No description available.

There is no abstract available for this thesis.

There is no abstract available for this thesis.

As new adhesive products become available in restorative dentistry, investigating their potential application for orthodontic use is warranted. Vertise Flow (Kerr) is a self-adhering flowable resin and is being marketed for use as a sealant, porcelain repair and small class I restorations. It has potential for use as an orthodontic adhesive. Objective: Determine if Vertise Flow (Kerr) is suitable for bonding fixed orthodontic appliances to enamel, restorative resin composite and porcelain with minimal surface preparation. Methods: Shear Bond Strengths (SBS) from six (6) groups of fifteen (15) bonded stainless steel lingual buttons (Ormco) were obtained over three time points (24hr, 7 days, and 3 months). The six test groups were: 1.Vertise Flow to enamel (Tt) with coarse pumice debridement, 2. Transbond XT (3M, Unitek) to enamel (Tc) with phosphoric acid etching [control], 3.Vertise Flow to Herculite Ultra (Kerr) (Cc) with coarse pumice debridement, 4. Vertise Flow to Filtek Supreme Ultra (3M, ESPE) (Ct) with coarse pumice debridement, 5. Vertise Flow (Kerr) to porcelain (Pt) with diamond bur roughening, and 6. Transbond XT (3M Unitek) to porcelain (Pc) with hydrofluoric acid etching. Samples were stored in distilled water and incubated at 37C. The buttons were then debonded with a Zwick Universal Testing machine using a 10 kN load cell with a crosshead speed of 0.5mm/min. Debonded buttons were evaluated based on a modified Adhesive Remnant Index (ARI). Statistical assessment of the data was performed using parametric and non-parametric tests, with p<0.05 as the threshold for statistical significance. Results: The mean SBS obtained in all groups at each time point were >4MPa and varied between 8.69MPa and 27.44MPa. Statistical differences were found within the composite and porcelain groups at T1, and the enamel and composite groups at both T2 and T3. Nearly half of the sample (47.2%) achieved an ARI score of 5 (100% adhesive left on button base). Conclusion: Vertise Flow potentially provides clinically acceptable bond strengths to enamel, restorative resin composite and porcelain with minimal surface preparation. Furthermore, upon removal, minimal adhesive clean-up is required thus saving valuable chair time. Based on the results in this study, future in vivo investigation is suggested.

Mobility plays an important role in determining quality of life in older adults as it is closely tied to health, participation, and independence in later years. Although much of the literature to date has focused on walking and stair climbing, mobility also encompasses driving and the use of public transportation to access the community. Comprehensive definitions of mobility and techniques for objectively measuring community mobility are generally lacking. This thesis describes a new theoretical framework for mobility that illustrates how impairments can lead to limitations in accessing different life-spaces, and stresses the associations among determinants that influence mobility. The feasibility of using global positioning system (GPS) watches and accelerometers to monitor community mobility in older adults was also examined. Data acquired from the equipment were quite variable. While the technology offers promise for capturing detailed information (e.g., the timing, distances covered, and speeds reached on foot and in-vehicle), new GPS solutions are required to allow for data collection over an extended period of time. In addition, projects were conducted to examine ankle strength and power in older women because these muscle groups are important for physical function and mobility. Test-retest reliability on the dynamometer was found to be generally good for isotonic and isokinetic tests, but relatively poor for isometric rate of torque development. Measures of dorsiflexion (DF) and plantar flexion (PF) strength and power-related variables were significantly correlated with functional performance (gait speed, stair climb power, and foot movement time). An intervention study was conducted to determine the effects of ankle DF and PF resistance training performed concentrically “as fast as possible” on movement time in a brake response task. Power training with elastic bands resulted in the greatest reduction in movement time, which suggests that this low-cost, practical form of exercise may benefit older adults in circumstances when rapid generation of ankle torque is required. This thesis adds to the literature by examining mobility from a number of perspectives. Mobility determinants are comprehensively defined, community and laboratory-based measures are examined, and the effects of an intervention are evaluated to improve mobility assessment and treatment techniques in older adults.

