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.

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.

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.

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

The improvement and modification of the surface hardness of glass-ionomer dental cements was investigated in the studies discussed in this thesis to allow the range of clinical applications of these cements to be extended. Storing the cements in non-aqueous media whilst heating at 60 oC increased the surface hardness compared to storage in water at 37 oC. The corresponding compressive strength showed no significant changes. The bioactivity of two commercially available glass-ionomer dental cements was investigated after it was established that the surface hardness of a dental cement was improved by storing the materials in biologically natural bovine milk. In particular the observations of the appearance of the surface were noted as well as cation release studies and calcium to phosphorus ratios calculated. The results indicated that a surface layer of calcium phosphate had formed and created a barrier around the cement preventing the loss of strengthening ions. An investigation was also made into formulating a novel hybrid cement. This process included the deployment of additives/co-reactants within the cement formulation. By incorporating zinc phosphate into a strontium based glass-ionomer elevated levels of fluoride release were obtained when compared to the original commercially available glass-ionomer. SEM images show that this additive had an effect on the surface morphology of the glass. The bioactivity studies performed on these cements show the uptake of calcium over one week, indicating that there is the possibility that these new hybrid cements are bioactive. Refinement of the new hybrid materials has produced cements with antimicrobial properties as well as higher surface hardness values than the original glass-ionomer.

This study aimed to measure the facial morphology and growth of 100 infants in the West of Scotland from the age of 3 months to 2 years using a three dimensional imaging system, C3D. One of the aims of the study was to validate the use of the C3D system to measure facial morphology in infants. Further aims were to establish references values for facial dimensions in infants, to establish the normal growth of facial parameters from 3 months to 2 years, to correlate facial and body growth, to ascertain any sexual dimorphism, to establish the degree of facial asymmetry and to determine any longitudinal changes in facial asymmetry in infant’s faces. Eighty three infants at 3 months, 93 infants at 6 months, 91 infants at 1 year and 92 infants at 2 years were successfully captured with a lips apart pose. Reference values for facial dimensions in infants at these ages were established. Significant gender differences were found for most facial measurements at all ages with the males being larger than the females. These differences were greatest for face height, depths and widths with mean differences ranging from 1.7 to 4.0 mm. No gender differences were found in any of the angles measured. Several dimensions on the right side of the face were found to be significantly larger than the left. This was most marked for face depths with mean differences of 0.8 mm. The range of normal facial asymmetry scores was determined. No significant difference in asymmetry was found between the males and females. The upper face was found to be the most asymmetric region studied and the nostrils were the least asymmetric. Correlation of facial measurements with body dimensions found weak but significant correlations with the highest correlation coefficient of 0.69 between face depth and body weight. Nasal tip protrusion, nostril dimensions and lip heights were not correlated with body dimensions. Seventy one infants, 37 males and 34 females, were successfully captured at all four ages with the lips apart and were included in the longitudinal analysis. The longitudinal changes in facial parameters were established from 3 months to 2 years and mean growth curves produced. The fastest growth was found from 3 to 6 months and the slowest from 1 to 2 years. There were no correlation between growth of the face and growth in body weight, length and head circumference. Significant reductions in the overall facial asymmetry score were found from 3 months to 2 years. The clinical significance of this reduction is still to be determined.

This study grew from a request for information as to the date of establishment of the Bachelor of Dental Surgery (BDS) as the professional qualification for dentists in the United Kingdom. In the process of answering this enquiry it became apparent that there was no simple answer and that university dental education was not covered by the existing literature. It also became clear that, while ubiquitous for new dentists by the late twentieth century, the dental degree had only comparatively recently become the standard path to a dental career. This study emphasises the role of professional education, and particularly university education and research, in the development of the dental profession and dental services. University dental education and research, it is argued, was a major factor in the professionalisation of dentistry, in convincing the government of the importance of dental health and thus in establishing dentistry as an essential part of the National Health Service (NHS). University dental education and research, it is argued, extended the therapeutic potential of dental treatment, promoted understanding of the relationship between oral and systemic disease, of the etiology and pathology of dental disease and of methods of prevention and control. Such was the impact of the new standards thus established, that the whole emphasis of dental treatment would shift within the space of one hundred years, from dental surgery and dental prosthetics to conservative and preventive dentistry. This study shows that, from the mid-nineteenth century, a dental elite campaigned for compulsory professional education and, from the late nineteenth century, for university dental education. By the beginning of the twentieth century professional education for doctors and surgeons, for the degree of MBChB, was carried out in university medical schools. Yet, although the dental curriculum was based on the surgical curriculum, it was not until the mid-twentieth century that the standards pioneered by the dental elite were extended to the majority of candidates for the dental profession. Indeed, the generally low standards which prevailed prior to the retiral of the generation of unqualified "Dentists, 1921" had damaging effects on the oral and general health of the British population. The study also suggests that the dearth of qualified dentists contributed to the delay in achieving legislation to eliminate unqualified practice. Arguably, the low standards of the majority of dentists also contributed to the delay in persuading the government that dental treatment was as important to the health and well-being of the population as any other aspect of health care. Just as the standards advanced by the dental elite ultimately persuaded the government of the relative importance of dental care. This study therefore examines the factors which delayed the achievement of a consistent and high standard of professional dental education for dental practitioners. In so doing the study identifies several factors which contributed to the lack of demand for professional dental education and qualification and thus delayed dentistry's establishment as a graduate profession.

