Oral health status declines with age and as a result the need for removable prostheses increases.T he microbiology of denture plaque has received little attention in comparison with dental plaque, yet it differs in location, and composition. Denture plaque and poor denture hygienea re suggestedto be causeso f denturer elateds tomatitis, may contribute to oral malodour,a nd can also facilitate colonisationo f the prosthesisb y potentially infectious pathogens. The aims of this study were to evaluate current and novel methods for detection and characterisationo f denturep laquea nd to contributet o the knowledgei n this neglecteda rea. In a clinical study the fluorescence of in vivo denture plaque was assessed using Quantitative Light-induced Fluorescence (QLF), which was developed for early dental cariesd etectionu sing a blue excitation light (405 nm) and capturing fluorescencee mission. Areas were seen to fluoresce red, orange and green and the causative microorganisms were recovered and identified. Red fluorescence was due to the anaerobes Prevotella melaninogenica and Actinomyces israelii and orange to Candida albicans. These species are generally acknowledged to be secondary colonisers, present in more mature plaque. Green fluorescence was observed in streptococcal species (early colonisers) and Fusobacterium nucleatum (important bridging organism in plaque development). Low recovery of red fluorescing species indicated a lack of cultivability, viability or an inter-species dependence. Denture plaque populations were therefore investigated using culture- independent PCR and denaturing gradient gel electrophoresis (DGGE). PCRDGGE profiling indicated a highly diverse personalised microbiota for each denture plaque sample, and the red fluorescent plaque harboured an increased bacterial diversity compared to green fluorescent plaque. However, problems with 16S rRNA gene sequence heterogeneityh ighlight the needf or resultst o be supplementedb y culture studies. Identification of the fluorophore responsiblef or fluorescencew as necessaryto validate the origin of fluorescence using QLF. The spectral characteristics of red fluorescing microorganismsw ere typical of fluorescentp orphyrins,p articularly protoporphyrini x. Most studies looking at plaque removal and antimicrobial efficacy use simple staining and visualisation for plaque removal in vivo, and batch culture for antimicrobial efficacy in vitro. Both methodsr equire improvementsa nd standardisationC. urrent and novel methods (including the QLF) for in vivo assessment of denture hygiene based on plaque quantification were investigated. Image analysis methods offer permanent images, improved accuracy and increased sensitivity over subjective visual ranking yet increase assessmenttim e considerably.F indings suggestt hat QLF may be suitablef or screeningf or the presence of mature plaque development with indications of the presence of specific obligate anaerobic bacteria, but not for plaque quantification. A constant depth film fermenter (CDFF) was used to investigate the stability and composition of oral salivary and denture plaque microcosms with and without C. albicans. Further characterisation of denture plaque enabled development of a more realistic 'model' denture plaque biofilm for in vitro antimicrobial efficacy testing methods using denture cleansing products. This study has contributed to knowledge concerning the microbiology of denture plaque, and, by evaluating a range of in vivo and in vitro methods, has enabled the recommendation of objective tests for the evaluation of denture hygiene products for full denture wearers.

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Conventional fixed bridge prostheses may fail due to one or more loose retainers, which may be difficult to diagnose. An objective and reproducible investigation to identify, at an early stage, loosening of a retainer could be of significant benefit. The aims of the current series of investigations were to record retrospectively the clinical performance of different types of conventional fixed prostheses used to replace missing teeth and to determine whether Resonance Frequency Analysis (RFA) was capable of measuring bridge stability, in-vitro. One hundred and twenty two patients with 168 bridges were referred to two consultants at the Department of Restorative Dentistry at Liverpool Dental Hospital between Jan 2004 - Dec 2008 with fixed prosthesis problems. Fixed-fixed designs were the most common (77.9%), with cantilever bridges constituting 19.0% of the total. The most frequent cause of failure (39.0%) was associated with a post and core abutment. Apical pathology was found in 20.2%, dental caries in 14.8% and loss of retention in 11.9%. Fixed-fixed bridges were therefore chosen for further study. In-vitro pilot studies were subsequently undertaken to determine the feasibility of using resonance frequency analysis (RFA) on all-metal fixed-fixed bridges affixed to different models (wholly dental stone, or incorporating a simulated periodontal ligament) and to determine a reliable method to record this using an Osstell Mentor apparatus. The use of a buccal approach to record RF A values was validated. Based on the results from the pilot studies and a subsequent power analysis to set sample size, 100 models with standardised acrylic tooth abutment analogues and simulated periodontal ligaments were fabricated. All-metal fixed-fixed bridges were constructed from the first molar to the first premolar using standardised methods on models based with dental stone to mimic 100% (n=SO) or SO% (n=SO) bone support. In each case, two equal groups of 2S specimens had either both retainers cemented, (control group) or the premolar left uncemented (test group) to mimic clinical failure, cemented by a second operator to allow blind analysis. A magnetic component (Smartpeg) was subsequently cemented to the bridge using low-shrink composite resin and the Osstell Mentor used to measure bridge stability expressed as Bridge Stability Quotients (BSQ). The BSQ recorded at the premolar site in both 100% and SO% bone support models demonstrated a highly statistical significant difference (p<0.003) between the control and test groups. ROC analysis determined that a cut-off point was BSQ >60 suggesting that the fixed bridge was stable (cemented to both abutments) whereas a BSQ >59 indicated a risk of the bridge being uncemented to the premolar. All 100% bone support models were subsequently tested to failure in tension using a Universal Testing Machine with a SOO (N) load cell and cross-head speed of 10mm/min. 37% of specimens from the control group debonded at loads between 82 to 120N with the other 63% failing through extraction of the analogue/fracture of the model. 89.2% of the test group specimens failed by extraction of the tooth analogue from one or both ends at loads below SON. Statistical analysis using Kruskal Wallis tests demonstrated that the destructive testing could detect a highly statistically significant difference between the test and control group (P<0.0001) These investigations identified mechanical and biological factors associated with failure of conventional fixed bridges and demonstrated that resonance frequency analysis measurements was able to identify, reliably and non-destructively, stable bridges and those with one retainer uncemented, in-vitro. With further developments of the technique it may be possible to identify fixed-fixed bridge failure clinically and provide appropriate early clinical intervention.

