Bleached Area Research Articles

Selective Roles for Cholesterol and Actin in Compartmentalization of Different Proteins in the Golgi and Plasma Membrane of Polarized Cells

To determine the roles of cholesterol and the actin cytoskeleton in apical and basolateral protein organization and sorting, we have performed comprehensive confocal fluorescence recovery after photobleaching analyses of apical and basolateral and raft- and non-raft-associated proteins, both at the plasma membrane and in the Golgi apparatus of polarized MDCK cells. We show that at both the apical and basolateral plasma membrane domains, raft-associated proteins diffuse faster than non-raft-associated proteins and that, different from the latter, they become restricted upon depletion of cholesterol. Furthermore, only transmembrane apical proteins are restricted by the actin network. This indicates that cholesterol-dependent domains exist both at the apical and basolateral membranes of polarized cells and that the actin cytoskeleton has a predominant role in the organization of transmembrane proteins independent of their association with rafts at the apical membrane. In the Golgi apparatus apical proteins appear to be segregated from the basolateral ones in a compartment that is sensitive both to cholesterol depletion and actin rearrangements. Furthermore, consistent with the role of actin rearrangements in apical protein sorting, we found that apical proteins exhibit a differential sensitivity to actin depolymerization in the Golgi of polarized and nonpolarized cells.

Colonization and decomposition of salal (Gaultheria shallon) leaf litter by saprobic fungi in successional forests on coastal British Columbia

The colonization of leaf litter by saprobic fungi was studied in old-growth and post-harvest successional Douglas-fir forests on southeast Vancouver Island, British Columbia. This study focused on leaf litter of salal (Gaultheria shallon Pursh.), a dominant understory shrub in all stands. Salal litter is characterized by the occurrence of bleached portions attributable to fungal colonization of the litter and to the variable decomposition of recalcitrant compounds, such as lignin. Analyses of proximate chemical fractions, fungal assemblages on the bleached leaf area, and pure culture decomposition assays indicated that Marasmius sp. and Coccomyces sp. were responsible for rapid decomposition and bleaching of salal leaf litter. The bleached area accounted for 17%-22% of total area of salal leaf litter collected in immature (40-60 years old), mature (85-105 years old), and old-growth (more than 290 years old) stands, but for only 2% in regeneration (5-15 years old) stands. The reduction of bleached leaf area occupied by Marasmius sp. and Coccomyces sp. in regeneration stands could be due to the changes in microenvironmental conditions on the forest floor, in litter quality, or in food-web structure in soils. The decrease of fungi able to decay recalcitrant compounds may lead to a reduction of salal decomposition rates in clear-cut sites that would persist until canopy closure occurs.

The Effect of Debonding and/or Bleaching on Enamel Color – an In-vitro Study

There are various studies in the literature on bonding brackets to bleached teeth and on the effect of bleaching material on the color of compomers. The purpose of this study was to investigate changes in tooth color depending on the process of bonding - debonding and/or bleaching. Ninety crowns of lower bovine permanent incisors were divided into nine subgroups. Three bonding materials (chemical, light- and pressure-cured) and three bleaching materials (15% CP, 35% CP, or 38% HP) were applied to the teeth, whereby each tooth was divided into quarters: untreated, bleached only, bonded-debonded only, and bleached after a bonding-debonding procedure. The Easyshade spectrophotometer was used to determine CIELCh coordinates (lightness, color, and hue) three times for each area. The areas' differences in color were expressed as the Euclidian distance DeltaE. Four examiners (two orthodontists and two dentists) rated each tooth concerning color differences in the four areas. The data collected was subjected to the sign and Wilcoxon or the Kruskal-Wallis and Mann-Whitney U tests using the SPSS 12.0 program. Examiners found significant differences between those areas with and those without bleaching within each group of specimens (p < 0.05), but there were no differences concerning the bonding and debonding procedures (p > 0.05). Furthermore, digital tooth-shade measurements revealed no statistically-significant group-associated differences between those areas treated with bonding material and those not so treated, nor between bonded and debonded areas (p > 0.05). Nor did we observe any statistically-significant differences between bleached areas and those areas bleached after bonding and debonding procedures (p > 0.05). The processes of bonding and debonding alone do not seem to have any statistically-significant influence on the tooth color of bovine enamel using these testing materials, nor does the subsequent bleaching procedure.

