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Inhibitory Effects on Selected Oral Bacteria of Antibacterial Agents Incorporated in a Glass Ionomer Cement

The objectives of the study were to investigate the antimicrobial efficacy, over time, of combining antibacterial agents with a glass ionomer cement (GIC). This was assessed using an agar diffusion test. Chlorhexidine hydrochloride, cetylpyridinium chloride, cetrimide and benzalkonium chloride were added to Fuji IX GIC at 0, 1, 2 and 4% w/w. Antibacterial-GIC specimens were placed onto agar plates inoculated with one of six bacterial species (Streptococcus, Lactobacillus and Actinomyces, two each) and the area of inhibition calculated after 24 h incubation. The experiment was repeated weekly and at week 11 the surface of the specimen was abraded prior to replacing on inoculated agar plates. Control specimens of the GIC produced no bacterial inhibition. The antibacterial-GIC combination specimens showed significant inhibition which decreased at different rates over the test period. Resurfacing of the specimens showed a dramatic increase of antibacterial action similar to levels produced on week 1. CT-GIC showed the greatest (p < 0.005) inhibitory effect throughout the experimental period for 4 out of 6 test bacteria. The addition of antibacterial agents to Fuji IX creates a GIC material with significant antimicrobial action in vitro which is dependent on concentration and type of antibacterial agent, and appears to be associated primarily with a release of the antibacterial from the surface layer of the specimen.

Fractional inhibitory concentration index of combinations of antibacterial agents against cariogenic organisms

OBJECTIVES To examine the inhibitory effects between paired combinations of four antibacterial agents that have been investigated in dentistry against six bacteria associated with dentinal caries. METHODS The antibacterial agents tested were: chlorhexidine dihydrochloride, benzalkonium chloride, cetrimide and cetylpyridinium chloride. Two organisms each belonging to Streptococcus, Lactobacillus and Actinomyces species were evaluated against these agents. A checkerboard microtitration method was used to determine the minimum inhibitory concentration and fractionary inhibitory concentration (FIC) and summation operator FIC index of the paired combinations of antibacterial agents against the six species of bacteria. Appropriate controls were included. The summation operator FIC index was then used to determine if synergy, antagonism, or indifference occurred as a result of interactions between the antibacterial agents and the test organisms. RESULTS The data from a total of 295 test results were evaluated. Using summation operator FIC values for synergy as < or = 0.5 and antagonism as > 4.0 as recommended by The American Society for Microbiology, no significant synergistic or antagonistic interactions were observed between the paired antibacterial agents when tested against selected organisms. However, a tendency for an additive antibacterial effect was observed with approximately a third of the test results. Nonetheless, no combination of antibacterial agents appeared to be superior to any other. CONCLUSIONS According to these in vitro results, there appears to be no beneficial effect of combining the antibacterial agents against the individual cariogenic micro-organisms selected. However, it may be beneficial to use combined antibacterial agents that have a broader range of activity against an ecosystem of bacteria than using individual agents.

Resin zirconia bonding promotion with some novel coupling agents.

OBJECTIVES To evaluate and compare three novel coupling agents: 2-hydroxyethyl methacrylate, itaconic acid and oleic acid to two silane coupling agents, one commercial silane product and 3-acryloxypropyltrimethoxysilane on the bond durability of resin composite to zirconia. METHODS Zirconia samples were silica-coated by air abrasion and each of the five coupling agents was then applied to give five test groups. Resin composite stubs were bonded onto the conditioned zirconia surfaces. The samples were stored: dry storage, 30 days in water and thermocycled to give a total of fifteen test groups. The shear bond strengths were determined using a universal testing machine and data analyzed by two-way ANOVA and Tukey HSD (p<0.05) with shear bond strength as dependent variable and storage condition and primers as independent variables. The bond formation of the five coupling agents to zirconia was examined by X-ray photoelectron spectroscopy (XPS). RESULTS Two-way ANOVA analysis showed that there was a significant difference for different primers (p<0.05) and different storage conditions (p<0.05) on the shear bond strength values measured. XPS analysis showed a shift in binding energy for O(1s) after priming with the five coupling agents which revealed different bond formations related to the functional groups of the coupling agents. SIGNIFICANCE The shear bond strength values measured for all coupling agents after water storage and thermocycling exceed the minimum shear bond strength value of 5MPa set by ISO. The silane coupling agent, 3-acryloxypropyltrimethoxysilane, showed the highest bond strength of the three storage conditions.

