Variability in cytotoxicity and fluoride release of resin-modified glass-ionomer cements

New-generation glass-ionomer cements contain resin to improve their restorative properties. These resin-modified glass-ionomer cements vary considerably in their chemistry, which could result in corresponding variability in their physical and biological properties. This study investigated the cytotoxicity and the fluoride release of two resin-modified glass ionomers, a conventional glass-ionomer cement, and a resin composite. Samples were prepared and extracted in distilled water for 1, 4, and 7 days; eluates were filtered and tested by means of 3T3 mouse fibroblasts. Cytotoxicity (MTT assay) values were low for all materials and extraction times, indicating minimal cytotoxicity of all materials (less than 30% inhibition). Cytotoxicity of one resin-modified glass ionomer was significantly higher than for the other materials (p < 0.001). One resin-modified glass ionomer and the conventional glass-ionomer cement released significantly more fluoride at each time interval (p < 0.001) than the other resin-modified glass-ionomer cement and the resin composite. Fluoride release and cytotoxicity were correlated (r2 = 0.60; p < 0.001), although the fluoride release does not account for the cytotoxicity observed. Cytotoxicity and fluoride release suggest that one hybrid behaved more like a conventional glass ionomer, and the other like a resin composite. These differences may have implications for material selection in specific clinical situations.     

The effect of dentin disinfectants on shear bond strength of resin-modified glass-ionomer materials

The purpose of this study was to investigate the effect of dentinal disinfection with a 2% chlorhexidine or a 0.11% I2-KI/CuSO4 solution on the shear bond strength of three resin-modified glass-ionomer cements: Fuji II LC, Photac-Fil, and Vitremer. The occlusal surfaces of extracted human teeth were flattened to dentin. Specimens were randomly assigned to one of nine treatment groups (n = 12). For each glass-ionomer material, there was a control group and two treatment groups in which the dentin was treated with either a 2% chlorhexidine or a 0.11% I2-KI/CuSO4 solution before the dentin was treated with the recommended dentin conditioner prior to glass-ionomer bonding. Specimens were stored for 1 day in water, thermocycled, and tested in shear until failure. The chlorhexidine solution did not significantly affect the shear bond strengths of any of the cements, but the I2-KI/CuSO4 solution significantly lowered the bond strengths of Vitremer and Fuji II LC compared to the controls.     

Interfacial characteristics of resin-modified glass-ionomer materials: a study on fluid permeability using confocal fluorescence microscopy

The tooth interface with resin-modified glass-ionomer cements (RM GICs) is poorly understood. This study examined the interface, especially with dentin. Cervical cavities in extracted teeth were restored with Fuji II LC, Vitremer, Photac-Fil, or a conventional GIC, Fuji Cap II. Fluorescent dye was placed in the pulp chambers for 3 hrs before the specimens were sectioned. Examination of the tooth/material interface with a confocal microscope showed that dye uptake by the restoration varied among materials. A "structureless", non-particulate, highly-stained layer of GIC was observed next to dentin in Fuji II LC. This layer varied in width, was prominent where the dentin tubules were cut "end-on" and in areas closer to the pulp, and was not seen adjacent to enamel. Vitremer showed minimal dye uptake, and the "structureless" layer was barely discernible. Photac-Fil showed more uniform uptake and absence of this layer. Cracking of enamel was also noted with these materials. The conventional GIC did not show any dye uptake, presence of a "structureless" layer, or enamel cracking. We elucidated the potential mechanisms involved in the formation of a "structureless" interfacial layer in Fuji II LC by studying the variables of cavity design, surface pre-treatment, water content of the tooth, time for it to develop, early finishing, and coating of the restoration. This layer, the "absorption layer", is probably related to water flux within the maturing cement, depending on environmental moisture changes and communication with the pulp in a wet tooth. The "micropermeability model" was useful in this study of the interfacial characteristics of RM GICs.     

Effect of dietary calcium on blood lead concentrations in occupationally exposed and nonexposed workers

PURPOSE: Evaluation of night glare after excimer laser in situ keratomileusis (LASIK) using two different ablation zone diameters. METHODS: One hundred and twenty eyes of 60 consecutive myopic patients received LASIK with the Nidek EC-5000 excimer laser. Eyes were randomized so that every patient had a single ablation zone of 5.5 mm on one eye and an ablation zone of 5.5 mm with a transition zone of 1.0 mm diameter larger on the other eye. Night glare was measured by two methods; a spot light test and a subjective questionnaire. RESULTS: At 6 months, 54 patients (90%) were examined; results of the spot light test showed that 40 patients (74.1%) perceived more glare with the eye with the single ablation zone; the subjective questionnaire indicated that 22 patients (40.7%) had more night glare with the eye with a single ablation zone compared to the other eye. The use of the transition zone increased the required total ablation depth by 20%. CONCLUSION: The use of a peripheral transition 1.0 mm diameter larger than the ablation zone significantly decreased night glare after LASIK with slight increase in the required central ablation depth.     

