Oxidative dissolution of Sb2O3 mediated by surface Mn redox cycling in oxic aquatic systems

Antimony trioxide (Sb₂O₃) is one of the primary forms of Sb in the environment, and its dissolution significantly impacts the migration and bioavailability of Sb. However, the dissolution of Sb₂O₃ coupled with abiotic redox of Mn processes is unclear. Here, we investigated the kinetics of Sb₂O₃ dissolution in the presence of the ubiquitous Mn(II) by kinetic experiments, spectroscopies, density functional theory calculations and the chemical kinetic modeling. The oxidative dissolution of Sb₂O₃ was catalyzed by Mn(II) through the in-situ generated amorphous Mn oxides (MnO_x) under oxic conditions, during which the generation of Mn(III) is a critical step in Sb(V) release. The released Sb(V) was partially retained on MnO_x through bidentate-binuclear (corner-sharing) complexes as revealed by extended X-ray absorption fine structure analysis. The coexistent morphological forms of Sb₂O₃, i.e., senarmontite and valentinite exhibited distinct dissolution patterns. Valentinite showed higher activity in catalyzing Mn(II) oxidation and faster oxidative dissolution than senarmontite, due to its higher surface energy and lower conduction band minimum of its exposed facets. These abiotic processes can extrapolate to other metal(loid)s (hydr)oxides, further supplying for the comprehensive understanding of the redox transformation of Mn.

Unraveling the molecular mechanisms of Cd sorption onto MnOx-loaded biochar produced from the Mn-hyperaccumulator Phytolacca americana

Engineered biochar represents a promising material for green remediation practices. In this paper, we present an innovative approach to produce MnO_x-loaded biochars by pyrolyzing the biomass of a Mn-hyperaccumulator species (Phytolacca americana). Batch sorption and stirred-flow kinetic experiments were combined with spectroscopic techniques to elucidate the mechanisms behind the Cd sorption onto those biochars, named here as PABCs. The incorporation of MnO_x into the PABCs increased their surface densities of oxygen-containing functional groups. The average Mn leaching (< 9%) from PABCs was lower than that measured for the non-pyrolyzed biomass of P. americana (30-43%). PABCs pyrolyzed at 500 °C had Cd sorption capacities as high as 212-337 mg/g, which achieved by far the best performance reported for biochar materials. The stirred-flow experiments showed that MnO_x loading was instrumental in increasing both the Cd sorption onto PABCs as well as its irreversibility. Extended X-ray absorption fine structure spectroscopy revealed that the Cd immobilization occurred mainly through its association with organic matter (Cd-OM) and, to a lesser extent, with carbonate (CdCO₃) and MnO_x (Cd-MnO_x). In short, MnO_x-loaded biochar prepared from the biomass of a Mn-hyperaccumulator species proved to be an effective, sustainable, and eco-friendly material for remediating Cd-contaminated waters.

Combining multisurface model and Gouy-Chapman-Stern model to predict cadmium uptake by cabbage (Brassica Chinensis L.) in soils

Cadmium is an extremely toxic substance known to cause serious health problems. The uptake of Cd in plants is critically affected by dissolved Cd in soil porewater, controlled by soil physicochemical properties. Rhizo-availability of Cd is assumed, as the Cd fraction is found on the plasma membrane of surface root cells. Based on the theory of Cd transformation in soil-crop systems, we established a novel combined mechanistic model related to soil, soil solutions, and crops. The combined model comprises a multisurface model (MSMs; solid adsorbent and porewater) and the Gouy-Chapman-Stern model (GCS; porewater and root surface). The results suggested that in mildly contaminated soil samples, optimum prediction was achieved when DTPA-extractable Cd was used as input variable (R² = 0.723). Our approach was superior to single-step model calculation (MSMs: R² = 0.613; GCS: R² = 0.629) and prediction based on extractable soil Cd (R² = 0.281). Introducing DTPA extraction expanded the range of model applications at different soil pHs. Our proposed mechanism model was based on soil physicochemical properties for Cd migration from soil to cabbage. Our model showed promise in predicting Cd bioavailability in soil with a wide pH range and evaluating soil risk near the standard Cd safety level.