Multimodality in Problem-Based Learning (PBL): An Interactional Ethnography

Black and Wiliam (Inside the black box: Raising standards through classroom assessment. London: King’s College London School of Education, 1998) introduced the term ‘inside the black box’ to research in educational assessment in the late 1990s. This metaphor can be applied to current research in problem-based learning (PBL). This chapter addresses the need to look inside the ‘black box’ of PBL by exploring two under-researched aspects – independent study and online learning. Using the Interactional Ethnographic (IE) approach to collect and analyse data in context and over time (across contexts), we systematically examined how students learn between tutorials, to explore how online learning supports independent study in a PBL curriculum. The data sources for this chapter are drawn from a single third-year PBL group (n = 8) in a five-year Bachelor of Dental Surgery (BDS) curriculum. By focusing on independent study and online learning, the results provide new insights into how multimodal texts and tools support learning across a blended, problem-based curriculum. Data sources included video and screen capture recordings of naturally occurring classroom and independent study activity across one problem cycle. Audio and video data were transcribed using Transana™. Application of key theories of semiosis provided further explanations of how the multimodal texts and mediating tools appropriated throughout a problem cycle were socially and academically consequential to knowledge construction. Evidence was found that the use of various texts and tools across a problem cycle supported a discursive shift from stimulus for hypothesising to evidence for final hypotheses.

PBL.2.0: blended learning for an interactive, problem-based pedagogy.

Context and setting In 2006, a standard learning management system (LMS) was adapted to support self-directed learning within an integrated, problembased learning (PBL) curriculum for undergraduate Bachelor of Dental Surgery students. Initially, PBL enquiry materials were archived on the LMS as digital learning objects for self-directed learning following the first tutorial. This asynchronous application did not support the increased need for synchronous accessing of in-house and open-access digital resources during face-to-face tutorials. Although the increased use of laptops in tutorials initially addressed this problem, it also contributed to some fragmentation of the group process. Curriculum developers sought a more group-oriented, technologically interactive solution. Why the idea was necessary Digital learning objects for PBL scenarios are increasingly used to stimulate student discussion, increase interest and engage ‘tech-savvy’ Net Generation learners. However, PBL facilitators and students reported that the increased use of individual laptops to access these digital resources led to some fragmentation of PBL discussions. Thus, we recognised the need to move from a digital repository approach towards an interactive blending of technology within face-to-face tutorials, but needed to establish how this progression might be supported and resourced. What was done In 2009, interactive whiteboards (IWBs) were introduced to small-group, problembased tutorials. The aims were: (i) to integrate learning technologies with face-to-face teaching to support group access to both in-house and openaccess digital resources, and (ii) to further enhance the group knowledge construction process through utilising the IWB features. Such features included enhanced visualisation and analysis facilitated by the IWB’s ability to display and manipulate digital objects, as well as to annotate, save and share images. Interactive whiteboards were installed in all PBL tutorial rooms and IT support was provided for all students and facilitators. Year 1 students (n = 55) received additional workshops and IWB support. The project evaluation strategy included the adoption of an interactional ethnographic methodology to analyse student engagement. Evaluation of results and impact The interactional ethnographic approach, which focused on classroom interaction (video) and learning artefacts, facilitated the exploration of knowledge construction both within specific contexts and over time. Analysis was based on 4 hours of learning activities undertaken by a Year 1 undergraduate PBL group (n = 8). This group was video-recorded on three occasions during the same week. These included the first tutorial (T1) with a facilitator, a self-directed learning discussion (directly following T1) without a facilitator, and a second tutorial (T2) with a facilitator. Event mapping focused on student engagement with digital materials. Corresponding talk was transcribed using Transana . Three key findings were: (i) the group accessed a range of in-house and open-access digital materials to support learning within and across all phases of a problem cycle; (ii) the use of learning objects and online resources within a problem cycle supported enquiry learning and the discursive shift in student talk from a stimulus for hypothesising in relatively lay terms in the first tutorial to evidence for making final hypotheses with greater control of medical discourse in the second tutorial, and (iii) the integration of faceto-face and virtual modalities through the use of an IWB within the tutorial was seamless and supported whole-group engagement in the problem process.

