The wisdom on mechanical removal of carious dentine based on hardness has been challenged and chemo-mechanical technique has been proposed as a more conservative method. However, the extent and comparison of excessive removal of sound dentine and insufficient removal of carious dentine have not been studied. The aims of the present study are to use X-ray microtomography (XMT) to determine the mineral concentrations of sound and carious dentine, and the excavated dentine using a hand excavation (HE) technique, a hand excavation technique aided by Caries Detector Dye (CD) and a chemo-mechanical removal technique using Carisolv (CSS). Comparison of the three techniques with respect to the mineral concentrations of the excavated dentine caries and the volumes of sound dentine removed were investigated. It was aimed to identify the boundary between ―infected‖ and ―affected‖ using the X-ray linear attenuation coefficients (LAC) from the XMT results and the ultrastructural images obtained from the Back Scattered Electron (BSE) imaging and Atomic Force Microscopy (AFM). Thirty eight deciduous molars with open carious cavities were sectioned in half. One half of each molar had the carious tissue removed by HE and the other by CSS or hand excavation plus CD. XMT images were taken before and after caries removal. From the data set, an assessor, who was ‗blind‘ to which technique was used, used LAC histograms to assess the efficacy of the excavation techniques. The volumes of sound dentine removed by the 3 techniques were calculated and compared. Detailed analyses were carried out using XMT slices to investigate the mineral concentration of removed and residual dentine. Remineralisation experiments of residual dentine were performed 7 after caries removal. Backscattered electron (BSE) microscopy and atomic force microscopy (AFM) were used to investigate the ultrastructure of the carious dentine. The results showed that CSS was a better technique; conforming to the principles of minimally invasive dentistry. Volume analyses showed that both CSS and CD were effective in removing less sound dentine than conventional hand excavation. It was shown for the first time that the partially demineralised layer of dentine in a natural carious lesion, which was maintained by the CSS technique, had the potential to remineralise up to 80% of the mineral level for sound dentine. Combining XMT results with AFM and BSE images, ultrastructural changes were found at the boundary around a LAC value of 0.8 cm-1 which corresponded to a KHN of 7.66 kgmm-2. It was concluded that carious dentine removal up to a hardness level of 7.66 kgmm-2 could be recommended in order to preserve dentine that has potential to remineralise.

Enamel development and structure have been studied in a number of placental and marsupial mammals, by light microscopy; electron-microscopy; and scanning electron microscopy. The relationship between the formative cells of the enamel and its structural organisation into "prisms" and interprismatic regions has been studied in particular. The crystallites in developing enamel tend to be oriented perpendicular to its mineralising front; but their orientation may be modified by either the translatory movement which may occur between certain surfaces of the TOMES' processes of the ameloblasts and the mineralising front, or the self directed growth of groups of groups of crystallites. The presence of a repetitive (prism) pattern of crystallite orientation in formed enamel is determined by changes of orientation of and within the mineralising front: these changes are 1) the result of the peculiar mode of secretion of the enamel precursor substances from and about projections from the ameloblasts; and 2) absent during the formation of the first and last layers of enamel (formed at the enamel-dentine junction and the true enamel surface respectively) by a given group of ameloblasts: hence there are no prisms in these regions. Abrupt changes in orientation of the mineralising front determine abrupt changes in crystallite orientation in the enamel (equivalent to the "prism-sheaths" of adult enamel). The secretory territories of individual ameloblasts are only equivalent to prisms in one particular pattern: one ameloblast may be related to more than one prism. Decussation of prisms is associated with the depressions in the mineralising front filling in from alternate sides in "zones". Zone formation begins as a spiral over cusp centres. Light scattering from enamel depends on 1) the size; and 2) the orientation of its ultrastructural elements and 3) the wavelength of the incident radiation; blue light being scattered preferentially; hence the visibility of: - 1) the incremental striae; and 2) the decussating zones of prisms; and 3) the brown colour of the incremental striae when viewed by transmitted light. The calcium content in developing enamel measured by the x-ray emission microanalytical method was found to increase steadily, from the surface of the developing enamel inwards.

