Abstract： First permanent molar may be positioned too mesially during eruption and result in the resorption of the distal root of the second primary molar. Ectopic eruption of first permanent molar ususlly causes the loss of the space and decrease of the arch length， and in severe cases leads to premature loss of the second primary molar. Two types of ectopic eruption of first permanent molars were identified--reversible and irreversible. Intervention should be done toward irreversible ectopic eruption. Therapy could be active or passive. Active therapy methods include separators and distalizing appliances. Passive therapy methods include dissecting the crown or extraction of second primary molar. Clinical manifestation of ectopic eruption of first permanent molar and routine therapy methods were discussed in this article.
