Realization of Organocerium-Based Fullerene Molecular Materials Showing Mott Insulator-Type Behavior

Electron-rich organocerium complexes (C5Me4H)3Ce and [(C5Me5)2Ce(ortho-oxa)], with redox potentials E1/2 = -0.82 V and E1/2 = -0.86 V versus Fc/Fc+, respectively, were reacted with fullerene (C60) in different stoichiometries to obtain molecular materials. Structurally characterized cocrystals: [(C5Me4H)3Ce]2·C60 (1) and [(C5Me5)2Ce(ortho-oxa)]3·C60 (2) of C60 with cerium-based, molecular rare earth precursors are reported for the first time. The extent of charge transfer in 1 and 2 was evaluated using a series of physical measurements: FT-IR, Raman, solid-state UV-vis-NIR spectroscopy, X-ray absorption near-edge structure (XANES) spectroscopy, and magnetic susceptibility measurements. The physical measurements indicate that 1 and 2 comprise the cerium(III) oxidation state, with formally neutral C60 as a cocrystal in both cases. Pressure-dependent periodic density functional theory calculations were performed to study the electronic structure of 1. Inclusion of a Hubbard-U parameter removes Ce f states from the Fermi level, opens up a band gap, and stabilizes FM/AFM magnetic solutions that are isoenergetic because of the large distances between the Ce(III) cations. The electronic structure of this strongly correlated Mott insulator-type system is reminiscent of the well-studied Ce2O3.

Synthesis and Characterization of a Bridging Cerium(IV) Nitride Complex

Complexes featuring lanthanide-ligand multiple bonds are rare and highly reactive. They are important synthetic targets to understand 4f/5d-bonding in comparison to d-block and actinide congeners. Herein, the isolation and characterization of a bridging cerium(IV)-nitride complex: [(TriNOx)Ce(Li₂μ-N)Ce(TriNOx)][BAr^F₄] is reported, the first example of a molecular cerium-nitride. The compound was isolated by deprotonating a monometallic cerium(IV)-ammonia complex: [Ce^IV(NH₃)(TriNOx)][BAr^F₄]. The average Ce═N bond length of [(TriNOx)Ce(Li₂μ-N)Ce(TriNOx)][BAr^F₄] was 2.117(3) Å. Vibrational studies of the ¹⁵N-isotopomer exhibited a shift of the Ce═N═Ce asymmetric stretch from ν = 644 cm^-1 to 640 cm^-1, and X-ray spectroscopic studies confirm the +4 oxidation state of cerium. Computational analyses showed strong involvement of the cerium 4f shell in bonding with overall 16% and 11% cerium weight in the σ- and π-bonds of the Ce═N═Ce fragment, respectively.

Versatile Fe-Sn Bonding Interactions in a Metallostannylene System: Multiple Bonding and C-H Bond Activation

The metallostannylene Cp*(ⁱPr₂MeP)(H)₂Fe-SnDMP (1; Cp* = η⁵-C₅Me₅; DMP = 2,6-dimesitylphenyl), formed by hydrogen migration in a putative Cp*(ⁱPr₂MeP)HFe[Sn(H)DMP] intermediate, serves as a robust platform for exploration of transition-metal main-group element bonding and reactivity. Upon one-electron oxidation, 1 expels H₂ to generate the coordinatively unsaturated [Cp*(ⁱPr₂MeP)Fe═SnDMP][B(C₆F₅)₄] (3), which possesses a highly polarized Fe-Sn multiple bond that involves interaction of the tin lone pair with iron. Evidence from EPR and ⁵⁷Fe Mössbauer spectroscopy, along with DFT studies, shows that 3 is primarily an iron-based radical with charge localization at tin. Upon reduction of 3, C-H bond activation of the phosphine ligand was observed to produce Cp*HFe(κ²-(P,Sn)═Sn(DMP)CH₂CHMePMeⁱPr) (5). Complex 5 was also accessed via thermolysis of 1, and kinetics studies of this thermolytic pathway indicate that the reductive elimination of H₂ from 1 to produce a stannylyne intermediate, Cp*(ⁱPr₂MeP)Fe[SnDMP] (A), is likely rate-determining. Evidence indicates that the production of 5 proceeds through a concerted C-H bond activation. DFT investigations suggest that the transition state for this transformation involves C-H cleavage across the Fe-Sn bond and that a related transition state where C-H bond activation occurs exclusively at the tin center is disfavored, illustrating an effect of iron-tin cooperativity in this system.

Efficient and selective alkene hydrosilation promoted by weak, double Si-H activation at an iron center

Cationic iron complexes [Cp*(ⁱPr₂MeP)FeH₂SiHR]⁺, generated and characterized in solution, are very efficient catalysts for the hydrosilation of terminal alkenes and internal alkynes by primary silanes at low catalyst loading (0.1 mol%) and ambient temperature.

Cationic iron complexes [Cp*(ⁱPr₂MeP)FeH₂SiHR]⁺, generated and characterized in solution, are very efficient catalysts for the hydrosilation of terminal alkenes and internal alkynes by primary silanes at low catalyst loading (0.1 mol%) and ambient temperature. These reactions yield only the corresponding secondary silane product, even with SiH₄ as the substrate. Mechanistic experiments and DFT calculations indicate that the high rate of hydrosilation is associated with an inherently low barrier for dissociative silane exchange (product release).

