terminal plane; or mesial step.
Table 7.3 Calcification and eruption dates of the permanent dentition. Root formation is usually complete 24–36 months after eruption.
| Eruptive sequence | Calcification begins (months) | Eruption(years) |
| First molars | Birth | 5–6 |
| Mandibular central incisors | 3–4 | 6–7 |
| Maxillary central and mandibular lateral incisors | 3–4 | 7–8 |
| Maxillary lateral incisors | 10–12 | 8–9 |
| Mandibular canines | 4–5 | 9–10 |
| Maxillary first premolars | 18–21 | 10–11 |
| Mandibuar first premolars | 21–24 | 10–12 |
| Maxillary canines | 4–5 | 11-–12 |
| Maxillary second premolars | 24–27 | 10–12 |
| Mandibular second premolars | 27–30 | 11-–12 |
| Second molars | 30–36 | 12–13 |
| Third molars | 80–120 | 17–25 |
Figure 7.1 (A) The ugly duckling stage of dental development: (i) the maxillary lateral incisors are distally splayed and there is a midline diastema; (ii) the radiograph shows that the distal splaying is due to pressure on the lateral incisor roots by the developing canines. (B) The combined mesio-distal width of the deciduous canine, first molar and second molar is greater than the combined width of the permanent canine, first and second premolar. The difference is termed the Leeway space.
Teeth develop from the dental lamina with first evidence of formation at 6–7 weeks in utero. The stages of tooth development can be subdivided into bud, cap and bell stages.
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