Date of Award

Spring 2012

Document Type


Degree Name

Master of Science (MS)



First Advisor

Liu, Dawei

Second Advisor

Bradley, Gerard

Third Advisor

Bosio, Jose


Orthodontic movement of teeth with compromised periodontium is risky because heavy orthodontic force could exacerbate the damaged periodontal status. Guidelines for moving periodontally-compromised teeth have not been established due to the lack of scientific evidence about the relationship between periodontal inflammation and mechanical force. In periodontitis, lipopolysaccharide (LPS) is recognized in the periodontal ligament (PDL) by toll-like receptors (TLR) which leads to destruction of periodontal tissues through inflammatory cascades. Recent studies have demonstrated that absence of TLR2 and TLR4 leads to reduced alveolar bone loss in mice. Therefore, reduction of TLR2 and TLR4 on PDL cells can have a protective effect against the attack by periodontal pathogens and, accordingly, decrease susceptibility to periodontal disease.

The objective of the study was to explore the effect of mechanical stress on the expression of toll-like receptors on human periodontal ligament fibroblasts (hPDLF).Human periodontal ligament fibroblasts (hPDLF) were cultured and seeded on glass slides. Upon confluence, the cells were starved for 24 hours and then subjected to fluid shear stress (FSS) for 1 hour. After FSS, the cells were lysed to test the phosphorylation of extracellular regulated kinase (ERK)1/2 and the expressions of TLR2 and TLR4. To explore the possible involvement of MAPK (ERK1/2) signaling pathway, a specific ERK1/2 inhibitor was added during the flow. The whole cell lysates from each group were immunoblotted with anti-TLR2 and anti-TLR4 antibodies. The signals of interest were determined using the ECL method. For quantification, densitometries of gel bands of interest were normalized to that of vinculin.

One-way ANOVA with Tukey's post hoc test was used to compare the results among the experimental groups, with p value being set at 0.05. As found, TLR4 but not TLR2 was abundantly expressed in hPDLF cells. Compared to the static controls, FSS significantly reduced the expression of TLR4. When PD98059 was added, the FSS-induced reduction of TLR4 was significantly recovered back to the control level. Conclusively, mechanical stress down-regulates the expression of TLR4, which is mediated by MAPK signaling pathway. Our findings suggest that FSS (mimicking light orthodontic force application) could possibly alleviate the compromised periodontal status via down-regulation of TLR4.