24.1 Dental Development, Eruption Chronology and Examination of the Child
Key Takeaways
Primary teeth usually erupt in the order central incisor, lateral incisor, first molar, canine, second molar, starting with the mandibular central incisors at about 6-10 months and completing by about 2.5-3 years.
The first permanent molars and mandibular central incisors erupt at about 6-7 years, and the common maxillary sequence is first molar, central, lateral, first premolar, second premolar or canine, then second molar.
Primate spaces lie mesial to the maxillary primary canines and distal to the mandibular primary canines, and a distal step terminal plane leads to a Class II molar relationship.
A midline diastema with flared maxillary incisors at about 8-11 years (the ugly duckling stage) is normal and usually closes as the canines erupt.
The first dental visit should occur when the first tooth erupts and no later than 12 months of age, and recall bitewing intervals depend on the child's caries risk.
Knowing what is normal for a child's age lets you recognize delayed eruption, ectopic teeth and developing malocclusion. Expect chronology questions and "is this normal?" vignettes.
Tooth Formation
- Primary teeth begin to calcify in the second trimester (about 14-19 weeks in utero); the first permanent molar begins to calcify at birth.
- Primary roots are complete about 1-1.5 years after eruption; permanent roots about 2-3 years after eruption, so a recently erupted permanent tooth has an open apex (important for trauma and pulp therapy).
- Nolla stages describe tooth development from crypt to apex closure and help estimate dental age.
Eruption Chronology (approximate)
| Primary tooth | Maxillary | Mandibular |
|---|---|---|
| Central incisor | 8-12 months | 6-10 months |
| Lateral incisor | 9-13 months | 10-16 months |
| First molar | 13-19 months | 14-18 months |
| Canine | 16-22 months | 17-23 months |
| Second molar | 25-33 months | 23-31 months |
| Permanent tooth | Maxillary | Mandibular |
|---|---|---|
| Central incisor | 7-8 years | 6-7 years |
| Lateral incisor | 8-9 years | 7-8 years |
| Canine | 11-12 years | 9-10 years |
| First premolar | 10-11 years | 10-12 years |
| Second premolar | 10-12 years | 11-12 years |
| First molar | 6-7 years | 6-7 years |
| Second molar | 12-13 years | 11-13 years |
| Third molar | 17-21 years | 17-21 years |
Sequences: maxillary 6-1-2-4-5-3-7 or 6-1-2-4-3-5-7; mandibular 6-1-2-3-4-5-7 (the first molar or the central incisor may appear first). Mandibular teeth generally erupt before their maxillary counterparts. A delay of more than about 6 months from the contralateral tooth, or eruption out of sequence, should be investigated (supernumerary tooth, cyst, missing tooth, ankylosis).
Primary Dentition and Developing Occlusion
- Morphology: thinner enamel and dentin, larger pulps with high (especially mesiobuccal) pulp horns, marked cervical constriction, a prominent buccal cervical ridge on first molars, and thin, flared molar roots that surround the developing premolars. The mandibular second primary molar resembles the mandibular first permanent molar (three nearly equal buccal cusps), and the maxillary second primary molar resembles the maxillary first permanent molar. The mandibular first primary molar is unlike any other tooth. Details matter for cavity preparation and pulp therapy (see the pulp therapy section).
- Spacing: generalized spacing in the primary dentition is favorable. Primate spaces lie mesial to the maxillary canines and distal to the mandibular canines.
- Terminal plane (distal surfaces of the second primary molars):
| Terminal plane | Likely permanent molar outcome |
|---|---|
| Flush (most common) | End-on at first, then Class I after the early or late mesial shift (or remains end-on) |
| Mesial step | Class I, or Class III if the step is large and mandibular growth continues |
| Distal step | Class II |
- Leeway space and its use in space management are covered in the interceptive orthodontics section.
- Ugly duckling stage (about 8-11 years): diastema and distally flared maxillary lateral incisors caused by the developing canines pressing on the lateral roots; usually self-corrects as the canines erupt. A diastema under about 2 mm normally closes; larger spaces or a persistent frenum need assessment.
Teething and Newborn Findings
- Teething may cause local irritation, drooling and mild temperature rise, but not high fever or diarrhea; look for another cause. Offer chilled teething rings; avoid benzocaine gels in infants (methemoglobinemia risk) and amber necklaces (strangulation and choking).
- Epstein pearls (palatal midline), Bohn nodules (buccal and lingual ridges) and dental lamina cysts (crest of ridge) are small keratin-filled inclusion cysts in newborns that resolve without treatment.
- Eruption cyst / hematoma: bluish swelling over an erupting tooth; usually resolves as the tooth erupts.
Examining a Child
- History: medical (including medications and allergies), dental, developmental, social, diet and sugar frequency, fluoride exposure, oral hygiene routine and habits.
- Behavior assessment (Frankl scale; see behavior guidance).
- Extraoral: growth, facial symmetry, lymph nodes, lips, TMJ.
- Intraoral: soft tissues, dental stage, caries (visual-tactile on clean, dry teeth), plaque, gingiva, occlusion, habits, trauma signs.
- Infants and toddlers are examined knee-to-knee with the parent.
First visit: when the first tooth erupts and no later than 12 months, establishing the dental home.
Caries risk assessment (AAPD CRA tool): risk indicators include caries experience or white spot lesions, visible plaque, frequent sugary snacks or drinks (more than about three between meals daily), a bottle or sippy cup with sugary drinks at bedtime, active caries in the mother or caregiver, low socioeconomic status and special health care needs. Protective factors include optimally fluoridated water, twice-daily brushing with fluoride toothpaste and professional topical fluoride. The risk category sets the recall interval, fluoride regime and radiograph frequency.
Radiographs: prescribe by individual need (ALARA/ALADA). Bitewings are taken when proximal surfaces cannot be seen or probed; for recall patients, about every 6-12 months for high caries risk and every 12-24 months for low risk in the primary and mixed dentitions. A panoramic view in the mixed dentition assesses development, missing and supernumerary teeth.
Exam Traps
- A child with a fever above 38.5 °C and "teething" needs a medical cause excluded.
- The maxillary canine erupts after the first premolar in most children; the mandibular canine erupts before the premolars.
- A distal step at age 4 predicts a Class II molar relationship.
A mother asks when her 9-month-old's next teeth will erupt. Only the mandibular central incisors are present. Which teeth usually erupt next?
The primary mandibular second molars
The primary maxillary central incisors
The primary maxillary canines first
The primary mandibular first molars
In a 4-year-old with complete primary dentition, the distal surface of the mandibular second primary molar is distal to that of the maxillary second primary molar. What permanent molar relationship is most likely?
End-on that always becomes Class III
Class III molar relationship
Class I molar relationship
Class II molar relationship
A 9-year-old's parents are worried about a 1.5 mm midline diastema and distally flared maxillary lateral incisors. The canines are unerupted and the frenum is normal. What is the best advice?
This is the normal ugly duckling stage, which usually corrects as the canines erupt
Immediate frenectomy is needed, because every diastema is caused by the labial frenum
A mesiodens is certain, so surgery should be booked without any radiograph
Fixed appliances should start now to close the space before the canines erupt
Sections you finish are checked off in the contents.