Magister Scientiae Dentium - MSc(Dent) / The treatment objectives in the restoration of an endodontically treated tooth are maximum retention of post and core and to create a design in which the tooth is preserved when the restoration fails. The ferrule effect in root treated teeth requiring cast post and core has been studied extensively and has been shown to greatly improve fracture resistance (Gluskin et al 1995, Libman & Nicholls, 1995. Hemmings et al, 1991. Barkhordar et al, 1989. Rosen & Partida-Rivera, 1986). Studies have also shown that in the case of cast post and core, the longer the ferrule, the greater the fracture resistance (Libman and Nicholls, 1995). The use of the new bonding agents, composite resin cements and core materials, have led to a more conservative approach to post and core restorations. However few studies have considered the effect of different ferrule designs on prefabricated post and composite core systems (Volwiler et al 1989, Al Hazaimeh and Gutteridge 2001). There is little information as to whether the ferrule is of additional value in providing reinforcement in these restorations. This study investigated the effects of different ferrule designs on the fracture resistance of teeth incorporating prefabricated posts and composite cores. In addition teeth restored with a composite core but with no prefabricated post were included in the study to assess the necessity of a post in the restoration of endodonticallytreated teeth. Sixty extracted maxillary incisors (centrals and laterals) and carunes were randomly assigned into three groups and restored. Two groups had a prefabricated post and composite core with varying ferrule designs. A third group had a core with composite packed into the root canal but no post. All teeth were restored with cast crowns to simulate the clinical situation. A Zwick universal testing machine was used to apply compressive loads progressively on the restored teeth until failure occurred as a result of either root, tooth or post fracture. Failure loads, modes of fracture, post and core systems and tooth preparation were recorded and statistically analysed. The results showed no significant difference in the amount of force needed to break the teeth in the different groups irrespective of whether the teeth had a ferrule or not. They also showed no significant difference in the amount of force needed to break the teeth in the different groups irrespective of whether the teeth had a post or not.

Morphological and anatomical studies demonstrated the root formation characteristics of sweet potato. The presence and importance of preformed root primordia is recorded for the first time. On the vines root primordia are present in sets of four to ten adjacent to the leaf bases. These roots originate from the procambium on both sides of the leaf gap. Macroscopically the root tips of preformed root primordia protruding through the cortex and epidermis of the stems are prominent. The preformed root primordia produce adventitious roots, with pentarch, hexarch or septarch steles. Storage roots will under normal circumstances only originate from undamaged root primordia on the nodes of cuttings, or on nodes of newly formed vines, or from wound roots originating from the cut ends of the stem or leaf cuttings. Lateral roots originating from damaged root primordia, or directly from the adventitious roots, exhibit tetrarch steles and develop into fibrous roots without the potential to develop into storage roots. This understanding of the origin, anatomy and morphology of sweet potato roots should improve production practices, which will contribute to improved crop establishment and increased yield. Differences in the contribution of individual subterranean nodes to storage root yield were studied. On average cuttings with three subterranean nodes produced 3.7 storage roots, with 33.2% on subterranean node 1, 30.0% on node 2 and 36.8% on node3. However, in terms of fresh mass of the storage roots node 1 contributed 45.4%, node 2 contributed 27.1% and node 3 contributed 27.4%. The effect of temperature (20, 24, 28 and 32oC constant), orientation of cuttings (vertical vs. horizontal) and size of cuttings (1 or 3 nodes) on the development of adventitious roots was observed in plant growth chambers. Twenty-one days after planting, the longest total root length of 4m per plant was recorded from the 24oC growth chamber. The effect of soil moisture content on early root development was investigated by wetting and equilibrating sandy soil to 100, 80, 60 and 40% of field capacity. Although the 80% of field capacity treatment resulted in the best root development, differences among treatments were small, demonstrating the capacity of cuttings to successfully establish under a range of soil moisture contents. Changes in dry mass of storage roots, stems, and leaves of three sweet potato cultivars (Awasa-83, Bareda and Falaha) were studied at Awasa and Melkassa. At the final sampling the early maturing cultivar Falaha had diverted a higher proportion of the total dry mass into storage roots at Melkassa because of the early initiation and growth of storage roots. The late maturing cultivar Awasa-83 had a smaller proportion of the total dry mass diverted into the storage roots at