Gauging aromatic conjugation and charge delocalization in the aryl silanes PhnSiH4−n (n = 0–4), with silicon K-edge XAS and TDDFT

Si K-edge X-ray absorption spectra (XAS) have been measured experimentally and calculated using time-dependent density functional theory (TDDFT) to investigate electronic structure in aryl silanes, Ph_nSiH_4−n (n = 0–4).

Activations of all Bonds to Silicon (Si-H, Si-C) in a Silane with Extrusion of [CoSiCo] Silicide Cores

The [BP₃ ^iPr]Co(I) synthon Na(THF)₆{[BP₃ ^iPr]CoI} (1, [BP₃ ^iPr] = κ³-PhB(CH₂P ⁱPr₂)₃^-) reacts with PhSiH₃ or SiH₄ to form unusual {[BP₂ ^iPr](SiH₂R)CoH₂}═Si═{H₂Co[BP₃ ^iPr]} species (R = Ph, 2a; R = H, 2b; [BP₂ ^iPr] = κ²-PhB(CH₂P ⁱPr₂)₂) that result from activation of all Si-H and Si-C bonds in the starting silanes. Solution-spectroscopic data (multinuclear NMR, IR) for 2a,b, and the solid-state structure of 2a, indicate substantial Co═Si═Co multiple bonding and minimal interaction of the core Si atom with nearby hydride ligands. In the presence of 4-dimethylaminopyridine (DMAP), 1 reacts with PhSiH₃ to give [BP₃ ^iPr](H)₂CoSiHPh(DMAP) (3). Complexes 2a,b eliminate RSiH₃ upon thermolysis in the presence of DMAP to generate {[BP₂ ^iPr]Co(NC₅H₃NMe₂)}═Si═{H₂Co[BP₃ ^iPr]} (4).

Base-Free Iron Hydrosilylene Complexes via an α-Hydride Migration that Induces Spin Pairing

Two new base-free hydrosilylene complexes of iron were synthesized using the novel starting material Cp*( ⁱPr₂MeP)FeMes. These Cp*( ⁱPr₂MeP)Fe(H)SiHR (R = DMP, Trip) complexes are in equilibrium with the corresponding iron silyl complexes, Cp*( ⁱPr₂MeP)FeSiH₂R, which can be trapped and characterized for R = Trip. Unlike the Ru analogues, the Fe silylene complex with R = DMP is observed to undergo an intramolecular C-H activation involving formal addition of a benzylic C-H bond across the Fe-Si bond. This increased activity for bond activations is also observed for reactions with hydrogen, where Fe reacts faster than a Ru analog to form the hydrogenation product, Cp*( ⁱPr₂MeP)H₂FeSiH₂DMP.

Expanded Helicenes: A General Synthetic Strategy and Remarkable Supramolecular and Solid-State Behavior

A divergent synthetic strategy allowed access to several members of a new class of helicenes, the "expanded helicenes", which are composed of alternating linearly and angularly fused rings. The strategy is based on a three-fold, partially intermolecular [2+2+n] (n = 1 or 2) cycloaddition with substrates containing three diyne units. Investigation of aggregation behavior, both in solution and in the solid state, revealed that one of these compounds forms an unusual homochiral, π-stacked dimer via an equilibrium that is slow on the NMR time scale. The versatility of the method was harnessed to access a selenophene-annulated expanded helicene that, in contrast to its benzannulated analogue, exhibits long-range π-stacking in the solid state. The new helicenes possess low racemization barriers, as demonstrated by dynamic ¹H NMR spectroscopy.

Cancer survivors' self-efficacy to self-manage in the year following primary treatment

PURPOSE

Cancer survivors are increasingly expected to manage the consequences of cancer and its treatment for themselves. There is evidence that self-efficacy is important for successful self-management and that this can be enhanced with support. The purpose of this study was to assess self-efficacy to manage problems in the year following primary treatment.

METHODS

This cross-sectional online survey included cancer survivors who had completed their treatment within the past 12 months. Self-efficacy was assessed and variables expected to be associated with self-efficacy were measured using validated scales including quality of life, well-being, illness perceptions, depression and social support.

RESULTS

One hundred eighty-two respondents (mean age 50; 81% female) completed the survey. They had been treated for a range of cancers; most commonly breast (45%). Self-efficacy scores varied between individuals and according to the illness-related task to be managed. Respondents were least confident in managing fatigue and most confident in accessing information about their cancer. Individuals most likely to report low self-efficacy were women, those experiencing higher levels of pain and/or depression, lower well-being scores, lower socio-economic status, low levels of social support, or a more negative perception of cancer.

CONCLUSIONS

Self-efficacy to self-manage problems faced as a consequence of cancer and its treatment can vary widely in the year following treatment. Fatigue may be particularly difficult to manage.

IMPLICATIONS FOR CANCER SURVIVORS

Variations in self-efficacy highlight the importance of assessing specific problems faced and people's confidence to manage them in order to tailor appropriate self-management support.

Dynamic CT for parathyroid disease: are multiple phases necessary?

BACKGROUND AND PURPOSE

A 4D CT protocol for detection of parathyroid lesions involves obtaining unenhanced, arterial, early, and delayed venous phase images. The aim of the study was to determine the ideal combination of phases that would minimize radiation dose without sacrificing diagnostic accuracy.

MATERIALS AND METHODS

With institutional review board approval, the records of 29 patients with primary hyperparathyroidism who had undergone surgical exploration were reviewed. Four neuroradiologists who were blinded to the surgical outcome reviewed the imaging studies in 5 combinations (unenhanced and arterial phase; unenhanced, arterial, and early venous; all 4 phases; arterial alone; arterial and early venous phases) with an interval of at least 7 days between each review. The accuracy of interpretation in lateralizing an abnormality to the side of the neck (right, left, ectopic) and localizing it to a quadrant in the neck (right or left upper, right or left lower) was evaluated.

