Ectopic Eruption of the First Permanent Molar
Ectopic eruption is the eruption of a tooth into an atypical position. In the classic presentation, the maxillary first permanent molar erupts mesially and becomes locked beneath the distal aspect of the second primary molar, resorbing its distal root. It is reversible when the molar spontaneously self-corrects into a normal position, or irreversible when it remains blocked by the primary molar.
Epidemiology
- Incidence 2–6%; affects both sexes equally; occurs ~25× more often in the maxilla than the mandible.
- ~4× more likely in cleft lip/palate patients (Barberia: 21.8% vs 4.3% in the general population).
- Spontaneous self-correction in 50–69% of cases, usually completed before 7 years of age (Barberia: 69.4%).
Aetiology
Multifactorial — a strong genetic/familial tendency (higher in cleft patients and siblings) combined with local factors: mesial angulation or larger-than-average width of the first permanent molar, crowding, and an unfavourable crown shape of the second primary molar.
Diagnosis
- Clinical (age 7+): first permanent molar crown clearly locked behind the second primary molar, tilted mesially.
- Radiographic: a bitewing is usually sufficient — the molar sits high and intimately associated with the distobuccal root of the second primary molar; an OPG helps confirm the presence of the second premolar. Asymmetric left/right eruption of the first molars should raise suspicion.
Grading (Hennessy, Table 1)
Severity is graded by resorption of the second primary molar:
| Grade | Severity | Resorption of primary second molar |
|---|---|---|
| 1 | Mild | Limited to cementum or minimal dentine penetration |
| 2 | Moderate | Dentine resorption without pulp exposure |
| 3 | Severe | Distal root resorption with pulp exposure |
| 4 | Very severe | Resorption affecting the mesial root |
Self-correcting cases are predominantly Grade 1–2; impacted cases are predominantly Grade 3–4.
Management guidelines
Decision factors
Patient age · status of the second primary molar · presence of the second premolar · severity grade.
- Diagnosed before age 8 → a 6-month observation period is advisable. If no correction occurs, treat the molar as irreversibly impacted and intervene. Early diagnosis is essential to halt root resorption of the primary molar.
- Grade 1 — observe (allow spontaneous correction).
- Grade 2 — active treatment: interproximal wedging or distal tipping.
- Grade 3 — active distal tipping (removable appliance or fixed brackets); may require extraction of the primary molar.
- Grade 4 — extract the primary molar and obtain a full specialist malocclusion assessment to decide whether space should be preserved.
- If the second premolar is absent, it may be best to extract the primary molar and allow the permanent molar to drift mesially and close the space.
Techniques — separation: elastomeric, Kesling, or brass-wire separators (close supervision; apical dislodgement risks infection). Distal tipping: transpalatal arch with a distal cantilever hook, or a sectional NiTi wire from a buccal bracket. Relapse is common after repositioning — maintain space with a band and distal extension on the primary molar, or a Nance/palatal arch once it is corrected.
| Treatment | Indication | Notes |
|---|---|---|
| Observation (6 months) | Grade 1; diagnosed before age 8 | 50–69% self-correct; intervene if no correction |
| Interproximal wedging | Grade 2; little movement needed | Elastomeric / Kesling / brass-wire separator; supervise closely |
| Distal tipping | Grade 2–3; significant mesial movement | TPA + distal hook, or NiTi wire from buccal bracket; removable or fixed |
| Extract primary molar | Grade 4, or absent second premolar | Specialist malocclusion assessment; allow molar to drift if premolar missing |
| Space maintenance | After repositioning (relapse risk) | Band + distal extension, or Nance / palatal arch |
Consequences if untreated
Pain and infection around the second primary molar, premature exfoliation of that molar, arch-length/space loss, and impaction or delayed eruption of the second premolar.