Developing conservative FPD designs in term of the preservation of tooth structure is not just a matter of cutting from the crown to form abutment. These designs need to prove that they show benign behaviour under occlusal forces. The aim of this study was to develop new single layer non-metal 3-unit posterior FPD designs as an alternative to the traditional FPD design without compromising the structure integrity of the natural dentition. The group designs were traditional, two different partial coverage crowns and two different inlay retained FPD. The CEREC CAD/CAM system was employed using a modified designing method and two resin bonded non-metal materials were used for the fabrication of these bridges. A series of tests were conducted in order to identify I) the volume of tooth structure loss with different designs 2) the ability of the CAD/CAM system to produce full-thickness FPD restorations 3) the fracture resistance of these restoration and 4) 2D and 3D FEA models were later developed involving some highly innovative steps. Micro CT, MIMICS and FreeForm DeskTop were used to create the 3D model. For meshing these models, due to the complexity of the 3D model, a sectional meshing technique was used by mechanical APDL and Workbench Ansys Y 12. The FEA data were compared with the results from the practical experiments. XIX Abdulsalam AI-Zahawi Benign non-metal fixed partial denture The results of the in vitro tests revealed that the four conservative designs showed less tooth structure loss compared with the traditional design and the inlay design was less than the partial coverage crown retained FPD. The CEREC CAD/CAM system was able to produce the suggested FPD designs in a full-thickness as an alternative to producing framework FPD. The fracture resistance test revealed that there is no significant influence of designs on the fracture strength excluding design V. The results showed that no fractures of the bridges in design V were recorded during the test. The FPD fabricated from the low elastic modulus material PEEK showed a higher fracture strength than one with the high elastic modulus ceramic. Part of the 2D FEA results showed agreement with the practical test results especially that the site of high stress concentration and the fracture site were at the gingival side of the connector. Nevertheless the 2D FEA results showed that there were many differences with the 3D FEA results. These differences include the overestimation in the stress level in the 2D FEA compared with 3D FEA model and the high stress located at the inlay cavity wall, which was difficult to see in the 2D FEA. 3D FEA results were in agreement with fracture strength tests results and these include that there is no influence of the partial coverage crown retained FPDs on the stress compared with the traditional design, the fracture site and the location of the higher stress were unaffected by the designs. Although both inlay retained FPD designs show more conservative preparations than partial crown retainers, they were found to be more destructive to the abutment teeth structure under a concentrated load. The clinical significant of this research project is that it is possible to create more conservative FPD designs without compromising the structure integrity of the restored dentition. xx

Denture soft lining materials are used as a cushion between the hard denture base and the oral mucosa. Fluid sorption and solubility may contribute to material hardening, roughening, cracking or tearing, loss of adhesion to the hard denture base or contamination by extrinsic stains or yeasts. The ideal material is required to have low fluid uptake, good wettability, retain compliance and surface integrity, and not support fungal growth. Evaluation of behaviour in the oral environment is difficult and a number of materials, such as artificial saliva and food simulating liquids, have been recommended to simulate the environment. The two types of denture soft lining materials commonly used in clinical practice are methacrylate and silicone based. These together with an experimental elastomer were evaluated in this study. Fluid sorption and solubility were determined by immersion of disc specimens in food simulating fluids (distilled water, 3% acetic acid, 10% ethanol and 50% ethanol) and artificial saliva at 37±1°C with weighing at set time intervals. Similar experiments were carried out using liquids representing fatty food constituents with coconut oil and 1113307H. ardness was determined using a Shore A durometer. In order to determine wettability, contact angle was measured using a computer microscope. The surface roughness was assessed using a non-contact laser profilometer. Finally, an attempt was made to identify leachable substances from the materials investigated using a Fourier transform infrared spectrometer. An additional part of this study was to look at the adhesion of one yeast species Candida albicans to commercial materials using various protective coatings to determine their efficacy. The resultsd emonstratedth at the type of liquid simulating foods or artificial saliva, and immersion time significantly influenced the behaviour of the commercial denture soft lining materials and the experimental elastomer during in vitro testing. The two groups of materials behaviour were different. The two methacrylate-basedd enture soft lining materials showed marked absorption and solubility which may be associated with the loss of plasticisers. The two silicone-based denture soft lining materials showed much less absorption and solubility under the same conditions. The experimental elastomer showed marked swelling in oils, which was not expected, its chemical structure being similar to a methacrylate. Shore A hardness remained unchanged during the fluid immersion with the two silicone-based materials but showed measurable changes with the two methacrylate-basemd aterials and the experimentale lastomer,I ncreaseds urface roughness was also demonstrated with the two methacrylate-based materials, and decreasedc ontact angle was found with the two silicone-basedm aterials. After various surface treatment, coconut oil reduced Candida albicans adhesion in all cases.