Biocompatibility of Clearfil Liner Bond 2 and Clearfil AP-X system on nonexposed and exposed primate teeth

Females, especially older women, historically have been excluded from coronary heart disease (CHD) studies. The PrimeTime program was a randomized clinical trial designed to study the effects of a comprehensive lifestyle management program (very low-fat vegetarian diet, smoking cessation, stress-management training, moderate exercise, and group support) on changes in behavioral risk factors among postmenopausal women with CHD. The study also explored program effects on four psychosocial clusters: coping with stress, distress, social support, and self-efficacy. The program produced significant behavioral improvements in 4- and 12-months adherence to diet, physical activity, and stress-management in the PrimeTime women compared to the Usual Care (UC) group. In addition, the PrimeTime participants demonstrated improvements relative to UC on psychosocial measures of self-efficacy, perceived social support, and ability to cope with stress. Strengths and weaknesses of the study, and implications for future research are discussed.     

Comparison of conventional and resin-modified glass-ionomer luting cements in the retention of post-crowns by fatigue loading

This study reviews the results of circumferential fusion in patients with degenerative disc disease who are at high risk for achieving spinal fusion. The fusion rate was 100% and the satisfactory clinical outcome slightly more than 50% in a patient population known to have high risk factors for a poor outcome.     

The effect of a resin-modified glass ionomer restorative material on artificially demineralised dentine caries in vitro

OBJECTIVES: Recurrent caries is one of the most common reasons for the replacement of restorations. One method of reducing the frequency of this problem may be by using fluoride-releasing restorative materials. The aim of this in vitro study was to evaluate the progression of artificial lesions around resin-modified glass ionomer (Vitremer) restorations placed in root surfaces. Class V cavities were prepared on the mesial and distal surfaces of 28 human premolar teeth. Artificial carious wall lesions were created in all cavities. The root of each tooth was then hemisected through the middle of the two cavities, before being restored with either the glass ionomer or amalgam, while the opposing cavities on the same root portion were varnished as negative controls. Forty-eight specimens were pH-cycled in remineralising and demineralising solutions for 20 h and 4 h, respectively, each day for 4 weeks, whilst in a smaller control group of eight specimens, the demineralising solution was replaced with deionised water. Mineral changes in the carious lesions were evaluated using contact microradiography. RESULTS: Results showed that varying degrees of subsurface demineralisation and remineralisation were evident, with a laminated appearance in lesions adjacent to the glass ionomer. There was higher remineralisation in the glass ionomer-filled cavities compared with the amalgam-filled cavities. In the water-cycled group, glass ionomer showed an increase in mineral content (p < 0.05), while no changes were observed in the amalgam-filled cavities. CONCLUSIONS: This model has shown that glass ionomer has a greater potential than amalgam for remineralisation of artificially created wall lesions within an acidic environment.     

Using response models to study coding strategies in monkey visual cortex

Usually the conditional probabilities needed to calculate transmitted information are estimated directly from empirically measured distributions. Here we show that an explicit model of the relation between response strength (here, spike count) and its variability allows accurate estimates of transmitted information. This method of estimating information is reliable for data sets with nine or more trials per stimulus. We assume that the model characterizes all response distributions, whether observed in a given experiment or not. All stimuli eliciting the same response are considered equivalent. This allows us to calculate the channel capacity, the maximum information that a neuron can transmit given the variability with which it sends signals. Channel capacity is uniquely defined, thus avoiding the difficulty of knowing whether the 'right' stimulus set has been chosen in a particular experiment. Channel capacity increases with increasing dynamic range and decreases as the variance of the signal (noise) increases. Neurons in V1 send more variable signals in a wide dynamic range of spike counts, while neurons in IT send less variable signals in a narrower dynamic range. Nonetheless, neurons in the two areas have similar channel capacities. This suggests that variance is being traded off against dynamic range in coding.     

Primate pulpal response to ultraviolet light-polymerized direct-bonding material systems

The results of this study, plus those of a previous study, show that a layer of CaOH lining the floor of the tooth cavity will protect the dental pulp against toxic irritants inherent to an UV light-polymerized cavity liner and a UV light-polymerized composite restorative resin. This study also showed that a layer of CaOH lining the floor of the cavity will protect the dental pulp against acid irritants inherent in the enamel etching solution. It is recommended to restorative dentistry that all primary dentin within clinically accessible areas of the cavity preparation be covered with a layer of CaOH before the enamel is etched with the acid-conditioning solution. Precautionary protection of primary dentin in this manner affords a margin of safety should the conditioning solution inadvertently spill onto the primary dentin during the enamel-etching procedure. Second, if the conditioning solution does accidentally spill onto the previously placed protective layer of CaOH during the enamel-etching procedure, then it logically follows that this acid-contaminated layer of CaOH should be mechanically removed and a new layer of CaOH that completely lines at least the floor of the tooth cavity should be placed before the resins are applied.     

