EVALUATION OF OSTEOCALCIN AND PYRIDINIUM CROSS-LINKS OF BONE-COLLAGENAS MARKERS OF BONE TURNOVER IN GINGIVAL CREVICULAR FLUID DURING DIFFERENT STAGES OF ORTHODONTIC TREATMENT

Osteocalcin (Oc) and the collagen cross-links pyridinoline (Pyr) and d eoxypyridinoline (dPyr) are used as markers of bone turnover in metabo lic bone diseases. The aims of this study were: 1) to establish if Oc, Pyr and dPyr can be detected in GCF and 2) using the orthodontic toot h movement model of alveolar bone resorption to evaluate GCF levels of osteocalcin and these collagen cross-links as markers of bone breakdo wn. Plaque, colour and bleeding indices, probing measurements and GCF samples were collected at two sites in each of 20 adolescents, during 4 stages of fixed appliance therapy: (1) prior to appliance fit, (2) p ost appliance fit, (3) during active retraction of the maxillary canin es, (4) during retention. GCF was collected onto filter paper strips a nd the volume determined by weighing. An ELISA kit was used for the de tection of osteocalcin, whereas Pyr and dPyr were assayed using high p erformance liquid chromotography (HPLC). Wilcoxon signed ranks test an d Bonferroni correction revealed statistically significant increases i n plaque (p= 0.012), GCF volume (p=0.024) and osteocalcin concentratio n (p=0.012), between stages 1 and 2. There were no statistically signi ficant differences between the other variables at this stage or betwee n any of the variables at stages 2 and 3, or between stages 3 and 4. A l but 3 of the GCF samples yielded detectable osteocalcin, with large site and subject variation. The median values of osteocalcin and osteo calcin concentration of all the samples were 87.5 pg and 66 pg/mu l, w ith a range of 0-1,248 pg, 0-1,572 pg/mu l. The detection of osteocalc in in GCF during every stage, the wide variation between subjects, and the lack of a consistent pattern related to stages of orthodontic tre atment, suggests that osteocalcin may merely be a constituent of GCF a ssociated with the developing dentition, which would reduce its potent ial as a marker of bone turnover in this group. None of the 16 GCF sam ples analysed for Pyr and dPyr gave a positive result. This study conf irms that fitting an orthodontic appliance results in plaque accumulat ion and increased gingival inflammation, and that GCF volume is the mo st sensitive indicator of that inflammation. Osteocalcin was detected in GCF collected from adolescents, whereas Pyr and dPyr could not be d etected. Further work is required to establish whether GCF osteocalcin levels can be used as a marker of bone turnover, and whether improvem ents in the sensitivity of detecting Pyr & dPyr make further study of these promising bone markers worthwhile.