RESULTS

The lateralization and localization accuracy (90.5% and 91.5%, respectively) of the arterial phase alone was comparable with the other combinations of phases. There was no statistically significant difference among the different combinations of phases in their ability to lateralize or localize adenomas to a quadrant (P = .976 and .996, respectively).

CONCLUSIONS

Assessment of a small group of patients shows that adequate diagnostic accuracy for parathyroid adenoma localization may be achievable by obtaining arterial phase images alone. If this outcome can be validated prospectively in a larger group of patients, then the radiation dose can potentially be reduced to one-fourth of what would otherwise be administered.

Fecal microbiota transplantation for fulminant Clostridium difficile infection in an allogeneic stem cell transplant patient

We present a case of severe Clostridium difficile infection (CDI) in a non-neutropenic allogeneic hematopoietic stem cell transplant recipient who was treated successfully with fecal microbiota therapy after standard pharmacologic therapy had failed. Following naso-jejunal instillation of donor stool, the patient's symptoms resolved within 48 h. Bowel resection was averted. This is the first case in the literature, to our knowledge, to describe fecal microbiota therapy in a profoundly immunocompromised host with severe CDI. We propose that fecal microbiota therapy be considered as a therapeutic option in immunosuppressed patients with refractory severe CDI.

Coordination and structural properties of encumbering 6-mesityl-2-picolinate complexes

In an effort to enforce a sterically hindered environment in transition-metal and main-group 2-picolinate complexes, the synthesis of the encumbering derivative 6-mesityl-2-picolinate ((Mes)pic) is presented. The coordination and structural properties of (Mes)pic are demonstrated with a range of transition-metal and main-group fragments. The 6-position mesityl group of (Mes)pic is shown to alter both the primary and secondary coordination spheres of metal centers relative to the ubiquitous and unencumbered parent 2-picolinate anion.

Colour match between porcelain and porcelain-repairing resin composites

The aim of this study was to evaluate the differences in colour between dental porcelain and porcelain-repairing resin composites. Porcelain discs were fabricated using four dentine shades in 1mm and 2mm thicknesses. Another series of discs was fabricated in 1mm and 2 mm thicknesses using three different brands of composite. Four single shades were used for the 1mm thick discs, and four single and 12 combined shades for the 2mm thick discs. The colour was measured using a spectrophotometer and colour differences deltaE* were calculated between samples. Colour differences were in the range of (deltaE* = 3.5-26.9), above the accepted threshold for perceptibility (deltaE* > 1) with a number above the threshold for what is considered to be clinically acceptable (deltaE* > 5.5). Improvements in colour match were seen for certain shade combinations of repairing composites, in contrast to when a single shade of composite was used.

Effect of post-brushing mouthwash solutions on salivary fluoride retention--study 2

OBJECTIVE

This study evaluated the effects of three post-brushing mouthwashes containing 0 ppm F, 225 ppm F, and 500 ppm F, respectively, on salivary fluoride retention after brushing with 1450 ppm fluoride (as NaF) toothpaste and rinsing with water immediately after brushing.

METHODS

In this three-phase, randomized, cross-over study, an ion-specific electrode was used to measure salivary F levels in thirty trial participants before brushing (Time 0), and after brushing, rinsing with water, and then rinsing with one of the three mouthwashes. Time points evaluated after brushing were one, three, five, 10, 20, 30, 45, and 60 minutes. For saliva sample collections, subjects were asked to pool saliva in their mouths for 10 seconds before spitting out into a container for each of the time points.

RESULTS

The AUC0-60 means for F in saliva were 554, 252, and 20 for the 500, 225, and 0 ppm F mouthwash groups, respectively. The 500 ppm F mouthwash resulted in a 2660% increase in total fluoride salivary retention over 60 minutes when compared with the 0 ppm F group, and a 120% increase when compared with the 225 ppm F group. A significant difference (p < 0.001) in the AUC0-60 means between the three groups was observed using analysis of variance (ANOVA). Paired t-tests also showed significant differences in the mean fluoride retention over 60 minutes for all three pair-wise group comparisons (p < 0.001).

CONCLUSION

Use of a fluoride mouthwash containing 225 ppm F or 500 ppm F produced a significant increase in salivary fluoride retention following brushing with a 1450 ppm F toothpaste and rinsing with water compared to rinsing without fluoride. The use of the 500 ppm F mouthwash may be of particular benefit to those at high caries risk.

Phosphorylation of RelA/p65 promotes DNMT-1 recruitment to chromatin and represses transcription of the tumor metastasis suppressor gene BRMS1

The majority of patients with lung cancer present with metastatic disease. Chronic inflammation and subsequent activation of NF-κB have been associated the development of cancers. The RelA/p65 subunit of NF-κB is typically associated with transcriptional activation. In this report we show that RelA/p65 can function as an active transcriptional repressor through enhanced methylation of the BRMS1 metastasis suppressor gene promoter via direct recruitment of DNMT-1 to chromatin in response to TNF. TNF-mediated phosphorylation of S276 on RelA/p65 is required for RelA/p65-DNMT-1 interactions, chromatin loading of DNMT-1, and subsequent BRMS1 promoter methylation and transcriptional repression. The ability of RelA/65 to function as an active transcriptional repressor is promoter specific as the NF-κB-regulated gene cIAP2 is transcriptionally activated while BRMS1 is repressed under identical conditions. Small molecule inhibition of either of the minimal interacting domains between RelA/p65-DNMT-1 and RelA/p65-BRMS1 promoter abrogates BRMS1 methylation and its transcriptional repression. The ability of RelA/p65 to directly recruit DNMT-1 to chromatin resulting in promoter-specific methylation and transcriptional repression of tumor metastasis suppressor gene BRMS1 highlights a new mechanism through which NF-κB can regulate metastatic disease, and offers a potential target for newer generation epigenetic oncopharmaceuticals.