Fungal colonization and decomposition ofCastanopsis sieboldiileaves in a subtropical forest

AbstractFungi play a crucial role in the decomposition of lignin in fallen leaves but few studies have examined the functional roles of ligninolytic fungi associated with the decomposition of fallen leaves on tropical forest soils. This study examined fungal populations responsible for lignin decomposition inCastanopsis sieboldiileaves in a subtropical evergreen broad‐leaved forest in southern Japan. Fallen leaves ofC. sieboldiiare characterized by the occurrence of bleached portions attributable to fungal colonization of leaf tissues and decomposition of lignin. The bleached area accounted for 29.7%, on average, of the total area ofC. sieboldiifallen leaves in the study site. Leaf mass per unit area (LMA) and lignin content were lower in the bleached area than in the surrounding nonbleached area of the same leaves, indicating that removal of lignin enhanced mass loss from leaf tissues and created small‐scale heterogeneity of decomposition within single leaves. An unidentified species of Lachnocladiaceae (Basidiomycetes) was isolated frequently from the bleached area and caused selective decomposition of lignin in leaves under pure culture conditions, indicating that this fungus was responsible for the bleaching. The greater hyphal length of basidiomycetes in the bleached area than in the nonbleached area supported the finding that this Lachnocladiaceae sp. was associated with the bleaching. The relatively rapid decomposition ofC. sieboldiileaves on the subtropical forest soil is partly attributable to colonization of the litter by this Lachnocladiaceae sp.

PARP1-dependent Kinetics of Recruitment of MRE11 and NBS1 Proteins to Multiple DNA Damage Sites

Poly(ADP-ribose) polymerase 1 (PARP1) is a nuclear enzyme that is rapidly activated by DNA strand breaks and signals the presence of DNA lesions by attaching ADP-ribose units to chromatin-associated proteins. The therapeutic applications of PARP inhibitors in potentiating the killing action of ionizing radiation have been well documented and are attracting increasing interest as a cancer treatment. However, the initial kinetics underlying the recognition of multiple DNA lesions by PARP1 and how inhibition of PARP potentiates the activity of DNA-damaging agents are unknown. Here we report the spatiotemporal dynamics of PARP1 recruitment to DNA damage induced by laser microirradiation in single living cells. We provide direct evidence that PARP1 is able to accumulate at a locally induced DNA double strand break. Most importantly, we observed that the rapid accumulation of MRE11 and NBS1 at sites of DNA damage requires PARP1. By determining the kinetics of protein assembly following DNA damage, our study reveals the cooperation between PARP1 and the double strand break sensors MRE11 and NBS1 in the close vicinity of a DNA lesion. This may explain the sensitivity of cancer cells to PARP inhibitors.

Platelet-Platelet Fusion Results from Fusing of Plasma Membranes and Is Augmented by Stimulation through PAR1 or CCR4.

