Melbourne Dental School - Theses
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ItemDynamic properties of nickel-titanium instruments( 1997)Root canal preparation in narrow, curved canals is a challenge even for experienced endodontists. Recently nickel-titanium (NiTi) hand files have played an important role in root canal preparation, particularly in curved root canals. Nickel-titanium endodontic instruments were first investigated in 1988 by Walia et al. who found that NiTi files have two to three times more elastic flexibility in bending and torsion, as well as superior resistance to torsional fracture compared with similar stainless steel files.
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ItemOral health status and treatment needs of the institutionalised elderly population in Melbourne( 1996-12)The purpose of this study was to determine the oral health status and treatment needs of elderly persons living in residential institutions in Melbourne. A total of 175 elderly persons aged 65 years and over were selected from 20 hostels located within a 10 km radius of the Melbourne GPO. A two stage field design was used to collect data. First, subjects were interviewed using a standard questionnaire, then clinical examinations were performed using a fiber optic light, plane mouth mirror, dental probe and periodontal probe. Coronal caries (DMFT), root caries (R-DF), periodontal status (CPITN), denture status, and treatment needs were assessed. The mean age of the subjects was 83.7 (sd 7.2) years. Eighty per cent were female and 20% were male.
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ItemAustralian weightings for the PAR Index( 1994)Critical review of orthodontic treatment results is a necessary procedure in the quest for quality control in orthodontic treatment provision. In order for valid information to be collected in such a review, a reliable method must be utilised. Traditionally, occlusal indices have been the method of choice. The index employed should however be reliable and utilised specifically for the purpose it was designed. This has not been the case in the few early attempts at assessing treatment standards. The PAR Index is an occlusal index designed specifically to fulfil such a purpose. The occlusal features comprising the components of the PAR Index have been weighted to reflect British and American orthodontic opinion. This study validates the PAR index using contemporary Australian orthodontic opinion in terms of the degree an occlusion deviates from the ideal. The resultant weightings may be used to allow valid data collection in quality control studies conducted in Australia.
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ItemEvaluation of changing normative needs for dental care in planning for the delivery of dental care to the Australian adolescent population( 1984)Normative needs represent a potential requirement for the use of dental resources. Therefore, changing normative needs should be anticipated in planning for the delivery of dental care. The aim of this study was to evaluate changing normative needs of the Australian adolescent population for restorative and exodontic treatment over the period 1980 to 1990. A predictive model composed of a population sub-model, disease sub-model, and resource requirements sub-model was developed. The disease sub-model was developed around the prediction of severity of dental caries (DMFT index). The severity of dental caries was predicted to decrease by 33.5 percent over the period. The backlog of untreated dental caries was found to be related to the severity of dental caries. Incidence of dental caries was calculated directly from the predicted severity of dental caries. Cross-sectional incidence overestimated the longitudinal incidence. The backlog and longitudinal incidence of dental caries decreased by 23.6 and 31.2 percent over the period. Backlog was two to three times the longitudinal incidence of dental caries. Backlog and incremental streams of needs were predicted on the basis of backlog and incidence of dental caries. In both streams the total number of teeth in need of treatment (TINOT) was equal to the number of teeth with dental caries plus a proportion of the previously restored teeth at risk of retreatment. In the backlog stream, previously restored teeth were related to the severity and backlog of dental caries. In the incremental stream, previously restored teeth were assumed to approximate the severity of dental caries (DMFT). In both streams a 0.10 proportion of restored teeth at risk one year and age earlier were indicated as requiring retreatment. Backlog TINOT was one-and-a-half to two times incremental TINOT. Over the period backlog TINOT decreased by 26.1 percent and incremental TINOT by 33.0 percent. Teeth in need of treatment were apportioned to individual items of treatment on the basis of a probable case-mix of treatment associated with the predicted severity of dental caries. As severity of dental caries decreased the case-mix of treatment items tended toward less complex items. Resource supply equivalents, rated skill units and 1980 dollars, were used to combine the need for different treatment items into single measures. The decrease in normative need expressed as resource supply was marginally higher than for TINOT. The predicted needs were multiplied by population number at each age and time to represent total population needs, demonstrating the "political-arithmetic" of the measurement and comparison of changing normative needs. The distribution of needs in the Australian adolescent population was investigated by the prediction of the prevalence of dental caries which represented the maximum percentage of the population with any need, and the percentage of the population with active caries in any one year who potentially require treatment. Approximately half the adolescent population have active caries in anyone year. The study demonstrated that changing needs must be correctly defined, predicted, and applied in planning for the delivery of dental care to the Australian adolescent population.
