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(1) To explore the influence of biofilm maturation and timing of exposure on fluoride anticaries efficacy and (2) to explore biofilm recovery post-treatment. Bovine enamel specimens were utilized in a pH cycling model (28 subgroups [n = 18]). Each subgroup received different treatments [exposure]: sodium fluoride [NaF]; stannous fluoride [SnF2]; amine fluoride [AmF]; and de-ionized water [DIW], at a specific period: early: days 1–4; middle: days 3–6; and late: days 7–10. During non-exposure periods, pH cycling included DIW instead of fluorides. Objective 1: part 1 (cycling for 4, 6, or 10 days). Part 2 (cycling for 10 days). Objective 2: early exposure: three sample collection time points (immediate, 3 days, and 6 days post-treatment); middle exposure: two sample collection time points (immediate, 4 days post-treatment). The enamel and biofilm were analyzed ([surface microhardness; mineral loss; lesion depth]; [lactate dehydrogenase enzyme activity; exopolysaccharide amount; viability]). Data were analyzed using ANOVA (p = 0.05). Objective 1: Early exposure to fluorides produced protective effects against lesion progression in surface microhardness and mineral loss, but not for lesion depth. Objective 2: Early exposure slowed the demineralization process. SnF2 and AmF were superior to NaF in reducing LDH and EPS values, regardless of exposure time. They also prevented biofilm recovery. Earlier exposure to SnF2 and AmF may result in less tolerant biofilm. Early fluoride treatment may produce a protective effect against demineralization. SnF2 and AmF may be the choice to treat older biofilm and prevent biofilm recovery. The study provides an understanding of biofilm-fluoride interaction with mature biofilm (e.g., hard-to-reach areas, orthodontic patients) and fluoride’s sustainable effect hours/days after brushing.

The aim of this study was to test the effects of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) creme, or MI Paste™ (MIP), on nicotine-induced Streptococcus mutans biofilm. The experiment utilized S. mutans biofilm assays with varying concentrations of nicotine and MIP aqueous concentrate levels. First hand exposure to nicotine has been demonstrated to significantly increase S. mutans biofilm formation, while the active component, CPP-ACP, in MIP has been shown to reduce S. mutans biofilm formation. A 24-h culture of S. mutans UA159 in microtiter plates were treated with varying nicotine concentrations (0–32 mg/ml) in Tryptic Soy Broth supplemented with 1% sucrose (TSBS) with or without MIP aqueous concentrate. A spectrophotometer was used to determine total growth absorbance and planktonic growth. The microtiter plate wells were washed, fixed, and stained with crystal violet dye and the absorbance measured to determine biofilm formation. The presence of MIP aqueous concentrate inhibits nicotine-induced S. mutans biofilm formation at different concentrations of nicotine (0–32 mg/ml). The results demonstrated nicotine-induced S. mutans biofilm formation is decreased in the presence of MIP. This provides further evidence about the cariostatic properties of CPP-ACP, the active soluble ingredient in the MIP, and reconfirms the harmful effects of nicotine. Smokers may gain dual benefits from the use of MIP, as a remineralization agent and as a cariostatic agent, by inhibiting nicotine-induced S. mutans biofilm formation.

This study evaluated the antimicrobial properties, cytotoxicity, and mineralization potential of methylcellulose hydrogels loaded with low concentrations of double antibiotic pastes (DAP). The direct and residual antibacterial effects of 1, 5, and 10 mg/mL of DAP loaded into hydrogels as well as calcium hydroxide (Ca(OH)2) were tested against single-species biofilms of Enterococcus faecalis and dual-species biofilms (Enterococcus faecalis and Prevotella intermedia). The effects of DAP hydrogels on proliferation and mineralization of dental pulp stem cells (DPSC) were tested using MTT assays, alkaline phosphate activity (ALP), and alizarin red staining. Fisher’s exact tests, Wilcoxon rank sum tests, and one-way ANOVA were used for statistical analyses (α = 0.05). All tested concentrations of DAP hydrogels as well as Ca(OH)2 demonstrated significant direct antibacterial effects against single- and dual-species biofilms. However, only 5 and 10 mg/mL of DAP hydrogels exhibited significant residual antibacterial effects against both types of tested biofilms. Only 1 mg/mL of DAP hydrogels did not have significant negative effects on DPSC viability, ALP activity, and mineralization nodule formation. However, 5 and 10 mg/mL of DAP hydrogels caused significant negative effects on cytotoxicity and mineralization nodule formation of DPSC. Hydrogels containing 1 mg/mL DAP offered significant direct antibacterial effects against single- and dual-species biofilms without causing significant negative effects on viability, ALP activity, and mineralization nodule formation of DPSC. The methylcellulose-based hydrogel proposed in this study can be used clinically as a biocompatible system to deliver controlled low concentrations of DAP.

