Background: Early detection strategies for oral cancer aim to decrease the mortality rates and improve outcomes of the disease through early diagnosis and treatment. Guidance and regulatory bodies have an expectation that general dental practitioners will be able to promptly detect and refer patients with suspected oral cancerous lesions. However, the opportunities for early detection of oral cancer in primary dental care settings (particularly considering the low overall volume of the disease, the potentially increasing incidence rates, and the possibility of certain communities exhibiting particularly high rates) have not yet been investigated. This thesis examines the feasibility of early detection of oral cancer in primary dental care services, and undertakes risk-stratification to identify “high-risk” communities that can be utilised to target future early detection efforts. It further explores potential or missed opportunities for early detection in dental and other healthcare settings (both primary and secondary care), and assesses the feasibility of exploring routes to diagnosis. Aim: The aim of this thesis was to investigate opportunities for the early detection of oral cancer in Scotland by measuring the current burden of the disease, examining the feasibility of early detection in a dental setting, and exploring the potential role of alternative health care settings in early detection efforts. Methods: Descriptive epidemiological and data linkage cohort studies utilising national routine administrative health datasets were undertaken. The descriptive epidemiological analysis included all cases of head and neck cancer diagnosed between 1975 and 2012 and registered on the Scottish cancer Registry and annual midterm population estimates. These data were used to examine the incidence trends between 1975 and 2012 and the projected burden up to 2025 by individual subsites (oral cavity cancer, oropharyngeal cancer, and laryngeal cancer), age, sex, health board region, and socioeconomic status. The cohort study included all patients diagnosed with oral cancer between 2010 and 2012 and registered on the Scottish Cancer Registry. The individual patient data were linked to NHS dental service activity in the two years prior to diagnosis, and this linked cohort dataset and published NHS Scotland dental workforce and registration and participation statistics were used to examine dental attendance rates and the feasibility of early detection of oral cancer in the primary dental care setting. The individual patient data from the cohort were also linked to the hospital outpatient, hospital inpatient/day case, primary dental care, and general practitioner prescription databases. These four healthcare services were selected based on data availability. The linked data were used to examine all healthcare service contacts made by the cohort in the two years prior to referral. Additionally, a preliminary exploration of the referral period (defined as the one-month period prior to diagnosis) was also undertaken. Results and conclusions: The findings of this thesis showed that the incidence rates of head and neck cancer had increased in Scotland between 1975 and 2012, and this appeared to be largely driven by a dramatic rise in the rates of oropharyngeal cancer in recent decades. This burden was predicted to continue to rise up to 2025, with the rates of oropharyngeal cancer bypassing the rates of oral cavity cancer, which were expected to exhibit only a modest increase. Males, individuals above 60 years of age, and those from the most deprived areas of Scotland consistently exhibited the highest rates of cancer, irrespective of subsite. Moreover, an almost dose-like effect was seen to exist, with the rates of cancer increasing with the level of deprivation. Therefore, contrary to previous reports that oropharyngeal cancer exhibited an inverse socioeconomic profile, Scotland country-level data showed that those from the most deprived areas consistently bore the greatest incidence burden of head and neck cancer. Despite these increasing trends, the overall burden of oral cancer in Scotland was relatively low, and just over half of the cohort examined in this thesis had not contacted a general dental practitioner in the two years prior to diagnosis, thus automatically limiting opportunities for early detection. Dentists were estimated to potentially encounter one patient with oral cancer every 10 years, one patient with oral cavity cancer every 17 years, and one patient with oropharyngeal cancer every 25 years. Therefore, strategies for early detection must consider the rarity of oral cancer incidence and the poor dental attendance patterns of patients, and the expectations of dentists in these efforts must be tempered. These results also highlight the importance of improving access and uptake of dental services among those at the highest risk of developing oral cancer (i.e. those from the most deprived communities). When examining the linked cohort data and undertaking a look-back analysis of their healthcare service contact history, just under half (45%) of the patients diagnosed with oral cancer were seen to have actually visited a primary care dental service clinic in the two years prior to the start of the referral period. However, the majority of the patients with oral cancer had contacted one of the four healthcare services examined (hospital outpatient, hospital inpatient/day-case, primary dental care, and general practitioner prescription) at least once over the same period, suggesting that there were potential or missed opportunities for the early detection of oral cancer in primary dental care and alternative healthcare settings. The proportions of patients contacting the four services increased closer to the start of the referral period, as did the mean number of contacts made with each service. Although not all of these instances would have necessarily been associated with missed opportunities for early detection, it was highly likely that there were potential or missed opportunities amongst at least some of the patients with oral cancer. The two most common services contacted most recently before the start of the referral period were general practitioner prescription and hospital outpatient, and there was a possibility that these services were the sources of referral. The hospital specialties contacted most frequently during the one-month referral period were ENT, oral surgery, oral and maxillofacial surgery, and general surgery, suggesting that these contacts were likely to have been associated with the signs and symptoms of oral cancer. While no significant opportunities for the early detection of oral cancer in hospital or secondary care settings were identified, these findings demonstrated considerable potential in other primary care settings, particularly general medical practices and community pharmacies.

