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Polymerisation kinetics and optical phenomena of photoactive dental resinsHadis, Mohammed Abdul January 2011 (has links)
Globally, several shortcomings of dental resin based composites (RBCs) remain. This may be related to problems associated with incomplete conversion (40-70%), polymerisation shrinkage (1-4% by volume) and the stress generated at the tooth/restoration interface. Additionally, the increased number of technique sensitive incremental steps required to fill relatively large cavities is due to inefficient light transmission at depths greater than 2mm. The current investigation demonstrates the applicability of the exposure reciprocity law in photoactive dental materials in order to try and improve these shortcomings. The development techniques that will allow dynamic monitoring of optical and physical change will aid material development with the goal of improving cure depths. The current investigation has demonstrated the use of several analytical techniques (FT-IR spectroscopy, UV-Vis Spectroscopy and low coherence interferometry) and shown the complexity of optical phenomena within RBCs, which are affected by material composition as well as cavity dimensions. Whilst research continues to develop a novel RBC with reduced shrinkage and improved depths of cure, there is currently no commercially available solution to such problems. Consequently a better understanding of the setting reaction, optical properties and physical properties will aid material development.
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Effect of cation substitutions in an ionomer glass composition on the setting reaction and properties of the resulting glass ionomer cementsKashani, Mitra A. M. P. January 2013 (has links)
This study investigated the effect of Ba\(^2\)\(^+\) and Sr\(^2\)\(^+\) substitutions for Ca\(^2\)\(^+\) in an ionomer glass composition 4.5SiO\(_2\)-3Al\(_2\)O\(_3\)-1.5P\(_2\)O\(_5\)-3CaO-2CaF\(_2\) on the setting reaction and properties of the resulting glass ionomer cements (GICs). Experimental GICs (Ca-GIC, Ca-Sr-GIC and Ca-Ba-GIC) were characterized via various techniques: Diametral tensile strength, compressive strength, flexural strength, Vickers hardness and nano-indentation measurements were conducted at different time points during setting. Real time Fourier transform infrared (FTIR) spectroscopy was used to study the effect of the glass composition on cement setting reactions. A resistance to penetration method evaluated the cement setting time. Additionally, the wear resistance of the experimental GIC was measured by a ball-on-flat wear test. Furthermore, fluoride (F\(^-\)) release and the antimicrobial behaviour of cements were investigated. The compressive, diametral and flexural strength of the cements in which Ca\(^2\)\(^+\) was substituted by Sr\(^2\)\(^+\) and Ba\(^2\)\(^+\) were both statistically significantly higher than the unsubstituted control at 1 hour after setting (P < 0.001). FTIR results confirmed that enhanced metal salt crosslinking occurred in the ion substituted materials, especially from 1 to 60 minutes. Therefore, it can be concluded that replacing Ca\(^2\)\(^+\) with larger cations (Sr\(^2\)\(^+\) and Ba\(^2\)\(^+\)) affects the setting reaction and resulting mechanical properties in the short term. All three experimental GICs inhibited growth of Streptococcus mutans over a period of 48 hours. The F\(^-\)release analysis showed that there was less F\(^-\) release in artificial saliva (AS) than in deionized water over 40 days.
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Potential involvement of epithelial-mesenchymal transition in the pathogenesis of periodontitisAbdulkareem, Ali Abbas January 2017 (has links)
Epithelial-mesenchymal transition is reportedly important in loss of epithelial integrity and cell migration in inflammatory/infectious diseases and cancer. Since Gram negative anaerobic periodontal pathogens are well-recognized to induce intense inflammatory responses; the present study investigated their ability to induce EMT in vitro. A 2D chronic inflammatory model was developed using either the H400 oral keratinocyte cell-line or primary rat oral keratinocytes which were exposed to heat-killed Fusobacterium nucleatum, Porphyromonas gingivalis and Escherichia coli LPS for up to 8-days. EMT-associated changes were determined using semi-quantitative-RT-PCR, PCR-arrays, ELISA, scratch/transwell migration assays, immunocytochemistry/immunofluorescence, and transepithelial electrical resistance. Chronically stimulated cultures increased extracellular levels of the EMT regulatory cytokines, TGF-β1, TNF-α and EGF, whilst subsequent EMT-induction was indicated by up-regulation of mesenchymal markers, including vimentin and N-cadherin, and concomitant down-regulation of epithelial markers including E-cadherin and β-catenin. In addition, intracellular signaling activity of key EMT regulatory transcription factors, Snail-1 and NF-ĸB, increased following chronic bacterial exposure and was associated with enhanced cellular migratory activity and reduced epithelial barrier integrity. These results indicated for the first time that EMT may be involved in the compromised epithelial barrier function observed during periodontitis pathogenesis which may occur in response to prolonged local bacterial exposure.