Human and monkey trabecular meshwork accumulate alpha B-crystallin in response to heat shock and oxidative stress

PURPOSE: Oxidative stress and other forms of injury to trabecular meshwork (TM) cells may contribute to changes seen with age and primary open-angle glaucoma. This study was designed to investigate if TM expresses alpha B-crystallin, a small heat-shock protein with chaperone activity, and whether it might be overexpressed under stress conditions. METHODS: The TM from human and monkey eyes, as well as organ and primary cell cultures derived from these eyes, were investigated for alpha B-crystallin by immunohistochemistry, two-dimensional gel electrophoresis, Northern and Western blot analysis. The TM cell cultures were stressed by heat shock (44 degrees C for 15 minutes) or hydrogen peroxide (200 mumol for 1 hour). Semiquantitation of alpha B-crystallin messenger RNA (mRNA) or protein was obtained by densitometry. RESULTS: In both species, alpha B-crystallin could be detected in fresh and cultured TM by two-dimensional gel electrophoresis in conjunction with Western blot analysis. Immunohistochemistry of fresh samples showed that alpha B-crystallin was expressed predominantly in the cribriform area. Protein expression was enhanced in 4- to 7-day organ cultures. Primary cultures from human TM cells expressed two sizes (approximately 0.8 and 1.1 kb) of alpha B-crystallin mRNA in Northern blots. In monkey TM cultures, a 0.8-kb band was observed, which comigrated with lens alpha B-crystallin. In both species, heat shock caused a significant increase in alpha B-crystallin mRNA with a peak after 4 hours. An increase in alpha B-crystallin mRNA also was observed after oxidative stress; however, the onset of mRNA induction was slower. After heat shock, but not after oxidative stress, a transient change in mRNA mobility was observed. Western dot blot analysis showed a 3.4-fold increase in protein 24 hours after heat shock and a 20-fold increase after 48 hours. No constitutive mRNA expression and only a minimal increase 4 hours after heat shock could be observed in simian virus 40 transformed cell lines from human TM. CONCLUSIONS: Overexpression of alpha B-crystallin might be an important mechanism for TM to prevent cellular damage associated with various stress conditions.     

Generalized temperature response charts for thick bodies exposed to radiative-convective heat transfer

Derivation of an approximate method enabling the utilization of existing temperature response charts for radiative environment for estimation of the response for radiation and convection. Application to heating-up of rectangular cross-section bodies. Error analysis for a certain relative value of the convective component. Criterion of applicability of the thermally thin body relations.     

The acoustoelastic response of a textured material during elastic-plastic deformation

Acoustoelasticity is a technique for the nondestructive evaluation of stress which relates changes in the speeds at which plane waves propagate through a solid to variations in the stress state. In the present work, the acoustoelastic behavior of a polycrystalline aggregate during elasticplastic deformation is investigated. Results are reported for a series of uniaxial tests in which the velocities of longitudinal and shear waves were monitored during elastic-plastic deformation of aluminum 5086-H32. A specific microstructural mechanism—the reorientation of grains due to plastic deformation—is investigated as a cause for the observed changes in acoustoelastic response which occur during elastic-plastic deformation. The Taylor theory analysis of the grain reorientation predicts velocity changes that are of the same sign and order of magnitude as the experimental results for shear waves but not for longitudinal waves.     

Viscous glass-ionomer cements: a new alternative to amalgam in the primary dentition?

Glass-ionomer cements offer advantages in the treatment of the primary dentition. New, colored, highly viscous glass-ionomer cements hold the promise of better abrasion properties. Owing to their high viscosity, their handling characteristics are similar to those of amalgam. Examination of their properties demonstrated increased resistance to abrasion in comparison to amalgam, although no improvement in fatigue or flexural resistance was found. Clinical experience extending over 2.5 years confirmed these results.     

Failure to learn to escape in rats previously exposed to inescapable shock depends on nature of escape response.

