Ectopic eruption of the maxillary first permanent molar: etiologic factors.

For clinical handling, it is important to determine whether any etiologic factors, alone or in combination, are of more importance than others in causing ectopic eruption of a maxillary first permanent molar. Etiologic factors involved in ectopic eruption of maxillary first permanent molars were investigated in 129 children with a mean age of 8.6 years. Ninety-two children (fifty-eight boys and thirty-four girls) had ectopic eruption and thirty-seven children served as controls and were matched by age and sex. Two types of ectopic eruption could be distinguished: a reversible type in which the permanent molar frees itself and an irreversible type in which the permanent molar remains in a locked position. Measurements were made on lateral head films, orthopantomograms, and dental casts. For 104 subjects all variables could be measured. Data was analyzed by discriminant analysis. Children with irreversible ectopic eruption had significantly larger permanent molars and a more pronounced mesial angle of eruption. A tendency toward a shorter maxilla was also found. No significant difference was found between sides with reversible ectopic eruption and sides with normal eruption. From the discriminant analysis between groups and all variables investigated, 90.7 percent of the cases could be correctly classified into groups. This study indicates that sufficient space may be gained for the premolars if the mesial tipping of the first molar is corrected, despite the tendency toward a shorter maxilla and larger than normal permanent molars.