[Clinical study of ectopic eruption of permanent incisors and first molars]

Using the X-ray films, plastic models and pathological photograph of 4824 patients seen at the Department of Pedodontics of Iwate Medical University, the patterns of ectopic eruptions of permanent incisors and first molars (restricted to these teeth in this study) were classified into 4 groups (I-IV) to investigate the conditions of its incidence, size of the teeth and dental arch, and conditions at the stage of the mixed and permanent dentitions.

1. The total frequency of ectopic eruptions was 5.6%. No difference based on sex was found. 2. By classification, ectopic eruptions of the upper and lower permanent central incisors (Group I) amounted to more than half of the total frequency. The incidence of ectopic eruptions of the upper and lower permanent first molars (Group III) was very low and amounted to only 4.6% of the total frequency. 3. In Groups I and III, the incidence was higher in the maxilla than in the mandible. 4. Based on sex, the incidence was higher in boys in Group III and in girls in group II. 5. Ectopia of the permanent central incisors was frequently bilateral and those of the lower permanent lateral incisors and upper permanent first molars were frequently unilateral. 6. The mesiodistal width of the ectopically erupted permanent teeth tended to be somewhat enlarged, but showed no significant differences from Ono's mean value. 7. In ectopic eruptions at the area of the incisors, the C-C distance was narrowed with an increase in the ectopically erupted permanent teeth. 8. In patients in whom the permanent dentition was formed without occlusal guidance, the basal arch length and dental arch length were large and basal arch width and dental arch width were small. 9. In cases which were followed from the deciduous dentitions to permanent dentitions, the anterior tooth area at the stage of the mixed dentition was frequently crowded. Occlusal guidance was carried out in more than half of these cases.