Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Clinical Dentistry

Program

Orthodontics

Supervisor

Hamilton, Douglas

2nd Supervisor

Tassi, Ali

Abstract

Human periodontal ligament (PDL) cells are able to undergo differentiation into an osteogenic phenotype. PDL cells lines from a 46-year-old female and a 59- and 68-year-old male were grown on a collagen scaffold for 7- or 21-days. Growth was carried out in a control media and one of three treatment conditions of osteogenic media by itself, with periostin, or with cementum protein 1. Alizarin red staining (ARS) and absorbance assays were used to quantify the amount of mineralization. Relative changes in expression of alkaline phosphatase (ALP), bone sialoprotein, periostin and osteocalcin (OCN) were determined using real-time quantitative PCR. All three treatment conditions had visible mineralization present at 21-days, while the 21-day controls and all 7-day samples did not. ARS concentrations were also much higher for these samples. All treatment conditions showed OCN and ALP levels to decrease from 7- to 21-days. Relative to controls, all treatment conditions showed higher OCN levels at 7-days and lower ALP levels at 21-days.

Summary for Lay Audience

Teeth are attached to the surrounding bone by the periodontal ligament, a fibrous network made up of collagen, other proteins, fluid and cells. This periodontal ligament is required for non-traumatic chewing, tooth eruption, and the orthodontic movement of teeth. During orthodontic tooth movement, bone is removed from the side to which the tooth moves, and new bone is deposited on the opposite side.

Fibroblasts are principally viewed as collagen and non-mineralized connective tissue forming cells. Existing research has shown that the fibroblasts within the periodontal ligament are able to convert from a collagen producing role to one of bone formation, functioning similar to osteoblasts. This process is not fully understood, and furthering knowledge in this field of study may prove to have clinical implications for orthodontics, as well as other areas of dentistry and possibly general medicine.

In this study, periodontal ligament cells from three different donors were grown on collagen coated plates in four different growth conditions. One of these was a control media, while three of the conditions were different treatment media expected to promote tissue mineralization. After one week and three weeks, the amount of mineralization and the changes in expression of four genes of interest were examined.

Mineralization was seen in all samples grown in treatment media after three weeks, but none was seen at one week, nor was it present in cells grown in the control media. The expression of genes for alkaline phosphatase and osteocalcin were shown to decrease from one week to three weeks for cells grown in the treatment media. Osteocalcin expression was higher for the treatment media cells at one week than it was for cells grown in the control media. Alkaline phosphatase expression was lower for the treatment media cells at three weeks than it was in cells grown in the control media.

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