Long-term dissolution and transformation of ZnO in soils: The roles of soil pH and ZnO particle size

The ongoing use of ZnO nanoparticles (NPs)-associated commercial products results in large release of ZnO NPs into soils and has prompted systematic investigation regarding their fractionation and fate in soils. To date, little information is available about the long-term dissolution and transformation of ZnO NPs in different soils. The distribution and speciation of Zn in two different soils (i.e., Red soil (RS) and Wushantu soil (WS)) treated with either ZnO NPs or bulk ZnO were elucidated by combining soil incubation study with synchrotron-based techniques. Results revealed that ZnO NPs and bulk ZnO were almost dissolved after 1 day, indicating their rapid dissolution upon entering RS (pH-acidic). Rapid dissolution of ZnO NPs was also observed even in WS (pH- circumneutral). The solubilized Zn²⁺ released from ZnO particles was completely transformed into stable forms (e.g., Zn-Al LDH, Zn-OM, and Zn(OH)₂) and Zn-Al LDH was the dominant species in WS after incubation for 360 days. A majority of solubilized Zn²⁺ released from ZnO particles was also transformed into Zn-Al LDH precipitate in RS. The findings of this study facilitate a better understanding of the fate of ZnO in soils, which could be leveraged for remediation of ZnO-polluted soils.

Role of Reduced Sulfur in the Transformation of Cd(II) Immobilized by δ-MnO2

Mn oxides are the major sinks for Cd(II) in the aquatic environment. At the redox interface, reduced sulfur might affect the fate of sorbed Cd(II) by either reducing Mn oxides or forming strong complexes with Cd(II). Here, we investigated the fate of Cd(II) immobilized on δ-MnO₂ affected by reduced sulfur (S^2- and cysteine). A low concentration of S^2- led to Cd(II) migration from vacant sites to edge sites, while a high concentration of S^2- largely converted Cd(II) adsorbed on the surface of δ-MnO₂ to CdS. At low pH, the cysteine addition led to the release of Cd(II) initially adsorbed at the δ-MnO₂ vacant sites into the solution and caused the migration of a small portion of Cd(II) to the δ-MnO₂ edge sites. At high pH, a high concentration of cysteine led to the detachment of Cd(II) from δ-MnO₂, Cd(II) readsorption by Mn(III)-bearing minerals, and Cd-cysteine formation. Changes of Cd(II) speciation were caused by δ-MnO₂ dissolution induced by reduced sulfur, the competition of generated Mn(II/III) for the adsorption sites, and the precipitation of Cd(II) with reduced sulfur. This study indicates that reduced sulfur is a critical factor controlling the fate of Cd(II) immobilized on Mn oxides in the aquatic environment.

Formation of Cd precipitates on γ-Al2O3: Implications for Cd sequestration in the environment

Apart from surface complexation, precipitation of minerals also plays an important role in reducing the mobility and transport of heavy metals in the environment. In this study, Cd(II) sorption species on surfaces of γ-Al₂O₃ at pH 7.5 were characterized using multiple techniques. Results show that in addition to adsorption complexes, Cd hydroxide phases (Cd(OH)₂ precipitates and Cd_x(OH)_y polynuclear complexes) were formed at the initial stages of Cd(II) sorption and gradually transformed to CdCO₃ with time. In addition, Cd(II) formed CdAl layered double hydroxide (LDH) on γ-Al₂O₃ under various conditions, independent of temperature and Cd loadings. The formation of Cd hydroxide phases and CdAl LDH could be ascribed to surface-induced precipitation because the bulk solution was undersaturated with respect to hydroxides. CdAl LDH formation on the Al-bearing mineral here is rather surprising because typically this occurs with elements of ionic radii similar to that of Al³⁺; this formation is unknown for metals such as Cd(II) with a much larger ionic radius. The thermodynamic feasibility of CdAl LDH formation was further confirmed by laboratory synthesis of CdAl LDH and density function theory (DFT) calculations. These results suggest that Cd precipitation on Al-bearing minerals can be an important mechanism for Cd immobilization in the natural environment. Additionally, the finding of CdAl LDH formation on Al-bearing minerals and the thermodynamic stability of CdAl LDH provides new insights into the remediation of Cd-polluted soils and aquatic systems.