A literature review of dental plaque biofilms formation, progression and detachment mechanisms is presented in this thesis. Various strategies that have been employed to reduce or eliminate dental biofilms are discussed. The focus of the thesis was on the mechanical properties and disruption of dental biofilms, especially from hard-to-access areas of the oral cavity, such as the interproximal (IP) sites between the teeth. Various methods to measure mechanical properties of dental biofilms were investigated, and physical and chemical strategies to disrupt these biofilms were employed. Streptococcus mutans, the bacterium responsible for initiation of dental plaque biofilms, was used in our studies. A uniaxial compressive test was utilized to characterize the mechanical behaviour of biofilms, while manipulating the chemical microenvironment. Initially, the mechanical properties of a dextran gel were characterized. The gel was used as an artificial dental plaque biofilm (Chapter 5). The elastic modulus of the gel was 17 kPa (± 12; n = 3), and the stress relaxation time was 25 seconds (± 18; n = 3), demonstrating a viscoelastic behaviour similar to that reported for real biofilms. After optimizing the technique with the gel, the mechanical properties of S. mutans biofilms were studied, the elastic modulus was 380 Pa (± 350; n = 30), and the stress relaxation time was 12 seconds (± 11; n = 10). The elastic modulus increased by increasing the sucrose percentage in the media, and decreased when the biofilms were treated with increasing concentrations of ethylene di-amine tetra acetic acid, EDTA. Treating the biofilms with different solutions of poly (ethylene glycol), PEG, resulted in behaviour similar to that previously observed for synthetic polymers. The flow field and local hydrodynamics of high velocity water microdrops impacting the interproximal (IP) space of typodont teeth, and their influence on the structure and detachment of both surrogate dental plaque and Streptococcus mutans biofilms, were studied experimentally and computationally. Water droplets of 115 μL were produced by a prototype AirFloss (PT-AirFloss) device provided by Philips Oral Healthcare, bursting water at a velocity of 60 m/s into the IP space between the maxillary central incisors. High-speed imaging, was used to characterise the PT-AirFloss microburst of pressurized air and water micodrops, and demonstrated the removal mechanism of a dental plaque biofilm substitute and the S. mutans biofilms. Using various microscopy and image analysis techniques, quantitative measurements of the removal rate and the percentage removal of biofilms from different locations in the IP space were obtained. Microcomputed Tomography (μ-CT) imaging was used to obtain 3D images of the typodont and the IP spaces. The shear stress distribution generated by the drop impacting the tooth surface was calculated by Computational Fluid Dynamics (CFD) simulations based on the finite element method (FEM). There was good agreement between experimentally measured biofilm removal and the pattern of predicted wall shear stress (τw) generated in the IP space by the microburst. High velocity water microdrops, with minimal fluid volume and time, effectively removed both the surrogate and the biofilm. The shear stress generated by the PT-AirFloss and its spatial distribution on the teeth surface played a key role in dictating the efficacy of biofilm removal. In addition, CFD models were used to predict optimal water drop or burst design with respect to more effective biofilm removal performance. Furthermore, the influence of fluid shear flow on the detachment of Streptococcus mutans biofilms inside microfluidic channels was studied using a commercially available flow-cell system. A critical biofilm detachment shear stress was estimated for the large biofilm-aggregates (CDSSagg). The CDSSagg value was used in the CFD model to predict