The objectives of this study were to examine the amount of expansion, the changes of molar inclination,
crown and root position of maxillary first molars, as well as changes of alveolar bone thickness, alveolar bone height
and buccal bone position by using cone-beam computed tomography (CBCT) after light controlled-tipping expansion
in young adult subjects. Factors related to changes in alveolar bone thickness (ABT) were also investigated. Maxillary
dental expansion was performed in twenty-four patients (age 15.3-26.5-year-old) with orthodontic fixed appliances
and a straight rectangular titanium molybdenum alloy (TMA®) wire which produced 126 ± 27 g of expansion force.
Dento-alveolar changes were evaluated using CBCT images acquired before (T0) and 3 months after expansion (T1).
Mann-Whitney U-tests, Wilcoxon matched pairs signed rank tests, Kruskal-Wallis test with the Dunn-Bonferroni tests
were used to compare the changes. Spearman’s rank correlation analysis was performed to identify factors associated
with the changes of ABT. The significance level was set at .05. Significant buccal controlled-tipping of the first molars
occurred leading to a significant increase of intermolar width (IMW) (P<0.01). ABT at bucco-crestal site of mesio-buccal
root (ABT-MB-L1) significantly decreased (P<0.05), while ABT at palatal sites (ABT-Pa) significantly increased (P<0.05).
Buccal bone position (BucBonePos) significantly displaced buccally (P<0.05). ΔIMW and the rate of expansion significantly
positively related to ΔABT-MB-L1 (P<0.05). Initial ABT was significantly negatively correlated with ΔABT-MB-L1 and
ΔABT-Pa (P<0.05). The study concluded that some degrees of ABT-MB-L1 reduction and ABT-Pa gain were observed
when applying force lower than 130 g for controlled-tipping maxillary dental arch expansion. These changes were
related to ΔIMW, rate of expansion, and initial ABT. Buccal displacement of outer surface of bucco-crestal bone
was observed.