Date of Award

Summer 2019

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)



First Advisor

Nimeri, Ghada

Second Advisor

Lobner, Douglas

Third Advisor

Liu, Dawei


Objectives:Orthodontic appliances with silver soldering can be in the oral cavity for several years and very few studies have been done to detect the biosafety of the silver solders. The aim of this in vitro study was to compare the cytotoxicity effects of two different solder materials on Human Periodontal Ligament Fibroblast cells (HPLF).Methods:Two commonly used solder materials from two companies, (Leone and Summit) with different metal elements and percentages were studied. The solder samples were exposed to HPLF cells for 48 hours and the cytotoxicity effect of soldered materials on HPLF cells was measured via the MTT colorimetric assay (n=10/sample) and morphological microscopic analysis. Furthermore, the mechanism of cytotoxicity of the Summit silver solder was investigated using both a caspase inhibitor Z-VAL-Ala-Asp-flu-oromethylketone (ZVAD) and the free radical scavenger Trolox (n=8/sample). Statistical analysis was performed with a one-way analysis of variance (ANOVA) with a Bonferroni correction. P<0.05 was considered statistically significant.Results:Compared to control (cells only), both Leone silver solder and Summit silver solder were cytotoxic (p<.001). The 3M Unitek stainless steel bands were significantly cytotoxic compared to control. There was a significant difference in cytotoxicity between the 3M Unitek stainless steel band and the Summit silver solder (P<.001), but not the Leone silver solder. Between the two silver solders, the Summit silver solder was significantly more cytotoxic than the Leone silver solder (p <.05). These MTT results were supported by the microscopic morphological changes of the HPLF cells. Cellular necrosis is likely the method of cytotoxicity as indicated using ZVAD. Furthermore, the addition of Trolox did not prevent cell death.Conclusions:The stainless steel bands were significantly cytotoxic compared to the control. Furthermore, the two silver solder materials demonstrated different levels of cytotoxicity to HPLF cells. Summit silver solder showed significantly higher cytotoxicity than Leone silver solder.


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