Background <p>This study evaluated three-dimensional volumetric changes in the palatal vault and pharyngeal airway following facemask therapy (FM) with or without slow maxillary expansion (SME) in late mixed and early permanent dentition. Additionally, it compared dimensional changes in the palatal vault, including its length, height, and width.</p> Materials and methods <p>The sample included 26 patients (16 females, 10 males), aged 10 to 14 years (mean age: 11.88 ± 1.18 years) with Class III malocclusion who had completed facemask therapy, either with or without slow maxillary expansion. Patients were divided into two groups: FM/SME (<i>n</i> = 13) and FM (<i>n</i> = 13). The palatal vault was subdivided into anterior and posterior sections, and the upper airway was divided into the nasopharynx, velopharynx, and glossopharynx. Changes were assessed using CBCT before (T0) and after (T1) treatment with standardized methods. Statistical analysis included the Shapiro-Wilk test for normality, paired t-test and Wilcoxon signed-rank tests for within-group comparisons, and independent samples t-test and Mann-Whitney tests for between-group comparisons.</p> Results <p>Both groups exhibited significant increases in total palatal vault volume and posterior palatal vault volume. Nasopharyngeal volume also increased significantly in both groups from T0 to T1, while no significant changes were observed in the lower pharynx (velopharynx and glossopharynx).</p> Conclusion <p>Both treatment groups demonstrated distinct effects on the palatal vault and nasopharyngeal volume. The FM/SME group yielded a greater increase in the palatal vault volume (16%) compared to the FM group (11.4%); however, this difference was not statistically significant. Combining FM with SME did not yield significant additional effect on the pharyngeal airway volume compared to FM alone, suggesting limited clinical advantage.</p>