Abstract: Objective To investigate effects of rapid and slow maxillary expansion protocols on the levels of alkaline phosphatase (ALP). Methods Thirty patients (mean age 10.2years) were randomly divided into 2 groups: rapid maxillary expansion group(n = 15) and slow maxillary expansion group (n = 15) via Hass appliance. ALP activity was measured by a full automatic biochemical analyzer at the following time points: before activation, 1 week after activation, 1week, 4 weeks, 8 weeks,12 weeks in retention period. The clinical parameters, gingival index (GI) and periodontal depth (PD) were also recorded accordingly. Results No statistical difference was found between the two groups in terms of GI and PD with the exception of GI at 1 week after activation. ALP levels were significantly higher in rapid maxillary expansion group than those in slow maxillary expansion group from 1 week after activation to 4 weeks in retention, but there were no significantly difference between the two groups after 8 weeks in retention. Conclusion ALP in gingival crevicular fluid may be involved in the periodontal tissue remodeling, and the slow maxillary expansion could result in light and continuous force which might be more favorable to periodontal tissue.

Key words: alkaline phosphatase, maxillary expansion, gingival crevicular fluid