Antimony oxidation and sorption behavior on birnessites with different properties (δ-MnO2 and triclinic birnessite)

Birnessites are abundant naturally occurring minerals with high sorption and oxidation capacity that could therefore play an important role in antimony (Sb) migration and transformation. There are various types of birnessites in the environment. However, little is known about the similarities and differences in Sb oxidation and sorption on birnessites with different properties. In this study, the behavior of Sb oxidation and sorption on two contrasting birnessites (δ-MnO₂ and triclinic birnessite (TrBir)) were investigated via batch and kinetic experiments and various spectroscopic techniques. Our results showed that the reaction mechanisms between Sb and the two birnessites were similar. The edge sites of birnessites were responsible for Sb(III) oxidation. Mn(IV) was reduced to Mn(III) and Mn(II), bound with birnessites and released to the solution, respectively. Because of the rapid rate of electron transfer of adsorbed Sb(III) to birnessites, the only Sb species on δ-MnO₂ after the oxidation reaction was Sb(V). Sb(V) was adsorbed at the edge sites of birnessites by replacing the OH group of birnessites, forming corner-sharing complexes with birnessites. However, the Sb sorption and oxidation capacities of the two birnessites were significantly different. Poorly-crystallized δ-MnO₂ exhibited a much higher oxidation and sorption capacity than well-crystallized TrBir because the former had many more edge sites than the latter. This study reveals the general mechanism of the reaction between Sb and birnessite and indicates that birnessite with a high number of edge sites would exhibit a huge capacity in Sb oxidation and sorption.

Wien effect of Cd/Zn on soil clay fraction and their interaction

BACKGROUND

The coexistence of Cd²⁺ and Zn²⁺ ions in nature has a significant influence on their environmental behaviors in soils and bioavailability for plants. While many studies have been done on the mutual toxicity of Cd²⁺ and Zn²⁺, few studies can be found in the literature focused on the interaction of Cd²⁺ and Zn²⁺ on soil clay fractions especially in terms of energy relationship.

RESULTS

The binding energies of Cd²⁺ on boggy soil (Histosols) particles and Zn²⁺ on yellow brown soil (Haplic Luvisols) particles were the highest, while those of Cd²⁺ and Zn²⁺ on paddy soil (Inceptisols) particles were the lowest. These results indicated that Cd²⁺ and Zn²⁺ have a strong capacity to adsorb in the solid phase at the soil-water interface of boggy soil and yellow brown soil, respectively. However, both Cd²⁺ and Zn²⁺ adsorbed on paddy soil particles easily release into the solution of the soil suspension. Unlike the binding energy, the higher adsorption energies of ions in boggy and yellow brown soils showed a weak binding force of ions in boggy soil and yellow brown soil. A 1:1 ratio of Cd²⁺ to Zn²⁺ promotes the mutual inhibition of their retentions. Cd²⁺ and Zn²⁺ have high mobility and bioavailability in paddy soil and yellow drab soil (Ustalfs), whereas they have high potential mobility and bioavailability in boggy soil and yellow brown soil.

CONCLUSION

In the combined system, Zn²⁺ had preferential adsorption than Cd²⁺ on soil clay fractions. Boggy soil and yellow brown soil have a low environmental risk with lower mobility and bioavailability of Cd²⁺ and Zn²⁺ while paddy soil and yellow drab soil present a substantial environmental risk. In the combined system, Cd²⁺ and Zn²⁺ restrain each other, resulting in the weaker binding force between ions and soil particles at a 1:1 ratio of Cd²⁺-Zn²⁺.

Oral health-related quality of life among HIV-infected and at-risk women

OBJECTIVES

Objective measures of dental diseases reflect only their clinical end-point. There is a need to use multidimensional measures of diseases that consider their psychosocial aspects and functional impact. The aim of this study is to compare the oral health-related quality of life (OHRQOL) between a group of HIV-infected women and a similar group of at-risk HIV-uninfected women, and to investigate the role of potential confounding clinical oral health and behavioral factors.

METHODS

Our sample included HIV-infected women (87%) and women at risk for HIV infection (13%) followed up for 5.5 years. OHRQOL was measured using the short version of the Oral Health Impact Profile (OHIP-14), which is a validated and reliable instrument.

RESULTS

HIV-infected women averaged 10% poorer OHRQOL than HIV-uninfected women; this difference was not apparent after adjusting for the number of study visits attended and significant behavioral and clinical oral health factors. The OHRQOL was inversely related to dental and periodontal diseases and to smoking and freebase cocaine use; these relationships were not confounded by HIV status.

CONCLUSIONS

The study identified specific clinical and behavioral factors where dental professionals can intervene to possibly improve the OHRQOL of HIV-infected or at-risk HIV-uninfected women.

