Melbourne Dental School - Theses
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ItemA study of endodontically-related bacteria(University of Melbourne, 2008)
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ItemInsertion sequence ISPg4 as a genetic virulence marker for porphyromonsa gingivalis in chronic periodontitis patients(University of Melbourne, 2006)
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ItemEffectiveness and efficiency: systematic reflections on single- and multiple-visit root canal treatment( 2008)Single-visit root canal treatment was first documented in 1887. The controversy and debate within the dental community has been ongoing for over a century without resolution. The concept of evidence-based health practice has provided a structure on which the clinically-relevant questions in this debate can be dealt with systematically. When clinicians are faced with choices of which treatment regimen should be offered to patients, the central issues that should be considered are effectiveness, complications, patient/operator preference/satisfaction, and cost. Systematic review and meta-analysis techniques were used to reach definitive conclusions where high quality primary studies are available. The issue of satisfaction was studied using a quality of life concept, while the issue of cost was addressed by an economic evaluation (cost-minimization analysis). Treatment effectiveness and complications of single- and multiple-visit approach were similar. Patients overwhelmingly preferred single- over multiple-visit treatment with high satisfaction scores for both regimens. Australian endodontists were reluctant to embrace single-visit root canal treatment. Single-visit root canal treatment costs society less than multiple-visit treatment. On balance single-visit treatment offers substantial advantages with no identified adverse effects.
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ItemThe diffusion of innovation in dentistry: factors associated with the adoption of rotary nickel-titanium endodontic instruments( 2004-01)The aim of this research was to investigate possible reasons for the adoption or non-adoption of new technology in dentistry, using rotary nickel-titanium (NiTi) technology as a model.This thesis first investigated the proportions of Australian dentists and endodontists who were using rotary NiTi instruments and their experiences with them. A questionnaire survey was conducted that explored general and specific issues concerning rotary NiTi instruments and techniques. An assessment of response rate and non-response bias was made by analysing responses to a question requiring a simple yes/no answer. Secondly, intraoperative defects, specifically fracture, of rotary NiTi instruments were assessed by collecting and examining over 7,000 rotary NiTi instruments used in patients by 14 endodontists from four countries and subsequently discarded. Thirdly, an assessment was made of whether rotary NiTi instruments can be predictably cleaned in the busy private practice setting.Analysis of the response rate and non-response bias in the questionnaire survey indicated the existence of differences between early and late responders despite no apparent demographic differences. Respondents to the questionnaire indicated many different reasons for adoption or non-adoption of the new technology, which could be interpreted as demonstrating behavioural differencesbetween adopters and non-adopters. Analysis of the discarded instruments indicated that the differences in technical ability between the endodontists was a more important clinical consideration in defect and fracture rates of rotary NiTi instruments than the perceived fragility of the instruments themselves. Also, a simple and effective protocol was developed for the predictable cleaning of rotary NiTi instruments. Therefore, overall, the results of the three parts of this thesis – the questionnaire survey, the instrument defects and the instrument cleaning – indicated the existence of personality and behavioural factors
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ItemFactors affecting fracture susceptibility of tooth root: a laboratory and finite element analysis (FEA) study( 2004-11)From a fracture mechanics viewpoint, structural defects, cracks or canal irregularities are likely to play a major role in fracture susceptibility of the roots, because stresses can be exponentially amplified at these sites. By incorporating defects into a smooth round canal using rotary NiTi, theoretically the roots could be strengthened. The aims of the study were to determine whether rotary NiTi canal preparation strengthens roots, and whether the fracture pattern can be predicted by finite element analysis (FEA) models. 25 teeth were prepared using hand file and another 25 using rotary NiTi. After obturation, all teeth were subject to loading until fracture; load and patterns were recorded. Four FEA models were created from fractured roots. No significant difference of fracture load between the two techniques was found. Mesio-distal fracture occurred more often in the rotary NiTi group. Stress patterns in three of the four FEA models correlated well with the observed fracture patterns. The aim of the subsequent study was to determine the extent to which canal size, radius of curvature and proximal root concavity influence fracture susceptibility and pattern. A standardized cross-section of the mid-root region of a mandibular incisor was created by averaging the dimensions of ten extracted teeth, and the basic FEA model was created. By varying canal diameter, shape and proximal concavity, these factors could be examined for roles in fracture susceptibility and pattern. The factors all interact in influencing fracture susceptibility and pattern, with dentine thickness not the only determining factor. The removal of dentine does not always result in increased fracture susceptibility.