both locations because of late root initiation and growth. The high yielding cultivars Bareda at Melkassa, and Awasa-83 at Awasa, had higher crop growth rates and higher net assimilation rates than the other cultivars. The effects of cultivar (Kudadie, Bareda and Awasa-83), planting position (horizontal and vertical), type of planting material (terminal cuttings with and without leaves) and cutting length (20, 25 and 30 cm) on the number and yield of storage roots were quantified in field trials at Awasa and Melkassa. Cultivar Kudadie produced the highest storage root yield at both locations. Horizontal planting of cuttings resulted in the highest total storage root yield at both locations. Cutting length did not affect storage root number and yield. The effect of population density (50,000, 55,555, 75,000, and 100,000 cuttings per hectare) on the performance of the three Ethiopian sweet potato cultivars was studied at Awasa. The highest planting density consistently produced the best root yield, indicating the potential to increase yields with plant populations much higher than normally used. Early maturing cultivar Falaha produced more small and medium storage roots per plant, while the intermediate cultivar Bareda produced more large storage roots. Copyright 2003, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Belehu, T 2003, Agronomical and physiological factors affecting growth, development and yield of sweet potato in Ethiopia, PhD thesis, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-07262004-141704 / > / Thesis (PhD (Plant Production and Soil Science))--University of Pretoria, 2005. / Plant Production and Soil Science / unrestricted

<p>Studies were performed on methodological issues on vitamin A intake, status and improvement in three Asian countries, to improve the dietary approach recommended by FAO/WHO to alleviate vitamin A deficiency in low-income countries.</p><p>The reliability of the practical 24-hour dietary recall method to assess individual intake of vitamin A during pregnancy was investigated in Central Java, Indonesia. The usual mean intake of vitamin A can be reliably measured, but data on attenuation of simple regression coefficients suggest that it is difficult to establish associations between vitamin A intake and some health outcome. The majority of women was below the recommended daily intake of vitamin A in all three trimesters and strategies to improve vitamin A intake in all women are thus needed.</p><p>The applicability of the simplified "Helen Keller International Food Frequency Method" to assess community risk of vitamin A deficiency in South Asia, even though it excludes breastmilk and animal milk, was tested in rural Bangladesh and rural India. Breast milk was found to be an important source of vitamin A even in the second and third years of life in rural areas of Bangladesh. Similarly, animal milk is likely to be an important source of vitamin A among preschoolers in certain areas of India. The method should be revalidated to make it a useful tool even in settings where breastmilk and animal milk are common in the diets of preschool children.</p><p>Whether it is possible to improve vitamin A status with dark green leafy vegetables in children free of <i>Ascaris lumbricoides</i> was investigated in northern Bangladesh. A substantial increase in serum β-carotene was seen after supplementary feeding of these vegetables for 6 weeks. The impact on serum retinol concentrations was less substantial.</p>

Studies were performed on methodological issues on vitamin A intake, status and improvement in three Asian countries, to improve the dietary approach recommended by FAO/WHO to alleviate vitamin A deficiency in low-income countries. The reliability of the practical 24-hour dietary recall method to assess individual intake of vitamin A during pregnancy was investigated in Central Java, Indonesia. The usual mean intake of vitamin A can be reliably measured, but data on attenuation of simple regression coefficients suggest that it is difficult to establish associations between vitamin A intake and some health outcome. The majority of women was below the recommended daily intake of vitamin A in all three trimesters and strategies to improve vitamin A intake in all women are thus needed. The applicability of the simplified "Helen Keller International Food Frequency Method" to assess community risk of vitamin A deficiency in South Asia, even though it excludes breastmilk and animal milk, was tested in rural Bangladesh and rural India. Breast milk was found to be an important source of vitamin A even in the second and third years of life in rural areas of Bangladesh. Similarly, animal milk is likely to be an important source of vitamin A among preschoolers in certain areas of India. The method should be revalidated to make it a useful tool even in settings where breastmilk and animal milk are common in the diets of preschool children. Whether it is possible to improve vitamin A status with dark green leafy vegetables in children free of Ascaris lumbricoides was investigated in northern Bangladesh. A substantial increase in serum β-carotene was seen after supplementary feeding of these vegetables for 6 weeks. The impact on serum retinol concentrations was less substantial.

