Secular changes of overjet and overbite among middle school students

Objective: To assess secular changes of overjet and overbite and prevalence of malocclusion of anterior tooth among early teenagers over thirty years. Methods: We recorded the overjet and overbite of 882 students (445 male and 437 female) from 1878 to 1987 (J80s group) and 481 students (269 male and 212 female) from 2000 to 2009 (J00s group), at the same middle school in suburban Sendai city, according to the chart of Handicapped Labio-Lingual Deviation (HLD) index. We excluded the students who had visited the orthodontic treatments from this study, which were 1.5% of J80s group and 10.9% of J00s group. Results: Average of overjets were significantly increased from 3.58+/-1.96 of J80s group to 4.10+/-2.07 of J00s group in male students at age 13, and also from 3.07+/-1.89 (J80s) to 3.92+/12.51 (J00s) in female students at age 13. The modes of overjet were changed 3mm to 4mm in male students at age 13 and 15 and in female students at age 15. Average of overbite was increased from 2.57+/-2.40 (J80s) to 3.01+/-1.73 (J00s) in male students at age 13, however, it was not significant. There were significantly increased overbites from 3.07+/-1.89 (J80s) to 3.92+/12.51 (J00s) in female students at age 13. The modes of overbite were changed 3mm to 4mm in male students at age 13, and 2 mm to 3mm in female students at age 13 and 15. Conclusion: Increasing overjet and overbite suggest that the prevalence of malocclusion in early teenagers might be increasing by years in Japan area. This changes, however, would be influenced by several skeletal and functional factors, including skeletal size and time course of development of alveolar/jaw bone and crown size of permanent tooth.