Crevicular alkaline phosphatase activity during the application of two patterns of orthodontic forces

The objective of this study was to test the hypothesis that using a gradually increasing orthodontic force would induce an increased activity of osteoblasts compared to a relatively constant orthodontic force.

Twelve orthodontic patients participated in this study. In a split mouth design, one maxillary canine undergoing distal movement received a relatively constant continuous retraction force, while the contralateral canine received a gradually increasing retraction force. Gingival crevicular fluid (GCF) samples were collected from both experimental sites at weekly intervals and analysed spectrophotometrically for the activity of alkaline phosphatase enzyme, which was used as a biological marker for osteoblastic activity.

With the exception of the maxillary first molar receiving gradually increasing orthodontic force, the results revealed a consistent pattern of alkaline phosphatase activity. This pattern included an initial rise from baseline to the first week, then a peak in the second week. This peak was followed by a reduction in enzyme activity in the third week. The overall increases in enzyme activity at the maxillary canines and the maxillary first molars in the relatively constant force group were 179·76% and 332·90%, respectively. The overall increases in enzyme activity at the maxillary canines and the maxillary first molars in the gradually increasing force group were 304·81% and 493·08%, respectively.

The use of gradually increasing orthodontic force induces increased activity of osteoblasts during the initial stage of orthodontic tooth movement compared to that induced by a relatively constant orthodontic force.