Recent findings on the effects of smoking and nicotine on oral microorganisms and on microbial interactions with human cells were reviewed. A PubMed search identified recent publications in English that addressed the effects of smoking and nicotine on oral microorganisms: growth, biofilm formation, plaque composition, enzyme regulation, and cross-species interactions. Interactions of tobacco-exposed microbes with human tissues are also discussed. Smoking alters the oral microbiome. Nicotine increases the pathogenicity of oral microorganisms, either by increasing expression of virulence factors or by increasing the amount of biofilm formed. Nicotine affects human cells via nicotine acetylcholine receptors (nAChRs), and the prokaryote homolog may explain how nicotine affects microbial cells. Interactions of nicotine exposed microbial and human tissues likely contribute to cardiovascular disease. The evidence supports the destructive oral and systemic effects of smoking and nicotine exposure, leading to development or exacerbation of dental caries, periodontitis, stomatitis, and heart diseases.

The purpose of this investigation was to determine the ability of tetracycline-containing fibers to inhibit biofilm formation of peri-implantitis-associated pathogens [i.e., Porphyromonas gingivalis (Pg), Fusobacterium nucleatum (Fn), Prevotella intermedia (Pi), and Aggregatibacter actinomycetemcomitans (Aa)]. Tetracycline hydrochloride (TCH) was added to a poly(DL-lactide) [PLA], poly(e-caprolactone) [PCL], and gelatin [GEL] polymer blend solution at distinct concentrations to obtain the following fibers: PLA:PCL/GEL (TCH-free, control), PLA:PCL/GEL + 5 % TCH, PLA:PCL/GEL + 10 % TCH, and PLA:PCL/GEL + 25 % TCH. The inhibitory effect of TCH-containing fibers on biofilm formation was assessed by colony-forming units (CFU/mL). Qualitative analysis of biofilm inhibition was done via scanning electron microscopy (SEM). Statistical significance was reported at p

Nicotine has well-documented effects on the growth and colonization of Streptococcus mutans. This study attempts to investigate the effects of nicotine on pathogenic factors of S. mutans, such as the effect on biofilm formation and viability, expression of pathogenic genes, and metabolites of S. mutans. The results demonstrated that addition of nicotine did not significantly influence the viability of S. mutans cells. The biofilms became increasingly compact as the concentrations of nicotine increased. The expression of virulence genes, such as ldh and phosphotransferase system (PTS)-associated genes, was upregulated, and nlmC was upregulated significantly, while ftf was downregulated. The lactate concentration of S. mutans grown in 1 mg/mL of nicotine was increased up to twofold over either biofilm or planktonic cells grown without nicotine. Changes in the metabolites involved in central carbon metabolism from sucrose indicated that most selected metabolites were detectable and influenced by increased concentrations of nicotine. This study demonstrated that nicotine can influence the pathogenicity of S. mutans and may lead to increased dental caries through the production of more lactate and the upregulation of virulence genes.

Recent progress in endodontics, particularly encouraging regenerative outcomes achieved by evoked bleeding therapy in the treatment of necrotic immature permanent teeth, clearly suggests that establishment of a regenerative-based clinical strategy is closer than ever before. In this context, an efficient disinfection of the root canal system, mainly through the eradication of microbial biofilms, is a crucial step. Accordingly, numerous bacterial biofilm models have been used in vitro as an attempt to simulate the clinical conditions. To offer a comprehensive update on progress in the field, this review provides an overview of biofilm role in endodontic disease and in vitro biofilm models, the importance of disinfection, a brief review on antibiotic-containing polymer nanofibers and their antimicrobial properties, and future perspective of this novel intracanal drug delivery strategy in regenerative endodontics. Limitations in reproducing in vivo conditions will always exist; however, creating a laboratory-based biofilm model that very closely simulates clinical situations makes in vitro research reliable and the first step towards translation of new therapies.