Cell-cell fusion occurs between many cell types including hematopoietic stem cells and macrophages. Fusion between platelets has been proposed based on both early and more recent studies using light and electron microscopy, but these approaches have lead to conflicting conclusions. We addressed the question of whether or not mature platelets are capable of fusing with one another using videomicroscopy, fluorescence recovery after photobleaching (FRAP), and dye transfer studies. Studies using time-lapse DIC videomicroscopy revealed a process whereby lamellipodia of two adjacent platelets grow towards each other and develop contact points. Fusion of adjacent membranes subsequently occurs between contact points until the two platelets appear as one large platelet with two granulomeres. For studies using FRAP, DiO-labeled platelets were plated densely on coverslips and a laser was used to photobleach areas of approximately 6 x 4 μm2 within collections of large platelets with multiple granulomeres. Following photobleaching, recovery of fluorescence into the bleached areas and loss of fluorescence from areas outside the bleached portions was monitored. Fluorescence recovered within the photobleached areas to 90.4 ± 2.1% of baseline, along with a concomitant loss of fluorescence from adjacent areas. In contrast, FRAP was not observed following similar photobleaching of single platelets or of adjacent platelets without morphologic evidence of fusion. Dye transfer studies were used to determine whether cytosolic mixing occurred between platelets following fusion of membranes. Platelets were labeled with CMFDA, a thiol-reactive, cell-permeant dye that associates with cytosolic proteins. The diffusion of CMFDA from labeled platelets to unlabeled platelets was quantified using digital fluorescence microscopy. Plating of unlabeled platelets with CMFDA-labeled platelets resulted in a markedly increased radius of diffusion of fluorescence and a decrease in average mean fluorescence intensity in CMFDA-labeled platelets. In contrast, mean fluorescence intensity did not change over time when CMFDA-labeled platelets were plated in buffer alone or when CMFDA-labeled platelets were fixed with paraformaldehyde prior to incubation with unlabeled platelets. Diffusion of CMFDA increased in a linear fashion by 4.3 ± 0.9-fold as the density of unlabeled platelets increased from 5 x 103 to 8 x 104 platelets/mm2. The diffusion of CMFDA increased by 7.8 ± 1.4-fold when platelets were activated using SFLLRN, a peptide that stimulates platelets via the thrombin receptor PAR1. Diffusion of CMFDA to unlabeled platelets also increased following incubation of platelets with thrombin or macrophage-derived chemokine (MDC), which stimulates through the chemokine (C-C motif) receptor 4. Time course studies using thrombin- and MDC-stimulated platelets showed that dye transfer to unlabeled platelets was detected 1 h after plating and increased in a linear manner for 6 h. No further diffusion of CMFDA occurred from 6 to 24 h incubation. These studies show that membrane fusion with mixing of cytosolic contents occurs between mature platelets. Platelet-platelet fusion is a relatively slow event and is significantly augmented by physiologic platelet agonists including thrombin and MDC. Platelet-platelet fusion may function in remodeling thrombi that form following vascular injury.

CD4 Interacts Constitutively with Multiple CCR5 at the Plasma Membrane of Living Cells

The entry of human immunodeficiency virus into target cells requires successive interactions of the viral envelope glycoprotein gp120 with CD4 and the chemokine receptors CCR5 or CXCR4. We previously demonstrated, by Förster resonance energy transfer experiments, the constitutive association of CD4 and CCR5 at the surface of living cells. We therefore speculated that this interaction may correlate with compartmentalization of CD4 and CCR5 within the plasma membrane. Here, we characterize the lateral distribution, the dynamics, and the stoichiometry of these receptors in living cells stably expressing CD4 and/or CCR5 by means of fluorescence recovery after photobleaching at variable radii experiments. We found that (i) these receptors expressed alone are confined into 1-microm-sized domains, (ii) CD4-CCR5 associations occur outside and inside smaller domains, and (iii) these interactions involve multiple CCR5 molecules per CD4.

Heterodimerization with Jun Family Members Regulates c-Fos Nucleocytoplasmic Traffic

c-Fos proto-oncoprotein forms AP-1 transcription complexes with heterodimerization partners such as c-Jun, JunB, and JunD. Thereby, it controls essential cell functions and exerts tumorigenic actions. The dynamics of c-Fos intracellular distribution is poorly understood. Hence, we have combined genetic, cell biology, and microscopic approaches to investigate this issue. In addition to a previously characterized basic nuclear localization signal (NLS) located within the central DNA-binding domain, we identified a second NLS within the c-Fos N-terminal region. This NLS is non-classic and its activity depends on transportin 1 in vivo. Under conditions of prominent nuclear localization, c-Fos can undergo nucleocytoplasmic shuttling through an active Crm-1 exportin-independent mechanism. Dimerization with the Jun proteins inhibits c-Fos nuclear exit. The strongest effect is observed with c-Jun probably in accordance with the relative stabilities of the different c-Fos:Jun dimers. Retrotransport inhibition is not caused by binding of dimers to DNA and, therefore, is not induced by indirect effects linked to activation of c-Fos target genes. Monomeric, but not dimeric, Jun proteins also shuttle actively. Thus, our work unveils a novel regulation operating on AP-1 by demonstrating that dimerization is crucial, not only for active transcription complex formation, but also for keeping them in the compartment where they exert their transcriptional function.

