Introduction: Bone-borne maxillary expander (BBME) are designed to provide additional anchorage to widen the maxillary arch for patients who exhibit maxillary transverse deficiency. One form of BBME is the hybrid BBME which uses mini-implants (bone-borne) and posterior teeth (tooth-borne) as anchorage for maxillary expansion. The other form of BBME is absolute BBME which only uses mini-implants as anchorage. It is not clear in the literature if there is a difference in skeletal and dental changes with these two types of expanders. The objective of this study was to compare the skeletal, dentoalveolar, and periodontal changes between the hybrid and the absolute BBME using cone-beam computed tomography (CBCT). Materials and Methods: Thirty four adolescent patients with transverse maxillary deficiency were divided into two groups; the first group (16 patients) was treated with the hybrid BBME, and the second group (18 patients) was treated with absolute BBME. CBCT scans were taken pre-treatment (T1); and immediately post-expansion (T2) to measure the changes in midpalatal suture opening, total expansion (TE), alveolar bone bending (ABB), dental tipping (DT), and buccal bone thickness (BBT) at the first molar (M1) and first premolar (PM1) levels. Data were analyzed using paired t-test and sample t-test. Results: Midpalatal suture separation was found in 100% of the patients and the pattern of midpalatal suture opening was parallel in both groups. The total expansion at M1 level was 5.9 mm in the hybrid, and 4.7 mm in the absolute BBME group. The skeletal contributions were 56% and 83% of the TE in hybrid and absolute BBME groups at the M1 level, respectively. Subjects in the absolute BBME group experienced significantly less dental buccal tipping (0.5◦ for M1, and -1◦ for PM1), and BBT loss (0.2 mm for M1, and 0.4 mm for PM1) than the hybrid BBME group, (