the spatial distribution of biofilm aggregates detachment from the IP surface caused by the PT-AirFloss microburst. Next the effect of three biofilm matrix-degrading enzymes on the structure and detachment of Streptococcus mutans biofilms inside microtiter plates and on typodont teeth was studied experimentally. The enzymes used were: Bromelain (a protease), DNase, and RNase. The biofilms were treated with different enzymatic preparations, stained with Live/Dead and Crystal Violet, and the corresponding optical density (OD) and fluorescence intensity (FI) were measured by a microplate reader. The results detailed the degradation effect of each enzyme, separately and in combination. The three enzymes demonstrated different efficacies in degrading the biofilm in 6, 24 and 96 well-plates, as well as on the typodont teeth. Also, there was a large variability which could be explained by the heterogeneity of the biofilm. Using epifluorescence microscopy and image analysis, quantitative measurements of the percentage surface area coverage were obtained, and the preliminary results were consistent with the datafrom the plate reader. Furthermore, pre-coating the plates with the three enzymes did not inhibit biofilm from formation and accumulation. Lastly the use of a biocompatible copolymer of methylvinyl ether and maleic anhydride, with excellent mucosal adhesive properties and biocompatibility to improve enzymatic digestion by offering a prolonged contact of the enzymes with the teeth and oral tissues, was investigated. The rationale was to eliminate a major obstacle facing the efficacy of the enzymatic therapy which was the relatively short residence time of the enzymes at the site of administration. The adhesive copolymer could possibly enhance enzyme biofilm degradation. Combining the adhesive copolymer with the enzymes could potentially allow near total degradation of the laboratory-grown S. mutans biofilms.

Within the genus Homo, we observe a decrease in mandibular robusticity and in the size of anterior and postcanine dentition, a trend that is usually referred to as reduction or gracilisation. Factors linked to diet, food processing and encephalization have been suggested to be the main drivers of this trend. Stone tools and fire would have allowed Pleistocene hominins to reduce food toughness, thus relaxing the selective pressures on the masticatory apparatus. In the Holocene, the changes in human lifestyle triggered by agriculture would have determined the reduction in human tooth size. Brain expansion may have acted as a constraint on the development of the lower jaw. In this work, a primate perspective was adopted to clarify the relative influence of adaptive and non-adaptive factors on mandibular and dental reduction in the genus Homo. The effect of diet and structural constraints (allometry and encephalization) on dental and mandibular size and robusticity were analysed. The results show that incisor size and mandibular robusticity correlate significantly with diet proxies in non-human extant catarrhines and with neurocranium shape changes in the neurocranium in Homo sapiens. In non-human African apes, the elongation of the neurocranium influences postcanine tooth size. In Homo, body size plays an important part in tooth size allometry, but not in robusticity. These results suggest that improvements in tool-based food preparation may have been a leading factor in the reduction of incisor size in hominins. Molars and premolars were probably influenced by the expansion of the neurocranium during Pleistocene, and incisor size may be constrained by neurocranium shape changes in H. sapiens. This work confirmed the importance of food processing in the trend of reduction and produced convincing evidence for the significance of structural constraints in the evolution of the hominin anatomy. These findings contribute to explain the complex evolution of the human skull.