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ItemInvestigations into the mechanical properties and curing characteristics of dental glass-ionomer cements( 2005-11)Conventional glass ionomer cements (GICs), which continue to gain acceptance as superbly biocompatible dental materials, were first released in the early 1970s as a result of research into combining the advantages of silicate cements and polyalkenate cements. The chemistry of GICs is based upon the aqueous reaction between an ion-leachable fluoride glass and polyacid which yields the final cross-linked insoluble ionomer (ionic polymer). The significant advantages of GICs include direct adhesion to tooth structures, fluoride release, minimal dimensional change on curing, significant ease of use and superb biocompatibility, to the extent that affected proximal tooth structures may be retained, remineralised , and strengthened against further caries. GICs have, however, been unfavourably compared with other restorative materials in their mechanical properties and setting characteristics, in particular their relative weakness, the time limitations for the acid-base reaction to proceed to acceptable maturity, and the susceptibility of the immature cement to water sorption or desiccation.
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ItemAn analysis of the effectiveness of a continuing professional development (CPD) program for dentists in Victoria( 2009)Periodontitis is a common condition resulting in destruction of periodontal tissues and eventually tooth loss. Every patient requires appropriate diagnosis and treatment by their dental practitioner. Periodontics has undergone many innovations in recent years. It is the onus of the treating dentist to keep abreast of developments in order to provide quality care to their patients. Unfortunately there is literature indicating that some Victorian dentists may not be following appropriate clinical practice in the identification and management of the periodontal needs of their patients. To address this, the School of Dental Science, the University of Melbourne, began conducting a Continuing Professional Development course titled ‘Periodontics via Distance Learning’. The course was composed of a mixture of hands on, distance learning and didactic components. This study assessed changes in clinical practice of course participants via the use of a delayed impact on practice questionnaire. All those who participated in the course in 2005 and 2006 were sampled. A response rate of 85% was recorded. Overall, an increase in practitioner confidence in periodontal diagnosis and periodontal treatment was reported and with many respondents indicated changes in their clinical practice had occurred. However, the reported changes recorded were not universal to all participants. Further research is required to determine how best to structure a dental CPD course.
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ItemApplication of 3D mapping of the face for forensic application using reconstructive anatomical techniques( 2009)The human face has especially important functions in interactions between people whose capacity to recognise other individuals and interpret their emotions is largely an innate skill reinforced by early life experiences. The human face not only plays a key role in everyday communication but it also helps define the individual’s identity because it is highly likely that any particular combination of facial features is unique. The concept of “race” is controversial amongst anthropologists. There are, however, groups of people who share physical characteristics that have evolved in response to long-term prevailing environmental conditions. Similarly, when asked to identify the ancestry of themselves and their family group, people align themselves with others having shared facial characteristics. In the past, defining such characteristics quantitatively has proved to be difficult largely because of shortcomings in measurement techniques. Most of these techniques take measurements directly from the face. More recently, advances in 3D scanning technology has enabled researchers to collect accurate information from the face such as topography, colour and texture indirectly. The first aim of this study was to collect a set of facial images of people identifying themselves as ‘Malays’ who originated from Malaysia and to develop a characteristic adult facial archetype (“average face”) for men and women. Facial images from 50 volunteer participants (25 male and 25 female) with self-declared Malay ethnic background had their faces scanned using the Konica Minolta VIVID 910 3D laser scanner. Data collected were processed through Geomagic® software to produce the final digital images. Male and female Malay facial archetypes were created from these 50 images. Then, using the software developed in-house by Claes (2007), 36 predefined anatomical landmarks were indicated on each individual’s facial image and the corresponding facial archetype, (male or female). This process was repeated 10 times to measure reproducibility of landmark identification. The second aim was to compare the data from individuals to determine variances within the Malay population to their corresponding archetype. Comparisons of these results with data representing Australian Caucasian and Japanese populations were also made. The analysis took several approaches in a logical sequence striving to find the most meaningful way to interpret the data for the purposes of comparing different populations in a quantifiable way. The first analysis used Euclidean Distance Matrix Analysis (EDMA) in which 5 groups were compared: males and females from the Malay population, Malay and Australian Caucasian males, Malay and Japanese males, Malay and Australian Caucasian females and lastly between the Malay and Japanese females. For the Malay cohort the position of landmarks indicated on the facial images of individuals were compared with corresponding landmarks indicated on the corresponding facial archetypes as a measure of intra-operator error and thus provided an indication of the validity of sparse landmark based analysis. The finding that intra-operator error was of the same order as measurable differences between individuals meant that such an approach is practically worthless and so the final analyses were done using automatically generated sets of dense corresponding landmarks on the Malay facial images and the same five groups compared previously. Contrary to what has been believed previously by many other workers, even with implementation of very rigorous internal quality assurance, the results from the analysis of the facial data using EDMA demonstrated that sparse sets of landmarks were not useful to distinguish between populations. This was because of the difficulties in locating landmarks sufficiently accurately and reproducibly. The dense correspondence landmark method was more successful in providing quantifiable differences between the groups that can be easily depicted. This provides the first 3D archetypes of Malay men and women.
