LAUSR

Background Cervical headgear (CH) is a commonly used orthodontic appliance and its dentoalveolar changes are known. However, the effects related to gender and timing have gained less attention. Objectives To examine dimensions of dental arches among children with Class II occlusion without posterior mandibular rotation according to timing of Kloehn-type CH treatment. Trial design Prospective, randomized, parallel-group controlled trial. Methods Sixty-seven seven-year-old children with a Class II occlusion were included in the study. The children were randomized into two equal-size groups in 1:1 ratio by sealed-envelope randomization. The early group (EG, n = 33) was treated between T0 and T1 (26 months), right after eruption of the first maxillary molars. The late group (LG, n = 34) was treated between T1 and T2 (24 months). The children were treated with CH until normal Class I occlusion on first molars was achieved. Impressions for dental casts were taken from all participants at T0, T1, and T2. Blinding was applicable for outcome assessors. Changes in dental cast measurements were compared between the groups and genders using t-test, Mann-Whitney U-test, and repeated measures analysis of variance. Results Of the children, 56 completed the study. The maxillary arch length and the transversal changes between the upper canines and upper first molars were significantly increased in EG at T0-T1 (P < 0.001). At T2, the transversal dimension between the upper first molars was larger (P < 0.05), and in the lower arch the mandibular arch length (P < 0.05) and the transversal dimension between the lower first molars (P < 0.01) were increased in EG males compared to LG males. No harms were encountered. Conclusions The male gender benefits most from early timing of the CH treatment, showing larger dimensions at the end of the follow-up. The results clearly indicated a wider and longer upper dental arch and spontaneous expansion of the lower dental arch after treatment. Clinical Registration NCT02010346.