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[Etiological study of relationship between impacted permanent teeth and malocclusion].

This investigation was undertaken to determine the causes of impacted permanent teeth and whether they have any influence on dentition, occlusion and skeletal patterns. The materials used were dental X-rays, occlusal dental X-rays, panoramic radiograms and cephalograms and dental casts of 194 cases (51 males and 143 females) which revealed impacted permanent teeth among 3979 cases (1215 males and 2764 females) from 1964 to 1985 in the Department of Orthodontics, School of Dentistry, Aichi-Gakuin University. The results obtained were as follows: 1. The incidence of impacted permanent teeth in these samples was 4.9% of the entire number of orthodontic patients. There was no significant difference between sexes. 2. The incidence according to the number of impacted permanent teeth was as follows: one impacted tooth, 74.8%; two impacted teeth; 21.1%, three impacted teeth; 3.6%, four impacted teeth; 0.5%. The incidence of two symmetrically impacted teeth was 61.5%. 3. As to the type of impacted teeth, the frequency of maxillary central incisors was the largest (33.7%), followed by 3 (25.0%), 5 (22.2%), 5 (11.9%), 2 (4.4%), 3 (1.2%), 4 (0.8%), 4 (0.4%), and 7 (0.4%). But no impacted teeth were found in the regions of 1, 2, 6, 6, 7 and 7. 4. As to impacted teeth and the type of malocclusion, the spaced arch in the anterior region had impacted teeth most frequently followed by crowding, open bite and lateral cross bite. Malocclusions with the smallest incidence were cross bite and upper protrusion. The spaced arch had a higher incidence of impacted teeth than bimaxillary protrusion. In the posterior region (impacted molar teeth), the lateral cross bite, spaced arch, and upper protrusion had impacted molars most frequently, crowding was second and cross bite had the least. 5. In the direction of long axis, the impacted tooth with a horizontal direction was found most frequently (35.2%), followed in the order of frequency by inverse direction (32.7%), labial or mesial tipping (22.0%), lingual or distal tipping (5.7%), and right-angled (4.4%). Moreover, the inverse maxillary central incisor and mesially tipped maxillary canine were found most frequently. The frequency of maxillary central incisors with crooked roots was 64.7%, which was higher than that of maxillary canines (19.0%). 6. Lack of space is the most frequently found cause of impacted teeth, and in the anterior region this was the main cause of canine impacted teeth. Eruption impediment by supernumerary teeth and trauma were found to be characteristic causes of anterior impacted teeth.