Oral mucosal lesions and HIV viral load in the Women's Interagency HIV Study (WIHS)

The prevalence of oral lesions was assessed in a five-center subset of the Women's Interagency HIV Study (WIHS) and correlated with other features of HIV disease. Oral examinations were performed by dental examiners on 729 women (577 HIV-positive and 152 HIV-negative) during baseline examination. Significant differences between the groups were found for the following oral lesions: pseudomembranous candidiasis, 6.1% and 2.0%, respectively; erythematous candidiasis, 6.41% and 0.7%, respectively; all oral candidiasis, pseudomembranous and/or erythematous, 13.7% and 3.3%, respectively. Hairy leukoplakia was observed in 6.1% of HIV-positive women. No significant differences were found for recurrent aphthous ulcers, herpes simplex lesions, or papillomas. Kaposi's sarcoma was seen in 0.5% of HIV-positive and 0% of HIV-negative women. Using multiple logistic regression models controlling for use of antiretrovirals and antifungals, in HIV-positive women the presence of oral candidiasis was associated with a CD4 count <200 cells/microl, cigarette smoking, and heroin/methadone use; the presence of hairy leukoplakia was not related to CD4 count but was associated with high viral load. Oral candidiasis and hairy leukoplakia are confirmed as being common features of HIV infection in women and appear to be associated with HIV viral load, immunosuppression, and various other behaviorally determined variables.

The use of demineralized freeze-dried bone-glycoprotein matrix grafts in treating baboon periodontal infrabony defects

In an effort to improve regenerative capacity and establish higher levels of predictability, the use of a new graft material was investigated in baboon infrabony periodontal defects. A graft matrix composed of human demineralized freeze-dried bone combined with human connective tissue glycoprotein was implanted in 20 defects in 9 baboons. Control, debrided-only sites in the same animal served as a comparison. Grafted sites achieved a 1.8-mm greater reduction in probing depth and attachment gain compared to controls. In addition, 25.3% greater defect fill was found in grafted sites. Histologic analyses provided evidence of bone induction by the graft matrix and regeneration of new cementum, periodontal ligament, and bone in the grafted sites.

A multi-center clinical trial of a new chairside test in distinguishing between diseased and healthy periodontal sites. II. Association between site type and test outcome before and after therapy

The aim of the present study was to evaluate the association between the outcome of a chairside test measuring gingival crevicular fluid (GCF) levels of the enzyme aspartate aminotransferase (AST) and other clinical measures of disease including probing depth, severity of inflammation, and GCF flow before and after therapy. We studied 91 patients with moderate to severe periodontitis. Eight sites with probing depths between 5 mm and 8 mm and obvious signs of inflammation were selected and designated diseased sites. Four sites with probing depth < or = 3 mm with no or minimal signs of inflammation were selected and designated non-diseased sites in patients. Thirty healthy individuals were enrolled and four sites in each were selected and designated healthy controls. Patients were treated with scaling and root planing and control subjects with supragingival prophylaxis. Measurements including GCF volume, gingival inflammation, and probing depth were performed at screening baseline, 1 week later at pretreatment baseline, and at weeks 2 and 4 after treatment. AST content of GCF was measured using a chairside colorometric test. It was concluded that the outcome of the test is an effective objective measure distinguishing between diseased sites and non-diseased sites in patients and control subjects when evaluated both prior to and following application of therapy. Use of this simple chairside test, when combined with other standard diagnostic procedures, provides an objective measurement permitting improved capacity to distinguish between diseased and non-diseased periodontal sites, and to better assess and monitor the outcome of therapy.

Platelet association with gingival tissue inflammation

Platelets (PL) may be involved in the inflammatory process through the release of a variety of factors which could contribute to gingival tissue injury. Thus, conditions which result in the localized discharge of PL constitutents could lead to amplification of the inflammatory process at these sites. The purpose of this study was to determine if there was evidence of PL activation in gingival crevicular fluid and whether the degree of gingival inflammation, as measured by the gingival index (GI), was associated with the degree of platelet activation. This was monitored by assaying for beta-thromboglobulin (beta-TG), a platelet specific protein released from alpha granules of PL when activated. One uL samples of the fluids were obtained from human subjects from gingival sites with various GI scores. Fluid samples were also obtained at probe-induced bleeding gingival crevicular sites. beta-TG levels in the various fluids obtained from the crevice were determined by radioimmunoassay (RIA). The RIA data indicated that detectable beta-TG levels were observed in all samples, the means ranging from 5.5 ng/ml to 45.2 ng/ml. Additionally, a positive association between the GI scores of 0 and 1 and the beta-TG levels where observed. For GI scores of 2 and above the beta-TG concentrations appeared to approach a maximum value. These findings provide evidence for PL activation and suggest a relationship with gingival inflammation.