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ItemCharacterization of casein phosphopeptides( 1995)Casein phosphopeptides (CPP), containing the cluster sequence Ser(P)-Ser(P)-Ser(P)-Glu-Glu-, have been shown to stabilize amorphous calcium phosphate at neutral and alkaline pH and to be anticariogenic in various in vitro, animal and human experiments. Anticariogenic casein phosphopeptides (ACPP) therefore have commercial potential as toothpaste, mouthwash and food additives for the prevention of dental caries. The aim of this project was to comprehensively characterize the CPP produced under industrially-relevant conditions using the commercially available enzymes Novo trypsin PTN 3.0 S, Novo Alcalase® 2.4L and Pancreatin 4NF. To facilitate studies on the identification and characterization of CPP a simple and efficient purification procedure involving selective precipitation of Ca2+/ethanol-induced aggregates of the phosphopeptides from enzymic digests was developed. The individual peptides of the precipitates were purified using anion exchange FPLC and reversed-phase HPLC and then identified by solid-phase sequence analysis and amino acid composition analysis after vapour-phase hydrolysis. Prior to sequence analysis the phosphopeptides were covalently coupled to arylamine membranes and the phosphoseryl residues converted to S-ethylcysteinyl residues by calcium-ion-catalysed β-elimination in the presence of ethanethiol. Alternatively, in the event of low coupling efficiency to arylamine membranes, phosphoseryl residues were converted to S-ethylcysteinyl or S-propylcysteinyl residues and sequenced from polybrene-treated glass fibre discs. A method for the separation and identification of CPP using high performance capillary electrophoresis (HPCE) was also developed. The ability of HPCE to rapidly resolve phosphopeptides exhibiting varying degrees of phosphorylation, truncation and deamidation make it ideal for the product quality control of CPP. HPCE was also used to develop relationships between absolute electrophoretic mobility (µ) and peptide charge and size for CPP containing 2-5 phosphoseryl residues, with µ found to be proportional to q/M2/3 where q is the net negative charge and M is molecular mass of the peptide. The results showed that CPP can be produced using Novo trypsin and pancreatin with only minor modifications, relative to CPP produced using analytical-grade trypsin, such as slight truncation, deamidation and methionine oxidation. Deamidation and methionine oxidation most likely resulted from an elevated hydrolysis temperature and/or conditions employed during commercial casein (CN) production. Studies on the hydrolysis of casein at different enzyme:substrate (E/S) ratios by these enzymes suggest that for CPP production using Novo trypsin, a minimum degree of hydrolysis (DH) of 17.3% is required for maximal release of ACPP whilst for pancreatin, a DH of 19.0% is required. For pancreatin, it is recommended that this value is not exceeded so as to minimize the release of the truncated β-CN-4P(f7-24). CPP produced using alcalase were severely truncated relative to those prepared using Novo trypsin and pancreatin, resulting in the loss of residues suggested to be necessary for full anticariogenic activity. Decreasing E/S ratio slightly lowered the degree of truncation caused by alcalase, however, low E/S ratios also resulted in a reduction in CPP yield. It is likely that ACPP produced using alcalase would have much lower specific anticariogenic activity than those produced using Novo trypsin or pancreatin. In conclusion, it has been demonstrated that Novo trypsin PTN 3.0 S and Pancreatin 4NF are suitable enzymes for the production of CPP on a commercial scale and that Alcalase® 2.4L is unsuitable. For the production of CPP using Novo trypsin, a minimum DH value of 17.3% is required for maximal ACPP release whilst for pancreatin, a DH value of 19.0% is required. HPCE has been demonstrated to be an ideal method to monitor CPP quality.