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The influence of ‘nanocluster’ reinforcement on the mechanical properties of a resin-based composite materialCurtis, Andrew R. January 2009 (has links)
The introduction of innovative filled methacrylate resin composites has revolutionised the field of aesthetic restorative dentistry and provided a clinically viable alternative to amalgam-based restorations. The mechano-physical properties and resultant clinical longevity of these materials was insufficient. To improve these properties the on-going development of resin-based composites (RBCs) has sought to modify the filler size and morphology and to improve the loading and distribution of constituent filler particles. This has resulted in the introduction of so-called ‘nanofills’ which possess a combination of nano- and micro-sized filler to produce a hybrid material. A variation to this approach was the introduction of ‘nanocluster’ particles, which are essentially an agglomeration of nano-sized silica and zirconia particles. Although these materials have demonstrated a degree of clinical and experimental success debate remains as to their specific benefit compared with existing conventionally filled systems. Following placement RBC restorations are exposed to masticatory loading (repeated sub-critical stresses) which are typically detrimental to the clinical longevity of the material. The current study determined that RBCs reinforced with the ‘nanocluster’ particles possessed statistically similar or significantly increased bi-axial flexure strengths and associated Weibull moduli following pre-loading regimes which produced catastrophic failure of conventionally filled RBCs. This was attributed to the unique reinforcement provided by the ‘nanocluster’ particle, which were identified by a novel micromanipulation technique to possess distinctive fracture mechanisms, in addition to possessing an IPC-like structure. These acted in combination to absorb and dissipate loading stresses and to provide enhanced damage tolerance. Near-infra-red spectroscopy was also employed to determine the water sorption and it did not identify any direct correlation between water content and extent of strength reduction. However, immersion of the materials in water and also in sodium hydroxide or ethanol highlighted that the long-term hydrolytic stability of the ‘nanoclusters’ was limited. This suggested that degradation of the interfacial silane layer weakened the ‘nanocluster’ particle causing them to act as defect centres within the resin matrix and to consequently generate a greater loss of strength. Therefore, whilst the ‘nanocluster’ reinforced RBCs have the potential to provide enhanced damage tolerance and improved clinical longevity the limited long-term hydrolytic stability suggests further development of hydrophilic silane coupling agents and resin monomers is required to realize these properties.
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Neutrophil function in chronic periodontitisLing, Martin Robert January 2015 (has links)
Neutrophil function in the pathogenesis of chronic periodontitis was investigated. A case-controlled longitudinal intervention study of patients with chronic periodontitis and matched healthy controls was performed. Peripheral blood neutrophils from patients released more IL-8, IL-6, IL-1β and TNF-α in response to periodontally-relevant bacteria than controls. Hyper-reactive \(Fusobacterium\) \(nucleatum\)-stimulated neutrophil IL-8, IL-6 and TNF-α release from patient cells normalised to control levels following successful therapy. Hyper-reactive FcγR-stimulated IL-8, IL-6, IL-1β and TNF-α and \(Porphyromonas\) \(gingivalis\)-stimulated IL-1β release by patient cells persisted after therapy. Patient neutrophils displayed hyper-active and hyper-reactive superoxide release that normalised to healthy control levels post-therapy. Although neutrophil extracellular trap release was unchanged in periodontitis, patient neutrophils demonstrated impaired directional chemotactic accuracy, speed and velocity. Studies on control neutrophils demonstrated that physiologically-relevant concentrations of C-reactive protein (CRP) inhibited baseline reactive oxygen species (ROS) generation, and reduced FcγR–stimulated superoxide and \(F.\) \(nucleatum\)-stimulated luminol/isoluminol detectable ROS. However, CRP enhanced \(F.\) \(nucleatum\)-stimulated neutrophil superoxide release. The data demonstrate that chronic periodontitis is characterised by dysregulated neutrophil function, notably heightened cytokine and superoxide production and impaired chemotaxis. Furthermore, mildly elevated CRP levels in periodontitis could play a role in modifying the neutrophil respiratory burst and provide a link with periodontitis-associated systemic disease.
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The life expectancy of dental restorations placed within the General Dental Services in England and WalesLucarotti, Peter Stephen Kerr January 2003 (has links)
This study measured the distribution of the interval between placement and next intervention on the same tooth for direct restorations of teeth in the General Dental Services of the NHS in England and Wales between January 1991 and December 2002. Three different sets of treatment data covering the period were used, involving over 1.3 million restorations. Standard and modified Kaplan-Meier, and three different cross-sectional techniques were used to estimate empirical survival curves, and Cox-regression was used to model the relationship with risk factors associated with the dentist, the patient, geographical location, time, tooth position and type of restoration and cavity. Overall, median survival was slightly more than eight years from placement to re-intervention. The rates of survival without intervention after one year, five years and ten years were, respectively, 89%, 62% and 46%. Key risk factors associated with survival were type of cavity, tooth position, patient age, patient treatment history and patient attendance history. The underlying baseline function of the Cox-regression analysis was closely modelled by both a Weibull and a cubic function. The robustness of the findings was demonstrated by a full replication of the eleven-year analysis using a completely separate fourth sample from the DPB’s data archive.