Among various preventive approaches, non-invasive phototherapy/photodynamic therapy is one of the methods used to control oral biofilm. Studies indicate that light at specific wavelengths has a potent antibacterial effect. The objective of this study was to determine the effectiveness of violet-blue light at 380-440 nm to inhibit biofilm formation of Streptococcus mutans or kill S. mutans. S. mutans UA159 biofilm cells were grown for 12-16 h in 96-well flat-bottom microtiter plates using tryptic soy broth (TSB) or TSB with 1 % sucrose (TSBS). Biofilm was irradiated with violet-blue light for 5 min. After exposure, plates were re-incubated at 37 °C for either 2 or 6 h to allow the bacteria to recover. A crystal violet biofilm assay was used to determine relative densities of the biofilm cells grown in TSB, but not in TSBS, exposed to violet-blue light. The results indicated a statistically significant (P 0.05) decrease compared to the non-treated groups after the 2 or 6 h recovery period. Growth rates of planktonic and biofilm cells indicated a significant reduction in the growth rate of the violet-blue light-treated groups grown in TSB and TSBS. Biofilm viability assays confirmed a statistically significant difference between violet-blue light-treated and non-treated groups in TSB and TSBS. Visible violet-blue light of the electromagnetic spectrum has the ability to inhibit S. mutans growth and reduce the formation of S. mutans biofilm. This in vitro study demonstrated that violet-blue light has the capacity to inhibit S. mutans biofilm formation. Potential clinical applications of light therapy in the future remain bright in preventing the development and progression of dental caries.

This study evaluated selected properties of a prototype root repair cement containing surface pre-reacted glass ionomer fillers (S-PRG) in comparison to mineral trioxide aggregate (MTA) and intermediate restorative material (IRM). The antibacterial effect of S-PRG, MTA, and IRM cements was tested against Porphyromonas gingivalis and Enterococcus faecalis after 1 and 3 days of aging of the cements. The set cements were immersed in distilled water for 4 h to 28 days, and ion-releasing ability was evaluated. Initial and final setting times of all cements were evaluated using Gilmore needles. The push-out bond strength between radicular dentin and all cements was tested at different levels of the roots. S-PRG and IRM cements, but not MTA cement, demonstrated significant antibacterial effect against P. gingivalis. All types of cements exhibited significant antibacterial effect against E. faecalis without being able to eliminate the bacterium. S-PRG cement provided continuous release of fluoride, strontium, boron, sodium, aluminum, and zinc throughout all tested time points. Both initial and final setting times were significantly shorter for S-PRG and IRM cements in comparison to MTA. The push-out bond strength was significantly lower for S-PRG cement in comparison to MTA and IRM at coronal and middle levels of the roots. S-PRG cement demonstrated significant antibacterial effects against endodontic pathogens, multiple ion-releasing ability, relatively short setting time, and low bonding strength. S-PRG cement can be used as a one-visit root repair material with promising antibacterial properties and ion-releasing capacity.

A novel furanone-containing antibacterial resin composite has been prepared and evaluated. compressive strength (CS) and Streptococcus mutans viability were used to evaluate the mechanical strength and antibacterial activity of the composites. The modified resin composites showed a significant antibacterial activity without substantially decreasing the mechanical strengths. With 5-30 % addition of the furanone derivative, the composite kept its original CS unchanged but showed a significant antibacterial activity with a 16-68 % reduction in the S. mutans viability. Further, the antibacterial function of the new composite was not affected by human saliva. The aging study indicates that the composite may have a long-lasting antibacterial function. Within the limitations of this study, it appears that the experimental antibacterial resin composite may potentially be developed into a clinically attractive dental restorative due to its high mechanical strength and antibacterial function.

The purpose of this study was to determine if three strains of bacteria could impact the mechanical or surface properties of a dental resin material. Resin material specimens were incubated at 37°C in sterile saline, tryptic soy broth supplemented with sucrose (TSBS), or TSBS inoculated with Streptococcus mutans, Streptococcus gordonii, or Streptococcus sanguis. The specimens were subjected to Fourier transform infrared spectroscopy before and after incubation. The flexural strength test was performed once a week for 6 weeks. Microhardness and scanning electron microscopy (SEM) was performed on specimens at 1 and 6 weeks. Differences in the area under the carbonyl peak were statistically significant for the specimens incubated in the media inoculated with either S. mutans or S. gordonii. To determine why S. sanguis did not produce changes as the other bacteria did, triethylene glycol dimethacrylate, methacrylic acid, and triethylene glycol were added to bacterial cultures at increasing concentrations. Both methacrylic acid and triethylene glycol reduced the number of colony-forming units of S. sanguis. Specimens incubated in TSBS, saline or in culture with S. sanguis demonstrated a decrease in peak stress in week 1 of the flexure strength test. SEM demonstrated that surface topology changed for those specimens incubated in culture with S. mutans or S. gordonii. The changes in surface topology demonstrated here could contribute to the secondary caries and changes in esthetic properties seen clinically with the use of resin materials in dental restorations.