The efficacy of techniques for the disinfection of artificial sub-surface dentinal caries lesions and their effect on demineralization and remineralization in vitro

OBJECTIVES

The efficacy of three techniques for the disinfection of artificial sub-surface root caries lesions and their response to subsequent episodes of de- and remineralization was investigated quantitatively in vitro.

METHODS

Sub-surface dentinal lesions (n=20), cut into four experimental blocks and deliberately contaminated with Streptococcus mutans, were subject to either steam autoclaving (121 degrees C, 5min), gamma irradiation (4100Gy), immersion in 0.1% (w/v) thymol-distilled water solution (24h) or reserved as a control. Next, the lesions were incubated aerobically in sterile nutrient broth for 24h at 37 degrees C and resultant cultures plated onto blood agar and neutralisation agar. Ten blocks from each experimental group were then immersed in an acidic buffer solution or exposed to artificial saliva for 5 days. Baseline changes in the mineral content and distribution of the lesions were assessed by transverse microradiography (TMR).

RESULTS

Micro-organisms were recovered from each control block and one block treated by gamma irradiation. Steam autoclaving and immersion in a thymol solution significantly decreased (p<0.05) the amount of mineral lost from the body of lesions subject to a further acid challenge. Mineral ion uptake by lesions exposed to artificial saliva was significantly increased (p<0.05) through disinfection by steam autoclaving.

CONCLUSIONS

Gamma irradiation proved the most acceptable method for the disinfection of sub-surface root dentine lesions having the least adverse effect on demineralization and remineralization.

The microbiological origin of fluorescence observed in plaque on dentures during QLF analysis

The aim of this study was to determine the microbiological origin of plaque fluorescence observed during quantitative light-induced fluorescence (QLF) analysis. Plaque was sampled from dentures, because of easy accessibility and the homogeneous background provided by the denture tooth during imaging, and the acknowledged comparability to occlusal plaque. Forty removable poly(methyl methacrylate) dentures were screened for the presence of fluorescent plaque deposits during QLF analysis. Dentures were photographed, QLF images were recorded and samples of fluorescent plaque were taken. Plaque samples were cultured on fastidious anaerobe agar, Wilkins Chalgren agar and Sabourauds dextrose agar. Plates were screened under QLF and fluorescent colonies were subcultured and identified. Areas of red, orange and green fluorescence were detected on the fitting and non-fitting surfaces of dentures. The red and orange fluorescing species were Prevotella melaninogenica, Actinomyces israelii and Candida albicans, which 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 organism in plaque development). Non-fluorescent colonies were also cultured. Plaque which accumulates on susceptible surfaces tends to be associated with caries, but it may be its maturity, rather than the presence of cariogenic streptococci, that is more likely to provide a microbiological link between red fluorescence and caries.

The use of in situ models and QLF for the study of coronal caries

OBJECTIVES

The purpose of the paper is to review aspects of the systems available to model the caries process in enamel.

METHODS

The in situ model developed in Liverpool, and the new method of quantifying mineral loss, Quantitative Light-induced Fluorescence (QLF), are described. QLF is a powerful new diagnostic tool which can be used to measure demineralisation and remineralisation in tooth surfaces in vivo; studies to optimise, validate and use QLF in different clinical situations are described.

RESULTS

Examples of the use of in situ models show that they are particularly valuable for monitoring de and remineralisation of artificial lesions in relation to product testing as alternatives to clinical trials, and present significant advances over in vitro methods. Quantification of mineral loss by Transverse Microradiography (TMR) as in the traditional Liverpool model has produced much valuable information, but the destructive nature of the method limits experimental design, and removes the system from the clinical situation. As a possible alternative, QLF has been validated and optimised. Longitudinal measures can be made on the same surface, and examples of its use are for monitoring recurrent caries and demineralisation around orthodontic brackets.

CONCLUSIONS

While current in situ models provide a major advance over earlier caries models, measurement of de and remineralisation by destructive methods such as transverse microradiography limits the design of experimental investigations. QLF offers significant time saving, reduces the cost of clinical studies, and because the measurements can be carried out longitudinally in vivo, can remove the need for intra-oral appliances carrying experimental tissues.

Quantification of dental plaque in the research environment

OBJECTIVES

To review the established and novel methods of plaque quantification employed in dental research, including a discussion of their merits and to present a new method of planimetrically measuring plaque using light induced fluorescence.

METHOD

Quantitative light-fluorescence (QLF) images were acquired from the buccal surfaces of an individual who had refrained from oral hygiene both with and without traditional plaque disclosure. Digital photographs were also taken. Images were analysed using a novel method and a percentage plaque index produced.

RESULTS

Traditional plaque indices are problematic due to their integral nature and their failure to detect small, but potentially clinically relevant changes in plaque area. The use of a fluorescent technique demonstrated good reliability although there was no correlation between red fluorescent plaque and total disclosed plaque suggesting that the auto-fluorescing plaque is not a good measure of total plaque volume.