Aim: To investigate the effect of age, gender, socioeconomic status, academic achievement, learning styles, learning approaches, and the learning environment on the reflective process. Methods: All dental undergraduate students studying at King AbdulAziz University Faculty of Dentistry (KAUFD) agreed to participate on three occasions of approximately six month intervals between February 2008 and June 2009 (QMREC2007/67). Four previously validated structured questionnaires including demographic details were used to determine students’ learning style (Felder and Soloman, http://www.ncsu.edu/felder-public/ILSpage.html [ILS]), approach to learning and studying (Entwistle, http://www.ed.ac.uk/etl [ALSI]), reflection (Sobral, 2005 [RLS]) and perception of their educational environment as determined by the Dundee Ready Educational Environment Method (Roff et al. 2005, [DREEM]). Multiple linear regression was used to investigate the independent effects on the questionnaires. Results: A total of 624 students (F=347, M=277) were included in the analysis. ILS assessed the undergraduate learning styles: 20.7% active learners, 47.9% sensing, 68.2% visual and 18.1% sequential learners. Sudents adopted different approaches simultaneously. The mean overall DREEM score was (112.76, SD19.54) indicating a more positive view of their environment. Fifty eight percent were ample in their ability to reflect. Females, older students, and from higher socioeconomic background reflect more. In the final student learning model, reflection was positively associated with a deep approach, organised/effort approach, academic self perception and perception of learning, whilst a surface approach was negatively associated with reflection. Students with higher academic achievement were able to 3 reflect and adopt an organised/effort approach, whilst students with lower grades had low reflective scores and adopt a surface approach. Conclusion: KAUFD dental students demonstrate sensing and visual learning styles. An effective learning environment that facilitates reflection results in the development of self directed learners. Self directed students take control over their own learning and are able to employ strategies such as a deep and organised approach to studying that can influence and optimise their learning and academic performance.

In order to develop a successful soft lining material various factors have to be considered; physical strength, adhesion to the denture base ( or prosthetic) and the durability of the material's properties when in the mouth. It has been recognised that in order to fulfil these criteria the material must be stable and have a low water uptake from the aqueous environments of the mouth. In the dental field comparatively little work has focused on how soft lining materials behave in water where as water in polymers has received a considerable amount of interest, with many different types of behaviour being observed and explained. It has been realised by previous authors that the water uptake of elastomers is primarily driven by soluble impurities, these form solution droplets within the material. The nature of the growth is somewhat more debatable, with both Fickian and dual sorption kinetics being reported. Two basic types of materials were used in the study; silicone polymers and elastomer / methacrylate materials. Silicone polymers are characterised by a low water uptake and form the basis of perhaps the most successful soft lining material ('Molloplast B'). The elastomer / methacrylate materials were based on those developed by Parker (1982), Parker and Braden (1990) which showed considerable promise but suffered from an extensive protracted uptake. Water uptake at 370C in conjunction with the tensile strength were used to evaluate the materials produced as these simple tests enabled the behaviour of the material in service to estimated. Three different types of silicone polymers were used during the study classified by the curing mechanism (condensation, peroxide and hydrosilanised), various fillers and additives (such as calcium stearate) were incorporated into the materials and different uptakes observed. The condensation silicones demonstrated large weight losses (up to 20 wt%) in water which is attributed to hydrolytic instability of the siloxane bridge in the presence of an organo tin compound leading to a leaching of siloxane. The pure peroxide and hydrosilanised materials both demonstrated a low water uptake but when doped they form solution droplets in a similar way to that described in the literature. Other additives showed different behaviour with the formation of cracks within the silicone due to failure of the material around the droplets, the action of hydrophilic but insoluble fillers also promotes the uptake. The hydrosilanised silicone polymers showed considerable promise as soft lining materials with low water uptake and good tensile strength. 11 The elastomer / methacrylate materials were based initially on butadiene styrene copolymer and a higher methacrylate monomer which formed a gel this was then free radically cured. The water uptake of these materials was attributed to soluble separating agent added to the butadiene styrene (to prevent particle agglomeration) during the production of the powdered elastomer. The extent of the uptake could be controlled by improving the strength of the material but the overall uptake remained too high. When the material was placed in an osmotic solution (Na CI or glucose) the water uptake was significantly reduced and the behaviour could be described by a modified (for small strains) version of the Thomas and Muniandy (1987) theory for the growth of water droplets in a elastomer. In order to reduce the water uptake of the elastomer / methacrylate materials butadiene styrene copolymers without separating agent was used. The emulsion polymerised material contained soluble impurities from the polymerisation (i.e. soap)which acted to drive the water uptake. Solution polymerised butadiene styrene also demonstrated a high uptake but this is attributed to a clustering behaviour of carboxylic and hydroxyl groups which formed post production. Similar behaviour is also seen for a solution polymerised isoprene styrene elastomer. The role of crosslinking the material in restraining the growth of the droplets is also investigated with dramatic reductions in the uptake being observed as the crosslink density increased. The employment of a reinforcing silica filler proved more effective than simply using a dimethacrylate. Oxidation is another problem (characterised by an upturn in the absorption), although not observed in every case it was a problem for all of the unsaturated elastomers and was found to be promoted by ions present within saliva. Saturated butyl based (including chloro and bromo butyl) elastomers were used instead and did not show any tendency for oxidation but they still showed an uptake of approximately 3 to 4 wt%. Their stability however and reasonable strength makes them suitable for further development as soft lining materials. Theoretical considerations were investigated by HI NMR imaging with the formation of droplets being observed, the profiles seen indicating the absorption to be two stage rather than Fickian. The role of creep or stress relaxation is also identified as a mechanism for extending the uptake by reducing the restraining force. Further reasoning on all the data presented here concluded the role of chemical potential change associated with the water into the matrix or the droplets will determine the nature of the uptake observed.