N-Methyl-d-aspartate (NMDA) Receptor Subunit NR1 Forms the Substrate for Oligomeric Assembly of the NMDA Receptor

The time course of the assembly of the N-methyl-D-aspartate receptor was examined in a cell line expressing it under the control of the dexamethasone promoter. These studies suggested a delay between the appearance of the NR1 and NR2A subunits and their stable association as examined by co-immunoprecipitation of NR1 and NR2A. This prompted us to examine the stability and folding of the individual subunits using nonreduced polyacrylamide gels and the sulfhydryl cross-linker BMH. Both studies showed that the NR1 subunit was expressed in a monomer and dimer form, whereas both NR2 and NR3 showed substantial aggregation on both nonreduced gels and after cross-linking. Protein degradation experiments showed that NR1 was relatively stable, whereas NR2 and NR3 were more rapidly degraded. When co-expressed with NR1, NR2 was more stable. Fluorescence recovery after photobleaching experiments showed that, under conditions of reduced ATP, the diffusion rate of NR2 and NR3 in the endoplasmic reticulum was reduced, whereas that of NR1 was unaffected. Together these data show that NR1 folds stably when expressed alone, unlike NR2 and NR3, and provides the substrate for assembly of the N-methyl-D-aspartate receptor.

Demonstration of phycobilisome mobility by the time- and space-correlated fluorescence imaging of a cyanobacterial cell

The cell-wide mobility of PBSs was confirmed by synchronously monitoring the fluorescence recovery after photobleaching (FRAP) and the fluorescence loss in photobleaching (FLIP). On the other hand, a fluorescence recovery was still observed even if PBSs were immobile (PBSs fixed on the membranes by betaine and isolated PBSs fixed on the agar plate) or PBS mobility was unobservable (cell wholly bleached). Furthermore, it was proved that some artificial factors were involved not only in FRAP but also in FLIP, including renaturation of the reversibly denatured proteins, laser scanning-induced fluorescence loss and photo-damage to the cell. With consideration of the fast renaturation component in fluorescence recovery, the diffusion coefficient was estimated to be tenfold smaller than that without the component. Moreover, it was observed that the fluorescence intensity on the bleached area was always lower than that on the non-bleached area, even after 20 min, while it should be equal if PBSs were mobile freely. Based on the increasing proportion of the PBSs anti-washed to Triton X-100 (1%) with prolonged laser irradiation to the cells locked in light state 1 by PBQ, it was concluded that some PBSs became immobile due to photo-linking to PSII.

Myelin basic protein-dependent plasma membrane reorganization in the formation of myelin

During vertebrate development, oligodendrocytes wrap their plasma membrane around axons to produce myelin, a specialized membrane highly enriched in galactosylceramide (GalC) and cholesterol. Here, we studied the formation of myelin membrane sheets in a neuron-glia co-culture system. We applied different microscopy techniques to visualize lipid packing and dynamics in the oligodendroglial plasma membrane. We used the fluorescent dye Laurdan to examine the lipid order with two-photon microscopy and observed that neurons induce a dramatic lipid condensation of the oligodendroglial membrane. On a nanoscale resolution, using stimulated emission depletion and fluorescence resonance energy transfer microscopy, we demonstrated a neuronal-dependent clustering of GalC in oligodendrocytes. Most importantly these changes in lipid organization of the oligodendroglial plasma membrane were not observed in shiverer mice that do not express the myelin basic protein. Our data demonstrate that neurons induce the condensation of the myelin-forming bilayer in oligodendrocytes and that MBP is involved in this process of plasma membrane rearrangement. We propose that this mechanism is essential for myelin to perform its insulating function during nerve conduction.

