Abstract: Objective: To investigate maxillary changes of rapid and slow maxillary expansion protocols through cone beam CT （CBCT）analysis. Methods: Sixteen patients (mean age 9.5years) were randomly distributed into 2 groups: rapid maxillary expansion (n = 8) and slow maxillary expansion (n = 8) via Hass appliance. Maxillary changes were measured by cone beam computer tomography analysis. The buccal bone plate thickness, palatal cleft width， nasal cavity width, and maxillary width were also recorded accordingly. Results: We found no statistical difference between the two groups in terms of palatal cleft width， nasal cavity width, and maxillary width（P＞0.05).Buccal bone plate thickness reduction was smaller in slow maxillary expansion group than those in rapid maxillary expansion group, althrough there was no statistical difference. Conclusions: Rapid and slow maxillary expansion could expand the maxillary width, and the slow maxillary expansion might result in light and continuous force which might be more favorable to periodontal tissue.

Key words: cleft lip and palate, maxillary expansion, cone beam CT