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ItemAscorbic acid deficiency and Harvey-ras proto-oncogene expression in experimental oral mucosal carcinogenesis( 1996)The aims of the present project were to examine the role of L-ascorbic acid (L-AA) deficiency and expression of the proto-oncogene, Harvey-ras (H-ras), in in vivo rodent oral mucosal carcinogenesis. The inbred, mutant Osteogenic Disorder Shionogi (ODS) rats used in the present study are unable to synthesise L-AA because they lack the liver microsomal enzyme, L-gulono-y-lactone oxidase (GLO), needed in L-AA biosynthesis. Foot length measurements and random analyses of microsomal GLO, by using rabbit anti-GLO rat-antiserum, were undertaken to confirm the breeding of ODS rats. The minimal L-AA requirement for survival of ODS rats under experimental conditions were determined. Two levels of L-AA deficiency were examined in ODS rats, while outbred Wistar rats acted as controls in the carcinogenesis experiment. 0.5% m/v 4 nitroquinoline-1-oxide (4NQO) in propane-1, 2-diol was used topically to induce oral mucosal squamous cell carcinoma (SCC) in ODS (n=72) and outbred Wistar (n=48) rats with vehicle and untreated controls (n=168). Harvested palatal tissues were analysed qualitatively, by using a modified dysplasia index, and histometrically. Total RNA extracted from rat palatal SCC (n=22) were analysed for mutations in codons 12, 13, 59 and 61 of H-ras by using reverse transcription (RT)-polymerase chain reaction (PCR) and direct DNA sequencing. H-ras mRNA expression was examined in 4NQO-induced rat palatal SCC and untreated palatal samples using semi-quantitative RT-PCR. Foot length measurements differed significantly (p«0.01) between ODS and outbred Wistar rats, confirming the genotype of the former. Likewise, rat GLO was detected in the positive outbred Wistar control, but not in the six random ODS samples. ODS rats were shown to require 10 mg L-AA/day for prolonged survival under experimental conditions. Plasma L-AA levels in ODS rats were adjusted to one-eighth of one-half that of the outbred animals (48±2 µM). The carcinogenicity of 4NQO was confirmed in ODS and outbred rats, with palatal SCC detected after 20 weeks and by the 40th week, respectively. Dysplasia scores for 4NQO-treated ODS rats were significantly greater than for 4NQO-treated outbred Wistar rats at all time periods over the 24 weeks (p<0.05), but were not significantly different between ODS rats with plasma L-AA levels of 7µM and 26 µM (p=0.94). The mean palatal epithelial thickness measurements increased significantly with time in all 4NQO-treated animals (p=0.04) and were significantly different between varying levels of epithelial dysplasia (p<0.05), but the relative proportions of individual epithelial compartments were maintained. No H-ras mutation was detected in the specified codons in any 4NQ-induced palatal SCC samples compared to untreated palatal mucosal samples. It was concluded that L-AA deficiency, in the model of chemical carcinogenesis used, did not influence the process of experimental carcinogenesis. The absence of H-ras mutations at specified sites and the observed H-ras mRNA levels in 4NQO-induced rat palatal SCC suggested that the H-ras proto-oncogene was unlikely to have contributed to malignant transformation in the present study.
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ItemVertical root fracture and fracture-related properties of dentine( 1999)The prognosis of vertical root fracture (VRF) is unfavourable and endodontic procedures, especially lateral condensation, have been suggested as a cause of VRF. In addition, the mechanislTI of VRF resulting in a typical buccolinguaI fracture has not been investigated. The possibility of lateral condensation as a cause of VRF was investigated by comparing loads and strains during obturation with those at fracture. The mechanism of VRF was also investigated, in association with stress and strain distribution. Finally, selected tensile properties of dentine were examined in relation to patterns of fracture. Lateral condensation alone should not be a cause of VRF because loads and strains on the outer root surface generated during lateral condensation were much lower than at fracture in each tooth type. However, to avoid VRF, finger spreaders should be used to obturate root canals, because the results showed that loads and strains generated during lateral condensation using finger spreaders were significantly lower than when a hand spreader (D 11 T) was used. The mechanism of VRF was investigated using finite element analysis (FEA), and the results were validated by experimentally measuring outer root surface strains using strain gauges. The strain measurement results correlated well with predicted circumferential strain distribution from FEA models. FEA results showed that stress distribution was not uniform, and the highest tensile stresses were found on root canal surfaces in a buccolingual direction, concentrated in areas of greatest curvature of the root canal. The results suggested that the dentine thickness, root morphology and root canal shape, including root canal irregularities, all contributed to this pattern of non-uniform stress distribution. In addition, a root canal shape predisposing to stress concentration areas is a more influential factor than root morphology, and a severe oval root shape is more susceptible to VRF than less oval or circular root shape. The root with a combination of these factors is the most susceptible to VRF. The SEM photographs of fracture surfaces suggested that the microstructure of dentine may affect the tensile strength of dentine. Dentine was shown to behave as an anisotropic material with regard to ultimate tensile strength (UTS), with the highest UTS when the tensiIe force was perpendicular to tubule orientation. Thus, buccolingual fractures, which are the predominant pattern of VRF in all teeth, occur in a direction requiring the greatest energy to fracture. This suggested that the mechanisms which create local high tensile stress concentration or non-uniform stress distribution play a stronger role in VRF rather than dentine structure. UTS of dentine was shown to depend on the tubule orientation and location (distance from pulp cavity) of dentine. These suggested that both orientation and microstructure (hydroxyapatite and collagen fibrils) of intertubular and peri tubular dentine contributed to the anisotropy of dentine. Therefore, UTS of dentine should be described in relation to location (distance from pulp cavity) as well as tubule orientation. However, because of the complexity of dentine components and the small size of specimens, developing an improved testing system is necessary to achieve more information to understand fracture behaviour and other mechanical properties of dentine.