Statement of problem: The expansion of the novelty sweets market in the UK has major potential public health implications for children and young adults as they may cause dental erosion, dental caries and obesity. Aims and objective: To investigate the potential dental public health implications of novelty sweet consumption in children. The objectives of this study were to determine the available novelty sweets available to UK consumers, to determine the erosive potential of the most available novelty sweets, to establish the sensory thresholds in children and to determine any potential link between high sensory threshold individuals and their consumption of novelty sweets. Methodology: A list of the most commonly available novelty sweets was created by undertaking scoping visits of shops in the Cardiff area. Children’s use and knowledge of the ten most available novelty sweets were undertaken using focus groups, amongst 11-16 year old children. The focus groups informed the design of a questionnaire. The questionnaire was distributed to 46 children aged 11-16 years during a sensory analysis assessment involving sensory taste thresholds for sweet and sour, assessed using the intensity ranking method. The pH of the ten most available novelty sweets was assessed using an electronic pH meter; the neutralisable acidity was measured by titration against 0.1M sodium hydroxide; an erosion test was conducted on human teeth using a surfometer; contact angles were measured using a Dynamic Contact Angle Analyser; the viscosity was measured using a rotational viscometer and sugar content of the sweets was measured using a refractometer. Results: A wide range of novelty sweets were available, accessible to children in 73% of shops with an average price of 96p. The children were all familiar with novelty sweets, they reported buying and consuming them regularly. The majority of children (65%) required higher amounts of sugar and citric acid than the absolute taste threshold to recognise the sweet and sour tastes. There was an inverse relationship between the preference of the novelty sweets and perception of sweet and sour sensory thresholds (p < 0.05). The pH of eight of the ten novelty sweets was significantly lower than the orange juice (p < 0.05). The neutralisable acidity of seven of the sweets was significantly higher than the orange juice (p < 0.05). The erosive potential of six novelty sweets was significantly higher than the erosive potential of the orange juice (p < 0.05). Delayed ultrasonication by 1 h, reduced the amount of subsurface enamel loss by 0.52-1.45μm in presence of saliva. Some of the acidic solutions had low contact angles, lower viscosity and higher sugar content than orange juice. Conclusions: A wide range of acidic and free sugar sweetened novelty sweets were easily accessible and affordable to children. Children reported consuming these sweets regularly. The high sensory taste thresholds perception for sweet and sour in children may potentially affect their consumption of novelty sweets. Those personnel involved in delivering dental and wider health education or health promotion need to be aware of and able to advise on current trends in sweet confectionary. The potential effects of these novelty sweets on both general and dental health require further investigation.

Introduction Prediction of soft tissue changes following orthognathic surgery has been frequently attempted in the past decades. It has gradually progressed from the classic “cut and paste” of photographs to the computer assisted 2D surgical prediction planning; and finally, comprehensive 3D surgical planning was introduced to help surgeons and patients to decide on the magnitude and direction of surgical movements as well as the type of surgery to be considered for the correction of facial dysmorphology. A wealth of experience was gained and numerous published literature is available which has augmented the knowledge of facial soft tissue behaviour and helped to improve the ability to closely simulate facial changes following orthognathic surgery. This was particularly noticed following the introduction of the three dimensional imaging into the medical research and clinical applications. Several approaches have been considered to mathematically predict soft tissue changes in three dimensions, following orthognathic surgery. The most common are the Finite element model and Mass tensor Model. These were developed into software packages which are currently used in clinical practice. In general, these methods produce an acceptable level of prediction accuracy of soft tissue changes following orthognathic surgery. Studies, however, have shown a limited prediction accuracy at specific regions of the face, in particular the areas around the lips. Aims The aim of this project is to conduct a comprehensive assessment of hard and soft tissue changes following orthognathic surgery and introduce a new method for prediction of facial soft tissue changes.   