CONCLUSIONS

The use of planimetric techniques can increase the power of plaque studies, potentially reducing the number of subjects and time required to separate therapies or products. Fluorescent methods of quantification have potential as they enable clear separation of the plaque covered and non-covered tooth surfaces.

Development of an in situ root caries model. A. In vitro investigations

OBJECTIVES

The paper describes preliminary in vitro investigations, the objectives of which were to examine the influence of certain experimental parameters on artificial carious lesion formation in root hard tissues, and their remineralisation. These experiments formed part of a wider study that aimed to develop an in situ model of root caries, based on the existing coronal caries model used in Liverpool. The present studies examined the effects (a) of the anatomical origin of the dentine, the presence or absence of cementum, the exposure time and the type of demineralising system, on lesion development, and (b) of baseline lesion size on the extent and location of mineral re-precipitation.

METHODS

Mineral content parameters in plano-parallel sections taken from dentine lesions were determined by computer-controlled transverse microradiography.

RESULTS

The importance of the anatomical origin of the dentine on lesion formation was investigated by comparing in vitro lesion formation in premolar and molar dentine, and in dentine from apical, middle and coronal thirds of the root: no difference was observed between these sites. Lesions formed more rapidly in acid buffer solutions than in acid gel systems, and were more reliably produced when cementum was removed. The effect of baseline lesion size on subsequent in vitro remineralisation demonstrated that a small baseline mineral content was associated with a larger percentage mineral gain. The location of mineral deposition throughout the lesion was also influenced by baseline mineral content parameters.

CONCLUSIONS

The results form a basis for the further development of an in situ dentinal caries model, providing data to suggest that manipulation of parameters involved in the preparation of artificial carious lesions has a significant effect on the behaviour of the lesion, particularly the phenomenon of remineralisation. Further work is needed to investigate the behaviour of the model in situ.

Development of an in situ root caries model B. In situ investigations

OBJECTIVES

The aims of this pilot study were to assess the suitability of an in situ model for root caries studies, and to investigate the effect of sub-surface lesion mineral content and ultrastructural organisation on remineralisation.

METHODS

Subjects were selected by criteria generally used for coronal caries models. Plaque pH responses and salivary flow rates were determined by standard methods. The chosen substrate was human dentine with artificially induced caries-like demineralisation and sterilised by gamma-irradiation (4100 Gy). Two levels of baseline demineralisation were induced by exposure to an acid buffer for 2 or 5 days. Mineral content was measured by computer-controlled quantitative microradiography.

RESULTS

Remineralisation in situ was greater in smaller lesions with lower surface mineral content than in larger lesions in which the surface mineral content was high.

CONCLUSIONS

The model is suitable for further development for investigating dentinal caries. More work is needed to validate the model by means of a fluoride dose-response study.

Sialidase as a target for inhibitors of influenza virus replication

Structure-based drug design has led to the identification of potent and selective inhibitors of influenza virus sialidase, which have antiviral activity in vitro and in experimental animal models of influenza infection. Clinical studies with one such sialidase inhibitor, zanamivir, have shown this compound to be a safe and effective therapy for influenza infections in man. Passage of influenza viruses in the presence of zanamivir in vitro has been shown to result in the selection of viruses with reduced sensitivity to this drug. To date, however, there have been no reports of the isolation of zanamivir-resistant viruses during clinical studies of this compound. Further application of structure-based drug design is yielding novel classes of potent inhibitors of influenza virus sialidase.

The quality of dental casts used in crown and bridgework

OBJECTIVE

To assess the quality of dental casts used in crown and bridge construction.

DESIGN

Observational cross-sectional study of dental casts.

SETTING

Commercial dental laboratories and a university dental hospital laboratory in the UK.

MATERIALS AND METHODS

A sample (n = 150) of working and opposing casts used for crown and bridgework prescribed by general dental practices and a dental hospital were sampled from two commercial dental laboratories and an 'on-site' university dental hospital laboratory respectively. A simple '3 point' assessment scale of quality (good, fair and poor) was used to categorise the casts depending on the clarity of reproduction of soft and hard tissues.

RESULTS

The quality of opposing casts used for articulation purposes was significantly better (P<0.001) than that of the working casts. In addition it was found that for working casts the quality in the preparation area(s) was significantly better (p<0.001) than that in areas remote from preparation(s) in the same arch. In general, the quality of casts in the incisal or occlusal surfaces was better than the buccal and lingual surfaces.

CONCLUSIONS

This study has demonstrated that variation exists in the quality of casts used in crown and bridgework, specifically those used in the construction of indirect restorations and also those used for articulation purposes. This study highlights the need for clinicians to exercise continued vigilance with crown and bridge impressions, and casts, particularly in areas away from the prepared teeth.

What do patients expect from complete dentures?

OBJECTIVES

An investigation was undertaken with the aim of determining whether patients wearing complete dentures in dental hospital (DH) and dental practice (DP) had different expectations from their dentures, together with their requirements for information about denture construction and oral and denture care.

METHODS

A total of 214 edentulous patients, with a mean age of 69 years, from DP (125) and DH (89) participated in the questionnaire-based study. A valid questionnaire (P-DEQ) was constructed which demonstrated good test-retest reliability (Cronbach's alpha 0.86). The P-DEQ sought to determine how patients responded to a series of questions related to what dentists are urged to achieve with complete dentures. The questions covered not only what might be termed "normative" expectations but also patients' perceived needs for further information about the stages of prosthodontic treatment and oral or denture care.

