Thesis (M.S. in materials science and engineering)--Washington State University, December 2009. / Title from PDF title page (viewed on Feb 19, 2010). "School of Mechanical and Materials Engineering." Includes bibliographical references (p. 37-39).

The aims of this study were to, 1) investigate the surface characteristics of polished titanium plates/discs treated with acid-etching and ultraviolet irradiation (UV); and 2) investigate the change in surface characteristics of polished titanium plates/discs treated with acid-etching and UV irradiation after aging in air, saline and citric acid for six weeks. A total of one hundred and ninety-eight commercially pure grade two titanium plates and 50 titanium discs were prepared. Titanium samples were divided into four groups: 1) polished group, 2) polished and UV group, 3) acid-etched group and 4) acid-etched and UV group. Polishing was performed by abrasive silicon carbide paper grinding. UV treatment was performed by 15W germicidal UVC, 254 nm, for 48 h. Acid-etching was performed with 67% H2SO4 at 120 ºC for 75 s. The four groups were then subjected to an aging process for six weeks in sealed containers with three different media: air, physiologic saline and citric acid. They were analyzed immediately after treatment and after aging for surface characterization: topography, roughness, wettability, crystallinity, and chemistry. The polished surface showed relatively smooth surface with typical grooves from the grinding process. Acid-etching produced micro-roughened surface with sharp pits and ridges. The average surface roughness of polished, polished-UV was lower than that of the acid-etched and acid-etched-UV surfaces (p < 0.05). Storage of titanium in saline and citric acid did not provoke any morphological or roughness changes at micron scale level when compared to the samples stored in air. Immediately after preparation and treatment, the polished and acid-etched titanium surfaces appeared to be hydrophilic with similar contact angle values (p > 0.05). After UV treatment, there was a significant reduction in contact angles (superhydrophilic) in both surfaces (p < 0.05). After storage in air for six weeks, the contact angles of the four groups significantly increased (p < 0.05) and the surfaces converted to a hydrophobic state. In contrast to samples stored in air, samples stored in saline and citric acid revealed superhydrophilic surfaces regardless of the surface type. Titanium hydride crystals were present in the acid-etched and acid-etched-UV surfaces but not in the polished and polished-UV surfaces. Titanium tetrachloride crystals were present in saline-stored surfaces. The polished surface acquired significantly higher titanium and oxygen concentrations and lower carbon contaminants compared to acid-etched surface. UV treatment substantially decreased carbon contamination and increased the titanium and oxygen concentrations in the acid-etched groups (p < 0.05). After storage for six weeks in air, the four studied surfaces had no significant changes in the surface chemistry. Storage of the titanium samples in saline and citric acid relatively increased the carbon contamination and decreased titanium and oxygen concentrations. UV treatment may be an effective way to produce clean titanium surfaces with less carbon especially after roughening the titanium surface by acid-etching. Storage of the freshly prepared titanium surface in media such as saline or citric acid could preserve the hydrophilic property of these surfaces, however, it may also negatively influence the surface chemistry due to increased carbon contaminants. / published_or_final_version / Dentistry / Master / Master of Philosophy

published_or_final_version / Dental Materials Science / Master / Master of Science in Dental Materials Science