<p>Tauopathies are neurodegenerative diseases defined by the accumulation of pathological tau protein in neurons and glia. Alzheimer’s disease (AD), the most common tauopathy, is characterized by the presence of neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau protein aggregates in neurons. Emerging evidence suggests that the NFT burden correlates with neuron death and cognitive decline, contributing to disease progression. Besides AD, a similar deposition of tau inclusions is found to be associated with neurodegeneration in the brains of patients with other tauopathies including progressive supranuclear palsy, corticobasal degeneration, and Pick’s disease. These diseases display clinical, biochemical, and neuropathological heterogeneity. Little is known about how tau aggregation can lead to varied phenotypes in tauopathies, and there is no disease-modifying treatment. Thus, it is necessary to understand the role of diverse tau proteoforms in tauopathies for the development of new therapeutics to treat tauopathies, including AD.</p> <p>In the studies summarized in Chapter 2, we investigated how the molecular diversity of tau proteoforms could impact antibody-based assays of a phospho-tau variant serving as an AD biomarker. A tau variant phosphorylated on threonine 181 (pT181-tau) has been widely investigated as a potential AD biomarker in cerebrospinal fluid (CSF) and blood. pT181-tau is present in NFTs of AD brains, and CSF levels of pT181-tau correlate with overall NFT burden. Various immuno-based analytical methods, including Western blotting and ELISA, have been used to quantify pT181-tau in human biofluids. The reliability of these methods depends on the affinity and binding specificity of the antibodies used to measure pT181-tau levels. Although both of these properties could in principle be affected by phosphorylation within or near the antibody’s cognate antigen, such effects have not been extensively studied. Here, we developed a bio-layer interferometry (BLI)-based analytical assay to assess the degree to which the affinity of pT181-tau antibodies is altered by the phosphorylation of serine or threonine residues near the target epitope. Our results revealed that phosphorylation near T181 negatively affected the binding of pT181-tau antibodies to their cognate antigen to varying degrees. In particular, two of three antibodies tested showed a complete loss of affinity for the pT181 target when S184 or S185 was phosphorylated.</p> <p>In the studies outlined in Chapter 3, we examined the relative abilities of different tau proteoforms to induce seeded tau aggregation and to themselves undergo seeded aggregation in cultured cells. Accumulating evidence suggests that tau aggregates, including NFTs, spread in a stereotypical pattern across neuroanatomically connected brain regions. This spreading phenomenon is thought to occur via a prion-like mechanism involving the release of tau aggregates from a diseased neuron into the extracellular space, aggregate uptake by neighboring healthy neurons, and the formation of new aggregates in the cytosol of the recipient cells via a seeding process. Although research over the past decade has revealed key molecular events involved in the cell-to-cell transmission of tau aggregates, the impact of the protein’s domain structure and phosphorylation profile on the efficiency of prion-like propagation remains poorly defined. Here, we compared three tau variants – K18, 0N4R, and 2N4R – in terms of their aggregation and seeding efficiencies in recombinant protein solutions and in cell culture models. Our results revealed that K18 had the highest fibrillization rate and yield among the three tau variants. Recombinant preformed fibrils (PFFs) derived from all three variants had similar seeding efficiencies. Additionally, we investigated the relationship between tau phosphorylation and aggregation. We found that hyperphosphorylated tau did not undergo self-assembly in the absence of heparin, whereas it formed fibrils at low yield in the presence of the cofactor. Moreover, hyperphosphorylated tau PFFs produced under these conditions induced seeded tau aggregation in cell culture.</p> <p>Taken together, these results point to critical roles of tau proteoforms as both AD biomarkers and drivers of disease progression. Our results indicate that the presence of different combinations of phosphorylated residues near a target phospho-tau antigen can affect the accuracy of antibody-based biomarker assays. In addition, the domain structure and phosphorylation profiles of tau proteoforms associated with AD and other tauopathies likely have a profound influence on the evolution of tau pathology in these disorders. Our findings highlight the importance of accounting for the molecular diversity of tau proteoforms in tauopathies and provide valuable insights into molecular determinants influencing tau aggregation and propagation in the brains of patients.</p>