Methodology The study was carried out on the pre- and post-operative CBCT images of 100 patients who received their orthognathic surgery treatment at Glasgow dental hospital and school, Glasgow, UK. Three groups of patients were included in the analysis; patients who underwent Le Fort I maxillary advancement surgery; bilateral sagittal split mandibular advancement surgery or bimaxillary advancement surgery. A generic facial mesh was used to standardise the information obtained from individual patient’s facial image and Principal component analysis (PCA) was applied to interpolate the correlations between the skeletal surgical displacement and the resultant soft tissue changes. The identified relationship between hard tissue and soft tissue was then applied on a new set of preoperative 3D facial images and the predicted results were compared to the actual surgical changes measured from their post-operative 3D facial images. A set of validation studies was conducted. To include: • Comparison between voxel based registration and surface registration to analyse changes following orthognathic surgery. The results showed there was no statistically significant difference between the two methods. Voxel based registration, however, showed more reliability as it preserved the link between the soft tissue and skeletal structures of the face during the image registration process. Accordingly, voxel based registration was the method of choice for superimposition of the pre- and post-operative images. The result of this study was published in a refereed journal. • Direct DICOM slice landmarking; a novel technique to quantify the direction and magnitude of skeletal surgical movements. This method represents a new approach to quantify maxillary and mandibular surgical displacement in three dimensions. The technique includes measuring the distance of corresponding landmarks digitized directly on DICOM image slices in relation to three dimensional reference planes. The accuracy of the measurements was assessed against a set of “gold standard” measurements extracted from simulated model surgery. The results confirmed the accuracy of the method within 0.34mm. Therefore, the method was applied in this study. The results of this validation were published in a peer refereed journal. • The use of a generic mesh to assess soft tissue changes using stereophotogrammetry. The generic facial mesh played a major role in the soft tissue dense correspondence analysis. The conformed generic mesh represented the geometrical information of the individual’s facial mesh on which it was conformed (elastically deformed). Therefore, the accuracy of generic mesh conformation is essential to guarantee an accurate replica of the individual facial characteristics. The results showed an acceptable overall mean error of the conformation of generic mesh 1 mm. The results of this study were accepted for publication in peer refereed scientific journal. Skeletal tissue analysis was performed using the validated “Direct DICOM slices landmarking method” while soft tissue analysis was performed using Dense correspondence analysis. The analysis of soft tissue was novel and produced a comprehensive description of facial changes in response to orthognathic surgery. The results were accepted for publication in a refereed scientific Journal. The main soft tissue changes associated with Le Fort I were advancement at the midface region combined with widening of the paranasal, upper lip and nostrils. Minor changes were noticed at the tip of the nose and oral commissures. The main soft tissue changes associated with mandibular advancement surgery were advancement and downward displacement of the chin and lower lip regions, limited widening of the lower lip and slight reversion of the lower lip vermilion combined with minimal backward displacement of the upper lip were recorded. Minimal changes were observed on the oral commissures. The main soft tissue changes associated with bimaxillary advancement surgery were generalized advancement of the middle and lower thirds of the face combined with widening of the paranasal, upper lip and nostrils regions. In Le Fort I cases, the correlation between the changes of the facial soft tissue and the skeletal surgical movements was assessed using PCA. A statistical method known as ’Leave one out cross validation’ was applied on the 30 cases which had Le Fort I osteotomy surgical procedure to effectively utilize the data for the prediction algorithm. The prediction accuracy of soft tissue changes showed a mean error ranging between (0.0006mm±0.582) at the nose region to (-0.0316mm±2.1996) at the various facial regions.

Cette étude portant sur 17 journaux et 236 tracts conçus par des résistants allemands et autrichiens actifs en France pendant la Seconde Guerre mondiale a permis d’en révéler les enjeux théoriques et de mieux connaître leurs auteurs, en réévaluant notamment le rôle des ressortissants autrichiens et des groupes de gauche non alignés sur la politique de la IIIe Internationale. Les messages transmis se classent en trois catégories chacune liée à l’objectif poursuivi, à savoir le recrutement, la visibilité et la définition du positionnement du groupe. On constate que quatre principaux types de lecteurs sont visés : en premier lieu les sympathisants potentiels parmi les soldats de la Wehrmacht, mais également les services de répression, les autres groupes de résistants et, enfin, les Alliés, à la fin du conflit. Une première partie analyse les productions de groupes initiés par les partis communistes. De 1941 à 1943, le Travail Allemand (TA) vise à restructurer les réseaux démantelés en 1939. À partir de 1943, les militants sont regroupés en fonction de leur nationalité dans de nouvelles organisations, le CALPO et l’ÖFF, dont les objectifs consistent non pas à réaliser des projets nationaux mais plutôt à étendre l’influence soviétique dans les