A multicenter clinical trial of PerioGard in distinguishing between diseased and healthy periodontal sites. (I). Study design, methodology and therapeutic outcome

We designed and performed a multicenter clinical trial to determine the relationship between measurements of the level of the enzyme aspartate aminotransferase (AST) in gingival crevicular fluid (GCF) to other measures used to detect periodontal disease and monitor outcome of treatment, including pocket depth and gingival inflammation. 32 periodontitis patients were enrolled at the University of Washington, Seattle, 30 at the University of Florida, Gainesville, and 34 at the University of Illinois, Chicago. 10 periodontally normal control subjects were enrolled at each location. 8 diseased and 4 healthy sites were designated for study in each patient and 8 healthy sites designated in each control subject. Measures of disease included pocket depth, severity of gingival inflammation, and GCF volume. AST levels were measured using the PerioGard test kit. Clinical measurements were made and GCF samples harvested and tested 2x before and 2x after therapy consisting of scaling and root planing under local anesthetic. Specific design and other issues are discussed, including selection of patients and control subjects, sample size, selection of experimental test sites, methods for assessment of diseased and therapeutic improvement, harvesting of GCF and selection of appropriate biostatistical methods for data analysis. Demographics of the patient populations at the 3 locations are reported. As expected, therapy induced only negligible changes in the measures of disease at healthy sites in control subjects, and relatively minor improvement in healthy sites in patients. In contrast, statistically significant improvement relative to pretreatment baseline status in all 3 measures of disease was observed for diseased sites at all 3 study locations with all p-values less than 0.0002. The magnitude of improvement was comparable to that reported previously by others. The % of PerioGard-positive sites decreased significantly between the screening baseline and both post-treatment visits for patients at all 3 locations, with p values of 0.0001 to <0.0008.

Controlled tissue expansion with guided bone regeneration

Guided tissue regeneration techniques are used to create new bone around implant defects and to augment edentulous ridges prior to implant placement. A new technique, tested successfully in baboons, utilizes soft tissue expanders prior to implant placement and tissue regeneration procedures.

Association of gingival crevicular fluid aspartate aminotransferase levels with histopathology during ligature-induced periodontitis in the beagle dog

Previous investigations have shown a clear association between the presence of the enzyme aspartate aminotransferase (AST) in gingival crevicular fluid (GCF) and clinical evidence of periodontal disease in humans, as well as in the beagle dog model. This paper describes a 26-week study that uses the beagle dog model of ligature-induced periodontitis in which GCF-AST (corrected for collection time) was correlated with microscopic evidence of tissue destruction in the periodontium at the sites of fluid collection. GCF and clinical data were collected at baseline, at optimal gingival health, during gingivitis, and after ligation. A cross-mouth design was implemented so that six premolar teeth in each dog were ligated for periods up to five weeks. Formalin-fixed tissues from the sites of GCF collection were prepared for light microscopy and evaluated for the presence of epithelial ulceration, bone resorption, and inflammatory cell infiltration. The relationship between GCF-AST levels and microscopic findings was analyzed by calculation of sensitivity and specificity and by plots of Receiver Operating Characteristics. These data revealed a correlation between elevated enzyme concentration and microscopic evidence of disease activity. Taken together with human studies, these results provide support for the use of AST as a marker of periodontal disease progression.

Disarming canine teeth of nonhuman primates using the submucosal vital root retention technique

Removing or reducing the size of canine teeth of baboons and macaques has become an accepted practice to minimize the potential for injury to laboratory animal care personnel. A submucosal vital root retention procedure was adapted from the technique of root banking human teeth. In this technique, the crown of a tooth is amputated below the level of the alveolar bone crest, and the exposed pulp covered by a mucoperiosteal gingival flap. Our aim was to disarm the canine teeth of baboons and macaques with a single surgical procedure that would preserve a vital tooth root buried in alveolar bone under normal mucosa. Our long-term objective was to develop a technique that would not require further clinical management during the life of the animal. This paper presents the surgical techniques used.