Evaluación de la mezcla de ametrina + clomazone en caña de azúcar.

An experiment was established at Rancho Casablanca, located in the Municipality of Puente Nacional, in the State of Veracruz, Mexico, in order to evaluate the toxicity caused by the mixture of the herbicides ametryn + clomazone to the sugarcane varieties MEX-79-431, MEX- 69-290, MEX-68-P23 and CP-72-2086. Four weed control treatments were evaluated: 1. Ametryn + clomazone (1200 + 800 g/ha), 2. Ametryn + clomazone (1800 + 1200 g/ha), 3. Ametryn + 2,4-D (1225 + 650 g/ha) and 4. Weeded control. Herbicides were applied when sugarcane plants had from two to four leaves. The mixture of ametryn + clomazone caused leaf bleaching in all the sugarcane varieties. The bleached area varied from 36.3 to 47.5% with the highest dose of the mixture, and from 25 to 39.4%, with the lowest dose, and it practically disappeared about 45 days after application. On the other hand, the mixture of ametryn + 2,4-D did not cause any bleaching. Toxicity caused by the mixture of ametryn + clomazone did not affect the number of plant leaves, the number of stalks in 2 linear m, nor the plant height. Stalk yield and sucrose content were not affected either.

A hyper-dynamic equilibrium between promoter-bound and nucleoplasmic dimers controls NF-κB-dependent gene activity

Because of its very high affinity for DNA, NF-kappaB is believed to make long-lasting contacts with cognate sites and to be essential for the nucleation of very stable enhanceosomes. However, the kinetic properties of NF-kappaB interaction with cognate sites in vivo are unknown. Here, we show that in living cells NF-kappaB is immobilized onto high-affinity binding sites only transiently, and that complete NF-kappaB turnover on active chromatin occurs in less than 30 s. Therefore, promoter-bound NF-kappaB is in dynamic equilibrium with nucleoplasmic dimers; promoter occupancy and transcriptional activity oscillate synchronously with nucleoplasmic NF-kappaB and independently of promoter occupancy by other sequence-specific transcription factors. These data indicate that changes in the nuclear concentration of NF-kappaB directly impact on promoter function and that promoters sample nucleoplasmic levels of NF-kappaB over a timescale of seconds, thus rapidly re-tuning their activity. We propose a revision of the enhanceosome concept in this dynamic framework.

Organization of Calcium Channel β1a Subunits in Triad Junctions in Skeletal Muscle

In skeletal muscle, dihydropyridine receptors (DHPRs) in the plasma membrane interact with the type 1 ryanodine receptor (RyR1) at junctions with the sarcoplasmic reticulum. This interaction organizes junctional DHPRs into groups of four termed tetrads. In addition to the principle alpha1S subunit, the beta1a subunit of the DHPR is also important for the interaction with RyR1. To probe this interaction, we measured fluorescence resonance energy transfer (FRET) of beta1a subunits labeled with cyan fluorescent protein (CFP) and/or yellow fluorescent protein (YFP). Expressed in dysgenic (alpha1S-null) myotubes, YFP-beta1a-CFP and CFP-beta1a-YFP were diffusely distributed in the cytoplasm and highly mobile as indicated by fluorescence recovery after photobleaching. Thus, beta1a does not appear to bind to other cellular proteins in the absence of alpha1S. FRET efficiencies for these cytoplasmic beta1a subunits were approximately 6-7%, consistent with the idea that <10 nm separates the N and C termini. After coexpression with unlabeled alpha1S (in dysgenic or beta1-null myotubes), both constructs produced discrete fluorescent puncta, which correspond to assembled DHPRs in junctions and that did not recover after photobleaching. In beta1-null myotubes, FRET efficiencies of doubly labeled beta1a in puncta were similar to those of the same constructs diffusely distributed in the cytoplasm and appeared to arise intramolecularly, since no FRET was measured when mixtures of singly labeled beta1a (CFP or YFP at the N or C terminus) were expressed in beta1-null myotubes. Thus, DHPRs in tetrads may be arranged such that the N and C termini of adjacent beta1a subunits are located >10 nm from one another.

