78. Tooth Eruption and Malformations of The Teeth

  1. Tooth eruption: as the tooth grows, the crown gradually erupts through the oral mucosa, and the mucosa around the crown becomes its gum or gingiva. The crown itself, as it emerges, consists of a nucleus of dentine covered by a layer of enamel
    1. THE DECIDUOUS TEETH usually erupt between the 6th and 24th months after birth
    2. THE PERMANENT TEETH develop later, but in a similar manner to the deciduous teeth, and as they grow, the root of the corresponding deciduous tooth is resorbed by osteoclasts. Thus, when the deciduous teeth are shed, the portion shed consists of only the crown and upper portion of the original root
      1. The permanent teeth erupt usually during one's sixth year and continue to appear until early adulthood
  2. Malformations of the teeth generally are not visible at birth because the teeth do not erupt until after birth (usually)
    1. ENAMEL HYPOPLASIA: defective enamel formation resulting in grooves, pits, and fissures on the enamel surface due to a disturbance in enamel formation. One of its most common causes is rickets, due to vitamin D deficiency
    2. ABNORMALITIES IN SHAPE: quite common; due to aberrant groups of ameloblasts
    3. NUMERICAL ABNORMALITIES: One or more extra teeth may develop or the teeth may not form at all
      1. Partial anodontia: One or more teeth are absent
      2. Total anodontia: No teeth develop, a very rare condition
    4. NATAL TEETH AND CAPS: 1 or 2 mandibular incisors are found at birth
      1. Premature erupted teeth may be only small, loose enamel caps over a thin dentin sheet
    5. FUSED TEETH: a tooth bud may divide or 2 buds may partly fuse to form a fused or joined tooth
    6. AMELOGENESIS IMPERFECTA: the enamel of the tooth is soft and friable due to hypocalcification. In addition, the teeth are usually yellow to brown
      1. Probably due to an autosomal trait
    7. DENTINOGENESIS IMPERFECTA: the teeth are brown to gray-blue and have an opalescent shine. The enamel wears down easily, and the dentin is exposed
      1. Due to an inherited autosomal dominant trait
tooth eruption and malformations of the teeth: image #1