abstract / Dentistry / Doctoral / Doctor of Philosophy

Bacteria, in the form of biofilm, has been shown to play a critical role in the etiology and pathogenesis of periodontal and peri-implant infectious diseases. Studies have shown that distinctively different dental plaque is commonly found in healthy versus inflamed gingivae and mucosa. It should be noted, however, that in most of these studies, the healthy and diseased plaque samples were collected from different individuals. To address this important issue, in the two studies described within this thesis, I recruited subjects who were periodontally involved and/or had inflamed peri-implant tissues, and also had equivalent healthy control sites. In the first study, I analysed the subgingival microbiota of a cohort of tea labourers from Sri Lanka, who had never performed any oral hygiene practices. Within each of the 32 subjects, one ‘shallow’ (healthy) site and one ‘deep’ (diseased) site were chosen for subgingival plaque sampling. A 16S ribosomal RNA (16S rRNA) gene sequencing method was applied to investigate the diversity of the subgingival microbiome, and to compare the microbial composition between healthy and diseased sites. A taxonomically diverse subgingival microbiota was identified, with 318 operational taxonomic units (OTUs; 98% identity cut-off) from 1,887 cloned full-length 16S rRNA gene sequences. The subgingival microbiota was dominated by the phyla Firmicutes, Proteobacteria and Fusobacteria. A significant difference in the overall composition of microbial communities between shallow and deep sites was found ((-Libshuff, p<0.001) while pairwise comparisons within each subject revealed no significant differences. The absence of oral hygiene resulted in a highly diverse subgingival microbiota in this cohort. In the second study, 22 subjects who had both implants and teeth surrounded by healthy and inflamed tissues, were included for subgingival/submucosal microbiological sampling. Quantitative real-time polymerase chain reaction (q-PCR) was used to detect and to quantify six species, including putative periodontal pathogens, i.e., Porphyromonas gingivalis (P.g.), Treponema denticola (T.d.), Aggregatibacter actinomycetemcomitans (A.a.), Fusobacterium nucleatum (F.n.), Prevotella intermedia (P.i.), and Staphylococcus aureus (S.a.). Within the same subjects, putative periodontal pathogens were common to both periodontal and peri-implant sites irrespective of health status. The detection frequencies for each of the six target species at diseased tooth or implant sites were either equal to, or higher than, the respective detection frequencies at the corresponding healthy sites. Both periodontal and peri-implant sites, irrespective of their health status, were revealed to harbour S. aureus. Even though the target organisms were found in all clinical conditions, there were differences in the involvement of some of the pathogens for the diseased conditions. The prevalence and levels of P. gingivalis and F. nucleatum were significantly associated with periodontitis, but not with peri-implantitis. A. actinomycetemcomitans was associated with both disease conditions, periodontitis and peri-implantitis, but not with either gingival or mucosal health. In conclusion, results from my two studies indicated that the differences between the composition of subgingival microbial communities present in single sites within two different individuals, were always greater than the differences in microbial community composition present in two subgingival sites of differing health status within the same individual. / published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / toc / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

published_or_final_version / Orthopaedic Surgery / Master / Master of Philosophy

No description available.

No description available.

A study was carried in conjunction with the Orthodontic department at Halmstad General Hospital in Sweden to investigate the possibility of reducing cost and manufacture time of dental implant drill guides. The current system involves sending a digital image in STL format to the Materialise factory in Belgium where information of the position of dental implants is translated onto a moulded mouthpiece. Drill guides are placed in the mouth piece which is then returned to the surgeon. The mouthpiece complete with drill guides is then placed in the patients mouth and used as a guide for the implant drill holes. The cost of 10000 sek and a turnaround time of 2 weeks gave rise to the need for a faster and cheaper solution. A new mouthpiece was designed comprising of a solid cube which could be clearly seen on the x-ray. Linearisation of the cube faces is used to find a reference point from which to drive a 5 axis drilling platform. The mouthpiece is placed in the drill platform which is driven by stepper motors which in turn are controlled by a microcontroller. Co-ordinates are entered via a PC interface. The PC software then translates these co-ordinates into motor steps which are sent to the microcontroller. The drill platform then positions the mouthpiece in order to drill guide holes for the dental implants. The study showed that the machine design gave an acceptable degree of accuracy and repeatability. Further enhancements could be made by automating the detection of the cube using image analysis techniques. The study was also limited by the lack of graphical and geometrical data concerning the position of the implant. For the purpose of this study the co-ordinates for the implants guides is entered by hand. It was concluded that further software and hardware enhancement would be needed before the application could be developed commercially.