The pressure-tension hypothesis is the governing dogma of orthodontic tooth movement. This theory proposes that the application of loads to the crown of a tooth during orthodontic mechano-therapy results in differential site-specific reactionary strains in the para-dental tissues. Briefly, following the application of orthodontic load the bone and periodontal ligament (PDL) on one side of the tooth is placed in compression favoring bone resorption, while on the other side of the tooth they are placed in tension favoring osteogenesis The present in vitro model provides a surrogate for the PDL on the tension side of the tooth during orthodontic tooth movement and aims to identify mechanically induced changes in the expression of osteo-regulatory cytokines in human PDL cell cultures in response to tensile mechanical strain.
Materials and Methods: PDL explants were obtained from pathology free bicuspids of two human subjects following extraction of the teeth for orthodontic purposes. Following serial passage, cells were plated on Uniflex� plates and consigned to either the experimental or control groups. Experimental cells were exposed to a cyclic uniaxial tensile mechanical strain for 6,12 or 24 hours using the Flexercell FX 4000 strain unit. Total RNA was extracted using a two-step procedure and samples were analysed using real-time RT-PCR assays for a range of osteo-regulatory cytokines.
Results: Human PDL cells expressed mRNA for a range of cytokines of known significance to osteogenesis and osteoclastogenesis in response to mechanical stimulation.
Conclusions: The production of osteo-regulatory cytokines by PDL cells in response to mechanical strain suggests that these cells have the potential to contribute to the osseous modeling of orthodontic tooth movement. The presence of osteogenic signalling drive in response to tensile strain tends to support the basic assertions of the pressure-tension hypothesis.
| Identifer | oai:union.ndltd.org:ADTP/266464 |
| Date | January 2007 |
| Creators | Pinkerton, Mark Neil, n/a |
| Publisher | University of Otago. School of Dentistry |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Mark Neil Pinkerton |
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