Cross-sectional study of orthodontic treatment and missing of permanent teeth in two birth cohorts of Finnish students according to sex.

Undergraduate students (n = 451) at a Finnish university were studied. For analysis, the subjects were divided into two birth cohorts: those born before 1955, and those born in that year or later. Information about previous orthodontic appliance therapy was obtained from the students by using a structured questionnaire. Missing permanent teeth (second and third molars excluded) were recorded at a dental examination. Every 10th student had received orthodontic treatment; the proportion of orthodontically treated subjects was higher for females (14%) than for males (5%). Seven percent of students born in 1954 or earlier and 15% of the younger students had had orthodontic treatment before 1977. In 39% of subjects, at least one permanent tooth was missing while only 12% had lost more than two permanent teeth. The tooth missing most often was the permanent mandibular first molar (in 23% of subjects). Frequency of tooth loss was the same in males and females. At least one permanent tooth was missing in 48% of the older and in 31% of the younger students. At least one first molar had been lost by 36% of the older students and 20% of the younger ones. Fewer first molars but more permanent teeth anterior to the first molars were missing in subjects who had had orthodontic treatment than in subjects who had not had such treatment. Among Finnish students the frequency of extraction of permanent teeth because of caries is decreasing, and the frequency of orthodontic treatment is increasing. Females are more likely to seek orthodontic treatment than males are.