Tooth eruption: when the teeth come in
- Anatomy and histology
Baby teeth usually start at about six months and are all in by about three years; permanent teeth replace them from about six to twelve years.
What it is
Eruption is the movement of a tooth from its crypt in the jaw into the mouth. The primary teeth usually begin with the lower central incisors at around six months and are complete, with the second primary molars, by about two and a half to three years. The permanent dentition starts at around six years with the first permanent molars, which erupt behind the primary teeth and are often mistaken for baby teeth. Between six and twelve years the primary teeth are shed and replaced (the mixed dentition), and the third molars, if present, erupt from late adolescence.
Clinical anatomy
- Primary order (approximate): central incisors, lateral incisors, first molars, canines, second molars.
- First permanent molars (the «six-year molars») and lower central incisors are usually the first permanent teeth.
- Second permanent molars come in around twelve years; third molars from about seventeen to twenty-five years, or never.
- Lower teeth usually erupt slightly before the matching upper teeth.
- The timing varies by several months between children; the sequence and symmetry matter more than exact dates.
Clinical correlation
- Teething can cause drooling, gum soreness and irritability, but not high fever, diarrhoea or illness: look for another cause of fever.
- The first permanent molar erupts without a baby tooth falling out, so parents may not know it is permanent; caries there is common and lasting.
- No teeth by about eighteen months, or a marked asymmetry, can point to systemic causes (hypothyroidism, hypopituitarism, rickets, cleidocranial dysplasia) or local obstruction.
Next step / Initial management
- Teething: comfort measures (a cool teether, gum massage); avoid topical anaesthetic gels with benzocaine in infants because of methaemoglobinaemia.
- Fever or diarrhoea in a teething child: examine and treat as for any febrile child; do not attribute it to teeth.
- Delayed or asymmetric eruption: refer to the dentist for radiographs and consider endocrine or genetic causes with the paediatrician.
Test yourself
Think of the answer, then tap the question to see it.
Which permanent tooth erupts first, usually without a baby tooth falling out?
The first permanent molar (six-year molar), behind the primary second molar; the lower central incisors erupt around the same time.
Can teething explain a high fever in an infant?
No. Teething can cause drooling and irritability, but a high fever needs a search for another cause.
Why are benzocaine teething gels avoided in infants?
Because benzocaine can cause methaemoglobinaemia, which is dangerous in young children.
Elsewhere in DurgiPedia
Connections
Educational content; it does not replace assessment by a dentist or doctor and is not a clinical instruction. For facial or neck swelling with difficulty swallowing or breathing, a knocked-out tooth or bleeding that will not stop, go to an emergency department at once.
Sources: Anatomy, Head and Neck, Tooth Eruption (StatPearls Publishing (NCBI Bookshelf), 2023); Embryology, Teeth (StatPearls Publishing (NCBI Bookshelf), 2023); Developmental Disturbances of the Teeth, Anomalies of Number (StatPearls Publishing (NCBI Bookshelf), 2025).
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Representative model, for educational purposes only.