Nationwide institution-based survey of malocclusion in first-visit orthodontic patients aged 18 years or younger in Japan

Purpose We aimed to describe the distribution and characteristics of malocclusion among first-visit orthodontic patients aged 18 years or younger in Japan and provide baseline data for defining severe malocclusion using objective indicators.Materials and methods An online questionnaire survey was conducted among medical institutions affiliated with members of the Japanese Orthodontic Society, targeting patients aged ≤ 18 years who had their first visit between 1 April 2022 and 31 March 2023. Survey items included the classification of malocclusion types, occlusal indices (molar relationship, overjet, overbite, and midline deviation), impacted teeth, congenital absence of permanent teeth, crossbite, scissor bite, and the presence or absence of suspected developmental insufficiency of oral function (DIOF). Chi-square tests were used to compare groups (significance level: p < 0.05).Results Responses were obtained from 69 institutions (29 university hospitals and 40 private dental practices). Among 11,608 first-visit patients, 55.4% underwent orthodontic treatment. The most common malocclusion was crowding (1,865 cases), followed by maxillary (1,226 cases) and mandibular (960 cases) protrusion. The proportion of suspected DIOF was the highest among patients with open bite (45.1%). Significant differences were observed between university hospitals and private practices in the distribution of insurance-covered conditions, types of malocclusion, occlusal indices (overjet), impacted teeth, congenital absence of permanent teeth, and crossbite.Conclusion The results of this nationwide institution-based survey characterize the distribution of malocclusion among first-visit orthodontic patients aged 18 years or younger in Japan and provide foundational data for defining severe malocclusion using objective indicators.