Although soft lining materials are inadequate to their requirements, their use is widespread. - This investigation has been undertaken in an attempt to determine which are the better materials and how they may be evaluated. In addition some new materials have become available which may have advantages over existing materials. A representative selection of thirteen commercially available soft lining materials were chemically analysed. These, together with four experimental materials, were subjected to laboratory investigation of their water absorption and water solubility; their visco-elastic properties and the effect on these properties of bonding the materials to poly (methyl methacrylate); their rupture properties; their wettability and their effect on the growth of Candida albicans. An attempt was made to relate these properties to the chemical composition of the materials. Their water absorption and water solubility was in general unacceptably high with the exception of two silicone rubber materials and an experimental acrylic resin material. Conversely their compliance was generally satisfactory, two experimental acrylic resin materials being the exceptions. Two extremes of resilience were recorded but either may prove clinically satisfactory. With the exception of three of the silicone rubber materials their rupture properties were satisfactory, and only an experimental natural rubber material demonstrated completely unsatisfactory adhesion to poly (methyl methacrylate), although other materials may be unreliable in this respect. Eleven of the materials demonstrated satisfactory wettability, the OTHclZ Femaining six including four of the rubber materials. Only four materials inhibited the growth of Candida albicans and the constituents responsible were identified. Concern was expressed regarding the tissue compatibility of some of the constituents. In conclusion, only three of the materials investigated merit further study, two silicone rubber materials and an experimental acrylic resin material which utilises a polymerisable plasticiser.

Synthetic, biological and mineralogical carbonate-containing apatites have been studied, principally by infra-red absorption spectroscopy (using polarised or unpolarised radiation), The substitution of a carbonate ion for two hydroxyl ions in the apatite lattice has been confirmed, by chemical analyses, and the variation of the lattice constants with the degree of substitution determined. The orientation of the carbonate ion has been determined by using polarised infra-red radiation; its plane is approximately parallel with the c-axis. The carbonate ions in dental enamel are in two different environments; the lane of the carbonate ion in these two environments is nearly parallel and perpendicular to the c-axis. One of these environments is very probably the substitution for hydroxyl ions discussed above; this accounts for only a small fraction of the carbonate ions, the remainder are probably adsorbed on the surface of the apatite crystals. A number of carbonate-containing apatites prepared in aqueous systems have been studied. These show similarities to enamel but with the carbonate ions in different relative proportions in the two different environments present in enamel. Some apatites have been prepared which have absorption bands due to molecular carbon dioxide. This has been confirmed by preparing apatites containing the heavy isotope of carbon, carbon-13. The orientation of the carbonate ion in francolite has been determined and is consistent with it occupying the sloping face (with respect to the basal plane) of the space left by a phosphate ion. The environment of the carbonate ion in francolite is different from that in enamel, The hydroxyl ion in enamel and francolite is oriented 'with the 0-H bond parallel with the c-axis of the apatite lattice. The assignment of the hydroxyl band in the infra-red spectrum of enamel has been confirmed by deuteration experiments.