Destruction of chlorophyll in emerging seedlings of spring barley associated with environmental stresses

An unusual disorder occurred on spring barley seedlings in southern and central Bohemia in April 2005. Affected seedlings showed conspicuous bleached or straw-coloured areas on tips of the first leaves. There were very sharp, distinct, horizontal boundaries between the green basal and discoloured tip parts of the leaves. It was remarkable that these boundaries were at the same position on all affected first leaves of seedlings from the same field. Affected seedlings were randomly distributed in the fields, and their incidence ranged from about 20&amp;nbsp;to 70% according to location. Based on meteorological data it can be concluded that the colour abnormality in emerging seedlings was associated with specific environmental stresses, being effective in certain chronological order on sensitive plant tissues during the period from 6 to 8 days after seeding. These stresses include frosty mornings followed by clear days with high solar radiation with a high UV Index.

Effects of Organelle Shape on Fluorescence Recovery after Photobleaching

The determination of diffusion coefficients from fluorescence recovery data is often complicated by geometric constraints imposed by the complex shapes of intracellular compartments. To address this issue, diffusion of proteins in the lumen of the endoplasmic reticulum (ER) is studied using cell biological and computational methods. Fluorescence recovery after photobleaching (FRAP) experiments are performed in tissue culture cells expressing GFP–KDEL, a soluble, fluorescent protein, in the ER lumen. The three-dimensional (3D) shape of the ER is determined by confocal microscopy and computationally reconstructed. Within these ER geometries diffusion of solutes is simulated using the method of particle strength exchange. The simulations are compared to experimental FRAP curves of GFP–KDEL in the same ER region. Comparisons of simulations in the 3D ER shapes to simulations in open 3D space show that the constraints imposed by the spatial confinement result in two- to fourfold underestimation of the molecular diffusion constant in the ER if the geometry is not taken into account. Using the same molecular diffusion constant in different simulations, the observed speed of fluorescence recovery varies by a factor of 2.5, depending on the particular ER geometry and the location of the bleached area. Organelle shape considerably influences diffusive transport and must be taken into account when relating experimental photobleaching data to molecular diffusion coefficients. This novel methodology combines experimental FRAP curves with high accuracy computer simulations of diffusion in the same ER geometry to determine the molecular diffusion constant of the solute in the particular ER lumen.

Determining Diffusion Coefficients in Inhomogeneous Tissues Using Fluorescence Recovery after Photobleaching

Diffusion plays an important role in the transport of nutrients and signaling molecules in cartilaginous tissues. Diffusion coefficients can be measured by fluorescence recovery after photobleaching (FRAP). Available methods to analyze FRAP data, however, assume homogeneity in the environment of the bleached area and neglect geometrical restrictions to diffusion. Hence, diffusion coefficients in inhomogeneous materials, such as most biological tissues, cannot be assessed accurately. In this study, a new method for analyzing data from FRAP measurements has been developed, which is applicable to inhomogeneous tissues. It is based on a fitting procedure of the intensity recovery after photobleaching with a two-dimensional finite element analysis, which includes Fick's law for diffusion. The finite element analysis can account for distinctive diffusivity in predefined zones, which allows determining diffusion coefficients in inhomogeneous samples. The method is validated theoretically and experimentally in both homogeneous and inhomogeneous tissues and subsequently applied to the proliferation zone of the growth plate. Finally, the importance of accounting for inhomogeneities, for appropriate assessment of diffusivity in inhomogeneous tissues, is illustrated.