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Biological effects of low frequency ultrasound on bone and tooth cellsMan, Jennifer Sui-Sum January 2011 (has links)
Little is known about the biological effects of ultrasound on dental-derived cells and whether ultrasound may be used as a therapeutic tool in dental care. This thesis has investigated the functional responses of in vitro osteoblast and odontoblast model cell lines to low frequency ultrasound as a potential tool for dental tissue repair. Two methods for ultrasound delivery were used to stimulate cells in vitro; a dental ultrasonic scaler (EMS) capable of emitting ultrasound at a frequency of 30kHz; and the DuoSon (SRA developments) therapeutic ultrasound exposure system, which allowed the comparison of kHz, MHz and a combined frequency ultrasound. Odontoblast-like cells positively responded to all ultrasound frequencies applied and can increase VEGF expression, increase cell number and increase mineral deposition by enhancing differentiation when compared with sham-treated control. Furthermore, enhanced wound healing by increased cell migration and cell proliferation was demonstrated in ultrasound-stimulated osteoblast-like cells. Ultrasound induced a dose-dependent response in β-catenin staining in both odontoblast and osteoblast model cell lines, which implicates the Wnt/β-catenin pathway as a possible mechanism for intracellular ultrasound transduction. Taken together, it is tempting to speculate that direct low frequency ultrasound stimulation of the dentine-pulp complex or alveolar bone may be able to initiate or enhance regenerative events
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Comparison of light propagation in dental tissues and resin based compositeElgendy, Hanan Adel 01 May 2016 (has links)
Objectives:
This study used three lasers (red, green and blue) with a spectrophotometer to compare the light propagation [Absorption (A), Transmittance (T), Attenuation (K) and Scattering Anisotropy Coefficient (g)] in dental tissues and nano filled resin based composite using three incremental build-up techniques: one shade (Body), two shades (Enamel and Dentin), and three shades (Enamel, Transparent and Dentin).
Methods:
Twenty un-erupted recently extracted human 3rd molars (shade: B1) were used to obtain 40 tooth slabs (1.5 mm thickness x 4 mm length). The samples were randomized and equally distributed into four experimental groups: Positive Control (Dental Tissues – enamel, dentino- enamel-junction and dentin), Technique 1 (T1 = 1 shade, B1B), Technique 2 (T2 = 2 shades, A2Dentin/B1Enamel), and Technique 3 (T3 = 3 shades, A2Dentin/Transparent/B1Enamel). One calibrated operator performed all procedures and tests. Cavity preparation was standardized using a #58 carbide bur. Using the spectrophotometer, each specimen was irradiated by the three LASERs. A Voltmeter recorded the light output signal and from this raw data the following optical constants were calculated: absorption (A), transmittance (T), attenuation coefficient (K) and Scattering Anisotropy Coefficient (g). The data were analyzed using One-way ANOVA, followed by the post-hoc Tukey's test. All tests utilized a significance level of 0.05.
Results:
Regarding absorption and transmittance, dental tissues were significantly different compared to the three build-up techniques for all lasers. Regarding the attenuation coefficient, dental tissues were not significantly different for T2 and T3 for the blue and red lasers, however they were significantly different for the green laser. There was no significant difference among the three lasers for T2 and T3.
Conclusion:
Within the limitations of this study, none of the build-up techniques used was able to reproduce the dental tissues optical properties and Technique 2 (2 shades) and Technique 3 (3 shades) resulted in a similar pattern of light propagation.
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Prevalence and factors of sibling-recurrent dental treatment under general anesthesiaEdmonds, Brandy N 01 January 2018 (has links)
Objective/Aims: Assess the prevalence of sibling recurrent dental general anesthesia (DGA) at VCU Pediatric Dentistry. Assess factors that contribute to sibling recurrent dental general anesthesia. Methods: The guardian of patients with siblings were provided a questionnaire to assess the prevalence and factors associated with recurrent DGA. Results: A total of 40 families with a child presenting for GA and at least one sibling were included in the study. Of these, 45% had sibling-recurrent GA treatment (20% in one sibling; 25% in 2 or more siblings). Additionally, 13% of the children currently presenting for GA had already been treated under GA, and 15% of the siblings previously treated with GA had recurrent caries after GA. Conclusion: Sibling-recurrent general anesthesia is high at VCU Pediatric Dentistry Clinic. This increased prevalence could be due to parental acceptance and positive experiences with DGA. Dental providers should be pro-active with prevention methods.
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Association between visual characterization of root caries and histological severity In vitroMendieta Facetti, Carolina Elizabeth 01 December 2010 (has links)
No description available.
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