Tooth Count by Age: Primary vs. Permanent Dentition, Eruption Timeline, and Variations

Human dentition follows a predictable sequence, but individual variation is normal. Understanding the numbers and timing helps parents and clinicians monitor development.

Primary (Deciduous) Dentition — 20 Teeth

Tooth	Eruption (months)	Exfoliation (years)
Central incisors	6–10	6–7
Lateral incisors	9–13	7–8
Canines	16–22	10–12
First molars	13–19	9–11
Second molars	23–33	10–12

All 20 typically erupted by age 3. Spacing (primate spaces) is normal and necessary for permanent successors.

Permanent Dentition — 32 Teeth (including third molars)

Tooth	Eruption (years)	Notes
First molars (6-year molars)	6–7	First permanent teeth; key occlusion anchors
Central incisors	6–8
Lateral incisors	7–9
Canines	9–12	Upper canines often delayed/impacted
Premolars (1st & 2nd)	10–12	Replace primary molars
Second molars (12-year molars)	11–13
Third molars (wisdom teeth)	17–25 (or never)	Frequently impacted; may be congenitally absent

Common Variations

• Hypodontia (missing teeth): 3–6% (excluding 3rd molars); most common: mandibular 2nd premolars, maxillary lateral incisors.
• Hyperdontia (supernumerary): 1–3%; mesiodens (between maxillary centrals) most common.
• Ectopic eruption: Teeth erupting out of position (e.g., palatal canines).
• Transposition: Adjacent teeth swap positions.

Clinical Monitoring

• First dental visit by age 1 or within 6 months of first tooth.
• Panoramic radiograph at ~7–9 years to assess developing permanent teeth, rule out impactions/hypodontia.
• Orthodontic evaluation by age 7 (AAO recommendation).
• Wisdom tooth assessment (clinical + panoramic) at 16–18 years.

Variations are the norm. Regular dental visits ensure timely intervention when deviations affect function, esthetics, or health.