nouveaux États après la guerre. La deuxième partie est dédiée aux Revolutionäre Kommunisten (RK) qui sont des communistes conseillistes autrichiens dénonçant toutes les autres forces en présence pour construire une société radicalement différente. Ce travail dresse un portrait précis et inédit de ce groupe et de ses évolutions théoriques de 1935 à 1944. Une troisième partie est consacrée à l’étude de groupes trotskystes qui souhaitent concurrencer les organisations des communistes mais qui manquent de moyens logistiques et matériels pour y parvenir. Ce groupe est actif de 1943 à 1944 et sa production s’arrête brutalement suite à une vague d’arrestations. Notre étude démontre que deux philosophies politiques coexistent et sont concurrentes. Les communistes cherchent à renverser le régime nazi pour rétablir les structures étatiques traditionnelles et accroître l’influence soviétique. Les RK et les trotskystes étendent les enjeux à la lutte contre le « capitalisme », et, ce faisant, dépassent par leurs actions ce que l’on entend habituellement par « résistance ». / This study of 17 newspapers and 236 flyers conceived by German and Austrian resistance fighters in France during World War II have revealed the theoretical issues and to provide better knowledge of the authors, by re-evaluating the role of Austrians and Left groups which were not aligned with the politics of the Third Communist International. The messages are classified in three groups each linked to the objective pursued; recruitment, visibility and the definition of the group’s position. We can see that there are four main types of readers targeted: the first group are the potential sympathizers among the Wehrmacht soldiers, but also the repression services, the other resistance groups and finally the Allies, at the end of the conflict. The first part analyses the production of organisations initiated by the German and Austrian communist parties. From 1941 to 1943, the Travail Allemand (TA) aimed to restructure the networks which had been dismantled in 1939. From 1943, the militants were regrouped into new organizations like the CALPO and ÖFF depending on their nationality. Their objectives did not consist of carrying out national projects but rather to extend Soviet influence in the new states after war. The second part is dedicated to the Revolutionäre Kommunisten (RK) who were Austrian revolutionary communists denouncing all the other forces involved to build a radically different society. This piece of work draws an original and precise portrait of this group and its theoretical evolutions from 1935 to 1944. The third part is devoted to the study of Trotskyist groups which would like to have competed with communist organizations but who lacked the logistic and material means necessary. This group was active from 1943 to 1944 and its production brutally stopped with a wave of arrests. Our study shows that two political philosophies coexist and compete. The communists want to overthrow the National Socialist government to reestablish the traditional administrative and political structures and increase Soviet influence. The RKs and Trotskyists widen the stakes to fight against capitalism and by doing so, exceed the actions that we usually call “resistance”.

The overall aims of the studies were to obtain objective measures of oral precancerous lesions based upon studies of the cell cycle and to investigate these parameters as possible prognostic indicators with regard to malignant transformation of these lesions. The majority of the precancerous lesions in the present study were dysplastic. These are the lesions which cause the greatest concern clinically with regard to malignant transformation. The first part of the study investigated the S-phase, growth fraction and the relationship of these to each other and with the degree of dysplasia with the aim of achieving objective measurements of the dysplasia and prognostic information. This was achieved by the use of BrdU for labelling of cells in the S-phase and anti-Ki67 antibody as a marker of cells in the growth fraction. The BrdU labelling index was demonstrated to provide an objective assessment of the dysplastic lesions when compared to the semi-objective method of Smith and Pindborg (1969). The ratio of the S-phase to the growth fraction was higher in those lesions which progressed to malignancy and was cited as a possible prognostic indicator. A number of methodological problems were identified from this first part of the study and these were investigated further by the development of techniques in Chapter 3. Firstly, a method was developed to enable the BrdU labelled tissue to be formalin fixed and then allow other cell cycle associated markers to be studied on sequential sections of the same tissue block. Secondly, numerous antigen retrieval techniques were carried out in order to optimise the immunohistochemical staining of Ki67 and subsequently other antibodies utilised in later parts of the study. Normal oral epithelium, derived post-mortem, was studied in Chapter 4 to investigate the apparent underestimation of proliferating cells identified by anti-Ki67 antibody in Chapter 2. It was apparent that, as in dysplastic epithelia, Ki67 significantly underestimated progenitor cells of the morphologically identified progenitor compartment. Ki67 did not identify all of those cells which would have been expected to be in the cell cycle it was originally claimed to do.