Periodontitis is a multi-factorial disease characterised by the loss of connective tissue and underlying alveolar bone leading to the loss of teeth. Porphyromonas gingivalis (P. gingivalis) is a gram-negative black pigmented anaerobe associated with chronic periodontitis. Porphyromonas gingivalis possesses a range of virulence factors including gingipains, lipopolysaccharide (LPS) and fimbriae. Receptor activator of nuclear factor-κB ligand (RANKL) induces bone resorption whilst osteoprotegerin (OPG) blocks this process by binding to RANKL and acting as a decoy receptor. Cyclooxygenase-2 (COX-2) is an enzyme responsible for the synthesis of prostaglandin E2 (PGE2), a potent inflammatory mediator of bone resorption. Mitogen-activated protein kinases (MAPK) are intra-cellular signaling proteins that control fundamental cellular events, with implications in inflammation and bone metabolism. This thesis aimed to investigate the effect of P. gingivalis on bone marrow stromal cells, primarily on the regulation of molecular mechanisms involved in bone resorption, using gene and protein expression assays, and secondarily on changes in their global transcriptional profile, using microarray technology. It was determined that P. gingivalis upregulated RANKL and downregulated OPG gene and protein expression, resulting in an increased RANKL/OPG expression ratio. These regulations were partly attributed to its LPS and an unidentified synergistic factor. PGE2 was a key mediator in this regulation of RANKL expression. Further to this, P. gingivalis was shown to signal through p38 MAPK, contributing to the PGE2-mediated RANKL induction. The extension of this work using microarray technology demonstrated that in the present experimental system P. gingivalis positively regulates a broad spectrum of genes involved in promoting inflammation and bone destruction. 2 This thesis shows that P. gingivalis can exert its virulence on bone marrow stromal cells. An interplay of bacterial and host factors leads to the activation of molecular mechanisms of bone resorption, which may be implicated in initiating periodontal disease. Moreover, the identified mediators of bone resorption may serve as potential targets for treating P. gingivalis-associated periodontitis.

Aim: To develop a comprehensive, validated, evidence based, practical, user-friendly atlas of dental age estimation and compare its performance with two widely used atlases. Methods: Based on the radiographic appearance of tooth development in 528 individuals aged 2-23 years and 176 neonates, the median stage of tooth development for each tooth in each age category/chronological year was used to construct diagrams representing ages between 28 weeks in-utero and 23 years were developed (The London Atlas) Accuracy was determined by ageing skeletal remains/radiographs of 1514 individuals (aged 32 weeks in-utero to 23 years) using The London Atlas (LA), the Schour and Massler (SM) and Ubelaker (Ub) atlases. Estimated age was compared to real age. Bias, absolute mean difference and proportion of individuals correctly assigned by age were calculated. Intra-observer variation (Kappa) was measured by re-assessment of 130 radiographs. To test the application of The London Atlas, a questionnaire was used to validate its use. Ninety 3rd year dental students were divided randomly into three subgroups, and blinded from the researcher. Each group used one of the 3 atlases to estimate the radiographic age of 6 individuals and complete a questionnaire focussed on the design, clarity, simplicity and self-explanation of the three atlases. Results: Excellent reproducibility was observed for all three atlases (Kappa: LA 0.879, SM 0.838 and Ub 0.857). LA showed no bias (P=0.720) and correctly estimated 53% of cases. SM and Ub showed significant bias by consistently underestimating age (P=0.026 and P=0.002) with 35% and 36% correctly estimated for SM and Ub respectively. The mean absolute difference for LA (0.72 years) was smaller than SM (1.15 years) and Ub (1.17 years). LA was preferred over the other two atlases in all quality measures tested (clarity, design, simplicity and self-explanation). Conclusion: The London Atlas represents a substantial improvement on existing atlases facilitating accurate age estimation from developing teeth. Development of interactive online and mobile app versions is complete.