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ItemAnalysis of three-dimensional craniofacial images: applications in forensic science, anthropology and clinical medicine( 2008)The principal aims of this thesis were to use digital 3D craniofacial data to measure the difference between individuals in different populations, to provide a detailed holistic description of the population at large, as well as to investigate the feasibility of classifying individuals in different populations based on the morphology of their craniofacial features. In this thesis, three empirical studies were undertaken using a variety of digital 3D craniofacial images. Each study required digital 3D data of either the skull and/or the face to be acquired, represented in different forms and analysed morphometrically. The first study developed a method and recorded the results from soft tissue depth data collected from clinical X-ray computer tomography images of the head. Digital 3D images of the face and skull were acquired from 63 deceased adult males and the results for differing age groups and ponderal states recorded. The perpendicular distance between the skull and its overlying soft tissue surface (i.e. ‘tissue depth’) was measured at 34 anatomical landmarks for every individual. Statistically significant differences were only found between the weight subgroups, normal and overweight, overweight and obese and normal and obese; no statistically significant differences were found between persons of different age. The results of this study have shown that the acquisition of head and neck data using the Aquilion 16 combined with amira and Geomagic Qualify® software was an extremely effective method for measuring the depth of the soft tissue surface overlying the skull. Due to the absence of piercing or indentation of the skin, as used in other methods, the current method described in this thesis provides a suitable method for predicting the soft tissue surface of the face, required as the foundation for forensic facial approximation. The second study described and classified individuals into one of two populations in an anthropological collection. This study captured the 3D facial images of, and then visualised, described, measured and classified two distinct ancestral groups, Asian and Caucasian, which were further divided according to their gender. On each 3D facial image a sparse set of landmarks (18) and a dense set of landmarks (9327) were defined and identified. From the analyses applied to both the sparse and dense landmark sets, principal component analysis of the densely corresponding sets of landmarks on the 3D facial images of the anthropological collection was the more detailed and discriminatory method for describing gender and ancestral differences. The average densely corresponding 3D images defining each ancestral and gender group were clear tools for the visualisation and modelling of differences between the groups. The most accurate method for the classification of the anthropological collection was found after undertaking a discriminant analysis with cross validation using the 25 principal componenet scores from the dense landmark set that were found to have at least one statistically significant difference between the four groups. This fully automated process provided a total correct classification of 95% (range: 92 – 100%) of the anthropological collection (195 of 206) and no incorrect classification of any individual to a group that did not share at least one major characteristic, either gender or ancestry. Therefore, ancestry and gender of individuals in the anthropological collection could be predicted with a 95% accuracy using a digital 3D facial image. A major advantage of this classification process was its complete independence from any form of human judgement as the classification process was fully automated. The final experiment investigated the task of attempting to lateralise the source of the seizure of patients with temporal lobe epilepsy (TLE), a condition with facial manifestations. This study captured two digital 3D facial images, a neutral and voluntary contraction pose, from four different subgroups. These subgroups consisted of 16 patients with idiopathic generalised epilepsy (IGE); 28 patients with partial epilepsy on either the right (R-TLE) or left (L-TLE) side of the brain; as well as a control group of participants with no epileptic condition (28). Classification of these individuals into the four groups was done using the statistically significant principal component scores calculated from a principal component analysis on the normalised deformation fields. Correct classification occurred with 58% of all individuals in the epilepsy sample placed into their correct group, a figure that increased to 64% (18 of 28 patients) when only the TLE individuals were classified i.e. 60% of the L-TLE patients and 69% of the R-TLE patients. Although both of these classification results were better than chance, the classification results are still quite low and further work is required to improve them. It is predicted that if the time taken for the capture of fleeting facial expressions in 3D could be shortened then the power to lateralise the side of the epileptogenic lesion in the TLE patients would strongly increase. Finally, the current movement in clinical medicine and forensic science towards implementing hardware that now routinely acquires the morphometric characteristics of the craniofacial complex and represents them in digital 3D data presents more exciting opportunities for the future. The results of this thesis have enabled a greater understanding of the acquisition, representation and analysis of digital 3D craniofacial data. As a result of the awareness provided by this major body of work, many diverse fields may benefit. These include video surveillance, diagnosis of syndromes affecting the craniofacial region, planning and assessment of orthodontic treatments and craniofacial surgery, forensic science particularly the approximate reconstruction of the facial features of deceased individuals from their remnant skull evidence, prediction of facial features for archaeological remains displayed in museums, etc.