Background: Effective delivery of dental services must be based on reliable information regarding the prevalence and severity of disease in the target population. Evaluation of the various factors known to influence the severity and progression of disease is essential for health policy makers to promote oral health resources and address oral health needs. Objective: The overall aim of this research is to describe the situation of dental caries and investigate the associations of level of oral health knowledge, teeth irregularity, BMI and other life style variables (TV viewing, internet use, passive smoking and dietary habits) with dental caries, including the impact of socio-demographic factors amongst school children in Qatar. Materials and methods: A cross-sectional study was conducted in Qatar from October 2011 to March 2012. A total of 2,113 children aged 12-14 years were randomly selected from 16 schools from different areas. Clinical examination was conducted by three calibrated examiners using World Health Organization criteria for diagnosing dental caries. Teeth irregularity was determined clinically according to a method described by Björk et al (1964). A pre-tested and structured questionnaire was used to assess oral health knowledge and life style data. Data analyses were performed. Results: The mean decayed, missing and filled teeth index values was 4.62 (±3.2), 4.79 (±3.5), and 5.5 (±3.7), respectively, for the 12, 13 and 14 year old children. The caries prevalence was 85%. The mandibular incisors and canines were least likely to be affected by dental caries, while maxillary and mandibular molars were the most frequently attacked by dental caries. Of the total sample, only one quarter reported a high level of oral health knowledge. There were more incidences of teeth crowding (44.1%) than teeth spacing (9.5%). The overall prevalence of underweight, overweight, and obesity was 5%, 10%, and 5% respectively. Almost half of the children spent > two hours watching television and 46% spent > two hours using internet. Approximately 35.8% of children had exposure to passive smoking. Concerning dietary habits, 99.4% of children consumed sugar containing snacks in between meals. Approximately 65% consumed sugar containing snacks within one hour of bed time. Almost 49.1% skipped eating breakfast regularly and 22.7% skipped eating lunch regularly. Around 83.8% consumed diary snacks in between meals. Overall, 74.2% drank tea in-between meals and 80.1% chewed gum in-between meals. All variables were affected by socio-demographic factors, but significant differences were found in female children in that they were more at risk to dental caries than male children. Also, children who resided in semi-urban areas were more at risk to dental caries than children who resided in urban areas. The occurrence of dental caries is significantly associated with the level of oral health knowledge, teeth irregularity, and other life style variables. Conclusion: The need to reduce sedentary behaviors and to promote a more active and healthy lifestyle is becoming increasingly essential in Qatar. Implementation of a community-based preventive oral health programs on a healthy diet and practices of adequate oral hygiene should be promoted in schools through integration into the school curriculum and services to combat the growing problem of dental caries.

Antimicrobial resistance is an international public health problem and is associated with increased morbidity, mortality, and healthcare costs. Antibiotic consumption, particularly indiscriminate use of these agents, is recognised as a major cause of resistance. Clinical guidelines recommend that in otherwise healthy individuals, antibiotics should not be used in the management of acute dental conditions, in the absence of spreading infection and systemic upset. Instead, a surgical intervention should be the first-line treatment for such problems. This thesis describes the use of antibiotics for acute dental conditions in primary care in the UK, and explores factors that influence prescribing for dental problems using a mixed methods approach.

Current methods of dental biofilm removal are predominantly mechanical and are not effective in removing it from irregular surfaces in the mouth. Cavitation occurs around dental ultrasonic scalers and may be a more efficient and less damaging technique. Previous work has failed to quantify the cavitation bubble dynamics around ultrasonic scalers and its effects. The aim was to develop imaging and analysis protocols to analyse the cavitation and to investigate its ability to disrupt biofilms and deliver sub-micron particles into dentine. High speed imaging was used to characterise cavitation. Its effect on biofilm removal and dentinal tubule occlusion was studied using electron microscopy and x-ray micro computed tomography. We are able to demonstrate that cavitation occurs at the free end of scaler tips and increases with power and vibration amplitude. Biofilm can effectively be removed from dental implant surfaces using this cavitation. It can also be used to transport sub-micron particles further into dentinal tubules. The results show that ultrasonic scalers could be optimised for non-contact use and improved removal of plaque from the teeth. The protocols established in this study can be applied to future studies for quantitative investigation of biofilm growth and removal and analysis of cavitation dynamics.