A series of experiments were performed to understand the ionic processes in glass ionomer cements. Fluoride release from fluoroaluminosilicate glasses in deionised water and artificial saliva Inorganic artificial saliva was used to compare the release of fluoride from four fluoroaluminosilicate glasses (AH2. LG26Sr, LG125 and LG26). The glasses were used in their raw form and as an acid washed glass and pseudocement. Results showed two different trends. AH2 released more fluoride in artificial saliva relative to deionised water and the LG glasses released less in artificial saliva relative to deionised water. Kinetics of fluoride release from glass ionomer cements: influence of ultrasound and radiant heat Two conventional GIC’s Fuji IX and Ketac Molar were used, along with commercial GIC’s Amalgomer, Amalgomer CR and Glass Carbomer which was also radiant heat set. The experimental glass used was LG30 which is a fluoride free glass and was mixed at 7:1 ratio with 2% NaF solution. It was observed that ultrasound increases the release of fluoride whereas radiant heat reduces the release of fluoride. Investigation into secondary setting mechanism of glass ionomer cement: hydrolytic stability of aluminiosilicate-acetic acid cements Six glasses were used LG26, LG30, LG117, Anorthite, Na-Anorthite. Glasses were mixed with acetic acid and made into discs. These were matured for 1, 2, 3, 6 and 24 hours then immersed in 40ml of deionised water. After 24hours they were assessed for visual disintegration using a scale developed for this purpose. It was noted that MP4 never formed stable cement; LG26, LG117, Anorthite and Na-anorthite immediately formed a stable cement whereas LG30 formed a stable cement only after 24hours. Inductively Coupled Plasma analysis on the release of ions showed that Al was released in quantities comparable to glass-polyalkenoate cements hence suggesting that acetate cements are actually Al-acetate type cements.

Dental caries is a public health problem affecting over 30% of 3.5 to 4.5 year old children in the UK. One of its most important determinants is frequent consumption of sugary foods, without which plaque bacteria cannot produce sufficient acids to demineralise tooth structure. The aim of this study was to identify the contribution of family functioning in the domains behaviour control, affective responsiveness, affective involvement, communication, problem solving and roles towards the frequent consumption of sugary foods by three and four year old children in Outer North East London. The research questions were explored with data from the Outer North East London Family Study (ONEL-FS), which collected data through home visits, by trained dentists and interviewers, from a representative sample of adults and children living in the London boroughs of Redbridge, Barking and Dagenham and Waltham Forest in 2008-10. This study analysed data (N=698) from three and four year old children and their mothers and included unadjusted and adjusted logistic regression and mediation analysis. The results showed that 17% of the sample consumed sugary foods more than 4/day which was significantly associated with behaviour-control (OR 0.25; 95% CI: 0.11, 0.57), affective-responsiveness (OR 0.29; 95% CI: 0.14, 0.58), affective-involvement (OR 0.32; 95% CI: 0.17, 0.60), communication (OR 0.34; 95% CI: 0.14, 0.85) and roles (OR 0.22; 95% CI: 0.08, 0.62), after adjusting for confounders. The significant association between mother’s education and children’s sugar consumption (OR 0.35; 95% CI: 0.21, 0.58) was partially mediated through behaviour control, affective responsiveness, affective involvement, communication and roles. The significant association between mother’s ethnicity and sugar consumption (OR 3.46; 95% CI: 1.63, 5.25) was also partially mediated through these same five domains. The study findings contribute to the literature on protective influences within the family environment and confirm current knowledge regarding mother’s education and ethnicity.