A longitudinal study of aspartate aminotransferase in human gingival crevicular fluid

Previous studies have shown that aspartate aminotransferase (AST), an established serum marker for cardiac and liver damage in humans, appears in elevated concentrations in samples of gingival crevicular fluid (GCF) from ligated vs. non-ligated teeth in beagle dogs and in elevated quantities in cross-sectional GCF sampling, adjusted for collection time, from human sites with clinical signs of past or present periodontal disease as compared to healthy sites. This paper describes a longitudinal study in which AST was monitored quarterly over a 2-year period at 2 sites/tooth in 31 patients with mild to moderate adult periodontitis. In this study sample, 40 (2.6%) of 1536 sites exhibited confirmed loss of at least 2 mm of attachment during the 2-yr observation period. In comparison with healthy sites within the same patients, AST standardized to a 30-second collection interval (AST30) was elevated at these sites with new confirmed attachment loss, and at sites with past attachment loss or gingivitis in the absence of periodontitis. When both within- and between-patient variation were taken into account, observed odds-ratios associating enzyme with disease were higher for sites with new attachment loss (9-16 depending on test cut-point) than for sites with pre-study attachment loss (3-12), or gingivitis in the absence of periodontitis (5-8). AST in GCF is strongly related to human periodontal disease. The data are consistent with the hypothesis that the relationship is strongest during episodes of cumulative tissue breakdown, but the small numbers of sites with confirmed attachment loss during the study period, or with gingivitis in the absence of periodontitis, means that further clinical studies are necessary to clarify this issue.

A cross-sectional analysis of aspartate aminotransferase in human gingival crevicular fluid

Previous investigation has shown that the concentration of aspartate aminotransferase (AST), an established serum marker for cardiac and liver damage in humans, is significantly elevated in samples of gingival crevicular fluid (GCF) from ligated teeth in beagle dogs. This paper reports on a cross-sectional study of the relationships between AST in GCF and clinical indices of human periodontal disease in 60 patients with mild to moderate adult periodontitis. AST standardized to a 30-second collection interval (AST30) showed substantial (multiple regression R2 = 0.61) association with summary indices of patient disease status, modest association (partial R2 = 0.22) with tooth disease status within patient, and weaker (partial R2 = 0.12) but statistically significant association with site-to-site variation in disease at the same tooth. AST concentration showed modest (R2 = 0.30) between-patient relationship with clinical indices, but no clinically significant relationship with these indices between sites within patients, suggesting a rough proportionality between accumulated enzyme and GCF volume at sites with varying stages of disease. The relationship between GCF volume and probing depth also appears central to interpretation of enzyme assays. Clinical measures of past periodontitis and current inflammatory disease are cross-sectionally related to variation in AST30, across patients and sites within the same patient. Considerable residual variation, especially elevated AST30 in the absence of clear signs of disease, may result from varying levels of current disease activity, not reflected in clinical measures.

Topographic distribution of Thy-1 positive cells in epithelial tissues of BALB/c mice

Epithelial sheets prepared from murine oral epithelia (palate, lining mucosa, gingiva) and oesophagus contained dendritic and round Thy-1 positive (+) cells similar to those observed in epidermis by immunofluorescence microscopy. Bladder, intestine and tracheal epithelium did not contain such cells. Thus, cells bearing the cells-surface glycoprotein Thy-1, like Ia-antigen-bearing Langerhans cells, may be restricted to stratified squamous epithelia.

Direct effects of minoxidil on epidermal cells in culture

Minoxidil, a potent antihypertensive agent, induces generalized hypertrichosis when administered systemically, or localized hair regrowth when applied topically to sites of severe alopecia areata. The pharmacologic mechanisms by which minoxidil stimulates hair growth are unknown. This study was designed to examine whether minoxidil has direct effects on neonatal murine epidermal cells in culture. In the presence of minoxidil, cultures showed a marked dose-dependent second peak of DNA synthesis 8-10 days after culture initiation. In addition, two morphologically distinct cell types appeared. Indirect immunofluorescence staining with keratin-specific antibody revealed cytoplasmic keratin fibers, suggesting the epidermal origin of these cells. Our experiments demonstrate that minoxidil can affect epidermal cells in culture by altering their growth pattern and phenotypic appearance.

Periosteal activation and root demineralization associated with the horizontal sliding flap

A sliding flap technique for covering denuded root associated with periosteal activation and root demineralization "in situ" was described. The possible biological mechanisms involved were discussed. Two clinical cases were presented illustrating the successful results that can be achieved.