The purpose of this study was to determine the impact of insertion angle of orthodontic mini screws on the stability and resistance to movement of the mini screw, and on the peri-implant interface. Three orthodontic mini screws were placed in each tibia of six New Zealand white rabbits bilaterally (N=36), with randomized angulation (65° away, 65° toward, or 90° to the direction of applied force). After two weeks, two orthodontic mini screws within each tibia were loaded with a 200g Nitinol closed-coil spring for up to 14 days. No statistically significant differences were found among the variably angulated loaded and unloaded orthodontic mini screws in the amount of movement or change in angulation demonstrated over the experimental period. Micro CT analysis revealed no clinically significant differences in the amount of cortical bone-to-implant contact. Mini screw placement angulation seems to have minimal impact on stability and migration of orthodontic mini screws over time.

Nitric oxide (NO) is a short lived free radical regulating bone turnover and bone cell function (1, 2). Osteoclasts are multinucleated bone resorbing cells which form by fusion of pre-osteoclasts. In addition, NO is a signaling molecule in mechanical loading of the bone (3), and in orthodontic tooth movement (OTM) (4). In OTM, force is applied to the tooth and transferred to the bone resulting in bone remodeling leading to tooth movement. This project has two parts: 1) NO in osteoclastogenesis: a) An intense NO signal was observed in pre-osteoclasts preceding cell fusion. b) Osteoclastogenesis increased when cells were exposed to the NOS inhibitor, L-NMMA, during their differentiation phase. c) In contrast, pre-osteoclast fusion decreased in presence of to L-NMMA during the fusion phase. d) NOS inhibitors, decreased osteoclast formation. e) The inhibitory effect of L-NMMA on osteoclast formation was abolished with increasing concentrations of sRANKL. f) NO donors increased osteoclast formation. g) An increase in NO production coincided with pre-osteoclasts fusion. h) Inhibiting fusion decreased osteoclast formation and NO production. i) L-NMMA decreased, while NO donors increased actin free barbed ends. Conclusion: While NO initially negatively regulates pre-osteoclast differentiation, it later facilitates the fusion of mononuclear pre-osteoclasts, possibly by up regulating actin remodeling. 2) Involvement of NO in OTM: Differential expression of NOS isoforms was investigated in periodontal ligament (PDL) and bone in tension and pressure sides using immunohistochemistry with NOS isoforms in a rat model of OTM. a) Expression of all isoforms was increased in the tension side. b) iNOS and nNOS expressions in the pressure side with the cell free zone were decreased while in the pressure side without the cell free zone were increased. c) The intensity of eNOS staining was increased in the tension side. d) Duration of force only changed the pattern of nNOS expression. e) Osteocyte NOS expression did not change. Conclusion: All NOS isoforms are involved in OTM with different expression patterns between the tension and pressure with nNOS being more involved in early OTM. PDL cells, rather than osteocytes are the mechanosensors in early OTM with regards to NO signaling.

Thesis (M.D.S.)--University of Hong Kong, 1989.

Thesis (M. Orth.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 122-127).

published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

Malocclusion and orthodontic treatment can give rise to bacteria and nonbacterial induced gingival inflammations. Previous studies have shown that some natural compounds-containing mouthrinses (NCCMs) have clinical benefits for maintaining gingival health. The aim of the present study was to investigate the effectiveness of NCCMs in the management of dental plaque and gingivitis among orthodontic patients. The present study consisted of three parts: 1) a systematic review on the effectiveness of NCCMs as an adjunct to unsupervised oral hygiene in the management of dental plaque and gingivitis; 2) an in vitro study to evaluate the antimicrobial and antioxidant effects of Fructus mume (FM) extract; 3) a clinical study to test the clinical, microbiological and immunological effects of a NCCM (FM extract containing) among orthodontic patients. Firstly, an electronic search for clinical studies of NCCMs was conducted in Medline-PubMed, the Cochrane Central Register of Controlled Trials and EMBASE from the inception of these databases to February 2013. Plaque index (PI), gingival index (GI) and gingival bleeding index (BI) were selected as primary outcome measures. The result identified 11 clinical trials which tested 13 different NCCMs; however, the heterogeneity and limited number of studies on any individual NCCM precluded a meta-analysis, which indicated that substantial evidence of NCCM is still lacking. Secondly, the antimicrobial effect of FM extract on oral pathogens was tested by agar diffusion assay, broth micro-dilution assay, XTT reduction assay and fluorescence microscopy; the antioxidant effect of FM extract was tested by total antioxidant capacity assay. The results showed: 1) a significant bacteria inhibition effects of FM extract on oral pathogens; 2) a significant difference in the biofilm’s cell viability between FM extract and the negative control exposure (p<0.01); 3) FM extract significantly increased the amount of dead bacteria on the biofilms from microscope images; 4) the antioxidant capacities of FM extracts were 2.91 ± 0.03 uric acid equivalents (UAE). Thirdly, a six-month randomized, parallel controlled clinical trial consisted of 90 orthodontic patients who were allocated to: 1) negative control group: oral hygiene instruction (OHI) alone; 2) positive control group: OHI plus an essential oils (EO) mouthrinse; 3) experiment group: OHI plus a two-stage NCCM (stage 1: FM extract solution, stage 2: sodium bicarbonate solution). Clinical assessments of PI, BI and modified gingival index (MGI) were obtained. Salivary microbial quantification of aerobic and anaerobic bacteria, streptococci and lactobacilli counts was conducted. Salivary Interleukin-1beta (IL-1β) and macrophage migration inhibitory factor (MIF) levels were detected by ELISA assay. BI was significantly reduced in the two-stage NCCM group compared to the negative control group at 6-months (p<0.05). There was no significant inter-group differences in salivary bacteria counts (p>0.05). The salivary IL-1β level was significantly correlated with salivary aerobic and anaerobic bacteria counts (r 0.34-0.61, p<0.01). In conclusion: 1) evidence of the effectiveness of NCCM as an adjunct to unsupervised oral hygiene for plaque and gingivitis control is insufficient; 2) FM extract has a significant antimicrobial effect on oral pathogens in vitro; 3) the two-stage NCCM has moderate gingival health benefits among orthodontic patients. / published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

published_or_final_version / Dentistry / Master / Master of Orthodontics

Thesis (M.D.S.) -- University of Adelaide, Dept. of Dental Health, 1976.

Thesis (M.S.)--University of Michigan, 1964. / Typescript (photocopy). Includes bibliographical references (leaves 48-52). Also issued in print.

Thesis (M.S.)--University of Michigan, Ann Arbor, 1982. / Typescript (photocopy). Includes bibliographical references (leaves 39-42). Also issued in print.