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Master of Clinical Dentistry




Dr Douglas Hamilton

2nd Supervisor

Dr Ali Tassi

Joint Supervisor


Existing research alludes to the fact that human periodontal ligament cells differentiate into an ossifying phenotype in response to differential gene expression during orthodontic tooth movement. The purpose of this research was to validate the differentiation of human periodontal ligament cells of young individuals in the presence of specific proteins and stimuli (cementum protein, periostin and osteogenic media), which mimic the environment of the periodontal ligament. Another objective was to assess the differential gene expression within these cells under the same conditions. A protocol was developed to provide a collagen-protein scaffold on which human periodontal ligament cells were maintained for one or three weeks. A mineralization assay and reverse-transcription polymerase chain reaction were performed at each timepoint. The results indicated that in the presence of the aforementioned conditions, human periodontal ligament cells differentiate and produce calcium. The response of specific genes (ALP and OCN) supported this finding. Further research is indicated to support this claim and provide comparison of the response of human periodontal ligament cells in an older population.

Summary for Lay Audience

Orthodontics is a specialty within the broad spectrum of Dentistry comprising of dentofacial orthopedics and orthodontic movement of teeth. Movement of teeth requires bone removal in the direction of the root movement and new bone formation in areas where the root is moving away from. The periodontal ligament anchors the tooth root to the surrounding bone. Therefore, the periodontal ligament environment must change to allow the tooth root to move in a certain direction. Existing research provides evidence that specific proteins are expressed differently along different areas of the root during orthodontic tooth movement depending on the direction that the root is moving. Periostin and cementum protein 1 are two such proteins involved in this process.

To validate that these proteins alter the environment around the tooth root depending on whether bone is forming or bone is being removed, a protocol was developed to show that the periodontal ligament cells of young individuals can evolve into bone forming cells in the presence of these proteins. The aim of the environment created for these cells to grow and evolve was to best mimic the periodontal ligament. To fully understand that these evolved cells may produce bone, specific genes were analyzed to see if they were increased or decreased as a result of the presence of these proteins.

Using this methodology, it was determined that the cells evolve in the presence of these proteins and deposit calcium. Genes involved in bone formation were shown to increase as well, further supporting this claim. More research is indicated to evaluate the response of cells from an older population.