Alkaline phosphatase activity in gingival crevicular fluid during orthodontic treatment with different extraction protocols for maxillary canines: a randomized controlled trial

BACKGROUND: Alkaline phosphatase (ALP) activity in gingival crevicular fluid (GCF) reflects localized periodontal and alveolar bone remodeling during orthodontic tooth movement. Although ALP changes have been investigated during leveling and alignment or active orthodontic movement, the biological impact of tooth extraction timing relative to orthodontic force application remains insufficiently characterized. OBJECTIVE: This randomized controlled trial aimed to compare ALP activity in gingival crevicular fluid between different extraction protocols in maxillary canines over a 6-week period. The primary outcome was the between-group difference in ALP activity across repeated time points. METHODS: Sixty patients with moderate maxillary crowding were randomly allocated, using concealed allocation into three equal groups: Group A (leveling and alignment only with delayed extraction), Group B (extraction only), and Group C (simultaneous extraction with leveling and alignment). GCF samples were collected weekly from Mesial and Distal sites of maxillary canines from baseline to week six. ALP activity was quantified using a spectrophotometric method. Data distribution was assessed prior to analysis. Due to predominantly non-normal distributions, non-parametric tests were primarily applied, including Friedman's test for intragroup comparisons and Kruskal-Wallis test for intergroup comparisons, with appropriate post-hoc analyses. RESULTS: Distinct temporal patterns of ALP activity were observed across the three groups. Group B (extraction only) demonstrated the highest ALP activity during the early time points, particularly at weeks 1-3, while Group C showed intermediate responses and Group A exhibited consistently lower levels. At T1, significant intergroup differences were observed. At Mesial sites, Group C showed higher ALP activity than Group A (mean difference: 0.59 IU/L), followed by Group B (mean difference: 0.28 IU/L compared with Group A; p < 0.05). At Distal sites, Group B demonstrated the highest ALP activity compared to Group A (mean difference: 1.00 IU/L; p < 0.01), with Group C showing intermediate values compared with Group A (mean difference: 0.73 IU/L). CONCLUSIONS: Tooth extraction was associated with increased ALP activity in gingival crevicular fluid during the early phase of orthodontic treatment. Variations in ALP patterns between extraction protocols indicate that extraction timing modulates early biochemical responses in periodontal tissues.