Dentistry for Kids. Ulrike Uhlmann

Dentistry for Kids - Ulrike Uhlmann


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or basal enamel bulge.

      • Primary molars have a broader and flatter interproximal contact than permanent molars.

      Micromorphology

      • The enamel surface is characterized by a largely aprismatic enamel surface (layer thickness 30–100 μm).

      • The enamel prisms in the cervical area increase from the dentinoenamel junction toward the occlusal surface.

      • The mineral content of the primary tooth enamel is lower than in the permanent dentition.

      • In primary teeth the enamel formed postnatally is far less densely mineralized than the prenatal enamel mantle.

      • The structure of primary tooth dentin is different than permanent tooth dentin: The dentinal tubules are larger, the peritubular dentin is more highly developed, and the mineral content of the intertubular dentin is lower than in the permanent dentition.

      Fig 1-1 Morphologic differences between primary and permanent teeth.

      Fig 1-2 Cross section of a primary (a) versus a permanent (b) tooth revealing enamel layer thickness. In the primary tooth, the enamel layer is very thin compared with the permanent tooth. (Photographs courtesy of Peter Schaller.)

      Fig 1-3 Longitudinal section of a primary (a) versus a permanent (b) tooth. The size of the pulp cavity is much larger in the primary tooth, whereas the dentin layer between the enamel and the pulp is much thicker in the permanent tooth. (Photographs courtesy of Peter Schaller.)

      MINERALIZATION AND ERUPTION TIMES

      To understand disorders such as hypomineralization or dental fluorosis, we need to know exactly when primary and permanent teeth are mineralized (Tables 1-1 and 1-2). Furthermore, when assessing radiographs in the mixed dentition, it can be helpful to know when the dental crowns of the permanent premolars or molars should be visible so that any agenesis can be diagnosed. Table 1-3 shows the eruption times of the primary and permanent teeth. It should be noted that relatively wide variations in these timings are possible; those listed in the table should only serve as a guide.

Tooth Start of mineralization End of mineralization Root fully developed
Incisors 3–5 months in utero 4–5 months postnatal 1.5–2 years
Canines 5 months in utero 9 months postnatal 2.5–3 years
Primary first molar 5 months in utero 6 months postnatal 2–2.75 years
Primary second molar 6–7 months in utero 10−12 months postnatal 3 years
Tooth Start of mineralization Crown fully developed Root fully developed
Maxilla
Central incisor 3–4 months 4–5 years 10 years
Lateral incisor Up to 1 year 4–5 years 11 years
Canine 4–5 months 6–7 years 13–15 years
First premolar 1.5–1.75 years 5–6 years 13–15 years
Second premolar 2–2.25 years 6–7 years 12–14 years
First molar At birth 2.5–3 years 9–10 years
Second molar 2.5–3 years 7–8 years 14–16 years
Third molar 7–9 years 12–16 years 18–25 years
Mandible
Central incisor 3–4 months 4–5 years 9 years
Lateral incisor 3–4 months 4–5 years 10 years
Canine 4–5 months 6–7 years 12–14 years
First premolar 1.75–2 years 5–6 years 13 years
Second premolar 2.25–2.5 years 6–7 years 13–14 years
First molar At birth 2.5–3 years 9–10 years
Second molar 2.5–3 years 7–8 years 14–15 years
Third molar 8–10 years 12–16 years 18–25 years