Contents · 9 sections
Tooth eruption timing is tested in propedeutics of childhood diseases, pediatrics, and all dental departments, with varying formulations: a pediatrician views teeth as an indicator of biological age, while a dentist sees them as the basis for diagnosing developmental disorders. Below are both tables, formulas, and the thresholds beyond which a delay ceases to be within the normal range.
Deciduous teeth: timing and sequence
| Tooth | Mandible, months | Maxilla, months | Sequence |
|---|---|---|---|
| Central incisors | 6–8 | 8–10 | 1 |
| Lateral incisors | 10–12 | 9–12 | 2 |
| First molars | 12–16 | 12–16 | 3 |
| Canines | 16–20 | 16–20 | 4 |
| Second molars | 20–30 | 20–30 | 5 |
Total of 20 deciduous teeth: 2 incisors, 1 canine, and 2 molars in each half of the jaw; there are no premolars in the deciduous dentition. Full deciduous dentition is established by 2–2.5 years of age. The lower central incisors erupt first — an exception to the rule "lower before upper" is the lateral incisors, which frequently appear earlier in the maxilla.
Formulas for deciduous teeth
- Number of teeth up to 2 years: X = n − 4, where n is age in months. At 10 months — 6 teeth, at 1 year — 8, at 18 months — 14.
- Benchmarks: 1 year — 8 teeth (all incisors), 2 years — 16–20.
The formula works from 6 to 24 months and yields an average; a deviation of 2–4 teeth in either direction is normal.
Permanent teeth: timing and sequence
| Tooth | Mandible, years | Maxilla, years |
|---|---|---|
| First molars ("sixes") | 6–7 | 6–7 |
| Central incisors | 6–7 | 7–8 |
| Lateral incisors | 7–8 | 8–9 |
| Canines | 9–10 | 11–12 |
| First premolars | 10–12 | 10–11 |
| Second premolars | 11–12 | 10–12 |
| Second molars | 11–13 | 12–13 |
| Third molars | 17–25 | 17–25 |
The first permanent molars erupt distal to the deciduous second molars without replacing any predecessors — parents frequently mistake them for deciduous teeth, making this the most common cause of neglected caries in "sixes". The transition from deciduous to permanent teeth occurs from 6 to 12–13 years of age; the sequence mirrors the eruption order of deciduous teeth. Total of 28 permanent teeth excluding third molars, 32 including them; in some individuals, wisdom teeth never form.
Formula for permanent teeth
X = 4n − 20, where n is age in years (for ages 6–12). At 7 years — 8 permanent teeth, at 10 — 20. As with deciduous teeth, the formula yields an average.
Dental formula
In pediatrics, dental status is written as a fraction: the numerator represents the maxilla, the denominator represents the mandible, split by sides (right / left). Dentistry utilizes the international WHO system (ISO 3950): quadrants are numbered 1–4 for permanent teeth (1 — upper right, 2 — upper left, 3 — lower left, 4 — lower right, clockwise from the clinician's viewpoint) and 5–8 for deciduous teeth; the second digit indicates the tooth number from the midline (1 — central incisor, 8 — third molar). Thus, 36 is the lower left first permanent molar, and 51 is the upper right deciduous central incisor. An odontogram simulator with tooth number search is available in the propedeutic dentistry section on the platform.
Signs of eruption and management
Salivation, urge to chew, restlessness, low-grade fever up to 37.5 °C, and loose stools are acceptable for a day or two of eruption. Fever above 38 °C, diarrhea, cough, and rhinitis are not symptoms of eruption, but rather a concurrent infection; attributing them to teething is a classic mistake. Relief measures: teethers, gentle gum massage; lidocaine-containing gels are not recommended in children under 2 years of age.
Delayed and abnormal eruption
| Situation | When it is an abnormality | Differential diagnosis / Considerations |
|---|---|---|
| Absence of all deciduous teeth | After 12 months | Rickets, hypothyroidism, prematurity, hereditary syndromes, adentia |
| Premature eruption | Before 4 months; teeth present at birth (natal teeth) | Frequently a normal variant; natal teeth are extracted if mobile |
| Altered sequence | Canines erupting before incisors, etc. | Endocrine disorders, local factors |
| Delayed dental shedding | Absence of permanent incisors by age 8 | Retention, supernumerary teeth, hypothyroidism; X-ray required |
| Missing deciduous tooth without permanent successor | More than 6 months after loss | Adentia, retention — orthopantomogram |
Delayed eruption combined with delayed closure of the anterior fontanelle, muscular hypotonia, and growth retardation is an indication to check thyroid hormones and vitamin D levels.
Biological age by teeth
The number of teeth is one of the criteria for biological age in pediatrics, along with bone age and sexual development. A child with 4 teeth at one year of age is not "delayed" if other parameters are normal—the variation is wide, and heredity has a strong influence: late teeth in parents usually mean late teeth in the child.
Frequently asked questions
How many teeth should a one-year-old have? On average 8 (using the formula n − 4), with 4 to 12 being acceptable.
Which permanent teeth erupt first? The first molars and lower central incisors, erupting at approximately the same time at 6–7 years of age.
Do milk teeth need to be treated if they are going to fall out anyway? Yes: caries in a deciduous tooth progresses to pulpitis and periodontitis, destroys the permanent tooth bud, and causes malocclusion. Deciduous molars remain in place until 10–12 years of age.
See also: Physical development of the child · Normal heart rate, blood pressure, and respiratory rate in children · Program by faculties · Pediatrics Course