PATIENTS with scotomas or blind-spots in their visual field1–5 resulting from damage to the visual pathways often report that the pattern from the rest of the visual field 'fills in' to occupy the scotoma. Here we describe a novel technique for generating an artificial perceptual scotoma which enabled us to study the spatial and temporal characteristics of this filling-in process. A homogeneous grey square subtending 1.5° was displayed against a background of twinkling two-dimensional noise of equal mean luminance (Fig. 1). On steady eccentric fixation for 10 s the square vanished and was filled in by the twinkling noise from the surround. Using this display we found that 'filling in' is an active visual process that probably involves creating an actual neural representation of the surround rather than merely ignoring the absence of information from the scotoma; filling in can occur separately for colour and texture, suggesting separate mechanisms; the filling-in process does not completely suppress information from the scotoma, even after an image has faded completely from consciousness it can nevertheless contribute to motion perception; and the process can be strongly influenced by illusory contours.

The unusual case of a man who regained his sight after 40 years of blindness allows researchers to examine the neural and behavioral effects of losing visual experience on the establishment and maintenance of visual system function in humans.

It seems strange that Isaac Newton, for all his scientific achievements, was so attracted to the occult. Yet his vision of the power of symbols has resonance today.

Mind Design: Philosophy, Psychology, Artificial Intelligence. Edited by John Haugeland. Pp.368. Hbk ISBN 0-226-08110-5; pbk ISBN 0-226-58052-1. (MIT Press: 1981.) Hbk $21.50, £13.50; pbk $10, £6.20. Minds and Mechanisms: Philosophical Psychology and Computational Models. By Margaret A. Boden. Pp.311. ISBN 0-855-27064-0. (Harvester/Cornell University Press: 1981.) £20, $29.50.

So long ago as 1878, von Kries1 reported that adapting lights fail to upset colour matches. This observation was modified in 1934 by Prof. W. D. Wright, who showed that lights of very high intensity, above about 15,000 photons, do upset colour matches2. Wright considers the breakdown at glare intensities to be due to radical photochemical changes. G. S. Brindley has recently reported a detailed investigation of this breakdown at high intensities3. It might be suggested that the original findings of von Kries—that matches do not break down after adaptation with intensities within the normal range—has important implications for theories of colour vision, and in particular for the explanation of the Rayleigh equation.

PERHAPS it is difficult to demonstrate primary constancy scaling independently of the distortion illusions, but its effects are not limited to plane figures. For example, the apparent size of the Moon is not a simple function of its apparent distance—when low on the horizon it looks both large and near, which contravenes the classical Emmett's Law, and demands some kind of size scaling which is not locked to apparent distance. The worry about lack of perception of depth in luminous plane figures having exaggerated perspective but which give illusory distortions was in fact expressed by myself, in the (unpublished) paper cited by Humphrey and Morgan. If illusions do occur in figures not seen in depth though the countermanding depth-cues are removed, it would have to be supposed that primary constancy can work like a ‘super releaser’ (as found in ethology), working beyond the normal range at which it is useful. This is quite possible, but if true it would make precise predictions difficult. On present evidence, however, it does not occur: Measuring the apparent depth in luminous Muller–Lyer figures of various fin angles, with the technique briefly described1, I found that the apparent depth of the illusion figures correlates extremely closely with the measured illusions for each angle tested, over the full range of possible angles of the fins. The distortion and the apparent depth of the figures are both reduced for extreme angles, when normal perspective breaks down. To argue that the relation discovered between apparent depth and the illusions is fortuitous is to fly in the face of a correlation coefficient better than 0.9. There are other and quite different predictions which follow from the theory, and it is compatible with the curious finding that peoples who live in environments largely free of right angular corners and parallel lines, such as the Zulus who live in a ‘circular culture’ of round huts, do not suffer these illusions to anything like the normal extent2,3.

A Technique for Minimizing the Effects of Atmospheric Disturbance on Photographic Telescopes

FOR many purposes, such as tracing networks of neural structure in the brain, a normal microscope has the serious limitation that only a thin layer of the specimen can be studied at one time, owing to the limited depth of focus of microscope objectives. When a thin section is examined, only those structures which happen to lie in the plane of the section can be observed. This plane may be confused by such objects as fibres coming away from or toward the plane of the section. A microscope which gave a large depth of field, and which presented the image as a solid in a luminous block in which the structures could be observed in depth would have important advantages over existing optical microscopes. We have designed and constructed a primitive prototype of an instrument giving such a ‘solid image’. It is possible to observe this from any position and to see the structures with appropriate parallax.