Objective: Evaluate the effect of crosshead speed, load cell configuration and curing time on shear bond strengths. Methods: 160 human molars were divided into equal groups of 20 second and 40 second photopolymerization times and then into 1kN or 10kN load cell groups. Each of the groups were divided into 0.5mm/min or 5mm/min crosshead speeds. Results: Regarding photopolymerization time (20s vs. 40s) and crosshead speeds (0.5mm/min vs. 5.0mm/min) there were no significant differences in SBS (p>0.05). The load cell configuration (1kN vs. 10kN) however showed statistically significant differences (p<0.05) with the 1kN producing higher bond strengths.

No description available.

Melt blending of polyethylene, in particularly HDPE and LLDPE, have been shown to be a major success, especially in the film markets. In this thesis studies are reported on the stress rupture performance of pipes produced from selected polyethylene materials blended to a chosen MDPE pipe grade. The pipes were tested, notched or unnotched, at a single temperature of 80oC and at internal pressures designed to induce slit-mode failure. Results showed the simple concept of increasing the stress rupture performance of a pipe material by the addition of a higher molecular weight polymer was invalidated when applied to the blends system used in these studies. However molecular weight does have an influence to some degree as was illustrated by the addition of a very low molecular weight material, which produced the poorest stress rupture properties of the additives used. Charaterization techniques, including Differential Scanning Calorimetry and Dynamic Mechanical Thermal Analysis, showed good compatibility of the blends at all addition levels studied, illustrating that there was no seperation of the polyethylene phases. Fracture analysis of pipe failures showed variations between the blends, except for a MDPE additive which had similar molecular characteristics to the base resin. Some of the blends fracture surfaces were found to vary in fibre height and distribution from the bore region to the outside of the pipe. On the morphological front spherulites from pipe samples were found to be a poor indication of stress rupture behaviour. Pipe blends were produced which had fine/featureless morphologies but whose 80oC stress rupture behaviour was found to be good and poor in comparison to the control MDPE pipe resin which had a spherulitic structure much larger than all the blends studied. Models presented here infer that a number of mechanisms may be operating in producing these changes in stress rupture properties. One may be due to a dilution of a polyethylene system by materials of varying molecular weight and molecular weight distributions. This was evident in MDPE-AlMDPE-P blends (MDPE-P being a high molecular weight, low branch length additive), where the stress rupture performance initially decreased and then increased after addition levels of 10wt%. The main mechanisms for this system was postulated to be the initial dilution of octene branching levels within the MDPE-A blend causing a reduction in the ability of the branches to sterically hinder crack propagation under stress, to one of chain entanglement after sufficient levels of the additive was present in the blend to contribute to increasing the stress rupture behaviour. It was found that good blending can be produced using materials with similar branching types and distributions (especially in the high molecular weight tail), similar molecular weights and distributions and comparable crystallization temperatures.

The development of synthetic adhesives based on epoxy resins has opened new possibilities for bonding structural materials together. The present work was concerned with the use of epoxy resins to strengthen reinforced concrete beams by externally bonded steel plates. It was found in the first part that the assessment of the properties of the epoxy adhesive is of paramount importance as they varied considerably with the thickness of the test specimen and the rate of loading. The adhesive proved to offer a bond stronger than concrete in shear and resulted in a composite action between the beams and steel plates. Preloading the beams prior to strengthening them did not have any adverse effect on their behaviour. The added strength from the plates was fully exploited even in beams which were held under a preload of 70% of their ultimate strength while being strengthened. Stopping the plate in the shear span, short of the support, created a critical section where premature bond failure occurred beyond a certain plate thickness. Failure was caused by the combination of high peeling and bond stresses present in the region where the plate was stopped. These stresses were due to the transfer of tensile forces from the plate to the bars in that region and were higher with thicker plates. Bonding steel plates on the tension face of the beams increased their shear capacity by 9 to 15%. This may have been due to dowelling action from the plates which had a greater contact area with concrete than an equivalent amount of internal steel bars. The use of externally bonded steel as shear reinforcement was effective but requires further investigation. The external web strips failed prematurely as compared to equivalent stirrups. The long term deformations in plated beams were highly affected by the conditions of their environment but despite 47 month exposure no visual deterioration of the concrete-epoxy-steel joint was observed.

No description available.