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ItemThe effects of tooth preparation on intrapulpal pressure: a laboratory study( 1998)The objective of this study was to determine intrapulpal pressure changes during tooth preparation with either diamond or tungsten carbide burs in a dental highspeed handpiece, in the laboratory. Twenty premolar teeth were collected and randomly assigned to two groups. Group 1 received preparation with diamond burs, Group 2 with tungsten carbide burs. The teeth were mounted on a pressure transducer and the pulp chambers filled with saline. A thickness of 0.1 mm of tooth tissue was removed from the proximal surface of each tooth, alternating dry and wet-cutting, until the pulp chamber was exposed. Pressure and temperature changes were recorded during tooth preparation. At the 0 - 1 mm depth of remaining dentine level, dry cutting with diamond and tungsten carbide burs generated a mean positive pulpal pressure of 11.64 kPa and 6.06 kPa respectively. Wet cutting under the same conditions produced 0.58 kPa and 0.15 kPa respectively. The difference between wet and dry cutting was highly significant (p<0.001). Diamond burs produced significantly higher pressure increases than carbide burs, at all levels, for both wet and dry techniques (p<0.05). When cutting greater than 2 mm from the pulp, tooth preparation created an average 0.09 kPa pressure increase, which was not influenced by either coolant use or bur type. The temperature change was minimal during wet cutting and only minor temperature increases were recorded during dry cutting. It is concluded that significant pressure changes occur in the pulp chamber during tooth preparation when the remaining dentine thickness is less than 2 mm.
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ItemA longitudinal cephalometric study of the polar growth phenomenon and craniofacial proportions( 1990)Throughout the orthodontic and anthropological literature, craniofacial growth, in the absence of criminal intervention, has been the subject of numerous longitudinal and cross-sectional investigations. Historically, the assessment of craniofacial growth using longitudinal cephalometric data was initiated by Broadbent (1931), who instigated the first major longitudinal growth study, the Bolton study. Since this development, some investigators have measured the craniofacial growth rates and increments (Brodie, 1941; Nanda, 1955; Bishara, Peterson and Bishara, 1984), while others have focused upon growth accelerations (Bambha and Van Natta 1963; Hunter, 1966; Bjork, 1967; Pileski, Woodside and James 1973; Houston, 1977; Lewis, Roche and Wagner, 1982; Ekstrom, 1982; Lewis et al., 1985; Kreig, 1987). The direction of growth of various craniofacial landmarks, relative to a basal reference area has also been the subject of research (Hellman, 1935; Downs 1948; Bergensen, 1961; Ricketts, 1971a, b). Similarly, the dimensions of various craniofacial proportions with growth have been investigated by different workers (Steiner, 1953; Ricketts, 1971a, b; 1981; Anderson and Popovich, 1983; Kerr and Hirst, 1987). All of the above studies have relied upon the use of various references, both anatomical and constructed, in the vicinity of the cranial base, to show entire facial changes with growth, presuming a stability of this reference area. The present study will be directed towards the method adopted by Ricketts (1971a, b) who has advocated the use of the Pterygoid Root Vertical (PtV) and Frankfort Horizontal (FH) reference planes, in conjunction with the reference point, CF (the point of intersection of these planes) to study the craniofacial pattern of the individual, presupposing a constancy in growth direction of various facial landmarks radiating outward from CF Point (the Polar Growth Phenomenon). Ricketts (1971a, b; 1981), in keeping with the concept of constancy with growth, has also suggested that various craniofacial proportions exhibit gnomonic growth, implying maintenance of angular dimensions with growth. To date, the Polar Growth Phenomenon and the concept of gnomonic growth of craniofacial proportions have not been investigated in the literature, yet these form part of the basis of growth forecasting methods of Ricketts as these relate to growth and treatment changes in the individual (Ricketts, 1972a; 1975a, b).