Results of previous studies show that dogs exposed to inescapable shocks in a Pavlov harness subsequently fail to learn to escape shock in a shuttle box. The present 6 experiments attempted to replicate this finding with male Sprague-Dawley rats (N = 182). In agreement with many previous investigations, Exp I found that Ss exposed to inescapable shock did not fail to learn to escape in a shuttle box. Exp II, III, and IV varied the number, intensity, and temporal interval between inescapable shocks and did not find failure to learn in the shuttle box. An analysis of responding in the shuttle box revealed that Ss shuttled rapidly from the very 1st trial, whereas dogs acquire shuttling more gradually. Exp V and VI revealed that Ss exposed to inescapable shock failed to learn to escape when the escape response was one that was acquired more gradually. Exp V utilized a double crossing of the shuttle box as the escape response and Exp VI utilized a wheel-turn response. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age differences in response to conformity pressure for emotional and nonemotional material.

Most theories of social influence do not consider adult development. Theoretical and empirical work in life span developmental psychology, however, suggests that age may reduce susceptibility to social influence. The present study examined age differences in social conformity for 2 classes of stimuli: judgments of geometric shapes and emotional facial expressions. As predicted, older people, compared with their younger counterparts, displayed lower rates of social conformity, and this age difference was most evident when judging emotional facial expressions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of the T cell-independent antibody response of mice and rats exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

In a prospective population-based cohort study, we assessed whether bone mineral density (BMD) measurements of perimenopausal women and other risk factors for osteoporosis are predictive of subsequent fracture. Women aged 47-51 years chosen randomly from a population register who underwent a bone density measurement 2 years previously were followed up by questionnaire to assess the 2-year incidence of any self-reported fractures. We found that 44 women, out of 1857 who completed the questionnaire, sustained at least one fracture within a 2-year follow-up period. After adjustment for covariates, the odds ratio of sustaining a fracture was 1.6 (95% confidence interval [CI] 1.16-2.34) for every standard deviation reduction in BMD at the spine, for women with a prior history of fracture the odds ratio of a subsequent fracture was approximately 2 (95% CI 1.31-3.03), a family history of hip fracture (maternal grandmother) carried an odds ratio of 3.7 (95% CI 1.55-8.85), while being postmenopausal or having a hysterectomy resulted in an odds ratio of 1.98 (1.02-3.56). This study has shown that BMD measurements at the hip and spine and other risk factors predict any nonhip and nonspine perimenopausal fractures. Further follow-up is required to assess the predictive performance of BMD measurements and other risk factors for hip and spine fractures.     

Cell vs. noncell airway temporal response in rats exposed to sulfur dioxide

A modification of the sulfur dioxide (SO2)-exposed rat model proposed by Reid for the study of chronic bronchitis was employed to evaluate mucus retention and cytologic changes. Rats were exposed to from 600 to 700 ppm of SO2 for 3 hours per day, and groups were examined after 0, 9, 18, and 30 hours of cumulative exposure. Tracheal mucus retention and statistically significant increases (two- to four-fold) in the amount of solid material (cellular and mucus) recovered by bronchia lavage developed as a function of exposure time. The increase in bronchial solids was primarily due to inflammatory cells. The goblet cell population in secondary bronchi declined initially, with a significant increase after 30 hours of exposure (P less than .001). The cytologic data provide additional support to Reid's suggestion that the SO2-exposed rat may be considered as a chronic bronchitis model.     

Effect of moisture protective coatings on the strength of a modern metal-reinforced glass-ionomer cement

The strength of a modern, low metal:glass ratio, metal-reinforced glass-ionomer cement was measured evaluating a number of protective barriers: one light-cured resin, two solvent-based dental varnishes and petroleum jelly. The cement was exposed to water at 10 and 60 min from start of mix. The results obtained with these protecting agents were compared with those obtained where no protection was applied. A comparison of uniaxial flexural strength and biaxial flexural strength showed the latter to be more discriminating. Proprietary dental varnishes were superior to petroleum jelly, producing similar strengths of 50 MPa. Petroleum jelly was, however, preferable to no protection. Moisture protection during the first 30 min was found to be beneficial, thereafter no further strength increase was found. A second material, a cement which has a high metal:glass ratio, was found to be more moisture resistant but weaker in strength than the modern material, with a biaxial strength of 39 MPa.     

Antibody response patterns against Schistosoma mansoni in a recently exposed community in Senegal

Acquired immune resistance is believed to be largely responsible for age-dependent infection and reinfection patterns in schistosomiasis. In a recently established but intense focus of Schistosoma mansoni in Senegal, the humoral immune response was studied in a random population sample of 289. Antibody levels of various isotypes to schistosome worm and egg antigens were determined by ELISA and related to egg counts (eggs per gram of feces [EPG]), age, and sex. Both IgG1 and IgG4 followed age-related patterns similar to egg counts and strongly correlated with EPG, even after allowing for age. Specific IgE levels increased slowly with age. The humoral immune response patterns in this recently infected population appeared to be largely similar to those in chronically infected communities. Thus far, the observations do not support the current hypothesis that age-related resistance to Schistosoma is determined by IgE-mediated protective immunity acquired during many years of exposure.