Date of Award
Thesis - Restricted
Master of Science (MS)
Bradley, Gerald T.
The orthodontic literature has reported on the cytotoxicity of orthodontic materials in various culture systems. However, there have been no studies that have examined the cytotoxic effects of orthodontic archwires and cements on neuronal cells. Moreover, little is known concerning the mechanism of toxicity for these popular compounds. This investigation used murine cortical cell cultures to examine the in vitro neurotoxicity of two orthodontic adhesives and five commonly used orthodontic metallic archwire alloys. The materials examined included the composite resin, Transbond TM XT, the compomer cement. Band-Lok TM, 0.016 inch nickel-titanium. copper-nickel-titanium, titanium-molybdenum, Elgiloy, and stainless steel archwire alloys. Standard sized samples of each material were placed on tissue culture inserts suspended above the cell cultures. Neuronal death was determined using the lactate dehydrogenase release assay 24 hours after exposure to the archwires. The results indicated that Band-Lok™ was significantly toxic and remained so even after seven days of setting. Washing Band-Lok for seven days in Eagles ' MEM virtually eliminated neurotoxicity. Transbond™ XT was not significantly toxic. With respect to archwire alloys, the results indicated that nickel-titanium, copper-nickel-titanium and titanium-molybdenum alloys were not neurotoxic, while stainless steel and Elgiloy were significantly toxic. Washing the archwires for 7 days in Eagle's MEM did not alter the toxicity. However, the free radical scavenger, trolox blocked the toxicity of both stainless steel and Elgiloy indicating that the death was free radical mediated. The caspase inhibitor, ZVAD blocked the toxicity of stainless steel, but not Elgiloy, suggesting that stainless steel induced apoptosis. Further evidence that stainless steel induced apoptosis was provided by propidium iodide staining which showed nuclear chromatin condensation and fragmentation into discrete spherical or irregular shapes characteristic of apoptosis. Given the composition of the toxic archwires, the fact that the death was free radical mediated, and the type of death occurring, the results are most consistent with the toxicity of Elgiloy being caused by the release of iron and the toxicity of stainless steel being mediated by the release of chromium. While these results may not have direct clinical applications to orthodontic practice, clinicians should consider the biological properties of the materials they use in patients when performing orthodontic treatment.
David, Alexis D., "In Vitro Cytotoxicity of Orthodontic Cements and Archwires" (2003). Master's Theses (1922-2009) Access restricted to Marquette Campus. 5114.