RESULTS

Significant differences (p< or =0.001) emerged between the two groups; 82% of the DH group thought it essential that their dentures caused no pain compared with 59% of the DP group; for "absence of slackness" (DH 87%; DP 65%), and "good bite" (DH 82%; DP 55%). No significant differences emerged for the other parameters investigated, but both groups had high expectations for ease of chewing, speech, and good appearance. Differences (p<0.05) between the groups also emerged with respect to the demand for more information regarding the stages involved in denture construction (DH 57%, DP 76%) and how to care for dentures (DH 75%, DP 89%). Large proportions of patients from both groups would prefer to have more information about the selection of teeth (71% DH, 72% DP), and how to care for their mouths (84% DH, 86% DP), but there were no differences between the groups in these parameters.

CONCLUSIONS

Most patient expectations appear to equate with the normative view expressed in standard prosthodontic texts. However, expectations may differ not only between individuals but also between patient groups managed in teaching hospital and DP settings. Edentulous patients also need information regarding the stages involved in denture construction and how to care for their mouths and dentures. This may have implications for the management of edentulous patients in DP and dental hospital.

The Effect of Chewing Urea-Containing Gum on Plaque Acidogenic and Alkaligenic Parameters

The aim of this double-blind crossover study was to determine the effect of chewing urea-containing gum on selected microbiological plaque properties. Eleven subjects chewed either urea-containing or urea-free placebo gum 3 times daily, each for 4 weeks, with at least a 4-week separation between regimes. After each chewing regime, plaque was sampled from all available surfaces, and inoculated into media indicative of acid or base production. In addition, interdental pH measurements were taken using touch Beetrode electrodes following sucrose and sorbitol mouthrinses, and sucrose mouthrinses followed by urea rinse, urea gum, or placebo gum. No significant differences in plaque acidogenic and alkaligenic properties were found between the urea and placebo gum regimes. Urea rinsing, urea gum and placebo gum all reduced the depth and duration of the pH fall following a sucrose mouthrinse. They also enhanced a rise in pH above the resting pH, but although urea gum produced a larger increase than placebo gum, the difference was not significant.

Detection of in vitro demineralization adjacent to restorations using quantitative light induced fluorescence (QLF)

AIM

Quantitative light-induced fluorescence (QLF) is a technique for the detection, quantification, and longitudinal monitoring of early carious lesions. The technique is non-destructive and can be used in vivo. Using the natural fluorescence of teeth, and the loss of such fluorescence in demineralized enamel, QLF is a repeatable and valid optical caries monitor. Previously used in smooth and occlusal surfaces, the purpose of this pilot study was to determine if QLF could detect, and longitudinally monitor, demineralization adjacent to a range of restorative materials.

METHODS

Fifteen previously extracted lower third molars were selected based upon the lack of any visible demineralization. A single burr hole was placed on the buccal surface and the cavity restored with amalgam, composite, compomer, glass ionomer or a temporary filling material. The buccal surface was then coated in an acid resistant nail varnish leaving an exposed area around the restoration and also a similar sized control region. The teeth had QLF images taken at baseline and were then subjected to a demineralizing buffer, further QLF images were subsequently taken at 72 and 144 h. Transverse microradiography was used to confirm the presence of early, subsurface lesions at the completion of the cycle (144 h). QLF images were analyzed by a single blinded examiner and values for change in radiance fluorescence were computed. These values were recorded as loss of radiance fluorescence loss integrated over area of lesion and expressed as DeltaQ.

RESULTS

The appearance of each material under QLF and the change in fluorescence is described. Amalgam, glass ionomer and the temporary material all exhibited reduced fluorescence, while composite and compomer showed increased fluorescence, when compared with surrounding enamel. There was no change in fluorescence of the materials when subjected to experimental demineralizing conditions. Readings at 72 and 144 h demonstrated demineralization adjacent to the restorations and at the exposed control. Significant differences were detected between baseline, 72 and 144 h using ANOVA on all restorations with the exception of compomer where significance was noted between baseline and 144 h, p>0.05.

CONCLUSIONS

This pilot study has demonstrated the ability for QLF to detect and monitor secondary caries. Analysis techniques should be based upon the subtraction of baseline DeltaQ scores from subsequent images. Further research is required to assess the ability of QLF to detect secondary lesions in vivo.

The intra- and inter-examiner reliability of quantitative light-induced fluorescence (QLF) analyses

OBJECTIVE

To assess the reliability of the analysis stage of quantitative light-induced fluorescence (QLF). The QLF analysis involves subjective input from the user and this study examines the influence of this on the reproducibility of the QLF data.

METHOD

QLF images were taken of 20 human molar teeth that had been previously subjected to a demineralizing solution (phosphoric acid 37%) to create artificial white spot lesions on their buccal surfaces. Following examination of the images, 16 were chosen to represent a range of lesion size and severity. Three copies were made of the images and each was allocated a different filename. 10 examiners in three centres were asked to analyse each of the 16 images on three occasions, with at least seven days between each attempt. Simple instructions describing the analysis procedure were supplied and examiners were asked to adhere to these directions. Examiners were asked to rate each of the 16 teeth on their first attempt both quantitatively (5 point scale) and qualitatively in terms of difficulty of analysis. Data reported were the delta Q at 5% threshold for each tooth on each of three attempts.