Objectif : La dentisterie pédiatrique évolue vers des approches minimalement invasives pour la gestion des caries, transition accentuée par l'impact de la pandémie de la COVID-19. Parmi les procédures préconisées en dentition primaire, la technique de Hall s'est montrée efficace pour relever des défis tels que la coopération limitée des jeunes patients et l'accès restreint aux blocs opératoires. Malgré son efficacité avérée de 98%, son adoption demeure limitée parmi les dentistes pédiatriques. Le but de cette étude était d'évaluer l'enseignement de la technique de Hall dans les programmes de spécialité en dentisterie pédiatrique, d'analyser son utilisation, sa connaissance, et sa perception parmi les spécialistes américains et canadiens, ainsi que d'explorer les obstacles limitant son adoption. Méthodologie : Les dentistes pédiatriques du Canada et des États-Unis ont été sollicités à travers la liste de diffusion de l'American Academy of Pediatric Dentistry. Un questionnaire composé de 32 énoncés et d’une section spécifique destinée aux directeurs de programme a été distribué électroniquement en septembre (États-Unis) et en octobre (Canada) 2023, via la plateforme LimeSurvey. Des rappels ont été faits après 4 à 6 semaines. Résultats : Au sein de l'échantillon de 364 participants, l'analyse statistique a révélé des différences significatives dans l'utilisation de la technique en fonction de la région d'exercice (p=0,009), du type de pratique (p<0,001), de l'âge du professionnel (p<0,001), du nombre d'années d'expérience (p<0,001), des sources de remboursement (p=0,003) et si la technique leur avait été enseignée ou non (p<0,001). Conclusion : Les résultats indiquent une augmentation de l'utilisation de la technique de Hall parmi les dentistes pédiatriques, tout en soulignant la persistance d'obstacles. Ils proposent aussi des pistes d'intervention pour encourager davantage son adoption, en cohérence avec l'évolution vers des approches minimalement invasives de gestion de la carie. / Introduction: Pediatric dentistry increasingly favors minimally invasive approaches, discouraging extensive treatments such as complete caries removal. The COVID-19 pandemic hastened this shift, highlighting relevance of procedures like the Hall technique (HT) for managing carious lesions in primary dentition while addressing challenges such as patient cooperation and restricted access to operating rooms. Despite being recognized for its 98% efficacy, this technique continues to encounter limited adoption among pediatric dentists. Purpose: To assess the integration and teaching methods of the HT in graduate pediatric dentistry programs, evaluate its utilization, comprehension, and perception among American and Canadian specialists, and explore obstacles to its adoption. Methods: Pediatric dentists in Canada and United States (U.S.) were surveyed via the American Academy of Pediatric Dentistry mailing list, featuring a dedicated section for program directors. Using the LimeSurvey platform, a questionnaire of 32 potential inquiries was electronically available in early September (U.S.) and early October (Canada) of 2023, with reminders issued 4-6 weeks later. Results: Of 364 participants, statistical analysis indicated significant differences in HT use according to practice regions (p=0.009), settings (p<0.001), age (p<0.001), years of experience (p<0.001), reimbursement sources (p=0.003), and education exposure (p<0.001). This offers a comprehensive understanding of the nuanced landscape surrounding the HT among pediatric dentists in Canada and the U.S. Conclusion: This investigation reveals a growing acceptance of the HT, despite persistent challenges faced by pediatric dentists in Canada and the U.S. These findings provide actionable insights for improving the adoption of the HT in contemporary pediatric dentistry practices, aligning with today's emphasis on minimally invasive approaches.