The relationship between TNF-alpha and RANKL during tooth root formation

Objectives: Tooth root formation requires alveolar bone resorption, and tumor necrosis factor-alpha (TNF-alpha) is known as crucial protein in this events. Furthermore, receptor activator of NF-kappa B ligand (RANKL) is known as osteoclastgenesis. The purpose of this study was to investigate the relationship between TNF-alpha and RANKL during tooth root formation in terms of molecular level.

Methods: The tooth germ of first molar was surgically isolated from the Sprauge-Dauley rats of postnatal day 1, 3, 5, 7 and 13 and examined histologically. Dental follicle was removed by mechanical means. After total RNA was extracted from dental follicle at each of the postnatal day, the expressions of TNF-alpha, RANKL and beta-actin mRNAs were analyzed by quantitative RT-PCR. The data were analyzed using Fischer's PLSD.

Results: The expression of TNF-alpha mRNA increased up to postnatal day 3, and then decreased up to postnatal day 13. The expression of TNF-alpha mRNA atpostnatal day 3 was significantly higher than those at postnatal day 5, 7 and 13 (p<0.01). The expression of RANKL mRNA increased up to postnatal day 7, and decreased at postnatal day 13. The expression of RANKL mRNA at postnatal day 7 was significantly higher than those at postnatal day 1, 5 and 13 (p<0.01).

Discussion: These results suggest that cells of dental follicle might have the capacity to synthesize TNF-alpha on postnatal day 3, which is a stage of enamel organ was constructed. The expression of RANKL mRNA is significantly up regulated on postnatal day 7, which is a stage of crown formation was completed, and then osteoclastgenesis around the portion of root formation might start at postnatal day 10.

Conclusions: These results suggest that the expression of TNF-alpha mRNA first occur and then RANKL mRNA, induce resorption of alveolar bone and start root formation.