RESULTS

Using ANOVA and paired t-tests to detect statistical differences, the three attempts of each examiner were used to determine intra-examiner reliability. Only one examiner (a novice at the technique) demonstrated differences between all three attempts and two demonstrated difference between one attempt. When the mean scores were compared to determine the inter-examiner reliability, only one examiner's results were statistically different when compared with two others.

CONCLUSION

This study has demonstrated that the analysis stage of QLF is reliable between examiners and within multiple attempts by the same examiner, when analysing in vitro lesions. Novices at the technique should be trained before analysing experimental data.

Good occlusal practice in simple restorative dentistry

Many theories and philosophies of occlusion have been developed. 1-12 The difficulty in scientifically validating the various approaches to providing an occlusion is that an 'occlusion' can only be judged against the reaction it may or may not produce in a tissue system (eg dental, alveolar, periodontal or articulatory). Because of this, the various theories and philosophies are essentially untested and so lack the scientific validity necessary to make them 'rules'. Often authors will present their own firmly held opinions as 'rules'. This does not mean that these approaches are to be ignored; they are, after all, the distillation of the clinical experience of many different operators over many years. But they are empirical. In developing these guidelines the authors have unashamedly drawn on this body of perceived wisdom, but we would also like to involve and challenge the reader by asking basic questions, and by applying a common sense approach to a subject that can be submerged under a sea of dictate and dogma.

Time-division multiplexing of large serial fiber-optic Bragg grating sensor arrays

Time-division multiplexing is a promising method for the interrogation of fiber-optic Bragg grating sensors arrays for measurement of strain and temperature. We examine the performance of these systems to determine the parameters for high-sensitivity, low-cross-talk operation. It is shown that the performance can be greatly improved by use of a short time resolution in the demultiplexing process. We propose a new method of demultiplexing with an electro-optic modulator to read out the sensor pulses by gating the signal with 400-ps resolution. The system is demonstrated experimentally to provide 0.15-microepsilon/square root(Hz) strain resolution in a 50-Hz bandwidth within a full-scale range of 8000 microepsilon. The system parameters are capable of handling at least 50 time-addressed sensors on a single fiber.

A cost analysis of encapsulated spray-dried milk fat

Anhydrous butter oil or cream was encapsulated in all-purpose flour, modified cornstarch, or sucrose and then spray-dried. We estimated the processing cost for a plant designed to produce 57,000 kg/d (125,000 lbs/ d) of encapsulated milk fat powder. Powder with a 50% milk fat content could be produced for about $0.23/kg plus the cost of the butter oil or cream, the encapsulant selected, and the other ingredients. Spray-drying of milk fat improved ease of handling and reduced storage costs.

Association models for a multivariate binary response

Models for a multivariate binary response are parameterized by univariate marginal probabilities and dependence ratios of all orders. The w-order dependence ratio is the joint success probability of w binary responses divided by the joint success probability assuming independence. This parameterization supports likelihood-based inference for both regression parameters, relating marginal probabilities to explanatory variables, and association model parameters, relating dependence ratios to simple and meaningful mechanisms. Five types of association models are proposed, where responses are (1) independent given a necessary factor for the possibility of a success, (2) independent given a latent binary factor, (3) independent given a latent beta distributed variable, (4) follow a Markov chain, and (5) follow one of two first-order Markov chains depending on the realization of a binary latent factor. These models are illustrated by reanalyzing three data sets, foremost a set of binary time series on auranofin therapy against arthritis. Likelihood-based approaches are contrasted with approaches based on generalized estimating equations. Association models specified by dependence ratios are contrasted with other models for a multivariate binary response that are specified by odds ratios or correlation coefficients.

Antimicrobial use in long-term-care facilities. SHEA Long-Term-Care Committee

There is intense antimicrobial use in long-term-care facilities (LTCFs), and studies repeatedly document that much of this use is inappropriate. The current crisis in antimicrobial resistance, which encompasses the LTCF, heightens concerns of antimicrobial use. Attempts to improve antimicrobial use in the LTCF are complicated by characteristics of the patient population, limited availability of diagnostic tests, and the virtual absence of relevant clinical trials. This position paper recommends approaches to management of common infections in LTCF patients and proposes minimal standards for an antimicrobial review program. In developing these recommendations, the position paper acknowledges the unique aspects of provision of care in the LTCF.

Case report: restorative maintenance of prostheses stabilised by non-endosseous implants

For over a century, dentists have looked to dental implants to enhance the stability of dental prostheses. During this time, many approaches and different materials have been used. The purpose of this article is to report on two cases where non-endosseous implant systems were used and to outline how the replacement prostheses were customiZed to comply with the different implant types. Intramucosal inserts and sub-periosteal implants are briefly reviewed in the context of current prosthodontic practise. There are still a small number of patients with clinically acceptable intramucosal and subperiosteal implant retained prostheses, which will continue to need servicing and replacement.