PH-dependent Intraluminal Organization of Mucin Granules in Live Human Mucous/Goblet Cells

To study the mechanism of gel-forming mucin packaging within mucin granules, we generated human mucous/goblet cells stably expressing a recombinant MUC5AC domain fused to green fluorescent protein (GFP). The fusion protein, named SHGFP-MUC5AC/CK, accumulated in the granules together with native MUC5AC. Inhibition of protein synthesis or disorganization of the Golgi complex did not result in diminished intragranular SHGFP-MUC5AC/CK signals, consistent with long-term storage of the fusion protein. However, SHGFP-MUC5AC/CK was rapidly discharged from the granules upon incubation of the cells with ATP, an established mucin secretagogue. Several criteria indicated that SHGFP-MUC5AC/CK was not covalently linked to endogenous MUC5AC. Analysis of fluorescence recovery after photobleaching suggested that the intragranular SHGFP-MUC5AC/CK mobile fraction and mobility were significantly lower than in the endoplasmic reticulum lumen. Incubation of the cells with bafilomycin A1, a specific inhibitor of the vacuolar H+-ATPase, did not alter the fusion protein mobility, although it significantly increased (approximately 20%) the intragranular SHGFP-MUC5AC/CK mobile fraction. In addition, the granules in bafilomycin-incubated cells typically exhibited a heterogeneous intraluminal distribution of the fluorescent fusion protein. These results are consistent with a model of mucin granule intraluminal organization with two phases: a mobile phase in which secretory proteins diffuse as in the endoplasmic reticulum lumen but at a lower rate and an immobile phase or matrix in which proteins are immobilized by noncovalent pH-dependent interactions. An intraluminal acidic pH, maintained by the vacuolar H+-ATPase, is one of the critical factors for secretory protein binding to the immobile phase and also for its organization.

Stable and erasable patterning of vanadium pentoxide thin films by atomic force microscope nanolithography

Long lasting colored pattern formation on sol–gel deposited vanadium pentoxide (V2O5) thin films is demonstrated by atomic force microscope (AFM) nanolithography. The films can be locally colorized by application of a positive dc bias voltage on the conductive AFM tip. The patterns can be erased, or “bleached,” by application of a negative bias voltage. The changes in optical reflectivity, topography, and conductivity measurements made on as-deposited, colored, and bleached areas were consistent with a model in which the incorporation of hydrogen ions into V2O5 thin films is responsible for the coloration process.

The effect of bleaching on enamel susceptibility to acid erosion and demineralisation

The purpose of this in vitro study was to determine if enamel that had been bleached by carbamide (urea) peroxide gel (CPG) was at increased risk of either acid erosion or demineralisation (early caries) than un-bleached enamel. Human incisors were employed. The samples were randomly assigned to one of 4 groups; a) 10% CPG, b) 16% CPG, c) 22% CPG and d) 10% CPG with xylitol, fluoride and potassium. Each specimen was moistened with saliva and the appropriate formulation placed for 2 hours for a total of 40 hours of exposure. In order to ensure that bleaching had taken place, tooth shades were monitored using the Shade-Eye device. Following the bleaching process, one half of the specimen was subjected to an erosive challenge, the other to a demineralisation system with one half of each sub-sample retained as a non-bleached control. Samples were assessed longitudinally with quantitative light-induced fluorescence (QLF) and at the conclusion of the study with transverse micro-radiography (TMR). Erosion was detected in all samples (DeltaQ 126+/-23.4), in both bleached and non-bleached areas. There was no statistical difference between the bleached and non-bleached areas either within the treatment groups or between them. Caries-like lesions were detected on all samples; TMR revealed sub-surface lesions on all teeth and QLF data supported this (DeltaQ 89+/-18.9). Following statistical analysis there were no differences detected between the bleached and non-bleached areas, nor between the different concentrations of the bleaching solution. These results suggest that tooth bleaching with carbamide (urea) peroxide (using commercially available concentrations) does not increase the susceptibility of enamel to acid erosion or caries.