Biphasic calcium phosphates bioceramics (HA/TCP): Concept, physicochemical properties and the impact of standardization of study protocols in biomaterials research

Biphasic calcium phosphates (BCP) bioceramics have become the materials of choice in various orthopedic and maxillofacial bone repair procedures. One of their main advantages is their biodegradation rate that can be modified by changing the proportional ratio of the composition phases. For enhanced bone tissue regeneration, the bioactivity of BCP should be increased by optimizing their physicochemical properties. To date, the ideal physicochemical properties of BCP for bone applications have not been defined. This is mostly related to lack of standard study protocols in biomaterial science especially with regards to their characterizations and clinical applications. In this paper we provided a review on BCP and their physicochemical properties relevant to clinical applications. In addition, we summarized the available literature on their use in animal models and evaluated the influences of different composition ratios on bone healing. Controversies in literature with regards to ideal composition ratio of BCP have also been discussed in detail. We illustrated the discrepancies in study protocols among researchers in animal studies and emphasized the need to develop and follow a set of generally accepted standardized guidelines. Finally; we provided general recommendations for future pre-clinical studies that allow better standardization of study protocols. This will allow better comparison and contrast of newly developed bone substitute biomaterials that help further progress in the field of biomaterial science.

Long-term clinical evaluation of 211 two-unit cantilevered resin-bonded fixed partial dentures

OBJECTIVES This retrospective study aims to evaluate the long term clinical performance of two-unit cantilevered resin-bonded fixed partial dentures (RBFPDs) relating to their retention, success and survival rate. MATERIALS AND METHODS Prostheses that were placed at least four years previously were clinically reviewed to evaluate retention, success and survival rate. Additional information was also collected, including patients gender, age and satisfaction on their prosthesis, operators experience, prosthesis service life, root canal therapy if performed, abutment mobility, bone support, the presence of shim-stock contacts on the abutment or pontic in intercuspal position, and the presence of proximal axial contacts adjacent to the prosthesis. The date of any debonding with subsequent treatment was also recorded. RESULTS A total of 211 two-unit RBFPDs were placed in 153 patients, with a mean service life of 113.2±33.5 months. Twenty-eight prostheses debonded, resulting in a retention rate of 86.7 percent, and another five teeth were extracted with the prostheses, resulting in a success rate of 84.4 percent. 90.0 percent prostheses were functioning (survival rate) by means of rebonding at the time of review. The location of the replaced tooth had a significant effect on the retention of RBFPDs with posterior RBFPDs lower than anterior (p=0.020). Kaplan-Meier analysis revealed 5-, 10- and 15-year cumulative probability of surviving was 0.97, 0.91 and 0.84, respectively. CONCLUSIONS 211 two-unit RBFPDs were observed to have a success, retention and survival rate of 84.4, 86.7 and 90.0 percent, respectively, with a mean service life of 9.4 years. CLINICAL SIGNIFICANCE Based on the clinical results, two-unit RBFPD are shown to be a durable prosthesis over the long term with high patient satisfaction. The posterior prostheses, particularly in the lower arch appeared to have a higher failure rate, and improved design features should be considered.

