Melbourne Dental School - Theses
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ItemA study of endodontically-related bacteria(University of Melbourne, 2008)
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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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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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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.
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ItemThe influence of surface characteristics on adhesion to enamel and dentine( 2009)This body of research investigated the bonding efficiency of self-etching primer adhesives to enamel and dentine with various surface characteristics. A series of preliminary experiments was carried out to determine the effect of operator experience, dentine tubule orientation, bond strength test method and resin composite material used on bond strengths. The results of the preliminary tests concluded that it is essential to develop skills in material handling and the test methods used; 2-step self-etching primer adhesives exhibit higher but more variable microshear bond strengths (µSBS) than ‘all-in-one’ adhesives on dentine at different depths and tubule orientations; fracture toughness and bond strength test results suggest that the fracture toughness of a resin composite may not be of significant influence on microtensile and µSBS tests outcomes for nano-filled hybrid materials. An investigation of the bonding ability of self-etching primer adhesives under various tooth preparation conditions was carried out. Enamel and dentine specimens were prepared from human teeth and finished with various rotary cutting instruments and the erbium, chromium:yttrium, scandium, gallium, garnet laser. Specimens were bonded with two 2-step self-etching primer adhesives and two ‘all-in-one’ adhesives with a resin composite. The results showed that one of the 2-step adhesives exhibited higher but more variable µSBS than the ‘all-in-one’ adhesives and a silorane-based self-etching primer adhesive system to enamel and dentine. The relationship between enamel microhardness and µSBS was evaluated. Enamel specimens were prepared and finished with one half of the surface tested for hardness using the Vickers test. The other half of the enamel surface was bonded using either a 2-step self-etching primer adhesive or an ‘all-in-one’ adhesive and a hybrid resin composite. Mean Vickers hardness numbers and µSBS for each enamel surface were calculated. Analysis using Pearson’s parametric test for regression analysis evaluated the correlation between Vickers hardness and µSBS. The results revealed a weak negative insignificant correlation between VHN and µSBS for the 2-step adhesive and no correlation for the ‘all-in-one’ adhesive. The effect of conditioning and casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) on bonding to bleached and unbleached enamel was investigated. Four groups of enamel specimens: untreated control; bleaching with 16% carbamide peroxide gel for 90 min daily x 14 days; treated with CPP-ACP paste (Tooth Mousse, GC Corp., Japan) for 60 min daily x 7 days and bleached and CPP-ACP-treated were used. The specimens were divided into a further two groups and bonded with a total-etch adhesive or a 2-step self-etching primer adhesive. Specimens bonded with the self-etching primer adhesive were sub-divided into four conditioning subgroups before bonding: no conditioning; 30 – 40% phosphoric; 15% EDTA; 20% polyacrylic acid. Specimens were tested in shear mode until failure and analysed by 2-way ANOVA, one-way ANOVA and Tukey’s post-hoc test. The µSBS of the total-etch adhesive was not affected by enamel treatment. Bleaching reduced the µSBS of the self-etching primer adhesive but preconditioning with phosphoric acid and polyacrylic acid improved bond strengths after CPP-ACP application. Bond failure analysis revealed a predominance of adhesive failures after bleaching, but prior conditioning reduced the proportion of adhesive failures. Scanning electron microscopy (SEM) revealed that the interfacial morphology produced by the 2-step self-etching primer adhesive was independent of enamel treatment except after bleaching. Phosphoric acid etching was not inhibited by CPP-ACP treatment. Resin tag formation was observed with prior phosphoric acid and polyacrylic acid conditioning. The effect of conditioning and CPP-ACP application on dentine bonding was also investigated. Dentine specimens with and without the smear layer were prepared and divided into a further two groups, CPP-ACP paste applied to one group for 60 min daily x 7 days and the other group was untreated. The two groups were divided into three subgroups for conditioning: no conditioning; 30 - 40% phosphoric acid; 20% polyacrylic acid. The dentine was bonded using a 2-step self-etching primer adhesive and an ‘all-in-one’ adhesive, and tested as previously described. Statistical analysis was carried out using one-way ANOVA and Tukey’s post-hoc test at α = 0.05. The results showed that the µSBS of both adhesives were not significantly affected on smear-covered dentine but was affected on smearless dentine. Conditioning did not improve bond strengths. Bond failure analysis showed more adhesive failures for the ‘all-in-one’ adhesive, particularly on smearless dentine and with prior polyacrylic acid conditioning. SEM revealed a similar morphology of the bonded interface for the 2-step self-etching primer adhesive regardless of conditioning; and areas of bond failures for the ‘all-in-one’ adhesive. The 2-step self-etching primer adhesives exhibited higher bond strength and more regular bond integrity than the ‘all-in-one’ adhesives, as shown on the SEM observations. However, the ‘all-in-one’ adhesives exhibited less variability in bond strengths to tooth surface characteristics.
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