Refining the mouse chromosomal location of Cdm, the major gene associated with susceptibility to cadmium-induced testicular necrosis

Cadmium (Cd++) is a widespread environmental pollutant and classifed as an IARC 'Category I' human carcinogen. Cd++ can also cause severe renal toxicity and may be involved clinically in cardiovascular disease and osteoporosis. Genetic differences in sensitivity to cadmium toxicity have been noted in humans, whereas, among inbred mouse strains, unequivocal genetic data exist. Resistance to cadmium-induced testicular damage was reported in 1973 to be associated with a single major recessive gene, named Cdm, which has now been localized to mouse chromosome (Chr) 3. Using polymorphic microsatellite markers and semiquantitative histological parameters, we have corroborated the original 1973 data concerning mendelian inheritance and have further refined the region containing the Cdm gene from more than 24 cM to 0.64 cM (estimated 40-80 genes). We phenotyped 26 recombinant inbred lines generated from C57BL/6J (B6, resistant) and DBA/2J (D2, sensitive) inbred mice, and determined that the Cdm gene maps between microsatellite markers D3Mit110 and D3Mit255. Although toxicity to numerous heavy metals is well known, virtually no molecular mechanisms have yet been uncovered either in humans or laboratory animals. Identification and characterization of the mouse Cdm gene should enhance our understanding of heavy metal toxicity by identifying and characterizing, for the first time, a major mammalian gene responsible for susceptibility to diseases caused by heavy metal toxicity.

Microbiologic survey of long-term care facilities

BACKGROUND

We undertook a microbiologic survey of long-term care facilities to categorize bacteria found in cultures of residents. Culture and sensitivity data were collected on 566 samples from indwelling bladder catheters, percutaneous gastrostomy tubes, nares, stool, wounds, pressure ulcers, and tracheostomies in 25 Nebraska and Iowa facilities. Information was also collected on resident factors (eg, presence of indwelling urinary catheter, prior antibiotic administration) and institutional variables (eg, number of beds, nosocomial infection rates).

RESULTS

There were 478 gram-negative isolates, the leading organisms being Pseudomonas aeruginosa, Proteus mirabilis, Escherichia coli, and Klebsiella pneumoniae. There were 221 gram-positive isolates, the most frequently seen of which were enterococci and Staphylococcus aureus. Of the 442 residents sampled in the study, 168 (38%) were taking, or had within the previous month been taking, a systemic antibiotic. Quinolones were the most frequently prescribed antibiotic class. The institutional prevalence of urinary catheterization averaged 6.7%.

CONCLUSIONS

Significant antibiotic pressure exists in long-term care facilities, a fact that is reflected in antibiotic resistance patterns. A variety of gram-positive and gram-negative bacteria were found in nursing home culture specimens.

A novel technique to measure laser beam spot sizes

In this letter we report a novel technique to measure small laser beam spot sizes. We use the open aperture z-scan technique as a tool to measure the laser beam spot size. This technique measures small spot sizes with accuracy better than 10%.

The design and use of special trays in prosthodontics: guidelines to improve clinical effectiveness

This paper looks at how carefully prescribed special trays can be helpful in everyday dental practice. Guidelines are suggested for the design of custom trays, that will, hopefully, lead to improvements in the quality of working impressions.

Rhodesian trypanosomiasis in a splenectomized patient

We report the first apparent case of a splenectomized individual who developed severe trypanosomiasis with central nervous system involvement. The patient was a 41-year-old man who participated in an east African safari. Upon his return to the United States, the patient presented with an infection with Trypanosoma brucei rhodesiense that was treated successfully with suramin and melarsoprol. The onset of symptoms, laboratory studies, and disease progression did not differ from previously reported cases in the literature. The role of the spleen in trypanosomiasis is not well understood and the few reports available describe only animal models. This report suggests that asplenia had no apparent effect on the onset of symptoms and overall severity of illness. Further studies are necessary to ultimately define the role of the spleen in trypanosomiasis.

Wavelength-encoding/temporal-spreading optical code division multiple-access system with in-fiber chirped moiré gratings

We propose an optical code division multiple-access (OCDMA) system that uses in-fiber chirped moiré gratings (CMG's) for encoding and decoding of broadband pulses. In reflection the wavelength-selective and dispersive nature of CMG's can be used to implement wavelength-encoding/temporal-spreading OCDMA. We give examples of codes designed around the constraints imposed by the encoding devices and present numerical simulations that demonstrate the proposed concept.

Exact tests of goodness of fit of log-linear models for rates

We propose Metropolis-Hastings sampling methods for estimating the exact conditional p-value for tests of goodness of fit of log-linear models for mortality rates and standardized mortality ratios. We focus on two-way tables, where the required conditional distribution is a multivariate noncentral hypergeometric distribution with known noncentrality parameter. Two examples are presented: a 2 x 3 table, where the exact results, obtained by enumeration, are available for comparison, and a 9 x 7 table, where Monte Carlo methods provide the only feasible approach for exact inference.

Infected pressure ulcers in the long-term-care facility

Pressure ulcers occur with some frequency in the elderly, debilitated population in long-term-care facilities. Pressure ulcers cause morbidity and mortality and, by virtue of breaking the integumentary barrier, predispose to skin and soft-tissue infections. The latter often are deep and require lengthy medical and surgical therapy. Prevention depends on avoidance of pressure, as well as providing adequate nutrition and meticulous skin care.

Synthesis of tetrasubstituted bicyclo[3.2.1]octenes as potential inhibitors of influenza virus sialidase

Several racemic bicyclo[3.2.1]octene derivatives have been synthesised and evaluated as inhibitors of influenza virus sialidases. The 5-acetamido-bicyclo[3.2.1]octenol 4 showed modest activity against influenza A and B virus sialidases.

Synthesis of a tetrasubstituted bicyclo [2.2.2] octane as a potential inhibitor of influenza virus sialidase

A novel synthesis of the bicyclo [2.2.2] octane ring system has been achieved utilising a tandem Henry cyclisation as the key stage. This chemistry has been employed in the synthesis of a potential inhibitor of influenza virus sialidase.