Date of Award

Spring 2005

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Dentistry

First Advisor

Lobner, Douglas

Second Advisor

Bradley, Thomas

Third Advisor

Willalobos, Francisco

Abstract

Research into the ability of stem cells to differentiate into many different types of tissues is a new and exciting area of research. Recently, stem cells taken from adult tissues have been shown to have pluripotent abilities similar to embryonic stem cells. Adult stem cells may provide a way to restore or regrow tissues and organs that have been damaged due to disease or injury. These adult stem cells have been isolated from several tissues, including the dental pulp. In this study, we isolated stem cells from the dental pulp ofunerrupted third molars. These cells were grown in vitro. These cells were compared to several known cell types that were also grown in vitro: mouse glial cells, mouse pure neuronal cells, and mouse embryonic stem cells. The toxicity of two types of amalgam, mercury and zinc was tested on the four cell types. The MTT cytotoxjcity assay was performed on these cells using the different dental materials. It has been previously published that the zinc found in some dental amalgam is the main mediator for cell death of neurons. However, the toxicity of amalgam is unknown for dental pulp stem cells. We tested the toxicity of zinc-free amalgam to dental pulp stem cells and compared this to the toxicity of zinc-free amalgam to the three mouse cell lines. We also tested the toxicity of zinc-containing amalgam on all four cell lines. We compared the toxicity of zinc-free amalgam to the toxicity of zinc containing amalgam for the dental pulp stem cells. Later we tested the toxicity of two known toxic components of amalgam, mercury and zinc, on the dental pulp stem cells and the three mouse cell lines. We found that there were differences in the cytotoxicity of the different materials to the different types of cells. Amalgam that contained zinc was more toxic to dental pulp cells and the three mouse cell types than zinc-free amalgam. Interestingly, dental pulp stem cells were also the most sensitive to the toxicity of zinc-free amalgam of the four cell lines tested. When mercury toxicity was tested, embryonic mouse stem cells were the least sensitive followed by dental pulp stem cells, pure neuronal cells, and glial cells. When zinc toxicity was tested the glial cells and the dental pulp stem cells were less sensitive than embryonic mouse stem cells and pure neuronal cells. The differences in cytotoxicity that were found are interesting to note. It has been proposed to use dental pulp stem cells to regrow damaged dental pulp in the future. Because of the high toxicity of dental amalgam (even zinc-free amalgam) to dental pulp stem cells, the dental pulp stem cells should not be exposed to dental amalgam. The differences in the toxicity of mercury and zinc to the different cell lines show that cells behave differently to chemical insults. Thus, there can be no one cell type used to test for cytotoxicity of chemicals found in dental materials.

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