Reaction of silver diamine fluoride with hydroxyapatite and protein

UNLABELLED Silver diammine fluoride (SDF) is used as an anticaries agent; however, its mode of action is uncertain, whether chemical, physical, mechanical or antibacterial. As a preliminary study, the effect of SDF on hydroxyapatite (HAp) and gelatin (as a chemically-representative protein) was examined. METHODS 2.5mg HAp powder specimens and 0.5mL 10% gelatin (Riedel-de Haën) (initially as a sol at ∼37°C), were mixed with 0.5mL of 38% SDF (J. Morita), 4% NaF (Sigma) or 40% AgNO(3) (Sigma) and tumbled in 1.5mL polypropylene tubes (Sarstedt) for 48h at ∼23°C, in two series: exposed to laboratory lighting, and kept dark at all times. The HAp specimens were separated by centrifugation and decanting, then these and one set of gelatin specimens were dried at 60°C in situ; a second parallel set of gelatin specimens were dried at ∼23°C. Each was washed with 1mL deionized water for 1min, 3 times. Treated materials were observed, before and after washing, with scanning and transmission electron microscopy (SEM, TEM); energy-dispersive X-ray analysis (EDX), and electron diffraction (ED). RESULTS SDF appeared to produce globular particles of CaF(2) on the surface of the HAp, but these disappeared on washing, whilst with AgNO(3) yellow cubic crystals of Ag(3)PO(4) formed which were not dissolved on washing, but which darkened, converting gradually to metallic silver, on exposure to light. NaF had no effect on gelatin, whilst with SDF and AgNO(3), particles of silver were produced which were resistant to washing. CONCLUSIONS Both principal components of tooth tissue react with SDF; the solubility of the putative CaF(2) formed weakens the case for it exerting a caries-protective effect. The importance of the persistent silver needs further study.

Arginine Metabolism in Bacterial Pathogenesis and Cancer Therapy

Antibacterial resistance to infectious diseases is a significant global concern for health care organizations; along with aging populations and increasing cancer rates, it represents a great burden for government healthcare systems. Therefore, the development of therapies against bacterial infection and cancer is an important strategy for healthcare research. Pathogenic bacteria and cancer have developed a broad range of sophisticated strategies to survive or propagate inside a host and cause infection or spread disease. Bacteria can employ their own metabolism pathways to obtain nutrients from the host cells in order to survive. Similarly, cancer cells can dysregulate normal human cell metabolic pathways so that they can grow and spread. One common feature of the adaption and disruption of metabolic pathways observed in bacterial and cancer cell growth is amino acid pathways; these have recently been targeted as a novel approach to manage bacterial infections and cancer therapy. In particular, arginine metabolism has been illustrated to be important not only for bacterial pathogenesis but also for cancer therapy. Therefore, greater insights into arginine metabolism of pathogenic bacteria and cancer cells would provide possible targets for controlling of bacterial infection and cancer treatment. This review will summarize the recent progress on the relationship of arginine metabolism with bacterial pathogenesis and cancer therapy, with a particular focus on arginase and arginine deiminase pathways of arginine catabolism.

Assessment of the use of problem-orientated, small-group discussion for learning of a fixed prosthodontic, simulation laboratory course.

Aim To evaluate a simulation laboratory course that used student-centred small-group problem-orientated discussion activities as the main medium of instruction.Methods A structured questionnaire using a six-point Likert scale with 30 statements relating to a fixed prosthodontics course was distributed to 4th-year and 5th-year students who had completed the course.Results A 93% response rate was achieved for both years with a mean score for the 4th-year being 94.2 (±13.7) and the 5th-year 107.5 (±16.9). The differences between the scores of both years are highly significant (P=0.0006) indicating that the 5th-year were more favourable about the course and learning approach used. Consistency and reliability of the questionnaire was judged reliable according to Cronbachs alpha (4th-year = 0.7, 5th-year = 0.83). Many aspects of the small-group student-centred activities were highly valued by students however, students expressed a preference for learning and interacting with teachers than colleagues.Conclusion Small-group student-centred learning activities were reported as creating an active, safe learning environment with beneficial opportunities for peer-peer interaction such as questioning, teaching and learning from students. However, students expressed a preference for teacher-centred information dissemination and activities. An understanding of the rationale of student dependence to teacher-centred learning may allow improved modifications in a student-centred learning environment.