The aim of the work presented in this thesis was to investigate the interaction of pulsed Nd:YAG laser irradiation with both sound and artificially carious human enamel. More specifically, the aims were to characterise the effect of Nd:YAG laser irradiation on artificially created white spot enamel lesions (to simulate the effect of lasing carious enamel); to quantify the effects of pulsed Nd:YAG laser irradiation on enamel demineralisation; to investigate whether there is synergy between the action of pulsed Nd:YAG laser irradiation and fluoride in terms of impairing acid resistance to enamel; and finally to clarify the mechanism by which pulsed Nd:YAG laser irradiation physically interacts with enamel to induce acid resistance. Laser irradiation of artificial white spot lesions, at 50 mJ and 100 mJ (10 pps, 2 or 5 sec), was found to ablate tissue, causing crater formation. Ablation depth, as determined by microdensitometry, was correlated only with the power used, being greater at 100 mJ than at 50 mJ. SEM examination of the surface morphology of lased enamel, and the surrounding unlased area, was consistent with a process of melting and recrystallisation. It is evident, from this investigation, that in order to remove carious enamel selectively, while leaving sound enamel intact, successive applications of low power irradiation (50 mJ) are the most suitable. The work presented in this thesis has indicated the versatility of the Nd:YAG laser as a dental instrument. The laser can be used to ablate carious enamel and has potential as a prophylactic treatment for caries. The most significant aspect of the laser as a strategy to prevent caries, is that it seems to physically alter the structure of enamel so may, therefore, be a method of permanently increasing tooth resistance to decay.

The effect of fluoridated milk on plaque bacteria was investigated in fourteen complete denture wearers. These subjects were randomly split into two groups, seven in the treatment only group and seven in the treatment + dentifrice rinse group. There were five treatment regimes, each of six-week duration. The subject either consumed milk once or three times a day; milk with fluoride once or three times a day; or no beverage consumption as a control. The purpose of the additional dentifrice rinse was to mimic the effects of brushing twice daily with a fluoridated toothpaste. Six enamel slabs were embedded at strategic locations on the upper denture to investigate the influence of salivary flow rate on aciduric bacteria within dental plaque. Plaque samples were obtained from each enamel slab at Weeks 1 and 6 of the experimental treatments, and subjected to microbiological analysis. Enumeration of the bacteria was carried out to obtain the total counts of plaque bacteria, the counts of S. mutans on selective MSB agar and counts of Lactobacillus spp. on selective Rogosa agar.l Statistical analysis revealed a main effect of treatment within the treatment only group for the lactobacillus counts. No beverage consumption and milk with fluoride consumed three times a day produced the lowest counts. Proportions of lactobacilli within the overall plaque bacteria were compared at the two buccal sites and one lingual site. The proportions at the buccal sites with a good salivary flow rate were lower than those that were experienced at the lingual site where there is a poor salivary flow. To investigate strain variation among clinical S. mutans isolates identified from unrelated individuals, ribotyping was employed. Analysis revealed that carriage of S. mutans genotypes was stable within an individual but that strain variability was diverse when analysed across all individuals. Longitudinal investigation revealed the possibility that S. mutans genotypes could be lost and then reappear at the same tooth site.

The aim of this thesis was to investigate the effects of reduced concentrations of fluoride in dentifrices on the levels of fluoride in saliva, and to examine their potential role in the inhibition of artificial carious lesions, in vitro. A preliminary experiment studied ambient salivary fluoride levels three times weekly, in twelve subjects using dentifrices with fluoride concentrations of 0, 500, 1,000 and 1,500 ppm F (as sodium fluoride) in random order, each for one month. The results showed a significant carry-over effect. Hence, a definitive experiment was designed which employed increasing concentrations of dentifrice fluoride. Here, 20 volunteers had fluoride levels measured in saliva three times weekly whilst using the aforementioned concentrations of fluoride dentifrices for one month each. In addition, ten of these volunteers had fluoride levels assayed in plasma and plaque once per week. These data provided a range of ambient salivary fluoride values of from 0.01-0.04 ppm. The results of these experiments indicate that, lower fluoride-containing dentifrices reduce the ambient level of fluoride in whole saliva, and that in vitro, these lower levels of fluoride are associated with increased demineralisation of artificial carious lesions. Moreover, the oral mucosa is a site of fluoride retention from dentifrices and mouthrinses, and contributes to the ambient salivary fluoride levels. Thus it may be partly responsible for the prolonged nature of oral fluoride clearance and it would seem logical to conclude that further clinical and laboratory research on both the formulations and delivery of lower fluoride dentifrices is required.