Effects of fluoride in bone repair: an evaluation of RANKL, OPG and TRAP expression

The objective of this study was to evaluate comparatively the effect of fluoride in the expression of the receptor activator of nuclear factor kappa B ligand (RANKL), osteoprotegerin (OPG) and tartrate-resistant acid phosphatase (TRAP) in alveolar bone repair in rats. We used 3 groups of male Wistar rats (n = 5/group), which received drinking water containing different doses of F (NaF): 0, 5 and 50 ppm, for 60 days before the incisors extraction. The upper incisors were extracted and the animals were killed 7, 14, 21 and 30 days after extraction. The hemi-maxillae were collected for microscopic examination (histomorphometric and immunostaining for RANKL, OPG and TRAP). Histomorphometric analysis confirmed an increase in the volume density of neoformed bone between 7 and 30 days for groups control, 5 and 50 ppm of F, with a concomitant decrease in the volume density of connective tissue and blood clot. Higher blood clot for groups 5 and 50 ppm of F at 30 days was observed. The RANKL and OPG expressions were not changed by chronic exposure to fluoride in the drinking water during the studied periods; on the other hand, TRAP expression was changed (at 7 days) by chronic exposure to fluoride (p < 0.05). It was concluded that F in high concentrations can slow the blood clot remission and bone repair, and alter the TRAP expression in the beginning of the bone tissue repair. However, a better understanding about this blood clot remission phenomenon is required.