Most parents regard the appearance of an infant's first tooth as one of a series of significant developmental landmarks, and its precocious eruption as a sign of great intelligence. Tooth eruption or teething is the process by which a tooth moves from the pre-eruptive position in the alveolar bone through the mucosa into the oral cavity. It is believed that the dental follicle (sac containing the developing tooth and its odontogenic organ) rather than the tooth itself plays the essential role in this process. The dental follicle is a source of eicosanoids, cytokines, and growth factors and, thus, may contribute to some of the localized symptoms seen with teething. Prior to erupting, the crown of the tooth is covered by enamel epithelium. As the tooth moves upward in the jaw, this area of fused epithelium breaks down, and the tooth erupts. Prior to this, the gingiva may appear bluish and swollen as a result of a transient hematoma.

Primary teeth, also known as deciduous teeth or milk teeth, comprise 8 incisors, 4 canines, and 8 molars for a total of 20 teeth (Fig. 2). Beneath the primary teeth, 20 permanent (succedaneous) teeth are developing. The timing of tooth eruption varies widely, although most children get their first deciduous tooth around 6 months of age and their last between 24 and 30 months of age. The lower central incisors usually erupt first and the molars last. Teeth tend to emerge in pairs, and girls often get their teeth earlier than boys. The average number of teeth a child should have is roughly his or her age in months minus 6 until 24 months of age. Preterm infants acquire their teeth at a later chronological age but the same post-conceptual age as term infants.

A number of pathologic conditions are associated with a delay in tooth eruption (Table1).

Table 1. Causes of Delays in Tooth Eruption:

• Impacted Teeth
• Down's Syndrome
• Impedance of tooth eruption by adjacent or overlying tooth or bone
• Cleidocranial Dysplasia
• Congenital Hypothyroidism
• Gaucher's Disease
• Osteopetrosis
• Rickets